Full Text - Seismological Research Letters

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SSA 2012 Annual Meeting Announcement
Seismological Society of America
Technical Sessions
17–19 April 2012 (Tuesday–Thursday)
San Diego, California
IMPORTANT DATES
Meeting Pre-registration Deadline 9 March 2012
Hotel Reservation Cut-Off
24 March 2012
Online Registration Cut-Off 6 April 2012
SSA Annual Meeting Announcement
PROGRAM COMMITTEE
This year’s technical program committee is composed of cochairs David Oglesby (University of California, Riverside) and
Raul Castro (CICESE, Ensenada, Mexico), as well as members
Tom Rockwell (San Diego State University), Jose Restrepo
(UC San Diego), Bernard Minster (UC San Diego), Kim
Olsen (San Diego State University) and Luciana Astiz (UC
San Diego)
Meeting Contacts
Technical Program Co-Chairs
David Oglesby and Raul Castro
[email protected]
Abstract Submissions
Joy Troyer
510.559.1784
[email protected]
Registration
Sissy Stone
510.559.1780
[email protected]
Exhibits
Katie Kadas
510.559.1783
[email protected]
Press Relations
Nan Broadbent
408-431-9885
[email protected]
TECHNICAL PROGRAM
The following special sessions have been formed for the technical program.
Advances in Rapid Earthquake and Tsunami Detection
and Modeling using Geodetic and Seismic Data
Experience with the great earthquakes and ensuing tsunamis of
the last decade has shown that traditional seismic monitoring
can be greatly improved in its ability to rapidly estimate accurate earthquake magnitude and fault slip parameters by the
addition of real-time GPS measurements of static and dynamic
seismic deformation. This session focuses on the exploitation
of near-field real-time GPS data alone or in combination with
seismic data to directly estimate displacements with sufficient
accuracy to significantly improve the timeliness of earthquake
parameter estimation, thereby also enhancing tsunami early
warning and modeling. We welcome contributions on earthquake and tsunami early warning approaches for large/great
earthquakes, scaling relationships for estimating earthquake
magnitude, rapid centroid and moment tensor solutions, nearreal-time finite fault slip inversions and tsunami modeling. Also
of interest are preparations for monitoring expected large events
in Western North America, including the Cascadia megathrust, the San Andreas fault, and the Mexican subduction zone.
Chairs: Yehuda Bock ([email protected]), Shri Krishna
Singh ([email protected]), Timothy Melbourne (tim@
geology.cwu.edu)
316 Seismological Research Letters Volume 83, Number 2 March/April 2012
doi: 10.1785/gssrl .83.2.316
Challenging the Idea of Seismic Coupling along
Subduction Zones: Chile, Sumatra, Tohoku…
What’s Next?
Over the last decade the occurrence of a significant number of
subduction related mega-events (Sumatra-Andaman Islands,
Tohoku-Oki, Alaska) has openly questioned the state of knowledge about the lithospheric processes behind these earthquakes.
After Sumatra earthquake, the seismological model supporting
strong coupling between the convergence rate and the age of the
subducting lithosphere has been challenged. In the Cascadia subduction zone, an increasing number of paleoseismic data available is being used to re-evaluate historical events, leading to new
estimates of its behavior. After March 2011 the question is Will
Tohoku earthquake change the way we think about seismic coupling along subduction zones and the maximum expected magnitude? In this session we invite studies related to the mapping
of seismic coupling along subduction zones considering the spatiotemporal variability of seismic energy release, including time
periods and sub-regions for which the plate interface appears to
be locked. Are there any specific plate boundaries where a reevaluation of the maximum expected magnitude is more critical than ever? Are seismic hazard estimates that assume most
of a subduction boundary is aseismic still viable? This session
also aims to re-evaluate seismological data using either relocated
catalogs or re-determined epicenters of important mega- events
which will aid future studies of seismic coupling. The overall
target of this session would be to promote the discussion about
new directions in research related with earthquake forecasting
and monitoring along subduction zones.
Chairs: Margarita Segkou ([email protected]), William
Ellsworth ([email protected])
Continental Lithospheric Structure and Tectonics of
Central North America
As USArray Transportable Array moves into the continental
interior, new insights are being made into the lithospheric and
deep seismic structure of North America. Delineating crustal
and mantle interfaces, strength heterogeneities, velocity gradients, and structure can provide important constraints for the
formation and composition of the continents and evolution of
cratons. Mapping of seismotectonic structures may help understand the interaction of different tectonic provinces within
central North America, and their role in the seismogenic
processes in intraplate regions. We seek contributions from
Earthscope or other projects on the North American continental lithosphere and upper mantle structure that include passive
and active source seismology, geodynamic modeling, tectonics,
geodesy, and other integrated multidisciplinary studies.
Chairs: Meghan S. Miller ([email protected]), M. Beatrice
Magnani ([email protected]), Luciana Astiz (lastiz@
ucsd.edu)
Debating Fault Model Input Data
Stochastic and physics-based models of fault systems have been
developed in an attempt to provide reliable rules for models of
seismogenic regions that can have a predictive power. Whether
it be the rate and maximum magnitude of aftershocks, the
probability for a rupture to jump from a fault segment to
another, or the recurrence behavior of large events on simple
faults, our predictions all depend on noisy and potentially
incomplete datasets. This affects both empirical, stochastic,and
physics-based models. In this session, we encourage modelers to
choose first order, general rules about slip distributions, ground
motion, and other parameters that arise from their model outputs, and discuss which subset of the input data they are most
sensitive to. We also encourage data providers to explain how
well these critical data are known and what amount of complexity or variability (in space or time) we could expect these
properties to exhibit, based on their observations. Finally, we
welcome contributions from modelers and statisticians on how
the data should be reported to be most useful, and from data
gatherers on how their data should be used. We considered
welcome contributors from deterministic and stochastic modeling, probabilistic modeling, seismology, geodesy, earthquake
geology (including geomorphology, paleoseismology, etc), fault
and rock mechanics.
Chairs: Delphine Fitzenz ([email protected]), Andrew
Michael ([email protected])
Deformation Processes and Properties of the San
Jacinto Fault Zone
The San Jacinto fault is one of the most active branches of the
San Andreas system in southern California, and it consists of
multiple segments that exhibit considerably different properties and behaviors both at the surface and at depth. As such,
it provides an excellent natural laboratory for studying the
mechanics, architecture and evolutionary processes of a young
transform plate boundary system. This session will provide a
platform for discussing these topics based on in-situ geological, geodetic and seismological data from the San Jacinto fault
zone, along with related laboratory and theoretical results.
Chairs: Yehuda Ben-Zion ([email protected]), Tom
Rockwell ([email protected] ), Frank Vernon ([email protected])
Detecting, Modeling, and Predicting the Seismic Source
The seismic source has a controlling effect on ground motion
and thus seismic hazard, but it is also the most uncertain and
difficult to characterize. This session combines seismic observations, laboratory work, and modeling studies to better estimate
the size, potential slip patterns, and timing of earthquakes.
Chair: Yoshihiro Kaneko ([email protected])
Dynamics of Seismicity Beyond Universal Scaling Laws
Finding genuine aspects of seismicity that reflect local properties of faults or the crust, beyond the average regional
Gutenberg-Richter magnitude distribution and Omori-Utsu
aftershocks decay, is a highly challenging problem because
of the inherent complexity of the earthquake process combined with the limited and noisy available data. Using large
spatial domains increases the amount of data, but may suppress important local properties of seismicity. This session will
Seismological Research Letters Volume 83, Number 2 March/April 2012 317
focus on statistical features of seismicity specific to various
sub-regions, and their relations to independent geophysical
observations (e.g. seismic velocity images, heat flow). Examples
include space-time variations of foreshock/aftershock clustering and productivity, bursts of activity, swarms, periodic seismicity, triggering and other patterns that go beyond the classical power laws.
Chairs: Yehuda Ben-Zion ([email protected]), Ilya
Zaliapin ([email protected])
Earthquake Debate #1: Concept of Segmentation
“Do known faults and their segmentation tell us anything
about the location and extent of large earthquakes? Did the
Tohoku earthquake kill the concept of segmentation?”
The Tohoku earthquake and the Canterbury earthquake
sequence stimulated discussions whether or not the concept of
fault segments is valid and useful. Segments seems clearly visible from a geological point of view. Microseismicity often seems
to ignore segment boundaries. Earthquake rupture forecasts
are taking into account the probabilities of rupturing through
segment boundaries and even from fault to fault. How valid
and useful is the concept of segments? Are segments limited by
only apparent boundaries or are these boundaries physical? Is
the knowledge of segments increasing our abilities to forecast
the size of earthquakes? Was Tohoku an exception or the rule?
We solicit presentations that contribute to this discussion and
try to shed light on this open question.
Chairs: Danijel Schorlemmer ([email protected]),
David Jackson ([email protected]), Matt C. Gerstenberger
([email protected]), Matthias Holschneider (hols@
math.uni-potsdam.de)
Earthquake Debate #2: PSHA Methodology
“PSHA has been an invaluable contribution to how seismic
hazard has been done in recent decades, but is it nearing it’s
maximum potential? Will future iterations be able to make
more than minor improvements or should we be putting more
effort into investigating alternative methodologies?”
PSHA is the gold standard in computing seismic hazard.
It is used worldwide on different scales, from global to sitespecific assessments. Its results are directly used for seismic risk
assessment. But can the large uncertainties be overcome within
its framework? Can other methodologies provide more reliable
and useful assessments? Did the Tohoku earthquake reveal
shortcomings of PSHA that are intrinsic to the method? We
solicit presentations that discuss the strengths and weaknesses
of PSHA or that show other, maybe more promising, ways for
hazard assessments.
Chairs: Danijel Schorlemmer ([email protected]),
David Jackson ([email protected]), Matt C. Gerstenberger
([email protected]), Matthias Holschneider (hols@
math.uni-potsdam.de)
Earthquake Location and Monitoring
Modern earthquake location and monitoring techniques have
revolutionized seismology, allowing better images of fault
structure, stress, and time-dependent frictional properties.
This session explores new techniques and results in this important seismological field.
Chair: Felix Waldhauser ([email protected])
Earthquake Strong-Motion Modeling
Data- and simulation-based models for strong ground motion
are key tools for seismologists who are interested in characterizing seismic hazard. Such studies require an understanding
source, path, and site effects. This session explores current
research in ground motion modeling, using historic data as
well as faulting simulations.
Posters only.
Earthquakes and Tsunamis at Coastal Archaeological
Sites
The study of earthquakes and tsunamis at coastal archaeological sites provides a view into their magnitude, timing, and
severity. Earthquake and tsunami risk is particularly prevalent
on the dynamic and sensitive coastal zones. Today, as in the
past, people are drawn to this dynamic niche due to its broad
resource base, often temperate climate, and access to trade
routes. While the effects of gradual, annual, decadal, or millennial changes might be possible to mitigate, punctuated high
energy events such as earthquakes and tsunamis can alter the
coastline permanently in a matter of minutes to days, impacting the livelihoods of residents, damaging infrastructure, and
remolding and modifying the coastline. Therefore, it is crucial
to be well informed of past events as a reference for advising
coastal management strategies and disaster preparation and
response guidelines. Reconstructing past earthquake and tsunami events with the use of information from coastal archaeological sites can provide a more complete and informative database of tsunami and earthquake history. This session explores
the records of earthquakes and tsunamis at coastal archaeological sites and methods for quantifying tsunami and seismic hazard parameters from archaeological data.
Chairs: Manuel Sintubin ([email protected] ), Beverly N. Goodman Tchernov (goodmanbeverly@
gmail.com ), Tina M. Niemi ([email protected])
El Mayor-Cucapah, Baja California M7.2 Earthquake of 4
April 2010: Research Results and Lessons
El Mayor-Cucapah earthquake on 4 April 2010 occurred
between the Laguna Salada rift basin and the Pacific-North
America plate boundary. This event has been one of the strongest earthquakes recorded on southern California and northern
Baja California. This earthquake has motivated several multidisciplinary studies, on both sides of the international border,
to understand the seismotectonics of the region, the rupture
process, and other geophysical phenomena observed during
this important earthquake sequence. We invite contributions
from all aspects of geophysical studies carried out in the epicentral region of El Mayor-Cucapah seismic sequence including:
earthquake relocation, strong ground motion, building damage, site amplification, ground failure, surface faulting, GPS,
InSar and other geophysical measurements related with the
seismic zone.
Chairs: Victor Wong ([email protected]), Raul Castro
([email protected])
Ground Motion Prediction Equations and Earthquake Site
Response
A new generation of empirically determined attenuation equations, which describe peak ground accelerations (PGA) and
peak ground velocity (PGV) as a function of magnitude and
distance, are presented together with methods to estimate site
response.
Chair: Alan Yong ([email protected])
Macroseismic Effects in Recent and Ancient
Earthquakes and their Relationship to Ground Motion
Parameters
Man-made constructions exhibit macroseismic effects from
earthquakes that are of primary interest for seismologists,
civil engineers and, occasionally, archaeologists. In its infancy,
modern seismology made use these effects to not only scale the
strength of an earthquake but also to deduce source parameters such as the epicenter. Specifically, objects of investigation
included such toppled and rotated objects as tombstones, simply structured monuments, and columns. While present-day
earthquake locations are achieved by seismic measurements,
the link between site-specific ground motions and damaged
constructions is still of great importance. The correlative factors, however, are even today not always fully understood. In
order to interpret effects of ancient earthquakes on simple
structures and buildings, instrumentally observed earthquakes
producing similar macroseismic effects offer a chance to refine
methods of back calculation of ground motion parameters.
The goal of this session is to bring together strong motion and
engineering seismologists, civil engineers, geologists, archaeologically interested seismologists and archaeologists to discuss possibilities and limitations of the deduction of ground
motion parameters from macroseismic effects. This includes
also the study of geological and geomorphologic factors to
local rotations. Contributions to methodo–logical developments are encouraged as well as presentations of field cases and
data collections.
Chairs: Klaus-G. Hinzen ([email protected]), Luigi
Cucci ([email protected]), Mariano Garcia-Fernandez ([email protected]), Andrea Tertulliani ([email protected])
Neotectonics, Fault Geology, and Paleoseismic Studies
Studies of fault zones and new fault structure facilitate better
estimates of slip rates and improve the evaluation of seismic
hazard New paleoseismic trenches reveal significant fault offsets generated by historical earthquakes. This session focuses
on studies of neo-tectonics and fault geology in seismically
active regions.
Chairs: Klaus-G. Hinzen ([email protected])
Posters only.
Non-Volcanic Tremor, Slow-Slip Events and Remote
Triggering
Episodes of non-volcanic tremors recorded in different regions
suggest that they may be associated with slow-slip events. New
results and models that explain these observations together
with new studies of remote triggering are presented in this session.
Chair: Michel Campillo ([email protected])
Numerical Modeling of Earthquake Motion and Seismic
Wave Propagation
Numerical modeling has been and will likely remain an important tool for investigating rupture propagation, earthquake
ground motion and seismic wave propagation. Refinements
and innovations in numerical modeling are being driven by
the demands to interpret increasing volumes of seismic data;
the scientific and engineering requirements to reproduce and
predict seismic motion in realistically complex media over
a broad frequency band; and the rapid development of computer resources. Advancements (e.g., in modeling capabilities,
accuracy levels, and computational efficiency) are spurred
when there is joint involvement of, and interactions among,
mathematical and computational scientists, algorithm developers, and those applying the methods. We invite contributions focused on development, verification and validation of
the numerical-modeling methods, and on methodologically
important applications. Contributions on the analysis of
methods, development of fast algorithms, GPU applications,
large-scale simulations, non-linear behavior, multiscale problems, and confrontation of methods with data are especially
encouraged.
Chairs: Emmanuel Chaljub ([email protected]), Steven Day ([email protected]), Peter Moczo
([email protected])
Physics in Seismology: The Legacy of Leon Knopoff
This special session solicits papers honoring the scientific
accomplishments of Leon Knopoff (1925-2011) by demonstrating their impact on modern seismology. Knopoff introduced
a wide range of physics topics to seismology, laying down the
foundation for much current work. Papers that demonstrate
the Knopoff heritage in recent developments in nonlinear
earthquake dynamics, earthquake statistics, theoretical elastodynamics, wave propagation, and tectonophysics would be
particularly relevant. Knopoff ‘s work involved representation
theory, spring-block sliders, self-organized criticality, earthquake statistics, stochastic branching models of the source,
physics of the ETAS model and Omori laws, Q, and application
of condensed matter physics to seismology. The objective of the
session is to highlight how this type of scientific approach can
serve as an example for future work.
Chairs: Paul Davis ([email protected]), Freeman
Gilbert ([email protected]), David Jackson (david.d.jackson@
ucla.edu), Thomas Jordan ([email protected])
Probabilistic Fault Displacement Hazard Analysis
Propagation of fault rupture to the ground surface can result
in disruption of lifelines and damage to engineered features.
Forecasting potential surface fault rupture displacement using
probabilistic methods has become more tractable in the last
decade. This session brings together speakers to discuss recent
advances in fault displacement hazard analysis on probabilistic methods, statistical models, numerical solutions, and case
histories. The goal of this session is to discern where there is
agreement and where there is disagreement in probabilistic
fault displacement hazard analysis to set the path for future
research.
Chairs: Robb Moss ([email protected]), Mark Petersen
([email protected])
Probabilistic Seismic Hazard Analyses, Models, Maps,
and Simulations
Probabilistic seismic hazard analyses have become an important tool in the construction of realistic earthquake scenarios
for regions of high seismic risk. New models, maps and simulations determined for different regions are presented in this
session.
Chair: Ivan Wong ([email protected])
Rotations in Strong-motion Seismology
Significant progress has been made in observing and analyzing rotational ground motions in recent years. Accurate measurements of these additional components of ground motion
are especially important in strong-motion seismology and
earthquake engineering. Rotational motion and its effects on
strong-motion data have been ignored for their much smaller
amplitudes than that of the translational motions. However,
recent observations from large ground motions suggest that
these effects might be underestimated and detailed analyses of these effects are necessary. Rotational components of
earthquake ground motion are usually not considered for
seismic analysis, design and performance assessment at this
time because time-series recordings of these components are
rare. A number of procedures have been proposed to extract
rotational components of ground motion from translational
time series recorded by arrays of closely spaced stations. There
are also new sensors capable of recording point rotations,
and some of them have already been used in field and laboratory measurements. We invite submission of presentations
that document progress in measurement, analysis, application, and theory of rotational strong-motion. We specifically
emphasize rotational strong-motions of the order of 10 –5 and
higher (up to ~ 10 –2) rad that can produce significant effect
on structures.
Chairs: Vladimir Graizer ([email protected]),
Maria Todorovska ([email protected])
Seamount Subduction and Earthquakes
Seamounts are ubiquitous topology features, with sizes ranging from a few to tens of kilometers in width and up to several kilometers in height. When they enter subduction zones,
they have profound effects on forearc morphology, fault
zone structure, material transfer, and earthquake generation.
Traditionally, subducting seamounts have often been assumed
to cause large megathrust earthquakes; however other studies
associate subducted seamounts with weak interplate coupling.
Many variables may affect whether seamounts result in relatively strong or weak patches on the plate boundary. A more
thorough observational and theoretical investigation of the
role of seamounts in seismogenesis is needed. In this session,
we solicit contributions on studies of subducting seamounts
including, but not limited to, imaging seamounts in subduction zones, modeling the mechanics of seamount subduction,
effects of subducting seamount on megathrust earthquake
ruptures, and indicators of tectonic erosion and forearc deformation caused by seamount subduction.
Chairs: Hongfeng Yang ([email protected]), Susan
Bilek ([email protected]), Anne Trehu ([email protected]), Kelin Wang ([email protected])
Posters only.
Seismic Imaging: Recent Advancement and Future
Directions
Seismic imaging is a powerful tool for geophysicists to probe
the Earth’s interior. The demand for higher resolution and
broader range of applications is rapidly increasing. This session welcomes contributions from seismic imaging in various
scales and application arenas, with special emphasis on recent
advances and future directions. Examples may include innovations and advances in 3D traveltime tomography, waveform
tomography, receiver function mapping, surface wave inversion, and joint inversion of multiple geophysical observations.
We also encourage case study papers using seismic imaging to
solve real problems. Discussions on the pitfalls, limitations,
and artifacts of common seismic imaging methods and potential remedies are most welcomed.
Chairs: Youshun Sun ([email protected]), Michael
Begnaud ([email protected]), Sidao Ni ([email protected]),
Junmeng Zhao ([email protected])
Seismicity in Volcanic Environments
Volcano seismicity takes a variety of forms including high- and
low-frequency events, tremor, and explosions. These signals are
used directly in volcano monitoring and risk mitigation and
provide a method for studying the physics of volcanic environments and eruptions. Recent advances in seismic instrumentation, multi-sensor studies (e.g., infrasound, doppler, video),
and numerical modeling have improved our ability to interpret
seismic signals recorded in volcanic environments. These studies demonstrate the variety of physical processes that may be
responsible for the generation of these signals. We invite contributions utilizing observational, theoretical, laboratory and/
or modeling techniques, particularly those connecting seismic
signals to physical processes in volcanic environments.
Chairs: Darcy Ogden ([email protected]), Eric Dunham
([email protected])
Sensors and Software Techniques
Seismic hardware and software play a key role in earthquake
monitoring and analysis. This session explores recent advancements in this important technical field, with its implications
for earthquake science.
Posters only.
Structure Models, Wavespeed, and Attenuation
The determination of accurate velocity structures using P and
S waves is essential to improving earthquake locations, ground
motion analyses and to understanding local and regional tectonic settings. This session presents new structure models
based on wave velocities and seismic attenuation studies.
Chair: Vera Schulte ([email protected])
Surface Deformation and Geodetic Techniques
Recent advances in geodetic techniques such as InSAR and
GPS allow researchers to better determine subsurface fault
structure and interseismic deformation, as well as coseismic
properties of earthquakes. This session brings together presentations that use these techniques to better characterize deformation in various potentially seismically active regions.
Posters only.
The M5.8 Central Virginia and the M5.6 Oklahoma
Earthquakes of 2011
Two rare, large, intraplate earthquakes struck the eastern US
in 2011. Both events were felt over broad areas in surrounding states, and they produced moderate local damage. For the
Virginia earthquake, significant damage occurred 135 km
away in Washington D.C. and minor damage 200 km away
in Baltimore. Large numbers of portable seismic stations were
deployed by several organizations following both main shocks.
Both main shocks were followed by vigorous aftershock activity making these two of the best-recorded aftershock sequences
in the eastern U.S. Scientific investigations of any aspect of
these rare intraplate events are appropriate; including source
properties, strong ground motion, attenuation, site amplification, building damage, ground failure, and paleo-seismology.
Chairs: Stephen Horton ([email protected]), Robert
Williams ([email protected])
The 11 March 2011 Tohoku, Japan, Earthquake:
Observations and Models
The 11 March 2011 Tohoku, Japan Earthquake produced a
huge tsunami, as well as some of the highest ground motion
ever recorded and the some of the highest fault slip ever
inferred. This session brings together observations of and models to reach a better understanding of this important event.
Posters only
The 23 October 2011 Van, Turkey Earthquake:
Observations and Implications
The October 23, 2011, Mw7.2 Van earthquake in eastern
Turkey is the latest of a number of recent large (M~7) earthquakes to cause many deaths and significant damage in a conti-
nental setting. This earthquake occurred in a tectonically complex area of convergence and right-lateral shear between Arabia
and Eurasia, far from the recognized major plate boundaries,
and with the relatively simple strike-slip systems of the North
and East Anatolian Faults located well to the west. This session will focus on scientific, technical and social studies of the
earthquake’s immediate and long-term effects. We welcome
contributions from the fields of seismology, geodesy, geology, engineering, and governmental and non-governmental
response that provide insights into all aspects of the earthquake
cycle in the area, the regional tectonics and structure, and the
local impacts of the earthquake and its aftershocks. Studies
that highlight comparisons to, or lessons learned from, other
similar major earthquakes in the last few years, for example the
Haiti and Christchurch earthquakes, and that discuss implications for analogous areas of oblique convergence in California
and elsewhere are also encouraged.
Chair: Gareth Funning ([email protected]) and Mike Floyd
([email protected])
Tying Nearfield Phenomenology to Farfield
Measurements: Explosion Source Physics and Energy
Propagation Through Complex Media
A key to improved explosion source characterization is a physical basis relating nearfield phenomenology to remote/farfield
observations. Developing a physical basis requires a comprehensive research program with at least three focus areas: field
experiments, first-principle calculations, and source-to-receiver
modeling. Core questions revolve around the manifestations
of multiple length- and time-scale source and path phenomena in band-limited recordings acquired at distant stations.
To be relevant, the results of studies of such phenomena must
be translated into useful methods for the verification community to characterize the source and quantify uncertainties. The
theme of this session is the identification of important source
and propagation phenomena, their manifestations in remote/
farfield observations, and the construction of physical basis
models for characterizing the source and quantifying errors.
We invite contributions from all research focus areas and technologies with emphasis on laying a physical basis for yield estimation and source-type discrimination.
Chairs: Robert Abbott ([email protected]), Tarabay
Antoun ([email protected]), Howard Patton (patton@lanl.
gov), Chandan Saikia ([email protected]), Catherine Snelson
([email protected])
Uncertainty in the Estimation of Earthquake Hazard
The primary focus of National Seismic Hazard Mapping
Project (NSHMP) is to develop the mean hazard. The project
considers explicitly both the aleatory (natural variability) and
the epistemic (modeling) uncertainty. Epistemic uncertainty is
typically considered in the hazard analysis by using logic trees.
The hazard curve from each of the possible branches defines
the uncertainty in the hazard. Since the primary objective of
NSHMP is to develop the mean hazard curve, sometimes some
of the logic tree branches are ignored because of little impact
of that branch on the estimation of mean hazard. But those
branches can be important in the calculation of uncertainty in
the hazard. The epistemic uncertainty in the hazard is expected
to be lower in California where the amount of information is
relatively high from frequent earthquake events compared to
uncertainties in New Madrid or Charleston area where limited
information is available from fewer events. The uncertainty in
hazard plays a significant role in assessing earthquake risks, e.g.,
for assessing uncertainty in risk-targeted ground motion for
designing buildings, or for assessing uncertainty in monetary
losses at different return periods for insurance companies. We
plan to explore the issue of hazard uncertainty in the upcoming NSHMP update. This session will focus on approaches
for quantifying uncertainties, guidance for the treatment of
uncertainties and quantification of the uncertainties in the
hazard parameters (e.g., b-values), components (e.g., deformation model), and overall model. We invite papers focusing on
how to assess uncertainties on inputs to the hazard model and
on global examples of hazard and risk uncertainties.
Chairs: Nilesh Shome ([email protected]), Mark D.
Petersen ([email protected])
U.S.-China Collaborations in Seismological and
Earthquake Studies
China is an important natural laboratory for seismological and
earthquake studies. From the rise of the Tibetan Plateau and
the Tianshan Mountains to extension and volcanism in North
China, China is one of the best places to study continental
collision and diffusive continental tectonics. With frequent
devastating earthquakes and more than 2000 years of historic
earthquake records, China is also a key test bed for earthquake
models and hypotheses. US and Chinese scientists have a long
tradition of collaboration in these studies, which have seen a
great acceleration in the past two decades, fueled in part by
China’s sharp increase in funding basic science research. The
aim of this session is to provide a stage for scientists from both
countries and others working on seismotectonics and earthquakes in China to share their results, discuss common problems, and explore future opportunities for collaborations.
Chairs: Mian Liu ([email protected]), Randy Keller
([email protected]),
Larry Brown ([email protected]),
Yongshuan (John) Chen ([email protected])
Validation of Strong Ground Motion Simulations for
Engineering Applications
Despite the thousands of strong ground motion records readily
available online, there remains a shortage of records for large
magnitude earthquakes at short distances, not to mention for
other specific source, path, and site characteristics. More and
more, physics-based and/or stochastic numerical simulations
of strong ground motions are able to offer realistic samples of
such records, but the simulation models should first be validated against available strong ground motion data. This special session focuses on efforts to statistically validate simulated
records for engineering applications. Such applications include
nonlinear response history analysis of geotechnical or struc-
tural (e.g. building, bridge) systems for building code or risk
assessments, and development of prediction models for ground
motion intensity measures (e.g. spectral acceleration).
Chairs: Nicolas Luco ([email protected]), Sanaz Rezaeian
([email protected]), Thomas H. Jordan ([email protected])
FEATURED SPEAKERS
Joyner Lecture
Jonathan D. Bray of the University of California at Berkeley
will speak on “Building Near Faults” at this year’s Joyner
Lecture. The Joyner Lecture was established to honor William
B. Joyner’s pursuit of bringing earthquake seismology and
earthquake engineering closer together, so as to provide for a
safer society. The lecture will be followed by a reception.
Public Policy Luncheon Speaker
“Lessons of L’Aquila for Operational Earthquake Forecasting”
will be the topic of this year’s Public Policy Luncheon presentation by Tom Jordan. He will focus on how seismologists communicate time-dependent hazard information, where things
went wrong in L’Aquila, Italy, and how we should structure the
delivery of hazard information to keep that from happening
again.
President’s Invited Speaker
Dr. Eddie Bernard, PhD, Scientist Emeritus, NOAA/Pacific
Marine Environmental Laboratory in Seattle, Washington
has been invited to be the speaker at Thursday’s luncheon. The
title of his talk is “Tseismologists and Tsunamis: How Well
Do They Mix?” He will be showing slides and video from his
research.
PUBLIC OUTREACH
“Earthquake and Tsunami Hazards for the San Diego Region”
is the topic of this year’s Town Hall Meeting to be held Tuesday
evening, 17 April 2012. Speakers and Discussion Panel members include Tom Rockwell and Kim Olsen, professors at San
Diego State University, Pat Abbott, emeritus professor at
SDSU, and Mark Legg of Legg Geophysical in Huntington
Beach. This event will be open to the public for the purpose
of informing the general population and public officials about
earthquake-related issues.
FIELD TRIPS
Both field trips will take place on Friday, 20 April 2012.
Departure and return times are approximate.
Trip 1: UCSD Large High Performance Outdoor Shake
Table (LHPOST)
Leaders: José Restrepo, Professor of Structural Engineering,
and Dan Radulescu, NEES@UCSD manager
The NEES@UCSD Large High Performance Outdoor
Shake Table (LHPOST) is a national earthquake test facil-
ity funded by the National Science Foundation through the
George E. Brown Jr. Network for Earthquake Engineering
Simulation (NEES) program. This facility, located at the
Englekirk Structural Engineering Center of the University of
California at San Diego, provides the earthquake engineering community with an earthquake simulator that allows
the accurate reproduction of severe near-source earthquake
ground motions for testing of very large structural and soilfoundation-structure interaction (SFSI) systems. In this network, earthquake engineers and students, located at different institutions around the nation and the world, are able to
perform experimental work and collaborate to develop better
and more cost-effective ways of mitigating earthquake damage.
The objective of the field trip is to visit the facility and
have a taste of the one-of-a-kind large-scale experiments usually made for the validation and calibration of analytical simulation tools, which cannot be readily achieved from testing at
smaller scale, or under quasi-static or pseudo-dynamic test conditions. The facility also contains two soil pits for testing deep
foundations and has a blast test simulator.
A 5-story building, fully outfitted all nonstructural elements, health rooms and a working elevator is currently on the
shake table. This building is the product of multi-institutional
research collaboration between government organizations,
national and international industry and academia, and will
be the largest test in earthquake engineering conducted in the
United States.
Lunch will be provided at the end of the tour. This is a
half-day trip, leaving from the Town and Country around 9
am and returning around 1 pm. Note: The Englekirk Center
has to meet all OSHA safety requirements. Please do NOT
come with open shoes or high heels.
Trip 2: Paleoseismic Slip Rates on the Elsinore Fault,
California
Field Trip Leader: Tom Rockwell, San Diego State University,
Department of Geological Sciences
The Elsinore fault is the western onshore branch of the
San Andreas fault zone in southern California. The slip rate
along the northern Elsinore fault is estimated at about 5 mm/
yr, but the activity and rate of the southern Elsinore fault has
come under some scrutiny lately, as InSAR implies a low slip
rate towards its southern end. On this field trip, we will examine evidence for several aspects that are relevant to the significance of the Elsinore fault in the Coyote Mountains, western
Salton Trough, near the very southern end of the fault. First,
we will walk along an approximately 1 km section of the fault
that ruptured in the past 300 years. Along this section, we will
see offsets from the most recent event plus at least two other
late Holocene events. In addition, we will look at alluvial fans
that have been laterally offset by tens to hundreds of meters in
the late Quaternary; these fans have been dated with u-series
on pedogenic carbonate and cosmogenic radionuclides, yielding a slip rate at the southernmost end of the fault of about
1.8 mm/yr. We will then drive a few kms to the NW where
the slip in past earthquakes is larger, and look at offset alluvial
fans that have distinct blast assemblages that indicate their
source canyons. Ongoing mapping and dating of these fans
indicates that the slip rate increases to the NW towards the
central part of the Coyote Mountains and may be as much as
3 mm/yr. We will discuss the tectonic implications of these
findings.
This trip will leave around 8:00 am from the Town and
Country and return at approximately 6:00 pm the same day.
Trip includes an estimated 4 hours of drive time plus moderate
walking (wear sturdy shoes). Lunch will be provided.
MEETING INFORMATION
Registration
Registration information is available online at www.seismosoc.
org/meetings/2012/reg/. Early bird discounts extend through
March 9, 2012.
If you would like to bring a companion (someone traveling with you, but not attending the technical meeting), they
may register as a companion for $70 which includes tickets to
the opening ice-breaker reception, light breakfast snacks each
morning, and the use of a companion lounge each morning and
the assistance of a person from the San Diego Visitor’s Bureau
to help them plan their time in San Diego.
Participants may also purchase lunch and field trip tickets
for their guests.
Preliminary Schedule
Please note that this year the technical sessions start on Tuesday,
rather than on Wednesday as in recent years and the sessions end
on Thursday. The field trips will be held on Friday. Events will be
held at the Town and Country Resort and Convention Center
in the Mission Valley area of San Diego, California.
Monday, 16 April
Board of Directors Meeting (9:30 am–5 pm)
Registration (3 pm–8 pm)
Icebreaker (6 pm–8 pm)
Tuesday, 17 April
Technical Sessions (8:30 am–6 pm)
Annual Luncheon (12 pm–2 pm)—Society Awards and
Recognition
Town Hall Meeting (7 pm–9 pm)
Wednesday, 18 April
Lunch (12 pm–1 pm)
Joyner Lecture & Reception (5:15 pm–7:30 pm)
Thursday, 19 April
Lunch (12 pm–1 pm)
Friday, 20 April
Field Trips
This schedule is subject to change.
HOTEL INFORMATION
Town and Country Resort and Convention Center
The Town and Country, a beautiful garden-filled resort,
includes five restaurants, two swimming pools and a day spa.
It is next door to a championship golf course and just minutes
from downtown, Old Town, and other attractions via trolley. By making your reservation from this URL, you will be
insured the SSA conference rate. https://resweb.passkey.com/
Resweb.do?mode=welcome_ei_new&eventID=3640472
Reasons to Stay at the Town and Country
When you stay at the conference hotel, you not only stay at
the most convenient location for the meeting, you help the
Seismological Society. The hotel gives us a significant discount
on our meeting rooms and food if we book a certain number of
guest rooms. We base the price of meeting registration on making that number. If we don’t, SSA loses money on the meeting
and our ability to serve our members is reduced. This year we
have negotiated an affordable room rate and complimentary
in-room Internet. We have blocked rooms in the nicest part
of the hotel. Of course, you can stay at other hotels nearby,
but you will have to pay for parking at the Town and Country
(around $20/day), your room will not be as convenient, and
you won’t have the satisfaction of knowing that your room reservation is helping make the SSA Annual Meeting a financial
success.
• Meeting Overview, 325
Overview of Technical Program
ORAL SESSIONS
Tuesday, 17 April
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
8:30–noon
Ground Motion
Advances in Rapid
Dynamics of Seismicity
Debating Fault Model
Prediction Equations and Earthquake and Tsunami Beyond Universal Scaling Input Data
Earthquake Site Response Detection and Modeling Laws
using Geodetic and
Seismic Data
2:15–3:45 pm
Seismic Imaging: Recent
Advancement and Future
Directions
4:15–5:45 pm
7:30–9:00 pm
Physics in Seismology: The Dynamics of Seismicity
Validation of Strong
Legacy of Leon Knopoff Beyond Universal Scaling Ground Motion
Laws
Simulations for
Probabilistic Fault
Displacement Hazard
Analysis
Town Hall Meeting—Town & Country Room
Wednesday, 18 April
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
8:30–noon
Tying Nearfield PheNumerical Modeling of
Seismicity in Volcanic
nomenology to Farfield
Earthquake Motion and
Environments
Measurements: Explosion Seismic Wave Propagation
Source Physics and Energy
Propagation Through
Complex Media
Earthquake Studies
1:30–3:00 pm
Earthquake Debate #1:
El Mayor-Cucapah,
Concept of Segmentation Baja California M7.2
Earthquake of 4 April
2010: Research Results
and Lessons
Structure Models,
Wavespeed, and
Attenuation
Macroseismic Effects
in Recent and Ancient
Earthquakes and their
Relationship to Ground
Motion Parameters
3:30–5:00 pm
PSHA Methodology
The M5.8 Central
Virginia and the M5.6
Oklahoma Earthquakes
of 2011
Non-Volcanic Tremor,
Slow-Slip Events and
Remote Triggering
5:15–6:15 pm
Joyner Lecture—Town & Country Room
doi: 10.1785/gssrl.83.2.325
Thursday, 19 April
Pacific Salon 1
8:30–noon
1:30–3:00 pm
3:30–5:00 pm
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Challenging the Idea
of Seismic Coupling
along Subduction Zones: Chile,
Sumatra, Tohoku…
What’s Next?
Pacific Salon 6 & 7
Deformation ProUncertainty in the
Rotations in Strongcesses and Properties Estimation of Earth- motion Seismology
of the San Jacinto
quake Hazard
Continental
Fault Zone
Lithospheric
Structure and
Tectonics of Central
Probabilistic Seismic The 23 October
Detecting,
North America Hazard Analyses,
2011 Van, Turkey
Modeling, and
Models, Maps, and Earthquake:
Predicting the
Simulations
Observations and
Seismic Source
Implications
Earthquake Location
and Monitoring
POSTER SESSIONS
Earthquakes and
Tsunamis at Coastal
Archaeological Sites
Golden Ballroom
Tuesday am
•
•
•
•
Neotectonics, Fault Geology and Paleoseismic Studies
Seismic Imaging: Recent Advancement and Future Directions
Tuesday pm
•
•
•
•
Advances in Rapid Earthquake and Tsunami Detection and Modeling using Geodetic and Seismic Data
Ground Motion Prediction Equations and Earthquake Site Response
The 11 March 2011 Tohoku, Japan Earthquake: Observations and Models
Wednesday am •
•
•
•
•
•
•
•
Challenging the Idea of Seismic Coupling along Subduction Zones: Chile, Sumatra, Tohoku… What’s Next?
El Mayor-Cucapah, Baja California M7.2 Earthquake of 4 April 2010: Research Results and Lessons
Macroseismic Effects in Recent and Ancient Earthquakes and their Relationship to Ground Motion Parameters
Non-Volcanic Tremor, Slow-Slip Events and Remote Triggering
The M5.8 Central Virginia and the M5.6 Oklahoma Earthquakes of 2011
Wednesday pm •
•
•
•
•
•
Deformation Processes and Properties of the San Jacinto Fault Zone
Numerical Modeling of Earthquake Motion and Seismic Wave Propagation
U.S.-China Collaborations in Seismological and Earthquake Studies
Thursday am
•
•
•
•
•
Continental Lithospheric Structure and Tectonics of Central North America
Earthquake Strong-Motion Modeling
Probabilistic Seismic Hazard Analyses, Models, Maps, and Simulations
The 23 October 2011 Van, Turkey Earthquake: Observations and Implications
Thursday pm
•
•
•
•
Earthquake Location and Monitoring
Sensors and Software Techniques
Surface Deformation and Geodetic Techniques
Tying Nearfield Phenomenology to Farfield Measurements: Explosion Source Physics and Energy Propagation
Through Complex Media
• Meeting Program, 327
Program for 2012 SSA Annual Meeting
Presenting author is indicated in bold.
Tuesday, 17 April—Concurrent SSA Oral Sessions
Time Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
Ground Motion Prediction
Equations and Earthquake
Site Response
Session Chair: Alan Yong
(see page 354)
Advances in Rapid
Earthquake and Tsunami
Detection and Modeling
using Geodetic and
Seismic Data
Session Chairs: Yehuda
Bock, Shri Krishna Singh,
and Timothy Melbourne (see
page 359)
Dynamics of Seismicity
Beyond Universal Scaling
Laws
Session Chairs: Yehuda BenZion and Ilya Zaliapin (see
page 364)
Debating Fault Model
Input Data
Session Chairs: Delphine
Fitzenz and Andrew Michael
(see page 368)
2012 Update of the
Campbell-Bozorgnia NGA
Equation. Campbell, K. W.,
and Bozorgnia, Y.
Invited: GPS Earthquake
Early Warning in Cascadia.
Szeliga, W. M., Melbourne,
T. I., Santillan, V. M., and
Scrivner, C.
Invited: Elucidating
Regional Tectonic and
Secondary Causes of
Seismicity in Southern
California: Application
of Waveform Relocated
Seismicity and High
Precision Focal Mechanisms
Understanding the NGAInvited: Application
and Other Geophysical Data
West Ground-Motion
of Real-Time GPS to
Sets. Hauksson, E., Yang,
Prediction Equations for
Earthquake Alerts in
W., and Shearer, P. M. (30
PGA and PGV SSA Abstract Northern California. Allen, minutes)
2012. Baltay, A. S., Hanks, R. M., Johanson, I., and Ziv,
T. C., and Beroza, G. C.
A.
Data Constraints on Models
for Earthquake Physics and
Forecasting. Rundle, J. B.,
Holliday, J. R., Graves, W.
R., Sachs, M. K., Heien, E.
M., Yikilmaz, M. B., and
Turcotte, D. L.
9:00
Applicability of the NGA
Ground-Motion Prediction
Equations for Europe.
Sandikkaya, M. A., and
Akkar, S.
Invited: Earthquake
Early Detection and
Rapid Characterization in
California Using Real Time
GPS and Accelerometer
Data. Bock, Y., Clayton, R.,
Crowell, B., Fang, P., Geng,
J., Kedar, S., Melgar, D.,
Squibb, M., Webb, F., and
Yu, E.
Stress Uncertainties of the
San Andreas Fault System
from 4-D Deformation
Modeling. Smith-Konter,
B. R.
9:15
for ENA: Learning from and
Limitations of the NGAEast Database. Al Noman,
M. N., Deshon, H. R., and
Cramer, C. H.
Determination of
Tsunamigenic Potential of a
Scenario Earthquake in the
Guerrero Seismic Gap Along
the Mexican Subduction
Zone. Pérez-Campos, X.,
Singh, S. K., Cruz-Atienza,
V., Melgar, D., Iglesias, A.,
and Hjörleifsdóttir, V.
8:30
8:45
doi: 10.1785/gssrl.82.2.327
Invited: Testing for
Poisson Behavior. Stark,
P. B., and Luen, B. (30
minutes)
Irregular Behavior of the
Dead Sea Transform,
Inferred from 3D
Paleoseismic Trenching.
Wechsler, N., Rockwell, T.
K., and Klinger, Y.
Aftershock Statistics
Constitute the Strongest
Evidence for Elastic
Relaxation in Large
Earthquakes—Take 2. Field,
E. H.
Tuesday, 17 April (continued)
Pacific Salon 3
Pacific Salon 4 & 5
9:30
Rupture Directivity
Correction Model for the
Fault-Normal, Fault-Parallel
and Fiftieth Percentile
Components of Horizontal
Ground Motion. Bayless, J.
R., and Somerville, P. G.
Seismic and Tsunami
Invited: Estimating ETAS.
Monitoring in the
Schoenberg, F. P.
Caribbean. Huerfano, V. A.,
Baez, G., von HillebrandtAndrade, C., and Lopez, A.
Invited: Under the Hood
of the Earthquake Machine:
IndentifyingImportant
Constraints for the
Predictive Modeling of the
Seismic Cycle. Barbot, S.,
Lapusta, N., and Avouac,
J. P.
9:45
How the Style-ofFaulting Ratios Change
with Database Features.
Sandikkaya, M. A., and
Akkar, S.
Rapid Estimation of Damage
to Tall Buildings Using
Near Real-Time Earthquake
and Archived Structural
Simulations. Krishnan, S.,
Casarotti, E., Goltz, J., Ji, C.,
Komatitsch, D., Mourhatch,
R., Muto, M., Shaw, J. H.,
Tape, C., and Tromp, J.
Integrating Seismicity
and Potential Fields Data
to Determine Structural
Controls on the Fairbanks
and Salcha Seismic Zones,
Interior Alaska. Doser, D.
I., Schinagel, S. M., and
Dankoff, C. J.
Invited: Supershear
Ruptures and the Rock
Strength. Shcherbakov, R.,
and Bhattacharya, P.
Pacific Salon 6 & 7
Break—Golden Ballroom
10:00
10:30 Critical Parameters
Affecting Bias and
Variability in Site Response
Analyses Using KiK-net
Downhole Array Data.
Kaklamanos, J., Bradley, B.
A., Thompson, E. M., and
Baise, L. G.
Invited: Automated RealTime Detection of Extended
Fault Ruptures during
Large Earthquakes. Boese,
M., Heaton, T. H., and
Hauksson, E.
10:45 Retrieval of Mechanical
Properties of a ConcreteFace Rockfill Dam
(CFRD) using Ambient
Seismic Noise during Its
Construction. MartínezRamírez, E., SánchezAlvaro, E., FernándezRamírez, S., León-Sánchez,
P. D., Marengo-Mogollón,
H., Sanchez-Sesma, F. J.,
Rodríguez-González, M.,
and Suarez, M.
Invited: A Rapid, Reliable, Invited: Are Earthquake
and Robust Method to
Magnitudes Clustered?
Estimate Mw and Other
Davidsen, J. (30 minutes)
Fault Parameters for Early
Tsunami Warning Based
on Coastal GPS Networks.
Singh, S. K., Pérez-Campos,
X., Iglesias, A., and Melgar,
D.
What Can Surface Slip
Distributions Tell Us About
Fault Connectivity at
Depth? Oglesby, D. D.
11:00 Final Report on ARRAfunded Site Characterization
Project. Yong, A., Martin,
A., Stokoe, K. H., and
Diehl, J.
Invited: Rapid
Centroid Moment Tensor
Computation for the Mw
9.0 Tohoku-Oki Earthquake
from Local and Regional
Displacement Records.
Melgar, D., Crowell, B. W.,
and Bock, Y.
Fault Interaction Deduced
from Characteristic
Geomorphic Offsets,
Southern San Andreas Fault.
Williams, P. L.
Sequence Clustering in
Earthquake Catalogs.
Newman, W. I., Turcotte,
D. L., Malamud, B. D.,
Holliday, J. R., and Rundle,
J. B.
Do We Understand
Stepovers Sufficiently to
Model Them? Michael, A. J.
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
11:15 Application of the H/V
Spectral Ratios for
Earthquake Ground
Motions at K-Net Sites in
Tohoku Region, Japan to
Delineate Soil Nonlinearity.
Kawase, H., Nagshima,
F., Matsushima, S., and
Sanchez-Sesma, F. J.
Near Real-Time Full-Wave
Centroid Moment Tensor
(CMT) Inversion for
Ground-Motion Forecast
in 3D Earth Structure of
Southern California. Lee,
E., Chen, P., Jordan, T. H.,
and Maechling, P. J.
High-Resolution Fault
Tomography from Accurate
Locations and Focal
Mechanisms of Swarm
Earthquakes. Vavrycuk, V.,
and Bouchaala, F.
Invited: Seemingly Minor
Details of Fault Geometry
May Strongly Affect Rupture
Propagation. Lozos, J. C.,
and Oglesby, D. D.
11:30 Automatic Determination of
Amplification for New Sites
Within a Seismic Network.
Edwards, B., and Fäh, D.
Invited: Rapid
Magnitude and Fault
Slip Determination from
Combined GPS and
Accelerometer Data.
Crowell, B. W., Bock, Y.,
and Melgar, D.
Relations Between
Seismic Clustering and
Physical Properties of the
Lithosphere. Zaliapin, I.,
and Ben-Zion, Y.
The Importance of
the Orientation of the
Maximum Remote Stress
in Quasi-Static Triggering
of Fault Slip in Multi-Fault
Earthquakes. Madden, E.
H., Maerten, F., and Pollard,
D. D.
11:45 Application of Microtremor
Array Measurements
and Three-Component
Microtremor Measurements
to Estimate S-Wave Velocity
Structure at San Francisco
Bay Area. Hayashi, K., and
Underwood, D.
Newly Developed an
Algorithm to Detect/
Estimate Static Ground
Displacements for NearField Tsunami Forecasting
Based on the RTK-GPS
Data. Ohta, Y., Kobayashi,
T., Tsushima, H., Miura, S.,
Hino, R., Iinuma, T., and
Fujimoto, H.
On the Relation of Stresses
to Aftershock Decay.
Gerstenberger, M. C., Fry,
B., Abercrombie, R., Doser,
D., and Ristau, J.
Testing Segmentation
Models. Jackson, D. D.
12:00
2:15
Annual Luncheon—Town & Country Room
Directions
Session Chairs: Youshun
Sun, Michael Begnaud,
Sidao Ni, and Junmeng Zhao
(see page 356)
Physics in Seismology: The Dynamics of Seismicity
Legacy of Leon Knopoff
Beyond Universal Scaling
Session Chairs: Paul Davis, Laws (continued)
Freeman Gilbert, David
Jackson, and Thomas Jordan
(see page 362)
Ground Motion
Simulations for
Session Chairs: Nicolas
Luco, Sanaz Rezaeian, and
Thomas H. Jordan (see page
370)
High-Resolution SeismicReflection Imaging Profiles
across the Grizzly Valley
Fault System, Northern
Walker Lane, California.
Gold, R. D., Stephenson, W.
J., Odum, J. K., Briggs, R.,
Crone, A., Worley, D., Allen,
J., Angster, S. and Bowden,
D.
The Burridge-Knopoff
Slider Block Model: A
Retrospective Analysis and
Future Outlook. Rundle, J.
B., and Turcotte, D. L.
Stress Driven Variations
in Microseismicity during
Laboratory Stick-Slip
Tests. Goebel, T. H. W.,
Schorlemmer, D., Dresen,
G., and Becker, T. W.
Invited: Progress of
the Southern California
Earthquake Center
Technical Activity Group on
Ground Motion Simulation
Validation. Luco, N., and
Jordan, T. H.
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
2:30
Invited: Seismic
Tomography Structurally
Constrained by a priori
Model Based on a CrossGradient Approach. Zhang,
H., Newman, G. A., and
Fehler, M.
Earthquake Prediction: The
Scientific Heritage of Leon
Knopoff. Keilis-Borok, V.,
and Zaliapin, I.
Systematic Analysis of
Foreshock Sequences in
Southern California. Chen,
X., Shearer, P. M., and
Hauksson, E.
Validation of Las Vegas
Basin Response to the
1992 Little Skull Mtn.
Earthquake as Predicted
by Physics-Based Nevada
ShakeZoning Computations.
Flinchum, B. A., Savran,
W. H., Smith, K. D., Louie,
J. N., Pullammanappallil, S.
K., and Pancha, A.
2:45
Invited: Adjoint
Tomography Reveals
European Upper Mantle
Structure. Tromp, J., Zhu,
H., Bozdag, E., and Peter, D.
Is the Global Sequence of
Large Earthquakes, with
Aftershocks Removed,
Poissonian? Shearer, P. M.,
and Stark, P. B.
Advances in Local b-value
Imaging and New Insight
on Physical Interpretation.
Tormann, T., Wiemer, S.,
and Hardebeck, J. L.
Invited: Validation of
a 4-Hz Physics-Based
Simulation of the 2008
Chino Hills Earthquake.
Taborda, R., and Bielak, J.
3:00
Invited: Full-3D
Waveform Tomography for
Southern California. Chen,
P., Lee, E., Jordan, T. H.,
Maechling, P. J., Denolle,
M., and Beroza, G. C.
Modulation of Tectonic
Tremor by the Tides:
Physical Models Descended
from Leon Knopoff with
Application to the Deep San
Andreas. Beeler, N. M.,
Thomas, A., Burgmann, R.,
and Shelly, D.
Magnitude Dependent
Seismic Quiescence
Investigated with a Fault
Simulator that Incorporates
Dilatancy and Hydrological
Effects. Smith, D. E., Sacks,
I. S., and Rydelek, P. A.
Invited: A Method for
Validation of Simulated
Ground Motions Using
Time-Domain Cumulative
Statistical Characteristics.
Rezaeian, S.
3:15
Invited: Full-3D
Waveform Tomography
for Northern California
Using Ambient-Noise
Cross-Correlation Green’s
Functions. Lee, E., Xu, Z.,
and Chen, P.
Physics of Q. Morozov, I. B. Cumulative Coulomb Stress
Changes—What Influence
do Small Events have on
Triggering and the Time
to the Next Earthquake?
Woessner, J., Meier, M.
A., Werner, M. J., and
Wiemer, S.
Ground Motion Simulations
for the 2009 L’Aquila
(Central Italy) Earthquake:
Modeling and Validation.
Ameri, G., Pacor, F., and
Gallovic, F.
3:30
SALSA3D—Improving
Event Locations Using
a Global 3D P-Velocity
Model of the Earth’s Crust
and Mantle. Ballard, S.,
Begnaud, M. L., Young, C.
J., Hipp, J. R., Encarnacao,
A. V., Chael, E. P., Phillips,
W. S., and Steck, L. K.
Probabilistic Earthquake
Forecasts Based on
Branching Models of
Seismicity: Tracing Leon
Knopoff’s Contributions.
Werner, M. J., Helmstetter,
A., Jackson, D. D., and
Kagan, Y. Y.
Invited: Comparison
of Nonlinear Building
Response Simulations Using
Recorded and Simulated
Ground Motions. Goulet,
C. A., Haselton, C. B., and
Bayless, J.
3:45
Correlation Fractal
Dimension Approach for
Estimating Temporal and
Spatial Pattern of Seismicity
in the Himalayan Region.
Singha Roy, P. N., and
Mondal, S. K.
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
Directions (continued)
Physics in Seismology: The Probabilistic Fault
Legacy of Leon Knopoff
Displacement Hazard
(continued)
Analysis
Session Chairs: Robb Moss
and Mark Petersen (see page
367)
Ground Motion
Simulations for
(continued)
4:15
Receiver Functions on Ice:
Crust and Mantle Properties
from POLENET. Chaput,
J. A., Hansen, S., Aster, R.,
Nyblade, A., Wiens, D.,
Huerta, A., Wilson, T., and
the POLENET group
Triggering Cascades and
Statistical Properties of
Aftershocks. Davidsen, J.,
Gu, C., and Baiesi, M.
Invited: Quantifying
Surface Fault Displacement
Hazard: What is the Status?
Schwartz, D. P., and
Dawson, T. E.
Invited: Validation
of Broadband Synthetic
Seismograms With
Earthquake Engineeringrelevant Metrics. Olsen,
K. B., Jacobsen, B. H., and
Takedatsu, R.
4:30
Onshore/Offshore Structure
of the Northern Cascadia
Subduction Zone Obtained
from Bayesian Receiver
Function Inversion. Brillon,
C., Cassidy, J. F., and Dosso,
S. E.
Velocities of Plate Motions,
Fault Rupture, and Epicenter
Migration: a Unified
Mesoscale Framework based
upon Statistical Mechanics
of Cracks. Ben-Menahem,
S., and Ben-Menahem, A.
Invited: Fault Rupture
Displacement at Caltrans
Bridges. Shantz, T.,
Merriam, M., and Yashinsky,
M.
Invited: Nonlinear
Response Potential
Evaluation Using
Stochastically Simulated
Accelerograms. Goda, K.,
and Atkinson, G. M.
4:45
A New Paradigm for Seismic
Imaging: Transdimensional
Inversion of Receiver
Functions and Surface Wave
Dispersion with Hierarchical
Bayes Algorithm. Tkalcic,
H., Bodin, T., Sambridge,
M., Gallagher, K., and
Arroucau, P.
Using Virtual Earthquakes
for Kinematic Rupture
Models. Denolle, M.,
Dunham, E. M., Prieto, G.,
and Beroza, G. C.
Invited: Non-Ergodic
Models for Probabilistic
Fault Rupture Hazard.
Abrahamson, N.
Invited: Wood Frame
Building Damage Prediction
Using Broad-band Synthetic
Ground Motions: A
Comparative Study. Pei, S.,
van de Lindt, J. W., Hartzell,
S., and Luco, N.
5:00
Long-Period Surface-Wave
Attenuation within the
Mantle. Morozov, I. B.
Ambient-Field Green’s
Functions From
Asynchronous Seismic
Observations. Ma, S., and
Beroza, G. C.
Reverse Faulting and
Probabilistic Surface
Displacement Estimates.
Moss, R.
Assessment of Synthetic
Ground Motion Records
Obtained from Alternative
Simulation Methods in
Dynamic Analyses of MultiStorey Frame Buildings.
Karimzadeh-Naghshineh, S.,
Askan, A., Ameri, G., and
Yakut, A.
5:15
Inversion of Surface Waves
Including Higher Modes of
Propagation. Hosseini, S.
M., Pezeshk, S., Pujol, J., and
Stovall, S.
Point Source Seismogram
using 2D Staggered-Grid
Finite Difference Method.
Li, D., Helmberger, D., and
Clayton, R.
Case Studies of Probabilistic
Analysis of Fault
Displacement and Related
Hazards. Thio, H. K., and
Somerville, P. G.
Invited: A Statistical
Analysis of the Response
of Linear and Nonlinear
Building Systems to
Observed and Simulated
Ground Motions for Past
Earthquakes. Galasso, C.,
Zhong, P., and Zareian, F.
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
5:30
Earthquake source physics
studied with elastodynamic
modeling and laboratory
seismology. McLaskey,
G. C., Kilgore, B. D., and
Beeler, N. M.
Surface Fault Displacement
Hazards for the Long Valley
Caldera—Mono Lake Area.
Chen, R., Wills, C. J., and
Branum, D. M.
Invited: A Statistical
Analysis of the Response of
Tall Buildings to Recorded
and Simulated Ground
Motions. Jayaram, N., and
Shome, N.
Performance of Geo-acoustic
Parameter Estimation
From Ambient Noise
Measurements: Aperture,
SNR, and Information
in Diffuse Wave Fields.
Walker, S. C.
Tuesday, 17 April—Morning Poster Sessions
(see page 373)
1. New Active Fault Map for the Inner Continental
Borderland, Southern California, Santa Monica Bay to
the Mexican Border. Conrad, J. E., Ryan, H. F., Paull, C.
K., McGann, M., and Edwards, B. D.
2. Kinematics of Displacement on the Central and Western
Agua Blanca and Santo Tomas Faults, Baja California,
Mexico. Wetmore, P. H., Malservisi, R., Wilson, J.,
Ferwerda, B., and Alsleben, H.
3. Evidence for Quaternary faulting along the Gales Creek
fault zone, northwest Oregon. Bemis, S. P., and Wells, R.
E.
4. Where are the Quaternary Strike-Slip Faults in
Northwestern Montana? Stickney, M. C.
5. Multi-scale Study of Quaternary Deformation in the
Sevier Desert Basin (Central Utah): Clear Lake Fault
Zone. McBride, J. H., Nelson, S. T., Tingey, D. G., and
Heiner, B. D.
6. The Blue Ridge Fault, a Newly Discovered Holocene Fault
near Mt. Hood, Oregon. Madin, I. P., and Ma, L.
7. Splay-Fault Origin for the Yakima Fold-and-Thrust Belt,
Washington State. Pratt, T. L.
8. Morphotectonic Segmentation Along the Nicoya
Peninsula Seismic Gap, Costa Rica, Central America.
Marshall, J., Morrish, S., LaFromboise, E., Butcher, A.,
Ritzinger, B., Wellington, K., Barnhart, A., Kinder, K.,
Utick, J., Protti, M., Gardner, T., Fisher, D., Simila, G.,
Spotila, J., Owen, L., Murari, M., and Cupper, M.
9. Progress in Linking Earthquakes to Seismogenic Faults
in the Lake Tahoe-Truckee Area, California and Nevada.
Reed, T. H., Lindsay, R. D., Cronin, V. S., and Sverdrup,
K. A.
10. Ground Penetrating Radar as a Tool for Paleoseismic Site
Evaluation: A Case Study on the Calabasas and Vallecitos
Faults of Northern Baja California. Wilson, J. A., Wetmore,
P. H., Kruse, S., Fletcher, J., Teran, O., and Yelil, R.
11. Paleoseismic study of the San Andreas Fault at the Crystal
Springs South site, San Mateo County, California.
Prentice, C. S., Zacariasen, J., Kozaci, O., Sanquini, A.,
Wolf, E., Sickler, R., Feigelson, L., Crankshaw, I., Rosa, C.,
and Baldwin, J.
12. Paleoseismic Results from 2011 SSA Fieldtrip Trench
across the Southeastern Reelfoot Rift Margin. Cox, R. T.,
VanArsdale, R., Clark, D., Lumsden, D., and Hill, A.
Physics in Seismology: The Legacy of Leon Knopoff (see
page 376)
13. Rupture Driving Force for Interlocking Heterogeneous
Plate Coupling and the Recent Megathrust Earthquake.
Tajima, F.
14. The Effects of Static Coulomb, Normal and Shear
Stress Changes on Earthquake Occurrence in Southern
California. Strader, A. E., and Jackson, D. D.
15. Interpreting Tsunami Source Clustering in Terms of a
Branching Process. Geist, E. L.
Seamount Subduction and Earthquakes (see page 376)
16. Dominant Roles of a Possible Subducting Seamount in the
2011 Mw 9.0 Tohoku-Oki Earthquake. Duan, B.
17. Earthquakes with Anomalously Steep Dip in the Source
Region of the 2011 Tohoku-Oki Earthquake—Possible
Indicators for Enhanced Plate Coupling. Zhan, Z.,
Helmberger, D. V., Simons, M., Kanamori, H., Wu, W.,
Hudnut, K. W., Chu, R., Ni, S., Hetland, E. A., and
Culaciati, F. H. O.
18. Effects of Subducted Seamounts on Megathrust
Earthquakes. Yang, H., Liu, Y., and Lin, J.
19. Examples of Seismic Behavior in Areas of Seamount
Subduction. Bilek, S. L., and Wang, K.
20. Short-Term Migration of Deep Tectonic Tremor along
Subduction Direction: Striations Due to Seamounts
Subduction? Ide, S.
21. Seismic Strong Motion Array Project (SSMAP) to Record
Future Large Earthquakes in the Nicoya Peninsula Area,
Costa Rica. Simila, G., Quintero, R., McNally, K.,
LaFromboise, E., Mohammad Ebrahim, E., and Seguro, J.
Directions (see page 377)
22. 3D Depth Migrations From Networks of 2D Seismic
Lines for Fault Imaging in Western Nevada. Frary, R. N.,
Louie, J. N., Pullammanappallil, S., and Eisses, A.
23. Characterization of Shallow S-Wave Velocities across the
Tacoma Basin, Washington State, from SPAC and HVSR
Microtremor Analyses. Stephenson, W. J., Odum, J. K.,
Dart, R. L., Angster, S. J., and Worley, D. M.
24. Time-Resolved Velocity Tomography at Mount Etna
Volcano (Italy) during 2000-2008. Barberi, G., Cocina,
O., Chiarabba, C., De Gori, P., and Patanè, D.
25. Evidence for a Bimaterial Interface along the Mudurnu
Segment of the North Anatolian Fault Zone from P Wave
Arrival Times and Polarization Analysis. Bulut, F., BenZion, Y., and Bohnhoff, M.
26. The LLNL-G3D Global P-wave Velocity Model and the
Significance of the BayesLoc Multiple-Event Location
Procedure. Simmons, N. A., Myers, S. C., Johannesson,
G., and Matzel, E.
27. Shear Wave Velocity-Depth from IMASW Measurements
in Teton County, Idaho: Updated NEHRP Site-Response
Classification and Seismic Amplification Maps. Turner, J.
P., Phillips, W. M., Zellman, M. S., and O’Connell, D. R.
H.
28. Virtual Seismic Receiver Array. Alhukail, I. A., and
Ikelle, L. T.
29. Anisotropy of the Mexico Subduction Zone Based on
Shear-Wave Splitting Analysis. Stubailo, I., and Davis, P.
M.
30. The Use of Direct Shear Waves in Quantifying Seismic
Anisotropy: Results from the Northeastern Tibet. Eken,
T., Tilmann, F., and Nunn, C.
31. Body Wave Attenuation Heralds Surfacing Magma at
Mount Etna (Italy): The 2001–2003 and 2007–2008
Case Studies. Giampiccolo, E., De Gori, P., Chiarabba, C.,
Cocina, O., and Patanè, D.
32. Crust and Upper Mantle Structure of Iran from the
Simultaneous Inversion of Complementary Geophysical
Observations. Maceira, M., Bergman, E. A., Rowe, C. A.,
and Zhang, H.
33. Crust and Upper Mantle Structure of the Western US
from Simultaneous Inversion of Surface-Wave Dispersion,
Gravity, and Receiver Functions. Steck, L. K., Maceira,
M., Herrmann, R. B., Ammon, C. J., and Stead, R. J.
34. A New 3D P-wave Velocity Model of Mount Rainier
Using Double-Difference Local Earthquake Tomography.
Feenstra, J. P., Thurber, C. H., and Moran, S. C.
35. 3D Seismic Models and Finite-Frequency vs Ray
Theoretical Approaches. Maceira, M., Larmat, C., Allen,
R. M., Porritt, R., Rowe, C. A., and Obrebski, M.
36. Shear Velocity Structure of the Iberian Peninsula Using
Seismic and Gravity Observations. Villasenor, A.,
Maceira, M., and Ammon, C. J.
37. Attenuation and Source Parameters for the Western US
Using Automated Amplitude Measurements. Phillips,
W. S., Mayeda, K. M., and Malagnini, L.
38. Teleseismic Imaging of the Eastern Tibetan Plateau. Ge, C.,
Sun, Y., Zheng, Y., Xiong, X., Toksoz, M. N., and Zheng, Y.
39. Upper Mantle Structure around the Mid-Ocean Ridge of
the Pacific Ocean with the Precursors of SS and PP. Sui, Y.,
Zheng, Y., Zhou, Y., and Sun, Y.
Tuesday, 17 April—Afternoon Poster Sessions
and Modeling using Geodetic and Seismic Data (see page
381)
40. Quick-and-Dirty Earthquake Parametrizations: Why
Short Analysis Times with Big Azimuth Gaps suffice for
Initial Tsunami Warning Operations. Sardina, V. H. R.,
Becker, N. C., Weinstein, S. A., Fryer, G., Koyanagi, K.,
Wang, D., Walsh, D., and McCreery, C.
41. Caltech/USGS Southern California Seismic Network:
Recent Upgrades of Instrumentation and Operational
Capabilities. Crummey, J., Bhadha, R., Devora, A.,
Guiwits, S., Johnson, D., Watkins, M., Hauksson, E., and
Thomas, V.
42. A Systematic Investigation of the “Nucleation Phase” of
Large Global Earthquakes Using Broadband Teleseismic
Data. Burkhart, E. T., and Ji, C.
43. Rapid Estimation of Tsunami Waveheights after Large
Earthquakes: Examples from the 2011 Tohoku and 2010
Maule Earthquakes. Thio, H. K., and Polet, J.
44. Radial Decay of Coseismic Displacement Amplitudes
from Thrust Earthquakes. Marrett, R.
45. Rapid Determination of Earthquake Source Parameters
Using an Earthquake Search Engine. Zhang, J., Zhang,
H., Chen, E., Zheng, Y., and Kuang, W.
46. Rapid Estimation of Slip Models for Large Shallow
Earthquakes using Teleseismic P Waves. Mendoza, C.,
Hartzell, S., Benz, H., and Herrmann, R.
47. Developments in Earthquake Early Warning at UCB:
CISN ShakeAlert. Hellweg, M., Allen, R. M., Brown, H.,
Henson, I., Kong, Q., Kuyuk, S., and Neuhauser, D. S.
48. Seismic Source Studies at the Berkeley Seismological
Laboratory. Dreger, D. S., Guilhem, A., Boyd, O. S.,
Chiang, A., and Hellweg, M.
49. Tohoku-Oki Tsunami Simulations Reveal Importance of
Sophisticated Seismic Source Parameters. Watts, P.
Debating Fault Model Input Data (see page 383)
50. What about the Influence of the Nature of the Pore Fluid
on Long-Term or Triggered Faulting Behavior? Fitzenz,
D. D., Crovisier, M., and Maury, V.
51. Earthquake Scaling Relationships Estimated from a 16
Year Catalog of Published InSAR studies. Funning, G.
J., Weston, J., Elliott, J., Ferreira, A. M. G., and RichardsDinger, K. B.
52. The Impact of Space-Geodetic Data on California
Earthquake Risk. Nyst, M., and Mak, L.
53. Earthquake Forecasts for California based on Adaptive
Space-Time Smoothing of Seismicity and Rate-and-State
Friction. Helmstetter, A., and Werner, M. J.
54. A Stochastic Earthquake Source Model Combining
Fault Geometry, Slip Rates, and Smoothed Seismicity:
California. Hiemer, S., Jackson, D. D., Wang, Q., Kagan,
Y. Y., Woessner, J., Zechar, J. D., and Wiemer, S.
55. Three Historical Earthquakes on the Southern Santa Cruz
Mountains Section of the San Andreas fault: Insights
from Three Paleoseismic Sites. Dawson, T. E., Streig, A.
R., and Weldon, R. J.
56. Major Earthquakes on a Nascent Fault Zone: Lenwood
Fault, Eastern California. Strane, M. D., Oskin, M. E.,
Khatib, F., Lindvall, S. C., Rockwell, T. K., Blisniuk, K.
N., and Iriondo, A.
57. Rupture Dynamics on Parallel Faults at a Restraining
Double-Bend and Corroboration with the Natural
Earthquake Record on the Altyn Tagh Fault, Western
China. Elliott, A. J., Duan, B. C., Oskin, M. E., and LiuZheng, J.
58. Scaling for Fault Models Toward Ground Motion
Prediction of Earthquakes in Taiwan Region. Ma, K. F.
Ground Motion Prediction Equations and Earthquake
Site Response (see page 385)
59. A New Empirically Based GMPE for Subduction Zone
Earthquakes. Gregor, N., Abrahamson, N., and Addo, K.
60. Investigation of Spatial Correlation of Single-Station
Ground Motion Residuals. Hollenback, J. C., and
Abrahamson, N.
61. A n Update of the Spudich and Chiou Directivity Model
Using the NGA-West 2 Dataset. Spudich, P., and Chiou,
B. S. J.
62. Ground-Motion Prediction Equations for Southeastern
Australia Assuming Variable Stress Parameters. Allen, T.
I.
63. Ground Motion Amplification at the Mexicali Valley, Baja
California, México. Vidal-Villegas, J. A., Vega-Guzmán, F.
J., and Huerta-López, C. I.
64. Explanatory Variables in Terrain-based VS30 Model.
Yong, A., and Iwahashi, J. J.
65. A Hybrid Slope-Geology VS30 Mapping Strategy.
Thompson, E. M., and Wald, D. J.
66. Sea-floor Marine Site Characterization Using Earthquake
Data Recorded at the Gulf of California, México. HuertaLopez, C. I., Castro-Escamilla, R. R., Gaherty, J. B., and
Collins, J. A.
67. A nalysis of Joint Time-Frequency Spectral Decomposition
of Acceleration Time Series from the 17 December 2011
Mw. 5.1 Puerto Rico Earthquake. Upegui-Botero, F.
M., Huerta-Lopez, C. I., Caro-Cortes, J. A., MartinezCruzado, J. A., Suarez Colche, L. E., and the Puerto Rico
Strong Motion University (PRSMP) of Puerto Rico at
Mayaguez Campus
68. Seismic Site Response in Christchurch (New Zealand)
from Dense Aftershock Recordings. Kaiser, A. E.,
Benites, R. A., Chung, A. I., Oth, A., Cochran, E. S., Fry,
B., and Haines, A. J.
69. In-situ Measurement of Velocity Change Under Induced
Strong Ground Motion. Larmat, C., Guyer, R. A., Lee,
R., Rutledge, J. T., Johnson, P. A., and Stokoe, K.
70. Analysis of Micro-Seismicity and Site Response Using
Waveform Data from a Small Broadband Deployment
on Cal Poly Pomona Campus. Lino, S. I., Ho, K. K., and
Polet, J.
71. Seismic Wave Propagation Profiles and Response Spectra
of Kuala Lumpur City Center under the Far Field
Earthquake Effects from Sumatra. Adnan, A. B., Suhatril,
M., Hendriyawan, and Masyur, I.
72. Seismic Noise in Antarctica. Anthony, R., Aster, R.,
Rowe, C., Wiens, D., and Nyblade, A.
73. Investigating the 2011 Rumblings in Windsor, Ontario
through Seismology. Bent, A. L., and Woodgold, C. R. D.
74. A n Experimental Study on Rock Physical Property Based
on Binary code Excitation. Wu, H. Z.
Observations and Models (see page 389)
75. Interpreting the 11th March 2011 Tohoku, Japan,
Earthquake Ground-Motions Using Stochastic FiniteFault Simulations. Ghofrani, H., Atkinson, G. M., Goda,
K., and Assatourians, K.
76. Long-term Change of Site Response and High-Frequency
Radiations Associated with the Mw9.0 Tohoku-Oki
Earthquake in Japan. Wu, C., Peng, Z., and Assimaki, D.
77. Ground Motions in the Triggered Fukushima Hamadori
Normal-Faulting Earthquake Following the 2011 Tohoku
Earthquake. Brune, J. N., and Biasi, G. (presented by
Anderson, J.)
78. Onshore Surface Fault Rupture and Crustal Deformation
from the 11 April 2011 Mw6.6 Hamadoori Earthquake,
Japan (an Aftershock of the 11 March 2011 Tohoku
Offshore Earthquake, Japan). Kelson, K. I., Ryder, I.,
Streig, A. R., Bray, J. D., Konagai, K., Harder, L., and
Kishida, T.
79. High-Frequency Back-Propagation Applied to the StrongMotion Data from the 2011 Tohoku Mw 9.1 Earthquake.
Yano, T. E., Shao, G., and Ji, C.
Wednesday, 18 April—Concurrent Oral Sessions
Time
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
Tying Nearfield
Phenomenology to Farfield
Measurements: Explosion
Source Physics and Energy
Propagation Through
Complex Media
Session Chairs: Robert
Abbott, Tarabay Antoun,
Howard Patton, Chandan
Saikia, and Catherine
Snelson (see page 390)
Numerical Modeling of
Earthquake Motion and
Seismic Wave Propagation
Session Chairs: Emmanuel
Chaljub, Steven Day, and
Peter Moczo(see page 394)
Seismicity in Volcanic
Environments
Session Chairs: Darcy
Ogden and Eric Dunham
(see page 399)
U.S.-China Collaborations
in Seismological and
Earthquake Studies
Session Chairs: Mian Liu,
Randy Keller, Larry Brown,
and Yongshuan (John) Chen
(see page 404)
8:30
The Source Physics
Experiments (SPE) at the
Nevada National Security
Site (NNSS). Snelson, C.
M., Chimpan, V. D., White,
R. L., Emmitt, R. F., and
Townsend, M. J.
FD Modeling of Seismic
Motion with a Stable
Arbitrarily Discontinuous
Staggered Grid. Kristek, J.,
Moczo, P., and Galis, M.
Invited: Migrating
Swarms of Brittle-Failure
Earthquakes in the Lower
Crust Beneath Mammoth
Mountain, California.
Shelly, D. R., and Hill, D. P.
New Opportunities of
US-China Collaborations
in Seismological and
Earthquake Studies. Liu,
M., Keller, G. R., Brown, L.,
and Chen, Y. J.
8:45
Analysis of Near-Field
Ground Motions from the
Source Physics Experiment.
Vorobiev, O., Antoun, T.,
Xu, H., Herbold, E., Glenn,
L., and Lomov, I.
Increasing the Frequency
Resolution in Realistic
Seismic Wave Simulations by
Using a 4th Order Accurate
Summation by Parts
Finite Difference Method.
Petersson, N. A., and
Sjogreen, B.
Invited: The Utility of
Tracking Multiplets Across
Several Eruptive Episodes at
Kīlauea Volcano, Hawaiì.
Thelen, W. A.
Invited: Opportunities
and Challenges for
Expanded US-China
Research in Seismology.
Simpson, D. W.,
Willemann, R. J., Dong, S.,
and Wu, Z.
9:00
Near Field Modeling of
High Explosive Sources: Use
of Abaqus Coupled EulerLagrange Capability for
Modeling the Source Physics
Experiment. Bradley,
C., Steedman, D., and
Greening, D.
Accuracy of Numerical
Schemes with Respect to
the P-wave to S-wave Speed
Ratio. Moczo, P., Kristek,
J., Galis, M., Chaljub, E.,
Chen, X., and Zhang, Z.
Locating a Microseism
Source in Southern Peru
from Ambient Noise Crosscorrelation. Ma, Y., Clayton,
R. W., and Zhan, Z.
Invited: A Review of the
Deep Seismic Structure
of the Crust of China.
Mooney, W. D., Wang, C.
Y., Zhang, Z. J., and Zhao,
J. M.
9:15
Factors Affecting the
Spallation Signature for the
Source Physics Experiment
(SPE-1). Rougier, E.,
Knight, E. E., Sussman, A.
J., and Broome, S. T.
Modeling of Wave
Propagation in Nonlinear
Media for Inversion of
Dynamic Soil Properties
from Earthquake Records.
Roten, D., Fäh, D., Laue, J.,
and Bonilla, L. F.
Local Micro-Seismic Study
the Menengai Geothermal
Prospect in the Central
Kenya Domes. Patlan, E.,
Wamalwa, A., Thompson,
L. E., Kaip, G., and Velasco,
A. A.
Invited: Project
INDEPTH: Origins and
Evolution of a 20-year
International Collaboration.
Brown, L. D., and Zhao, W.
Wednesday, 18 April (continued)
Time
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
9:30
Nonlinear Simulation of
Explosion Sources with
Gravity and Propagation to
Regional and Teleseismic
Distances. Stevens, J. L.,
and O’Brien, M. S.
Modeling Long Period (T
> 4 sec) Strong Ground
Motions for the 2011 Mw
9 Tohoku-Oki Earthquake
using an Enhanced Source
Representation and 3D
Seismic Velocity Models.
Graves, R. W., Wei, S., and
Helmberger, D.
Practical Considerations for
Applying Neural Network
Classification Techniques
to Volcanic Earthquakes.
West, E., and Bruton, P.
Invited: The Seismic
Structure at the edge of the
Tibetan Plateau. Sandvol,
E., Ceylan, S., Liang, X., Ni,
J., Hearn, T., Chen, Y., and
Liu, M.
9:45
Modeling Far-Field Seismic
Ground Motions from the
Explosions with ThreeDimensional Simulations,
Including Hydrodynamic
Modeling of the Source.
Pitarka, A., Mellors, R. J.,
Rodgers, A. J., Harben, P. E.,
Wagoner, J. L., Walter, W. R.,
Pasyanos, M. E., Petersson,
A., and Xu, H.
Why Should Stress Drop in
Dynamic Earthquake Source
Models Be Heterogeneous
with a Power-Law Spatial
Fourier Transform with
Exponent -1 ? Andrews,
D. J.
Volcanic Seismic
Earthquakes at Mount St.
Helens Exhibit Constant
Seismically Radiated Energy
per Unit Size. Harrington,
R. M., and Kwiatek, G.
Invited: Sino-US
Cooperation on Deep
Seismic Studies and
Education Focused on
Continental Tectonics:
Initial Results of
Cooperation on
SinoProbe02 Projects. Gao,
R., Keller, G. R., Liu, M., Li,
Q. S., Zhang, S. H., Li, Y. K.,
and Huang, D. D.
10:30 Seismic P and S Source
Functions of Underground
Chemical Explosions
(SPE). Xu, H., Antoun,
A., Rodgers, A., Glenn, L.,
Vorobiev, O., Lomov, I.,
Herbold, E., Walter, W., and
Ford, S.
Constraints on Strong
Ground Motion from
Complex Dynamic Rupture
Simulations in Elastic and
Plastic Media. Gabriel, A.
A., Ampuero, J. P., Mai, P.
M., and Dalguer, L. A.
Invited: A Mechanism for Invited: Joint Active and
Sustained, Energetic Tremor Passive Arrays for Study of
Heralding Rapid Onset of
Active Orogens. Wu, F. T.
the 2004–2008 Eruption
of Mount Saint Helens,
Washington. Denlinger, R.
P., and Moran, S.
10:45 Investigating How
and Why P/S Ratios
Discriminate Explosions
from Earthquakes Using the
at the NNSS. Walter, W.
R., Ford, S., Mellors, R.,
Pasyanos, M., Matzel, D.,
Rodgers, A., Pitarka, A., Xu,
H., Antoun, T., Vorobiev,
O., Lomov, I., Glenn, L.,
Myers, S., Hauk, T., Dodge,
D., and Ruppert, S.
Earthquake source dynamics
of the 2011 Mw 9.0 Tohoku
Earthquake Constrained
with Kinematic Source
Inversion Results. Galvez,
P., Dalguer, L. A., Ampuero,
J. P., and Nissen-Meyer, T.
Invited: A Comparison of
Tremor Before, During, and
After the Explosive Eruption
of Redoubt Volcano, Alaska
in 2009. Hotovec, A. J.,
Prejean, S. G., Vidale, J. E.,
and Gomberg, J. S.
Constraints on Regional
Stresses Prior to the 2008
Mw 7.9 Wenchuan, China,
Earthquake from Coseismic
Slip Models and Aftershock
Mechanisms. Hetland, E.
A., Medina Luna, L., and
Feng, G.
Time
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
11:00 SPE Source Characterization
Using Hydrodynamicto-Seismic Coupling and
Moment-Tensor Inversion.
Yang, X., Patton, H. J.,
Rougier, E., and Rowe, C. A.
Computation of H/V
Spectral Ratios of
Microtremors at Sites with
Strong Lateral Heterogeneity
using Diffuse Field Theory
and IBEM. MolinaVillegas, J. C., PerezGavilan, J. J., Suarez, M.,
Franco-Cruz, P., ChavezZamorate, N., SanchezSesma, F. J., Matsushima, S.,
Kawase, H., and Luzon, F.
Modeling of Volcanic
Tremor as Repeating
Earthquakes. Dmitrieva,
K., and Dunham, E. M.
Seismic Hazard Assessment
and Mitigation Policy for
Tianshui, Gansu Province,
China. Wang, Z., Woolery,
E., and Wang, L.
11:15 Moment Tensor Analysis of
SPE-1 and -2. Ford, S. R.,
Mellors, R. J., and Walter,
W. R.
On Numerical Solving the
Complex Eikonal Equation
using Ray Tracing Methods.
Vavrycuk, V.
Invited: Very-Long-Period
Earthquakes and Cycles
of Conduit Sealing and
Puffing at Fuego Volcano,
Guatemala. Waite, G. P.,
Lyons, J. J., Nadeau, P. A.,
and Brill, K. A.
Extent of Sedimentary Fill
beneath Tangshan, China
as Modeled by 3D Seismic
Survey. Chang, J. C., Keller,
G. R., Qu, G., and Harder,
S. H.
11:30 Analysis of the Influence
of Topography and Local
Wave propagation Model
on Waveforms Recorded
During the Source Physics
Experiments. Detecting
Deformation in the New
Madrid Seismic Zone using
Radar Interferometry.
Saikia, C. K., Woods,
M., Miller, J., Nguyen, B.,
Snelson, C., Townsend, M.,
and Dwyer, J. J.
Development and
Optimizations of a SCEC
Community Anelastic
Wave Propagation Platform
for Multicore Systems and
GPU-based Accelerators.
Cui, Y., Olsen, K. B., Zhou,
J., Small, P., Chourasia, A.,
Day, S. M., Maechling, P. J.,
and Jordan, T. H.
Invited: Santiaguito 2012:
Lower Explosion Rate,
Higher Intensity. Lees, J.
M., Johnson, J. B., Lyons, J.,
Anderson, J., and Nies, A.
EARTHSCOPE
and SINOPROBE
Magnetotelluric
Arrays: Contrasts and
Collaborations across
Interdisciplinary
Continental Scale Programs.
Schultz, A., and Hu, X.
11:45 Generation and Propagation
of Shear Waves from the
HUMBLE REDWOOD
Explosions. Bonner, J. L.,
Leidig, M. R., Reinke, R.,
and Lenox, E.
Topography Effects on a
Single Slope: The Effects
of SV Incidence Angle.
Mohammadi, K., and
Assimaki, D.
Photogrammetry and
Seismic Observations
of Eruptive Activity at
Santiaguito Volcano,
Guatemala 2007-2012. Nies,
A. P., Lees, J. M., Andrews,
B. J., Johnson, J. B., Lyons, J.
J., and Anderson, J.
Crustal Structure of the
Solonker Collision Zone:
Preliminary Interpretation
of A Deep Seismic
Reflection Profile in North
China. Zhang, S., Gao, R.,
Hou, H., Li, H., Li, Q., Li,
C., Randy, K. G., and Liu,
M.
12:00
Pacific Salon 1 & 2
Lunch—Town and Country Room
Time
1:30
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
Concept of Segmentation
Session Chairs: Danijel
Schorlemmer, David
Jackson, Matt C.
Gerstenberger, and Matthias
Holschneider (see page
393)
El Mayor-Cucapah,
Baja California M7.2
and Lessons
Session Chairs: Victor Wong
and Raul Castro (see page
396)
Structure Models,
Wavespeed, and
Attenuation
Session Chair: Vera Schulte
(see page 401)
Macroseismic Effects
in Recent and Ancient
Relationship to Ground
Motion Parameters
Session Chairs: Klaus-G.
Hinzen, Luigi Cucci,
Mariano Garcia-Fernandez,
and Andrea Tertulliani (see
page 407)
Invited: Segment
Boundaries: It May
be a Matter of Time.
Goldfinger, C. (30 minutes)
The Importance of Geologic
Coupling in Understanding
the Complexities of the
2010 El Mayor-Cucapah
Earthquake: Use of A Buried
High-Density Broadband
Geophone Network. Taylor,
O. D. S., McKenna, M., and
Lester, A.
An Integrated GeophysicalGeological Study of a
Landslide in Paleogene
Volcanic Deposits along
the Wasatch Front, Utah.
Hoopes, J. C., McBride,
J. H., Christiansen, E. H.,
Kowallis, B. J., Thompson,
T. J., Tingey, D. G., and
Okojie-Ayoro, A. O.
Using Chimney Damage to
Quantify Ground Motions
of Historic Earthquakes in
Eastern North America.
Ebel, J. E.
Coseismic Deformation for
the 2010 El Mayor-Cucapah
Earthquake Estimated from
Cross-Correlation of Preand Post-Event Airborne
Lidar Surveys. Borsa, A. A.,
and Minster, J. B.
True versus Apparent
Vertical Moho Offsets across
Continental Strike-Slip
Faults from Azimuthally
Dependent Joint Inversion
of Surface Waves and
Receiver Functions.
Schulte-Pelkum, V., and
Ben-Zion, Y.
ShakeMap Best Practices:
Historic and Modern
Events. Johnson, K. L.,
García, D., Worden, C. B.,
Lin, K., Mah, R., Marano,
K. D., Hearne, M., and
Wald, D. J.
UAVSAR Observations of
Slip on Faults in the Salton
Trough Associated with
the 2010 M 7.2 El MayorCucapah Earthquake.
Donnellan, A., and Parker,
J. W.
Three-Dimensional Vp and
Vp/Vs Structure Models,
Earthquake Relocations
for the Coso, Southern
California. Zhang, Q., and
Lin, G. Q.
Spatial Correlation of
Modified Mercalli Intensity
derived from High-Density
Internet-based Reports.
Worden, C. B., Wald,
D. J., Johnson, K. L., and
Quitoriano, V.
Fault Rupture Associated
With the 14 June 2010
Mw 5.7 Aftershock of
the El Mayor-Cucapah
Earthquake. Treiman, J. A.,
Rymer, M. J., Kendrick, K.
J., and Fielding, E. J.
Moho-Depth Diking
and Structural Controls
on Microplate Rifting
Mechanisms along the
Northern Sierra Nevada
- Walker Lane Boundary.
Smith, K. D., von Seggern,
D., Kent, G. M., Eisses, A.,
and Driscoll, N. W.
Computer-aided Assessment
of Macroseismic Intensity
by the Fuzzy Sets Method.
Tripone, D., Vannucci, G.,
Gasperini, P., and Ferrari, G.
1:45
2:00
Invited: Evidence Against
the Hypothesis of Fault
Segmentation. Hardebeck,
J. L. (30 minutes)
2:15
Time
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
2:30
Discussion
Precise Relocation of the
Northern Aftershock
Sequence Following
the 4 April 2010 Mw
7.2 El Mayor-Cucapah
Earthquake. Kroll, K. A.,
Cochran, E. S., Richardsand Dinger, K. B.
New Insights Into
Geometric Attenuation for
Eastern North America.
Crempien, J. G. F., and
Archuleta, R. J.
Peak Ground Acceleration
in Port-au-Prince, Haiti,
During the M7.0 12 January
2010 Haiti Earthquake
Estimated from Horizontal
Rigid Body Displacement.
Hough, S. E., and
Taniguchi, T.
Observations of Isotropic
Radiation from Aftershocks
of the 4 April 2010 (Mw
7.2) El Mayor-Cucapah
Earthquake, Baja California,
Mexico. Castro, R. R., BenZion, Y., and Wong, V.
Kappa Scaling for Western
U.S. Ground Motion
Prediction Equations.
Alatik, L., Kottke, A.,
Abrahamson, N., and
Renault, P.
The Earthquake Rotated
Obelisk in Lorca, Spain.
Hinzen, K. G., and
Fernandez, M. G.
2:45
3:30
PSHA Methodology
Session Chairs: Danijel
Schorlemmer, David Jackson,
Matt C. Gerstenberger, and
Matthias Holschneider (see
page 393)
El Mayor-Cucapah,
Baja California M7.2
and Lessons (continued)
The M5.8 Central Virginia
and the M5.6 Oklahoma
Earthquakes of 2011
Session Chairs: Stephen
Horton and Robert
Williams (see page 403)
Non-Volcanic Tremor,
Slow-Slip Events and
Remote Triggering
Session Chair: Michel
Campillo (see page 408)
Invited: Has PSHA
Done Its Time? The Hazard
Mapper’s Perspective.
Stirling, M. W. (30
minutes)
Stress Drop Spatial
Variability and Magnitude
Dependence for the 2010
El Mayor Aftershocks 3.5 <
Mw < 5.7. Crempien, J. G.
F., and Archuleta, R. J.
Foreshock and Aftershock
Sequences of the 2011 M5.6
Oklahoma Earthquake.
Keranen, K. M., Holland,
A., Savage, H., Atekwana,
E., Cochran, E., Sumy, D.,
Rubinstein, J., and Kaven, J.
Relations Between
Velocity Changes, Strain
Rate and Non-Volcanic
Tremors during the 20092010 Slow Slip Event in
Guerrero, Mexico. Rivet, D.,
Campillo, M., Zigone, D.,
Radiguet, M., Cruz-Atienza,
V., Shapiro, N. M., and the
G-GAP team
Preliminary Estimate of
Shallow Crustal Anisotropy
in the Yuha Desert,
California From Aftershocks
of the 2010 M7.2 El MayorCucapah Earthquake.
Cochran, E. S., and Kroll,
K. A.
Are Seismicity Rate Changes
in the Midcontinent Natural
or Manmade? Ellsworth,
W. L., Hickman, S. H.,
Lleons, A. L., McGarr,
A., Michael, A. J., and
Rubinstein, J. L.
Episodic Tremor as Slow-slip
events (SSE) at Parkfield,
CA. Guilhem, A., and
Nadeau, R. M.
3:45
Time
Pacific Salon 1 & 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
4:00
Invited: Probabilistic
Seismic Hazard Assessment
and the Hazards of
Overconfidence. Werner,
M. J. (30 minutes)
Coupling of Pore Pressure
and Ground Motion Data
Recorded During the 2010
El Mayor-Cucapah (Baja
California) Earthquake at
the NEES@UCSB Wildlife
Station. Seale, S. W. H.,
Lavallee, D., Steidl, J. H.,
and Hegarty, P.
The Rupture Process
of the 23 August 2011
Louisa County, Virginia
Earthquake. Chapman, M.
Modeling of 3D Complex
Tremor Migration Patterns.
Luo, Y., and Ampuero, J. P.
Electrical Resistivity
Change in the Upper
Crust of Mexicali Valley
after El Mayor-Cucapah
M7.2 Earthquake: From
Magnetotelluric Data.
Cortes, O. J., and Romo,
J. M.
Aftershock Imaging with
Dense Arrays (AIDA) after
the 23 August 2011, Mw
5.8, Virginia Earthquake:
Results from a Prototype
Rapid Deployment of Large
Numbers of Seismometers
for High Resolution
Source Characterization,
Structural Imaging and 4D
Monitoring. Brown, L. D.,
Hole, J. A., Quiros, D. A.,
Davenport, K., Han, L.,
Chen, C., Mooney, W., and
Chapman, M.
Observations of Tectonic
Tremor on the Alpine Fault,
New Zealand. Fry, B., Chao,
K., and Peng, Z.
Detecting Triggered
Earthquakes around Salton
Sea Following the 2010
Mw7.2 El Mayor-Cucapah
Earthquake Using GPU
Parallel Computing. Meng,
X., Peng, Z., Yu, X., and
Hong, B.
Finite Source Modeling
and Stress Drop of the
2011 M5.8 Virginia
Earthquake Based on
Seismic Waveforms. Shao,
G., Crempien, J. G. F.,
Archuleta, R. J., and Ji, C.
Investigating Interactions
of Creeping Segments
with Adjacent Earthquake
Rupture Zones in the
Mendocino Triple Junction
Region. Taira, T.
Evaluation of Predominant
Site Periods of Ground
Motion Stations During the
2010 El Mayor-Cucapah
Earthquake Using H/V
Response Spectral Ratio
Method. Liao, Y., and
Meneses, J.
Seismic Investigations of
Mineral, VA Earthquake
Impact to the North Anna
Nuclear Power Plant. Li, Y.
Can We Do Back-Projection
at Low Frequency? Meng,
L., Ampuero, J. P., Luo, Y.,
Wu, W., and Ni, S.
4:15
4:30
4:45
5:15
Discussion
Joyner Lecture—Town & Country Room
Building Near Faults. Bray, J. D. (see page 409)
Wednesday, 18 April—Morning Poster Sessions
What’s Next? (see page 409)
1. Stress Rotations and Stress Ratio Changes due to Great
Earthquakes: Implications for Subduction Zone Coupling.
Hardebeck, J. L.
2. Historical Seismograms: An Endangered Species? Okal,
E. A., Kirby, S. H., and Lee, W. H. K.
3. Seismicity Associated with a Stranded Plate Fragment
Above the Juan de Fuca Slab in the Vicinity of the
Mendocino Triple Junction. McCrory, P. A., Waldhauser,
F., Oppenheimer, D. H., and Blair, J. L.
4. A Multiscale Slip Inversion Study Focused on the Initial
Rupture of the 2011 Tohoku Earthquake. Uchide, T.
5. Giant Eruptions did not Frequently Occur in the Periods
When Giant Earthquakes Frequently Occurred and vice
versa after 1900. Fujii, Y.
6. Geologic Controls on the Rupture of the Semidi and
Fox Islands Sections of the Alaska-Aleutian Megathrust
with Implications for the Generation of a Trans-Pacific
Tsunami. Ryan, H. F., von Huene, R., Scholl, D. W., and
Kirby, S. H.
7. Role of Thermal-Pressurization on Megathrust Ruptures.
Cubas, N., Avouac, J. P., and Lapusta, N.
8. Exploring Relationships Between Three-Dimensional
Subduction Zone Geometry and Coupling in Subduction
Zones. Hayes, G. P., Wald, D. J., and Briggs, R. W.
9. Aftershocks of the 2011 Tohoku-Oki Earthquake and
Their Relation to Stresses in the Japan Trench Megathrust
Seismic Cycle. Medina Luna, L., West, S. E., Bai, L.,
Hetland, E. A., Ritsema, J., and Kanda, R. V. S.
10. Weakening of the near Surface in Japan after the 2011
Tohoku-Oki Earthquake Detected by Deconvolution
Interferometry. Nakata, N., and Snieder, R.
(see page 412)
11. Systematic Analysis of Spatial Symmetry Properties of
Aftershocks in California with Respect to Epicentral
Locations of Mainshocks. Ross, Z. E., Zaliapin, I., and
Ben-Zion, Y.
12. Using Cross Correlation to Indicate Induced Seismicity.
Oprsal, I., and Eisner, L.
13. Correlation of Peak Dynamic and Static Coulomb Failure
Stress with Seismicity Rate Change after the M7.2 El MayorCucapah Earthquake. Withers, K. B., and Olsen, K. B.
Earthquake Debate #1: Concept of Segmentation (see page
412)
14. The Impact of Fault Segmentation, Slip Variability and
Coupling on Probabilistic Tsunami Hazard Analysis.
Thio, H.
April 2010: Research Results and Lessons (see page 413)
15. Coseismic and Postseismic Deformation of the 2010 El
Mayor-Cucapah Earthquake from ALOS PALSAR and
GPS data. Funning, G. J., Ryder, I., and Floyd, M. A.
16. El Mayor Cucapah Earthquake: Postseismic Deformation
from InSAR and GPS Observations. Gonzalez Ortega,
A., Sandwell, D., Fialko, Y., Gonzalez Garcia, J., Nava
Pichardo, A., Fletcher, J., Lipovsky, B., and Floyd, M.
17. Slip on Faults and Destruction of Irrigation Canals
Triggered in the Mexicali Valley, Baja California,
Mexico, by the 4 April 2010 Mw 7.2 El Mayor-Cucapah
Earthquake. Glowacka, E., Robles, B., Sarychikhina, O.,
Suarez, F., Ramirez, J., Nava, F. A., Gonzalez, J., Gonzalez,
A., Mellors, R., Villela y Mendoza, A., Farfan, F., Diaz de
Cossio, B. G., and Garcia, M. A.
18. Analysis of Site Effects Observed at the NEES@
UCSB Wildlife Station from the 2010 Ocotillo Swarm.
Huthsing, D. A., Seale, S. W. H., and Steidl, J. H.
19. Detecting and Locating Earthquakes in the Northern
Gulf of California Using Surface Wave Back-Projection.
Butcher, A. J., Polet, J., and Thio, H. K.
20. Observations of Multiple Body Wave Phases of the 2010
El Mayor-Cucapah Earthquake Using a High-Density
Seismic Array. Lester, A., Taylor, O. D. S., and McKenna,
M.
21. Linear and Nonlinear Soil Response at the Mexicali
Valley, Baja California, México During the El MayorCucapah Earthquake of 4 April 2010 (Mw 7.2) and
other Past Earthquakes of the Region. Munguia, L., and
Gonzalez, M.
22. Structural Characteristics of the Southeast Mexicali,
Baja California, México, Region before the El MayorCucapah, M7.2 Earthquake of 4 April 2010, from Seismic
Reflection. Gonzalez-Escobar, M., Chanes-Martinez, J.
J., Suarez-Vidal, F., and Arregui-Ojeda, S.
23. A Crustal Velocity Model for Southern Mexicali Valley,
Baja California, México. Ramirez-Ramos, E. E., and
Vidal-Villegas, J. A.
Macroseismic Effects in Recent and Ancient Earthquakes
and their Relationship to Ground Motion Parameters (see
page 415)
24. Rotational Effects Produced by the Mw 6.3 2009
L’Aquila Earthquake: a Review on how the Seimological,
Geological, Topographical and Geomorphological Factors
Can Influence the Occurrence of Earthquake-induced
Rotations. Cucci, L., Tertulliani, A., Pietrantonio, G.,
and Castellano, C.
25. Rotation of Objects during the 2009 L’Aquila Earthquake
analyzed with 3D Laserscans and Discrete Element
Models. Hinzen, K.-G., Cucci, L., and Tertulliani, A.
26. Visualizing Structural Response and Site Amplification
Using Earthquake Data Recorded at the NEES@UCSB
Field Sites. Seale, S. W. H., Steidl, J. H., Seale, L. B., and
Chourasia, A.
Triggering (see page 415)
27. Array analysis for Cascadia tremor spectra and physical properties of non-volcanic tremor sources. Yao, H.,
Gerstoft, P., Shearer, P., Zhang, J., and Vidale, J. E.
28. Event Detection in 2009 Socorro, NM Earthquake
Swarm and Costa Rican Non-Volcanic Tremor Using the
Subspace Detector Method. Morton, E. A., Bilek, S. L.,
and Rowe, C. A.
29. Dual-Frequency Coherence, Repeated Events, and NonVolcanic tremor. Dorman, L. M., and Schwartz, S. Y.
30. Asperities in the Transition Zone Control Spatiotemporal
Evolution of Slow Earthquakes. Ghosh, A., Vidale, J. E.,
and Creager, K. C.
31. Constructing a Comprehensive Low-Frequency
Earthquake Catalog from a Dense Temporary Deployment
of Seismometers along the Parkfield-Cholame Segment of
the San Andreas Fault. Sumy, D. F., Cochran, E. S., and
Harrington, R. M.
32. Triggered Activity on an Adjacent Fault Deduced from
Relocated Aftershocks of the 2010 Haiti Earthquake.
Douilly, R., Symithe, S., Haase, J. S., Ellsworth, W. L.,
Bouin, M. P., Calais, E., Armbruster, J. G., Mercier de
Lepinay, B. F., Deschamps, A., Mildor, S.-L., Meremonte,
M., and Hough, S. E.
33. Triggered Microearthquakes on the Parkfield section of
the San Andreas Fault By the 2003 Mw6.5 San Simeon
earthquake. Meng, X., Peng, Z., and Hardebeck, J. L.
34. A Revisit of the 2000 Mw 8.0 New Ireland Earthquake:
Evidence of Dynamic Trigger. Li, X., Shao, G., and Ji, C.
35. Global Observations of Triggered Tectonic Tremor. Peng,
Z., Chao, K., Wu, C., Fry, B., Enescu, B., and Aiken, C.
Structure Models, Wavespeed, and Attenuation (see page
417)
36. A New 3-D Structural Model of the Cascadia Subduction
Zone Incorporating P and S Wave Velocities. Angster, S.
J., and Stephenson, W. J.
37. Global Correlations of Tomographic Models with
Tectonic Regions. Paulson, E. M., and Jordan, T. H.
38. High Resolution Interseismic Crustal Velocity Model of
the San Andreas Fault from GPS and InSAR. Tong, X.,
Sandwell, D. T., and Konter, B.
39. Gravity Profiles across the San Jose Fault on the Cal Poly
Pomona Campus. Potter, H., Pazos, C., and Polet, J.
40. The Obsidian Creep Project: Active and Passive Source
Imaging of Faults in the Brawley Seismic Zone and Salton
Sea Geothermal Field, Imperial County, California.
McGuire, J. J., Catchings, R. S., Lohman, R. B., Rymer,
M. J., and Goldman, M. R.
41. Crustal Reflectors In Nevada from Ambient Seismic
Noise Autocorrelations, at Scales of Meters to Tens of
Kilometers. Tibuleac, I. M., and von Seggern, D. H.
42. Using an Active Source to Analyze Coherence vs Distance
and Estimate Q at the Garner Valley and Wildlife NEES@
UCSB Field Sites. Steidl, J. H., and Civilini, F.
43. A Regional High-frequency Attenuation (Kappa) Model
for Northwestern Turkey. Sisman, F. N., Pekcan, O., and
Askan, A.
44. The Long Beach seismic experiment: A novel high-density
array to examine seismic scattering. Dominguez, L. A.,
Davis, P. M., and Hollis, D.
45. A Model-Based Approach to the Geophysical Estimation
of the Thickness of Lateritic Weathering Profiles. Nelson,
S. T., McBride, J. H., June, N., Tingey, D. G., Anderson,
J., and Turnbull, S. J.
Earthquakes of 2011 (see page 419)
46. Relocation and Comparison of the 2010 M4.3 and
2011 M5.6 earthquake sequences in Lincoln County,
Oklahoma. Toth, C. R., Holland, A. A., Keranen, K.,
and Gibson, A.
47. Statistical Modeling of Seismicity Rate Changes in
Oklahoma. Llenos, A. L., and Michael, A. J.
48. Deep Fluid Injection near the M5.6 Oklahoma
Earthquake of November, 2011. Horton, S. P.
49. The 2011 M5.7 Mineral, VA and M5.6 Sparks, OK
Earthquake Ground Motions and Stress Drops: An
Important Contribution to the NGA East Ground
Motion Database. Cramer, C. H., Kutliroff, J. R., and
Dangkua, D. T.
50. Bayesian Extreme Maximum Magnitude (Mmax)
Distributions. Tavakoli, B., and Gregor, N.
Wednesday, 18 April—Afternoon Poster Sessions
Deformation Processes and Properties of the San Jacinto
Fault Zone (see page 420)
51. What Tales Does San Jacinto’s Microseismicity Tell?
Tormann, T., Wiemer, S., and Hardebeck, J. L.
52. Assessing Strain Accumulation Rates across the San
Andreas and San Jacinto faults in the vicinity of San
Bernardino, California. Upton, E., McGill, S. F., Spinler,
J., and Bennett, R. A.
53. Time-Varying Deformation Adjacent to the San Jacinto
Fault, 1985-2011: Results from Pinon Flat Observatory.
Agnew, D. C., and Wyatt, F. K.
54. Modeling Spatio-Temporal Varaitons of Seismicity in the
San Jacinto Fault Zone. Zöller, G., Ben-Zion, Y.
Wave Propagation (see page 421)
55. Signatures of Ocean-Bottom Topography and Seawater
Layer Effects on Waveforms Recorded at the OceanBottom Floor and Teleseismic Distances from Offshore
Earthquakes. Pitarka, Graves, and Helmberger
56. Dynamic Ruptures with Off-Fault Visco-Elastic Brittle
Damage. Xu, S., Ben-Zion, Y., Ampuero, J. P., and
Lyakhovsky, V.
57. PyLith: A Finite-Element Code for Modeling QuasiStatic and Dynamic Crustal Deformation. Aagaard, B.
T., Williams, C. A., and Knepley, M. G.
58. Verification of 3D Numerical Modeling of Earthquake
Ground Motion in the Mygdonian Basin, Greece.
Chaljub, E., Maufroy, E., Hollender, F., Bard, P. Y.,
Kristek, J., Moczo, P., Klin, P., Priolo, E., Etienne, V.,
Bielak, J., Aoi, S., Iwata, T., Iwaki, A., and Mariotti, C.
59. 3D Finite-Difference Modeling of Tremor along the San
Andreas Fault near Cholame, California. Gottschaemmer,
E., Harrington, R. M., and Cochran, E. S.
60. Initialization of Spontaneous Rupture Propagation in a
Dynamic Model with Linear Slip-Weakening Friction—a
Parametric Study. Galis, M., Pelties, C., Kristek, J., and
Moczo, P.
61. Dynamic Rupture Process and Deformation of Sea Floor
associated with the Mw 9.0 Tohoku Oki Earthquake.
Tamura, S., Ide, S., and Ma, S.
62. Inclusion of Topographic Effects in Large Scale Ground
Motion Simulations Using an Octree/Quadtree Mesh
Based Finite Element Approach. Ramirez-Guzman, L.
63. Dynamic Response and Ground-Motion Effects of
Building Clusters During Large Magnitude Earthquakes.
Isbiliroglu, Y. D., Taborda, R., and Bielak, J.
64. Dynamic Rupture along the San Gorgonio Pass Section
of the San Andreas Fault. Shi, Z., Ma, S., Day, S. M., and
Ely, G. P.
65. Improving Resolution of Finite Fault Modeling, TohokuOki Earthquake. WeiS. J., Graves, R., Li, D. Z., and
Helmberger, D.
Rotations in Strong-motion Seismology (see page 424)
66. High Resolution Identification of Shear and Torsional
Wave Velocity Profiles of Buildings—Methodology and
Application to Millikan Library. Rahmani, M. T., and
Todorovska, M. I.
67. Generating of Rotational and Shear Seismic Waves by
Anthropogenic Sources. Malek, J., and Brokesova, J.
68. Forensic Analysis of the Effects of the 1918 Puerto Rico
Earthquake. LaForge, R., and McCann, W.
69. Report on progress at the Center for Engineering Strong
Motion Data. Haddadi, H. R., Stephens, C. D., Shakal,
A. F., Savage, W., Huang, M., Leith, W., and Parrish, J. G.
Seismicity in Volcanic Environments (see page 425)
70. Insight into Eruptive Cyclic Behavior of Mount Etna during 2011: Geophysical and Geochemical Constraints.
Coltelli, M., Patane, D., Aiuppa, A., Aliotta, M., Aloisi,
M., Behncke, B., Cannata, A., Cannavò, F., Di Grazia,
G., Gambino, S., Gurrieri, S., Mattia, M., Montalto, P.,
Prestifilippo, M., Puglisi, G., Salerno, G., and Scandurra, D.
71. Multi-Year Spatiotemporal Evolution of Seismicity in
Hawaii from High-Precision Relocations. Matoza, R. S.,
Shearer, P. M., Lin, G., Wolfe, C. J., and Okubo, P. G.
72. Excitation of Seismic Signals in Basaltic Fissure Eruptions.
Dunham, E. M., Lipovsky, B. P., and Soto, E. S.
73. Measurements of Volcanic Tremor at Kilauea from a
Temporary Seismic Deployment. Greenwood, R. N.,
Polet, J., and Thelen, W. A.
74. The August and October 2008 Earthquake Swarms on the
Explorer/Pacific Plate Boundary. Czoski, P. A., Trehu, A.
M., Williams, M. C., Dziak, R. P., and Embley, R. W.
75. A Comparison of Deformation and Seismicity at the
Yellowstone Caldera during the 2004-2010 Uplift
Episode. Puskas, C. M., Farrell, J., Hodgkinson, K.,
Chang, W. L., Massin, F., and Smith, R. B.
76. Temporal Variations in Shear-Wave Splitting Associated
with Kilauea’s Summit Eruptive Vent. Johnson, J. H.,
Poland, M. P., and Okubo, P. G.
Uncertainty in the Estimation of Earthquake Hazard (see
page 426)
77. Errors or Biases in Event mb: Influence on StressParameters Estimated by mb Vs Mw for Continental
Crust Earthquakes. Dewey, J. W., and Boore, D. M.
78. Invited: The Quantification of Consistent Logic Tree
Branch Weights for PSHA. Runge, A., and Scherbaum,
F.
79. Using Averaging-Based Factorization to Compare Seismic
Hazard Models Derived from 3D Earthquake Simulations
with NGA Ground Motion Prediction Equations. Wang,
F., and Jordan, T.
80. Significance of the Site Classification Map in Earthquake
Loss Estimation by HAZUS based on a Case Study of the
Gyeongju area, Korea. Kang, S., and Kim, K. H.
81. Testing of Ground-Motion Prediction Equations via
Mixture Models. Kuehn, N. M., and Scherbaum, F.
82. Invited: Constraints on the 1811–1812 New Madrid
Earthquake Magnitudes from a Direct Comparison of
Intensity Observations with Known M7 Earthquakes.
Cramer, C. H., and Boyd, O. S.
83. The Hard Shock Revisited: New and Revised Felt Reports
for the February 7, 1812 New Madrid Earthquake. Moran,
N. K.
84. 3-D Rocking Response of Precariously Balanced Rocks.
Veeraraghavan, S., and Krishnan, S.
Earthquake Studies (see page 428)
85. Late Pleistocene Paleoseismology on the Maoergai Fault,
Eastern Tibet: Implications for Seismic Hazard and
Selection of Trench Site on a Purely Strike-Slip Fault.
Ren, J. J., Ding, R., Xu, X. W., Zhang, S. S., Gong, Z., and
Yeats, R. S.
86. Dynamic Rupture Modeling of the 2008 Wenchuan
Earthquake. Liu, Q., Ji, C., and Archuleta, R. J.
87. Slip History of the 2008 Mw 7.9 Wenchuan Earthquake
Constrained by Jointly Inverting Seismic and Geodetic
Observations. Shao, G., Ji, C., Lu, Z., Hudnut, K., Liu, J.,
Zhang, W., and Wang, Q.
88. New Constraints on Crustal Structure and Moho
Topography in Central Tibet Revealed by Deep Seismic
Reflection Profiling by SINOPROBE. Lu, Z., Chen, C.,
Gao, R., Brown, L. D., Xiong, X., Li, W., and Deng, G.
89. Tectonic Interactions Between the Yangtze Block and
Songpan-Ganze Terrane: New Constraints from Deep
Seismic Reflection and Refraction Profiles, as Well as
Magnetic and Gravity Evidence. Guo, X., Gao, R., Keller,
G. R., and Xu, X.
90. Preliminary Results of a Deep Seismic Reflection Profile
Across the Great Xing’an Mountain Range, NE China.
Hou, H. S., Gao, R., Li, Q. S., Keller, R., Xiong, X. S., Li,
W. H., Li, H. Q., Zhu, X. S., Kuang, C. Y., and Huang,
D. D.
91. Crustal Structure of the Northern Margin of the North
China Craton and Adjacent Region from the Sinoprobe02
North China Seismic WAR/R Experiment. Li, W. H.,
Keller, G. R., Gao, R., Li, Q. S., Cox, C. M., and Hou, H. S.
Thursday, 19 April
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
of Seismic Coupling
along Subduction
Zones: Chile,
Sumatra, Tohoku…
What’s Next?
Session Chairs:
Margarita Segkou and
William Ellsworth
(see page 429)
Deformation
Processes and
Properties of the San
Jacinto Fault Zone
Session Chairs:
Yehuda Ben-Zion,
Tom Rockwell, and
Frank Vernon (see
page 434)
Uncertainty in
the Estimation of
Earthquake Hazard
Session Chairs: Nilesh
Shome and Mark D.
Petersen (see page
440)
Rotations in Strongmotion Seismology
Session Chairs:
Vladimir Graizer and
Maria Todorovska (see
page 448)
Earthquake Location
and Monitoring
Session Chair: Felix
Waldhauser (see page
447)
8:30
Variation of Seismic
Radiation Spectrum
With Source Depth
Along Megathrust
Faults in the Japan,
Chile, and Sumatra
Subduction Zones.
Lay, T., Ye, L., and
Kanamori, H.
Space Geodetic
Investigation
of Interseismic
Deformation along
the San Jacinto
Fault: Effects of
Heterogeneous Elastic
Structure and Fault
Geometry. Lindsey,
E. O., Sahakian, V. J.,
Fialko, Y., Bock, Y.,
and Rockwell, T. K.
Invited: Seismic
Sources at Surface,
in Geologic
Structures, and for
Hazard Modeling:
Discrepancies
and Uncertainties
in Continental
Environment.
Okumura, K.
Invited: Differential
and Rotational
Excitation of
Structures. Trifunac,
M. D. T. (30 minutes)
Accuracy of Locating
Seismic Sources:
Physical Modeling
and Interpretation.
Krasnova, M. A.,
Dyaur, N., and
Chesnokov, E. M.
8:45
Is the Mariana
Subduction Zone
Decoupled. Emry, E.
L., and Wiens, D. A.
Seismic Velocity
Structure in the
Trifurcation Area of
the San Jacinto Fault
Zone and Surrounding
Region from
Double-difference
Tomography. Allam,
A. A., and Ben-Zion, Y.
Active Faults, Geodesy
and Seismic Hazard in
the Northern Walker
Lane. Wesnousky,
S. G., Hammond,
W., Kreemer, C.,
Bormann, J., and
Brune, J. N.
Timing Signal’s
Spectral Amplitude,
MSE, For sesimic
Source Location.
Yacoub, N.
Thursday, 19 April (continued)
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
9:00
Seismic Potential of
the Lesser Antilles
Subduction Zone:
Insights from a
Reinterpretation of
the 8 February 1843
Earthquake. Hough,
S. E.
Comparison of
Tectonic Tremor in
California. Peng, Z.,
Chao, K., and Aiken,
C.
Attenuation
Relationships for
HPGA: Sensitivity
Analysis and
Applications.
Mebarki, A.,
Laouami, N., Benouar,
D., and Gherboudj, F.
Invited: Status
of Rotational
Instrumentation for
Earthquakes. Evans,
J. R., Hutt, C. R., and
Nigbor, R. L.
Real-Time DoubleDifference Location
and Monitoring
of Repeating
Earthquakes in
Northern California.
Waldhauser, F.,
Schaff, D. P., Zechar, J.
D., and Friberg, P.
9:15
Questioning the
Elastic Source
Models for Shallow
Subduction Zone
Earthquakes. Ma, S.
Heterogeneity,
Rotations of Source
Tensors, and
Volumetric Strain
near Faults from Focal
Mechanism Data.
Ross, Z. E., Ben-Zion,
Y., and Bailey, I. W.
Comparison of the
NGA Horizontal
Ground Motion
Prediction Models to
the Turkish Strong
Ground Motion
Database. Gulerce,
Z., Abrahamson, N.
A., and Kargioglu, B.
Invited: Parametric
Analysis of Horizontal
Surface Rotations
from Body Waves
Reflections. Zembaty,
Z.
Effect of Earthquake
Location and
Magnitude on
Moment Tensors
in a South African
Gold Mine. Kane,
D., Boettcher, M.,
McGarr, A., Fletcher,
J., Johnston, M., and
Reches, Z.
9:30
Maximum Earthquake
Size for Subduction
Zones. Kagan, Y. Y.,
and Jackson, D. D.
Ground Motion
Prediction Equations
for Data Recorded
in the Immediate
Vicinity of the San
Jacinto Fault Zone.
Kurzon, I., Vernon, F.
L., Ben-Zion, Y., and
Atkinson, G. M.
Invited:
Capturing Epistemic
Uncertainties in
PSHA within a Logic
Tree Framework:
Summing the Branch
Weights to One is not
Enough. Scherbaum,
F., and Kuehn, N. M.
Invited: Observed
Torsional Waves in
Buildings during
Use for Structural
Health Monitoring.
Todorovska, M. I.,
and Rahmani, M. T.
Using the QuakeCatcher Network’s
Christchurch, New
Zealand Array to
Improve QCN
Rapid Earthquake
Detections. Chung,
A. I., Cochran, E.
S., Christensen, C.,
Kaiser, A. E., and
Lawrence, J. F.
9:45
Seismology Cannot
Address Global
Clustering of M9
Earthquakes.
Goldfinger, C.
Using Spectral Ratios
of Pore Pressure and
Strain Observations
Recorded at
EarthScope PBO
Borehole Strainmeter
Sites to Analyze
Tectonic Deformation
and Changes in Well
Parameters due to
Nearby Earthquakes.
Civilini, F., and
Steidl, J. H.
Invited: Uncertainty
in Site Amplification
Estimation for Urban
Seismic Hazard
Mapping. Cramer,
C. H.
Comparision of
Apparent Wave
Velocities in Different
Areas. Luo, Q., Zhao,
S., and Hong, Z.
Foreshock Detection
for the 1999 Mw7.1
Hector Mine Sequence
Using Running
Autocorrelation.
Brown, J. A., Brown,
J. R., and Beroza, G.
C.
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
10:30 From Stable to
Destructive: How
Creeping Fault
Segments Can Join
Earthquakes and
Implications for
Seismic Hazard.
Lapusta, N., and
Noda, H.
Summary of
Paleoseismic
Observations Along
the San Jacinto
Fault. Rockwell, T.
K., Onderdonk, N.,
McGill, S. F., Buga,
M., Salisbury, J. B.,
and Pandey, A.
Statistical Study of
Ground Motion
Amplification in
the Mississippi
Embayment.
Malekmohammadi,
M., and Pezeshk, S.
Rotaphone, a New
Self-calibrated Sixdegree-of-freedom
Seismic Sensor and
Its Strong-motion
Records. Brokesova,
J., and Malek, J.
Seismicity in and
around Bangladesh.
Al-Hussaini, T. M.,
and Al-Noman, M. N.
10:45 Rupture to the
Trench in Dynamic
Rupture Simulations
of Megathrust
Subduction Zone
Earthquakes. Kozdon,
J. E., and Dunham,
E. M.
Temporally Steady
but Spatially Variable
Middle Pleistocene
to Holocene Slip
Rates across the San
Jacinto Fault Zone,
California. Blisniuk,
K., Oskin, M. E.,
Rockwell, T., Sharp,
W., and Fletcher, K.
Can Current New
Madrid Seismicity
Be Explained as a
Decaying Aftershock
Sequence? Page, M.
T., Hough, S. E., and
Felzer, K. R.
Using Broadband
Seismometers as
Tilt Meters: A Case
Study at Santiaguito
Volcano, Guatemala.
Lyons, J. J., Lees, J.
M., Johnson, J. B., and
Waite, G. P.
Queen Charlotte
2001 Earthquake
Aftershock Sequence.
Mulder, T. L., and
Rogers, G. C.
11:00 Frequency-Depth
Dependent Rupture
Modes of Subduction
Zone Megathrust
Earthquakes: Insights
from Seismic Array
Analysis. Yao, H.,
Shearer, P., and
Gerstoft, P.
Late Holocene Slip
Rate and Slip per
Event of the Northern
San Jacinto Fault
Zone. Onderdonk,
N., McGill, S., and
Rockwell, T.
A New Likelihood
Method for
Estimating Recurrence
Interval Parameters
from Paleoseismic
Event Series. Biasi, G.,
and Scharer, K.
Rotational Ground
Motions as Inferred
from Five Downhole
Vertical Array
Observations.
Graizer, V.
Energy, Spectral
Content, and
Characteristics of
Thunder in Central
New Mexico. Johnson,
R. L., Johnson, J.
B., Arechiga, R. O.,
Michnovicz, J. C.,
Edens, H. E., and
Rison, W.
11:15 Frequency-dependent
Energy Radiation and
Fault Coupling for the
2010 Mw 8.8 Maule,
Chile, and 2011 Mw
9.0 Tohoku, Japan,
Earthquake. Wang,
D., and Mori, J.
Slip Rate of the
Northern San
Jacinto Fault from
Offset Landslides
in the San Timoteo
Badlands. McGill,
S. F., Owen, L. A.,
Kent, E., Rockwell,
T. K., Kendrick, K. J.,
Onderdonk, N., and
Rhodes, E.
Invited:
Uncertainties in
Characterizing the
Cascadia Subduction
Zone and Their
Seismic Hazard
Implications. Wong,
I., Kulkarni, R.,
Zachariasen, J., Dober,
M., Thomas, P., and
Youngs, R.
Deep Mining Areas as
Potential, Magnitude
5 Test Fields for
Rotational Seismology.
Zembaty, Z., and
Cichowicz, A.
Seismicity in the
Central Valley of
Costa Rica. Quintero,
R., and Segura, T. J.
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
11:30 Rupture
Characterizations of
the 2011 Mw 9.1 off
the Pacific Coast of
Tohoku Earthquake
and Its March 9th Mw
7.4 Foreshock. Shao,
G., Ji, C., Archuleta,
R. J., and Zhao, D.
Preliminary
Paleoseismic Results
from Southern
Clark Fault, San
Jacinto Fault Zone,
Southern California;
Comparison to the
Hog Lake Paleoseismic
Record. Buga, M. T.,
Rockwell, T. K., and
Salisbury, J. B.
Fault Slip Rate
Variability and
Consequences for
Seismic Hazard
and Seismic Risk in
Japan Resulting from
Static Stress Changes
Following the M9.0
Tohoku Earthquake.
Apel, E., Nyst, M.,
and Williams, C.
An Autonomous Lowpower Accelerograph
to Obtain Strong
Motion Recordings
Near Large
Earthquakes. Shakal,
A. F., Petersen, C. D.,
and Reitz, T. R.
Developments at the
ISC: GEM Catalogue,
new Locator, GT &
Bulletin Re-Build.
Storchak, D. A.,
Bondar, I., Di
Giacomo, D. and,
Harris, J.
11:45 Lateral Stress Drop
Variations and the
Tohoku Aftershocks
in the Context of
Earthquake Source
Characteristics in
Japan. Oth, A.
The Fault Zone
Architecture of the
San Jacinto Fault,
Southern California.
Morton, N., Girty,
G. H., and Rockwell,
T. K.
Calculating
Earthquake
Recurrence Rates from
Partially Complete
Earthquake Catalogs
with Uncertain
Magnitudes—from
M* to N*. Youngs,
R. R.
A new Approach to
Miniaturized Seismic
Broadband Sensors.
Guralp, C., and
Rademacher, H.
Relationship Between
Seismicity and Oil
Production. Kerimov,
I. H. A., and Kerimov,
S. I.
Lunch—Town and Country Room
12:00
1:30
of Seismic Coupling
along Subduction
Zones: Chile,
Sumatra, Tohoku…
What’s Next?
(continued)
Deformation
Processes and
Properties of the San
Jacinto Fault Zone
(continued)
Uncertainty in
the Estimation of
Earthquake Hazard
(continued)
Continental
Lithospheric
Structure and
Tectonics of Central
North America
Session Chairs:
Meghan S. Miller, M.
Beatrice Magnani,
and Luciana Astiz (see
page 450)
Earthquakes and
Tsunamis at Coastal
Archaeological Sites
Session Chairs:
Manuel Sintubin,
Beverly N. Goodman
Tchernov, and Tina
M. Niemi (see page
447)
Interlocking of
Heterogeneous
Plate Coupling for
the 2011 TohokuOki Megathrust
Earthquake: An
Integral Account
of Asperity Model
with Effective Plate
Coupling. Tajima, F.,
and Grant Ludwig, L.
Permeability Structure
of the San Jacinto
Fault Zone, Horse
Canyon, California.
Mitchell, T. M.,
Girty, G. H., Morton,
N., Rockwell, T. K.,
and Renner, J.
Invited: The Use of
Multi-Layer Source
Zones in Assessing
Uncertainty in the
Spatial Distribution
of Earthquakes.
Leonard, M., Clark,
D., Burbidge, D., and
Collins, C.
LithosphereAsthenosphere
Structure beneath
the United States
from Joint Inversion
of Body Waves and
Surface Waves.
Porritt, R. W., Allen,
R. M., Pollitz, F. F.,
Hung, S. H., and
Obrebski, M. J.
The First Description
of a Tsunami in 479
BC by Herodotus:
Sedimentary Evidence
in the Thermaikos
Gulf (Greece).
Reicherter, K.,
Papanikolaou, I. D.,
and Mathes-Schmidt,
M.
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
1:45
Triggering of Tremors
and Slow Slip
event in Guerrero
(Mexico) by the
2010 Mw 8.8 Maule,
Chile, Earthquake.
Zigone, D., Rivet,
D., Radiguet, M.,
Campillo, M.,
Voisin, C., Cotte,
N., Walpersdorf,
A., Shapiro, N. M.,
Cougoulat, G., Roux,
P., Kostoglodov,
V., Husker, A., and
Payero, J. S.
Speculations On
the Role of Ground
Shaking In the
Production of
High Dilational
Volumetric Strains
In Saprock Adjacent
to the Elsinore
Fault, Southern
California. Maroun,
M., Replogle, C. T.,
Carrasco, T. L., Colby,
T. A., Girty, G. H.,
and Rockwell, T. K.
Probabilistic Seismic
Hazard Assessment in
Europe: Uncertainty
Treatment for
a Harmonized
Approach. Woessner,
J., Danciu, L.,
Giardini, D., and the
SHARE Consortium
P-velocity Structures
beneath the
Midwestern United
States Based on
Waveform Modeling.
Chu, R., Li, D., and
Helmberger, D.
Evidence for a
Potential Tsunami
on the Shelf of the
Northern Gulf of
Aqaba, Dead Sea
Transform. Galloway,
J., Niemi, T. M.,
Goodman Tchernov,
B., Ben-Avraham,
Z., Al-Zoubi, A., and
Tibor, G.
2:00
A 5600-Year Historic
and Paleoseismic
Record of 10
Great Subduction
Earthquakes and the
Seismic Cycle at the
Copper River Delta,
Alaska. Plafker, G.,
and Lienkaemper, J. J.
Reconciling
Precariously Balanced
Rocks with Large
Earthquakes on
the San Andreas
Fault System. Grant
Ludwig, L., Brune, J.
N., Anooshehpoor, R.,
Purvance, M. D., and
Brune, R. J.
Assessing Earthquake
Source Models Under
Uncertainty with
Bayesian Analysis
and Parallel MCMC
Algorithms. Cruz
Jimenez, H., Mai, P.
M., and Prudencio,
E. E.
A Three Dimensional
Crustal Structure
Target for the
Northern Embayment
Lithosphere
Experiment (Nele).
Langston, C. A.
Evaluating the Impact
of Earthquakes on
Minoan Coastal
Settlements: an
Example from the
Archaeological Site of
Sissi, North-Eastern
Crete (Greece).
Jusseret, S., Langohr,
C., and Sintubin, M.
2:15
Observation of a
“Locking Event”:
A Newly Observed
Transient variation
in the Pattern of Slip
Deficit at the Alaska
Subduction Zone.
Freymueller, J. T.
The July 7th 2010
M5.4 Borrego
Springs Earthquake
As Recorded By
PBO Geodetic And
Seismic Instruments.
Hodgkinson, K. M.
H., Borsa, A., Mencin,
D., Walls, C., Fox, O.,
and VanBoskirk
Stochastic Event
Sampling for M9
Cascadia Megathrust
Earthquakes:
Capturing the
Uncertainties in
the Potential Event
Characterization.
Williams, C. R.,
Grossi, P., and Molas,
G. L.
The Ozark-IllinoisINdiana- Kentucky
(OIINK!) EarthScope
Experiment:
Seismicity and
Structure in
North America’s
Midcontinent
Cratonic Platform.
Hamburger, M. W.,
Pavlis, G. L., Yang,
X. T., Sherrill, E. M.,
Gilbert, H. J., Larson,
T. H., and Marshak, S.
Did a Major
Environmental Event
Lead to the Late Bronze
Age Abandonment of
the Ancient Harbor
City of Hala Sultan
Tekke? Unraveling the
Sedimentary Record of
the Larnaca Salt Lake,
Cyprus. Heyvaert,
V. M. A., Sintubin,
M., Verstraeten, G.,
Kaniewski, D., and
Nys, K.
2:30
Panel Discussion on
of Seismic Coupling
along Subduction
Zones: Sumatra Chile,
Tohoku… What’s
Next? Segou, M.,
Ellsworth, W., and
Thatcher, W.
Geomorphic Evidence
for Structural
Evolution of the
Northern San Jacinto
Fault Zone in the San
Timoteo Badlands.
Kendrick, K. J., and
Morton, D. M.
Quantification of
Uncertainty in Seismic
Hazard Assessment.
Wang, Z.
New Results on
the Structure and
Evolution of Some
Major Structures
in the Central U.
S. Keller, G. R.,
Al-Refaee, H., and
Guo, L.
Searching for
Tsunamigenic
Signatures in the
Coastal Deposits of
Caesarea Maritima.
Goodman Tchernov,
B. N., Dey, H. W.,
Lopéz, G. I., and
Sharvit, J.
Pacific Salon 1
2:45
Pacific Salon 2
Question and Answer Local Fault Structures
Session
of the San Jacinto
Fault Zone Based
on Earthquake
Locations and Focal
Mechanisms. Kurzon,
I., and Vernon, F. L.
Pacific Salon 3
Pacific Salon 4 & 5
Pacific Salon 6 & 7
A New Tool for
Trimming the Logic
Tree: Assessing the
Value of Hazard
Information. Porter,
K. A., Field, E. H.,
and Milner, K.
Understanding Long- Question and Answer
Term Fault Behavior: Session
Lessons Learned from
Well-Exposed Ancient
Faults. Hatcher, R. D.
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
Probabilistic Seismic
Hazard Analyses, Models,
Maps, and Simulations
Session Chairs: Ivan Wong
(see page 433)
The 23 October 2011
Van, Turkey Earthquake:
Observations and
Implications
Session Chairs: Gareth
Funning and Mike Floyd
(see page 438)
Detecting, Modeling, and
Predicting the Seismic
Source
Session Chairs: Yoshihiro
Kaneko (see page 443)
Continental Lithospheric
Structure and Tectonics
of Central North America
(continued)
3:30
Site-Specific Probabilistic
Seismic Hazard Analyses for
Ground Shaking and Fault
Displacement in Downtown
San Diego, California.
Wong, I., Thomas, P.,
Zachariasen, J., Schug, D.,
and Stroop, R.
Seismotectonics of the
Lake Van Region and the
23 October 2011 Van
Earthquake (Mw=7.1).
Gülen, L., Utkucu, M.,
Budakoglu, E., Yalcın, H. D.,
Güneş, Y., and Kalafat, D.
Toward a Better
Understanding of the Time
Dependence of mN-M W in
Eastern Canada. Bent, A.
L., and Greene, H.
EarthScope’s
Multidisciplinary USArray:
Status and Results.
Frassetto, A., Woodward,
R., Busby, R., Hafner, K.,
Gridley, J., and Schultz, A.
3:45
Dynamic Probabilistic
Seismic Hazard Maps.
Holliday, J. R., and Rundle,
J. B.
Geologic and Engineering
Observations from the
Van Earthquake of 2011.
Scharer, K., Kuterdem,
K., Erkmen, C., Tekin, B.,
Çolakoğlu, Z., Çelebi, M.,
and Holzer, T.
Extracting Source
Characteristics and
Dynamics of the August
2010 Mount Meager
Landslide using Broadband
Seismograms. Allstadt,
K. E., Creager, K. C., and
Vidale, J. E.
Earthquakes Possibly
Triggered by Hydraulic
Fracturing in Southeastern
Oklahoma. Holland, A. A.
4:00
A Survey of Uses and Users
of the USGS ShakeCast
System. Lin, K., and Wald,
D. J.
Geotechnical Field
Observations from
23 October 2011 Van
Earthquake (Mw=7.1).
Gulerce, Z., Çetin K. Ö.,
Yilmaz, M. T., Huvaj, N.,
Ünsever, Y. S., Ünsal, S.,
Sağlam, S., and Sandikkaya,
M. A.
Rate/State Friction
Model Implementation
for Earthquake Forecasts
in Northern California.
Segou, M., Parsons, T., and
Ellsworth, W.
Path-Dependent Lg
Propagation in the
South-Central United
States Revealed by
the EARTHSCOPE
Transportable Array. Conn,
A., Chapman, M., Pezeshk,
S., and Hosseini, M.
Pacific Salon 1
Pacific Salon 2
Pacific Salon 3
Pacific Salon 4 & 5
4:15
A Time-dependent Update
of the New Zealand
National Seismic Hazard
Model for the Canterbury
Earthquake Sequence.
Gerstenberger, M. C.,
Rhoades, D., McVerry,
G., Berryman, K.,
Christophersen, A., Fry, B.,
Nicol, A., Pettinga, J.R.,
Steacy, S., Stirling, M.,
Reyners, M., and Williams,
C.
Preliminary Investigation of
Co-Seismic and Immediate
Post-Seismic Deformation
Due to the 23 October 2011,
Mw 7.2 Van-Ercis, Turkey,
Earthquake Using SpaceBased Geodesy. Floyd, M.
A., Ergintav, S., Çakır, Z.,
Doğan, U., Özener, H.,
Çakmak, R., Akoglu, A. M.,
McCaffrey, R., King, R. W.,
and Reilinger, R. E.
Full-field Laboratory
Earthquake Measurements
with the Digital Image
Correlation Method.
Rubino, V., Lapusta, N.,
and Rosakis, A. J.
Evaluation of Attenuation
Models in North America.
Babaie Mahani, A., and
Atkinson, G. M.
4:30
Geomechanical Modeling
of Induced Seismicity for
Hazard Prediction. GoertzAllmann, B. P., Bachmann,
C., Gischig, V., and Wiemer,
S.
Finite Fault Slip Evolution
Model for the 23 October
2011 Mw 7.1 Van, Turkey
Earthquake from Geodetic
and Seismic Waveform
Analysis. Fielding, E. J.,
Polet, J., Lundgren, P. R.,
Yun, S. H., Motagh, M.,
Owen, S. E., and Simons, M.
Variability of Seismic Source
Spectra Derived from
Cohesive-Zone Models
of a Circular Rupture
Propagating at a Constant
Speed. Kaneko, Y., and
Shearer, P. M.
Sensitivity of Seismic
Soil Response to the
Soil/Bedrock Acoustic
Impedance Contrast
Ratio for Ottawa, Canada.
Motazedian, M., Khaheshi
Banab, K., Kolaj, M.,
Sivathayalan, S., Hunter, J.,
and Crow, H.
4:45
Probabilistic Seismic Hazard
Assessment of Eastern
Marmara Region. Gulerce,
Z., and Ocak, S.
The Source and Attenuation
Characteristics of Ground
Motions from the 23
October 2011 Van, Turkey
Earthquake. Yenier, E., and
Atkinson, G. M.
The Relation of University
of Utah Local and Coda
Magnitudes to Moment
Magnitudes. Pechmann, J.
C., and Whidden, K. M.
Crustal Velocities in the
Region Surrounding the
Charlevoix Seismic Zone,
Quebec, Canada. Powell,
C., Lamontagne, M., and
Kelemencky, S.
Thursday, 19 April—Morning Poster Sessions
Continental Lithospheric Structure and Tectonics of
Central North America (see page 453)
1. Teleseismic P-Wave Travel Time Residual Mapping In The
Eastern Tennessee Seismic zone. Agbaje, T. C., Arroucau,
P., Vlahovic, G., Powell, C., and Rawlinson, N.
2. Digital elevation model analysis in the eastern Tennessee
seismic zone. Stearns, C., Arroucau, P., Vlahovic, G.,
Mulrooney, T., and Love, G.
3. Ambient Noise Cross-Correlation in the Eastern
Tennessee Seismic Zone (United States). Kuponiyi, A. P.,
Arroucau, P., Yongan, T., Vlahovic, G., and Vlahovic, B.
4. The Relationship Between Earthquake Locations and
Velocity Structure in the Eastern Tennessee Seismic Zone.
Powell, C. A., and Chapman, M. C.
5. Crustal Structure Between Minnesota and the Gulf Coast
from Joint Inversion of Surface-Wave Dispersion and
Receiver Functions. Chang, Y., and Herrmann, R. B.
6. Regional Seismicity Recorded by the USArray: The ANF
Bulletin. Astiz, L., Vernon, F. L., Eakins, J. A., Martynov,
V. M., Karasu, G. H., Tytell, J., Cox, T. A., Newman, R.,
Reyes, J., and Davis, G. A.
7. Tuning Detection Algorithms for the Analysis of
Dynamic Earthquake Triggering Using EarthScope’s
USArray Data. Velasco, A. A., Kilb, D. L., Pankow, K. L.,
and Gonzalez-Huizar, H.
8. Resolving Variations in the Tectonostratigraphic Terrane
Structure of New England Using Receiver Functions.
Schuh, J. S., and Ebel, J. E.
(see page 455)
9. Generating Stochastic Source Models Using Insights from
Laboratory Earthquakes. Siriki, H., and Krishnan, S.
10. Joint Inversion for Moment Tensors and Amplifications of
Uncalibrated Sensors. Davi, R., and Vavrycuk, V.
11. Investigation of mLg Using Random Vibration Theory and
Actual Earthquakes. Rigsby, C. M., and Herrmann, R. B.
12. Stress Forecasting in Vrancea Seismically Active Region of
Romania. Apostol, A., Moldovan, I. A., Ionescu, C., and
Zugravescu, D.
13. Real Time Forecasting of Aftershock Sequences. Felzer,
K., and Page, M.
14. Lessons Learned from RELM: A Second-Generation
ALM Model. Hiemer, S., Tormann, T., and Wiemer, S.
15. Date, Lunar Phase and Time of Giant Earthquakes might
be Specified for Each Subduction Zone. Fujii, Y., and
Ozaki, Y.
16. Detection of Tectonic, Volcanic, and Cyrospheric Seismic
Sources in Antarctica using POLENET Seismic Array
and GSN Seismic Stations. Lough, A., Barcheck, C.
G., Wiens, D., Barklage, M., Nyblade, A., Aster, R. A.,
Anandakrishnan, S., Huerta, A., and Wilson, T.
Earthquake Strong-Motion Modeling (see page 456)
17. Stochastic Modeling of the Source and Attenuation
Characteristics of Moderate-to-Large Magnitude
Earthquakes: Investigation of Apparent Distance
Saturation Effects. Yenier, E., and Atkinson, G. M.
18. A Stochastic Ground-Motion Model for Switzerland.
Edwards, B., and Fäh, D.
19. Exploring the Space of Stochastic Ground-Motion Models
through High-Dimensional Visualization. Gianniotis, N.,
Kuehn, N. M., Riggelsen, C., and Scherbaum, F.
20. Spatial Statistics of the Clark County Parcel Map, Trial
Geotechnical Models, and Effects on Earthquake Ground
Motions in Las Vegas Valley. Savran, W., Louie, J. N.,
Pullammanappallil, S. K., and Pancha, A.
21. Scaling Low-Frequency Earthquake Spectra in a
Stochastic Finite-Fault Modelling Technique. Crane, S.,
and Motazedian, D.
22. High-Frequency Ground Motion Modeling. Mourhatch,
R., and Krishnan, S.
23. Simulation of Broadband Strong Ground Motion for the
2010 M 7.0 Haiti Earthquake. Mavroeidis, G. P., Scotti,
C. M., and Papageorgiou, A. S.
and Simulations (see page 458)
24. Large Scale Earthquake Hazard Class Mapping by Parcel
In Las Vegas Valley. Pancha, A., Pullammanappallil, S.
K., Louie, J. N., and Hellmer, W. K.
25. EqHaz: A Monte Carlo Simulation Program for Seismic
Hazard Applications. Assatourians, and Atkinson
26. A Site-Specific Seismic Hazard Analysis in Northern
Chile. Dober, M., Wong, I., Olig, S., and Bott, J.
27. Geospatial Liquefaction Hazard Model for Kobe, Japan
and Christchurch, New Zealand. Baise, L. G., Daley, D.,
Zhu, J., Thompson, E. M., and Knudsen, K. L.
28. The St. Louis Area Earthquake Hazards Mapping Project.
Williams, R. A., Cramer, C. H., Rogers, J. D., Bauer, R.
A., Chung, J. W., Gaunt, D. L., Hempen, G. L., Steckel, P.
J., Hoffman, D., Boyd, O.S., USGS, Memphis, TN; and
McCallister, N.S.
29. UNESCO IOC Tsunami and Other Coastal Hazards
Warning System for the Caribbean and Adjacent Regions.
Von Hillebrandt-Andrade, C. G., Inniss, L., and
Aliaga, B.
30. An Assessment of the USGS PAGER System’s Alerts and
Loss Estimates. Marano, K. D., Wald, D. J., Jaiswal, K.,
and Hearne, M.
31. Earthquake CAT Bond Trigger Design: Scenario-based
versus Station-Intensity-based Approaches. Goda, K.
Observations and Implications (see page 459)
32. Broadband Ground Motion Simulations of the 23
October 2011 Van (Eastern Turkey) Earthquake. Ameri,
G., Gallovic, F., Askan, A., and Zahradnik, J.
33. 23 October 2011 Mw 7.1 Van (Eastern Turkey) Earthquake:
Characteristics of Recorded Strong Ground Motions and
Post-Earthquake Condition Assessment of Infrastructure
and Cultural Heritage. Akansel, V., Ameri, G., Askan, A.,
Caner, A., Erdil, B., Kale, O., and Okuyucu, D.
34. 2011 Van Earthquake (Mw=7.2) Aftershocks using the
Source Spectra an Approach to Real-Time Estimation of
Moment Magnitude. Meral Ozel, N., Kusmezer, A., and
Korkusuz, Y.
35. The Van Earthquake (Mw=7.2) of 23 October 2011 and
Its Aftershocks. Kalafat, D., Kekovali, K., Suvarıkli, M.,
Ogutcu, Z., Yilmazer, M., Gunes, Y., and Gulen, L.
36. Coseismic Surface Deformation of the 23 October 2011
Van Earthquake from InSAR. Severson, C. M., and
Funning, G. J.
37. Fault Slip Distribution of the Mw 7.2 Van Earthquake
(2011) Imaged by DInSAR Data and Numerical Modeling.
Trasatti, E., Tolomei, C., Atzori, S., Merryman, J.,
Antonioli, A., Pezzo, G., and Salvi, S.
38. The 2010–2011 Canterbury Earthquakes, New Zealand:
Multiple Fault Segments, Slip Distribution and Seismic
Hazard. Elliott, J. R., Parsons, B., England, P. C., Nissen,
E. K., Jackson, J. A., Lamb, S., Li, Z., and Oehlers, M.
Thursday, 19 April—Afternoon Poster Sessions
Earthquake Location and Monitoring (see page 461)
39. Microseismic Monitoring of the Marmara Seismic Gap,
NW Turkey: Recent Results From the PIRES Network
and Challenges Ahead. Bohnhoff, M., Bulut, F., Eken, T.,
Aktar, M., and Dresen, G.
40. Determination of Hypocentral and Focal Mechanism
Solutions for 3 November 2010 Kraljevo Earthquake
Sequence (Mw=5.4). Knezevic Antonijevic, S.,
Arroucau, P., and Vlahovic, G.
41. Micro-Seismicity in Southwestern Yukon, Canada.
Meighan, L. N., Mazzotti, S., and Cassidy, J.
42. Relocation of Micro-earthquakes in the Youngduk
Offshore Region, Korea. Kim, K. H., Yoo, Y. G., Yu, C.,
Kang, S., and Kim, H.
43. Enhanced Real-Time Seismic Monitoring in Hawai‘i.
Shiro, B., Okubo, P., Koyanagi, K., Thelen, W., and
Gernold, R.
44. An Analysis of Haiti Earthquake (12 January 2010)
from Its Aftershock Sequence Using Land-Based and
Off-Shore Temporary Seismic Stations. Duchatelier,
M. J., Arroucau, P., Mulrooney, T., Vlahovic, G., and
Deschamps, A.
45. Discovering New Events Beyond the Catalog: A Look into
Salton Sea Geothermal Field Microseismicity. Templeton,
D. C., Wang, J., and Harris, D. B.
46. The PBO Borehole Seismometer Network, Filling in
Metadata Gaps. Fox, O., Pyatt, C., Mencin, D., Gallaher,
W., Johnson, W., Gottlieb, M., Van Boskirk, E., and
Hodgkinson, K.
47. Epicentral Infrasound from Small Earthquakes in the
Western United States. Hale, J. M., Pankow, K. L.,
Arrowsmith, S. J., Stump, B., and Hayward, C.
48. Bayesian Travel-time Inversion for Earthquake hypocentral location. Davies, J. A., Vlahovic, G., and and
Arroucau, P.
49. Refinement and Testing of the PEDAL Event Detection
and Signal Association Algorithm. Draelos, T. J., Ballard,
S., Young, C. J., Gonzales, M. A., and Brogan, R.
50. Lessons Learned from the SPEAR (Seismogram Picking
Error from Analyst Review) Project. Zeiler, C. P.
Sensors and Software Techniques (see page 464)
51. Assessment of GSN Sensor Response Information. Davis,
P., and Berger, J.
52. High-Resolution, Low Power, Intergrated Aftershock
System. Zimakov, L., and Passmore, P.
53. A Software Toolbox for Systematic Evaluation and
Recovery of Seismometer-Digitizer System Responses.
Ferris, A., Franks, J., and Bonner, J.
54. A Technique to Determine the Self-Noise of Seismic
Sensors for Performance Screening. Hart, D., Rademacher,
H., and Guralp, C.
55. Wave Gradiometry in Three Dimensions. Poppeliers, C.
Surface Deformation and Geodetic Techniques (see page
464)
56. Detecting Deformation in the New Madrid Seismic Zone
using Radar Interferometry. Esezobor, K. O., Yang, Z.,
and Vlahovic, G.
57. Surface Deformation and Slip Distribution of the 1994
Northridge Earthquake Determined from InSAR, GPS
and the Community Fault Model. Severson, C. M.,
Funning, G. J., and Marshall, S. T.
58. Application of Cluster Analysis to the Greek GPS Velocity
Field to Constrain The Active Tectonics of Greece and
Adjacent Regions. Thatcher, W., Simpson, R., and
Segou, M.
59. Preliminary Interpretation of Subsurface Deformation
across the Olympic, Washington State: Evidence for Active
Crustal Deformation in the Southern Puget Lowlands?
Odum, J. K., Stephenson, w. J., Pratt, T. L., Dart, R. L.,
Maharrey, J. Z., Volpi, C., King, B., and Hoffpauir, C. G.
60. Seismic Interferometry of the Salton Sea Geothermal
Region. Matzel, E. M.
Propagation Through Complex Media (see page 466)
61. A Damage Mechanics Model for S Wave Generation by
Explosions in Crystalline Rock. Sammis, C. G., Mihaly,
J. M., and Rosakis, A. J.
62. Can the Fisk Conjecture be Explained by Rock Damage
Around Explosions? Taylor, S. R.
63. “Prompt” Versus “Late-Time” Damage: The Case for
Explosion-Generated S Waves from Late-Time Damage
Due to Shock-Wave Interactions with the Free Surface.
Patton, H. J.
64. Correlating Near-Source Rock Damage from Single-Hole
Explosions to Seismic Waves: II. Seismic Observations.
Bonner, J. L., Stroujkova, A., Leidig, M. R., Boyd, P., and
Martin, R.
65. High Strain Rate Fracture Development in Granites:
Comparing Experimental and Modeling Results.
Sussman, A. J., Rougier, E., Broome, S. T., Knight, E. E.,
Schultz-Fellenz, E. S., and Townsend, M.
66. High-Resolution 3-D P- and S-wave Tomography of the
Nevada National Security Site. Preston, L. A.
67. Seismic Body Wave Velocities Derived from SPE P-Wave
Travel Times and Rg Phase Velocity Dispersion - Time
Domain and Frequency Domain Methods. Rowe, C. A.,
Patton, H. J., Yang, X., and Rougier, E.
68. Measured and Modeled Rotational Motions From SPE1,
SPE2, and Regional Earthquakes. Mellors, R. J., Harben,
P., Petersson, A., Rodgers, A. J., Walter, W. R., and Pitarka,
A.
69. The Influence of Pre-Stress on Shear Wave Generation
From Explosions. Aldridge, D. F., and Preston, L. A.
70. Investigating the Possibility Underground Explosions
Triggering Earthquakes by Means of Earthquake Rupture
Dynamic Models. Dalguer, L. A., and Haslinger, F.
71. 2D Modeling of Local Site Effects on Seismic Data from
Source Physics Experiments. Larmat, C. S., and Patton,
H. J.
72. Source Spectral Variation and Yield Estimation Derived
from High Frequency P and S Codas from Local High
Frequency Explosion Data. Mayeda, K., Yoo, S. H., and
Bonner, J.
73. Source Characterization of Near-Surface Chemical
Explosions at the San Andreas Fault Observatory at Depth.
Rubinstein, J. L., Pollitz, F. F., and Ellsworth, W. L.
74. A Fracture Decoupling Experiment. Stroujkova, A.,
Bonner, J., Leidig, M., Kim, W. Y., Rath, T., Carnevale,
M., and Lewkowicz, J.
75. Testing Event Discrimination over Broad Regions using
the Historical Borovoye Observatory Explosion Dataset.
Pasyanos, M. E., Ford, S. R., and Walter, W. R.
76. Progress Report on a Project to Digitize Data from
Hundreds of Nevada Underground Nuclear Tests
Recorded by the Sandia Seismic Network. Abbott, R. E.
• Abstracts, 354
SSA 2012
Abstracts of the Annual Meeting
Site Response
Oral Session · Tuesday 8:30 am, 17 April · Pacific Salon 1&2
Session Chair: Alan Yong
2012 Update of the Campbell-Bozorgnia NGA Ground Motion Prediction
Equation
Campbell, K. W., EQECAT, Inc., Beaverton, OR, [email protected];
BOZORGNIA, Y., PEER, University of California, Berkeley, CA, yousef@
berkeley.edu
In 2008, we published a ground motion prediction equation (GMPE) for PGA,
PGV, and 5%-damped response spectral acceleration (PSA) that is appropriate
for shallow crustal earthquakes in active tectonic regions. It was developed as
part of the highly successful Pacific Earthquake Engineering Research Center
(PEER) NGA-West1 project. Our GMPE and the other NGA-West1 GMPEs
are used throughout the world to estimate earthquake ground motions. Part of
the project’s success is that subsequent studies have shown that the NGA-West1
GMPEs are generally consistent with ground motions and other GMPEs from
shallow tectonically active regions located around the world. However, as successful as the original NGA-West1 program was, there were several ground motion
issues that could not be addressed because of time constraints, which we have now
incorporated in an updated GMPE as part of the new PEER NGA-West2 project. These issues include the incorporation of: (1) source directivity, (2) ground
motion directionality, (3) vertical ground motions; (4) over 30, 000 small-magnitude (5.5 ≥ M ≥ 3.0) recordings; (5) additional moderate and large magnitude
(M ≥ 6.0) recordings from around the world that occurred through 2011, (6)
spectral damping, (7) epistemic uncertainty, and (8) improved site-response
characterization. In addition, some of the more important improvements and
enhancements we have made to our GMPE include: (1) a better method for incorporating magnitude saturation in the prediction of near-source large-magnitude
ground motions, (2) incorporation of hypocentral depth as a parameter, (3) incorporation of depth to bedrock as a parameter in the shallow site response (Vs30)
term, (4) additional and improved estimates of the depth to the 2.5 km velocity horizon (i.e., deep site and basin response), (5) additional spectral periods for
a smoother predicted response spectrum, and (6) incorporation of an anelastic
attenuation term for a more reliable extrapolation to large distances.
Understanding the NGA-West Ground-Motion Prediction Equations for PGA
and PGV
Baltay, A. S., Stanford University, Stanford, CA; HANKS, T. C., USGS
Menlo Park, Menlo Park, CA, [email protected]; BEROZA, G. C., Stanford
University, Stanford, CA, [email protected]
Next Generation of Attenuation (NGA) ground-motion prediction equations
(GMPE) use as many as 19 parameters to empirically describe peak ground
acceleration (PGA) as a function of magnitude and distance; these parameters
are complexly related and may trade off in ways that are not easily understood.
We use the simple point-source model of Hanks and McGuire [1979] to fit PGA
dependent on magnitude and source-site distance to the NGA-West data set,
finding a single stress drop for all of the data. Assuming contributions to PGA
from points on the fault farther than 30 km are negligible at recording distances
less than 20 km, earthquakes above magnitude ~6.7 are theoretically saturated
for PGA. We indeed find a constant PGA of ~0.3g above this magnitude, albeit
in the midst of considerable scatter. Between M 4.5–8, the theoretical relation
for PGA matches the four most commonly used NGA-West GMPEs very well.
Only knowledge of stress drop, as well as the material parameters density, shear
wave velocity, and f max, are necessary to model the theoretical relationship. The fit
results in a stress drop of ~5 MPa for all events, consistent with stress drop studies
in similar active regions; mainshocks in the NGA data set, however, have stress
drops ~1.6 times greater than that of the aftershocks. We model peak ground
velocity (PGV) using a similar relationship from McGarr [1984], but find that
the NGA-West PGV data do not saturate as expected. Comparing the NGA data
set with PGA and PGV data from M 3–7 crustal earthquakes in Japan shows
excellent agreement, potentially extending the NGA data set to smaller magni-
tude earthquakes. That these very simple constant stress-drop, point-source models, together with the finite-fault approximation at large magnitudes, match the
NGA PGA and PGV data well suggest that considerable simplicity underlies the
parametrically complex NGA-West GMPEs.
Applicability of the NGA Ground-Motion Prediction Equations for Europe
Sandikkaya, M. A., Middle East Technical University, Ankara, Turkey;
AKKAR, S., Middle East Technical University, Ankara, Turkey.
The most recent global predictive models for shallow crustal earthquakes were
developed within the Next Generation of Ground-Motion Attenuation Models
Project (NGA; Power et al., 2008). Each NGA GMPE uses different parameters
and forms of equations to represent the source, path and site effects. Source and
path effects are fundamentally represented by moment magnitude, source-to-site
distance metrics and style-of-faulting. Other complementary parameters (i.e.,
depth to top of rupture, hanging wall effect, etc.) are also used by some of the
equation developers. When the site effect is of concern, the site classification
is generally described in terms of time-based average of the shear-wave velocity
profile variation in the uppermost 30 m soil (VS30) and the nonlinear behavior of the soil is also considered in the site terms. Besides, in some equations the
characteristics of the soil profile (the depth to rock) is implemented to capture
the longer period effects. Both Italian and Turkish strong-motion databases were
improved with metadata information (i.e., epicenter location, magnitude, depth,
style-of-faulting and source-to-site distance metrics) and site characterizations
(via geotechnical and geophysical testings) within the content of the ITACA
and TNSMD projects (ITACA Working Group, 2010; Akkar et al., 2010). The
usable data of these two databases will be used in order to evaluate the NGA
GMPEs. The residuals (difference between observed and estimated values in natural logarithm) are decomposed into inter- and intra- event residuals by mixedeffects regression technique proposed by Abrahamson and Youngs (1992). The
inter-event residuals that represent the source effect are investigated for Italian
and Turkish events if any correction is needed. Then the intra-event residuals that
represent both distance and site effects are evaluated to observe whether or not
the NGA GMPEs can satisfactorily represent the distance and site scaling for
these regions.
Ground Motion Prediction for ENA: Learning from and Limitations of the NGAEast Database
AL NOMAN, M. N., CERI, University of Memphis, Memphis, TN, malnoman@
memphis.edu; Deshon, H. R., CERI, University of Memphis, Memphis, TN,
[email protected]; CRAMER, C. H., CERI, University of Memphis,
Memphis, TN, [email protected]
The Next Generation Attenuation (NGA) East ground motion database has been
prepared through a detailed selection procedure by the NGA-East database group
for use by the NGA-East ground motion modelers to develop new ground motion
prediction equations (GMPEs) for Eastern North America (ENA). This database
contains ground motions from several recent ENA earthquakes including the
recent Canadian, Virginia and Oklahoma earthquakes, and contains a total of
22990 component records (horizontal and vertical) at distances of up to 3500
km from 89 earthquakes with moment magnitude ranging from Mw 2.2 to 7.6.
The approach of this paper is to develop an empirical GMPE from the updated
database and compare it to current ENA GMPEs. Least squares inversion is used
to determine regression coefficients of an empirical attenuation model accommodating terms for anelastic and geometrical spreading, style of faulting, and deep
soil, soil and rock site conditions. Previous comparisons of individual M~5-6
earthquake ground motions to current ENA GMPEs suggest that at short periods the current GMPEs, as a group, generally predict the observations, while at
long periods they over predict the observed ground motions. The goal of this
study is to explore the NGA-East database to learn its impact and limitations on
GMPE source, path and site terms.
doi: 10.1785/gssrl.83.2.354
Rupture Directivity Correction Model for the Fault-Normal, Fault-Parallel and
Fiftieth Percentile Components of Horizontal Ground Motion
BAYLESS, J. R., URS Corporation, Los Angeles, CA, [email protected];
SOMERVILLE, P. G., URS Corporation, Los Angeles, CA, paul.somerville@
urs.com
We have developed a revised rupture directivity model to supersede the Somerville
et al. (1997) model. This model predicts corrections to the horizontal geometrical
mean component of strong ground motion (GMRotI50), as obtained from the
2008 NGA-West GMPE’s. The model provides corrections in the fault-normal
(FN), fault-parallel (FP) and the fiftieth percentile based on period-dependent
rotation angles (RotD50) components, with distinct treatment for strike-slip
and dip-slip faults. We used the PEER NGA-West updated data set and created a
revised functional form, while maintaining the original Somerville et al. (1997)
directivity parameters and preserving simplicity in the functional form in order
to facilitate application of the model. The modified functional form was fit to
residuals of each of the four 2008 NGA-West GMPE’s using the random effects
method described in Somerville et al (1997). The compilation of these results led
to the creation of a standard directivity correction model, which we believe is
applicable to any generic GMPE. The results of this model have been compared
with those of Somerville et al. (1997), Abrahamson (2000), and Spudich and
Chiou (2008).
An empirical attenuation relation without directivity effect (Sa) can be
modified using our model to obtain the Sa with directivity effects (Sa_dir) by the
following equation:
ln(Sa_dir) = ln(Sa) + fD
where fD is the directivity effect. The directivity effect is quantified as the
product of the period and fault type dependent constant coefficient, the distance,
magnitude, and azimuth tapers, and the geometric directivity predictor (f_geom)
which correlates the directivity effects with the spatial variation of near-fault
ground motions. f_geom is a function of the fraction of the fault rupture surface
that lies between the hypocenter and the site (parameter X or Y), and the angle
between the direction of rupture propagation and the direction of waves travelling from the fault to the site.
How the Style-of-Faulting Ratios Change with Database Features
Sandikkaya, M. A., Middle East Technical University, Earthquake
Engineering Research Center, Ankara, Turkey, [email protected];
AKKAR, S., Middle East Technical University, Earthquake Engineering
Research Center, Ankara, Turkey, [email protected]
One of the source characteristics that affect the ground-motion prediction equations is the style-of-faulting (SoF) ratios. These ratios are described as the ratio of
the intensity measures for either normal or reverse events to those of strike-slip
events and obtained as dummy variables with considering the effect of magnitude, distance and site effects during regressions. The most recent studies show
that the reverse to strike slip ratios (R:SS) are higher than unity; whereas, normal
to strike-slip ratios (N:SS) are lower than unity (e.g. Akkar and Bommer, 2010,
[AB10]). Within the context of the ‘Seismic Hazard Harmonization in Europe’
project, the next generation predictive model for pan-European region will be
developed. One of the most important improvements of the recent model is to
extend the lower magnitude limit to 4.0. However, during the regression analysis,
it is found that the R:SS and N:SS are higher than unity. Though, there may be
several reasons to explain these unexpected trends, in this study, we investigate
the effect of the database features on SoF ratios and observe how these ratios vary
depending on the magnitude and distance distributions.
Critical Parameters Affecting Bias and Variability in Site Response Analyses
Using KiK-net Downhole Array Data
Kaklamanos, J., Tufts University, Medford, MA, james.kaklamanos@
tufts.edu; BRADLEY, B. A., University of Canterbury, Christchurch, New
Zealand, [email protected]; THOMPSON, E. M., Tufts
University, Medford, MA, [email protected]; BAISE, L. G., Tufts
University, Medford, MA, [email protected]
Due to the limited number of strong-motion records that have recorded ground
response at large strains, any statistical analysis of seismic site response models
is severely limited by the small number of observations. Recent earthquakes
in Japan, including the recent M9.0 Tohoku earthquake, have substantially
increased the observations of strong-motion records that can be used to compare alternative site response models at large strains. These observations subsequently provide new insights into the reliability and accuracy of site response
models. Using the Kiban-Kyoshin network (KiK-net) downhole array data in
Japan, we analyze the accuracy (both bias and variability) resulting from common site response modeling assumptions and identify key “problem character-
ization parameters” that contribute to the uncertainty in site response analyses.
We apply the validation framework of Bradley (2011) to 100 KiK-net sites that
have recorded 3720 large-amplitude ground motions using both linear and equivalent-linear site response methodologies. We find that the most helpful problem
characterization parameters for site response are the maximum shear strain in
the soil profile, and the observed peak ground acceleration at the ground surface.
The strains at which linear analyses begin to break down (illustrating bias due to
nonlinear soil behavior) is a function of period, and is between 0.01% and 0.1%
for periods less than 0.5 s. Equivalent-linear analyses begin to break down at
strains of approximately 0.15% over this range of periods. We find that, for the
sites and ground motions considered, site response residuals at spectral periods
greater than 0.5 s do not display noticeable effects of nonlinear soil behavior. The
bias and standard deviations (sigmas) offered by linear and equivalent-linear site
response models are similar, although equivalent-linear analyses exhibit a reduced
bias at short periods (less than 0.1 s).
Retrieval of Mechanical Properties of a Concrete-Face Rockfill Dam (CFRD)
Using Ambient Seismic Noise during Its Construction
MARTÍNEZ-RAMÍREZ, E., Comisión Federal de Electricidad, Augusto
Rodín, Mexico DF, Mexico, [email protected]; SÁNCHEZALVARO, E., Comisión Federal de Electricidad, Augusto Rodín, Mexico
DF, Mexico, [email protected]; FERNÁNDEZ-RAMÍREZ,
S., Comisión Federal de Electricidad, Augusto Rodín, Mexico DF, Mexico,
[email protected]; LEÓN-SÁNCHEZ, P. D., Comisión Federal
de Electricidad, Augusto Rodín, Mexico DF, Mexico, saledapa@gmail.
com; MARENGO-MOGOLLÓN, H., Comisión Federal de Electricidad,
Mississippi, Mexico DF, Mexico, [email protected]; SANCHEZSESMA, F. J., Instituto de Ingenieria, Circuito Escolar, Ciudad Universitaria
DF, Mexico, [email protected]; RODRÍGUEZ-GONZÁLEZ, M., Instituto de
Ingeniería, UNAM, Circuito Escolar, Ciudad Universitaria DF, Mexico, mrod@
pumas.iingen.unam.mx; Suarez, M., Instituto de Ingeniería, UNAM, Circuito
Escolar, Ciudad Universitaria DF, Mexico, [email protected]
Current trends in dam construction favor the use of rockfills with upstream
concrete face (CFRD). This is due to the high cost of impervious materials like
clay and its high deformability. The construction process implies then a high
quality control of the compaction process including, among other things, grain
size, water content, and rolling procedure. Despite this careful process there is a
need to measure and verify the actual value of mechanical properties like mass
density, rigidity and damping. To achieve this, measurement wells are set during
construction and localized measures are obtained like neutron-density and crosshole experiments.
To complement these measurements we rely on a new technique based on
the use of ambient seismic noise. In this technique the average of cross correlations of recorded motion allows to recover the surface wave part of the Green’s
function. This prominent part of the signal has dispersion behavior and its inversion leads to the shear velocity profile with depth. This technique is non invasive and can be applied virtually in any place of the exposed dam surface. On
the other hand, the average auto-correlations allows estimating the H/V spectral
ratio. Again the diffuse field assumption permits to calculate H/V in terms of the
properties of Green’s function.
We studied the mechanical properties of La Yesca dam that is being constructed in the limits of the Mexican states of Jalisco and Nayarit. This CFRD
is a CFE-Hydroelectrical Project of the Santiago river system and is about to be
finished. Our measurements along the construction process allow us to draw a
coherent spatial distribution of mechanical properties within the dam.
Final Report on ARRA-funded Site Characterization Project
Yong, A., US Geological Survey, Pasadena, CA, [email protected]; MARTIN,
A., GEOVision Inc., Corona, CA, [email protected]; STOKOE, K.
H., University of Texas, Austin, TX, [email protected]; DIEHL, J.,
GEOVision Inc., Corona, CA, [email protected]
We present the final results (Yong et al., USGS-OFR in prep.) of our geotechnical site characterization project at 189 seismographic station sites in California
and the central U.S. Funded by the 2009 American Recovery and Reinvestment
Act (ARRA), the consortium consisting of principals from academia and commerce applied geophysical techniques at: 129 Southern California Seismic
Network (SCSN), one ANZA seismic network, 25 California Geological
Survey (CGS), two Berkeley Seismic Network, 28 Northern California Seismic
Network (NCSN), and four Central U.S. (CEUS) sites. At each site, investigations included both passive and active surface- and body-wave techniques,
involving one or more of the established approaches: the horizontal-to-vertical
spectral ratio (HVSR), 2-D array microtremor, refraction microtremor (ReMi),
spectral analysis of surface wave (SASW), multi-channel analysis of surface
wave (MASW), and shear-wave refraction methods. From this multi-method
approach, we determined VS (shear-wave velocity) profiles and the calculated VS30
(the time-averaged shear-wave velocity in the upper 30 meters depth) for each
site. We estimate that approximately 60% of these sites have crystalline, volcanic
or sedimentary rock at the surface or at relatively shallow depth and 40% are of
Quaternary soils located in either rural or urban environments. Calculated VS30
covers the full range of site classes from D/E (soft/stiff soils) to A (hard rock) with
the vast majority of the sites in the Site Class D to B range. In general, our records
match expected values for surficial geology—unexpected results were typically
attributable to inaccurate or coarse map information and alternative explanations were verified through interpretations of local geology observed during field
investigations. However, several rock sites are categorized as Site Class D, demonstrating the importance for site characterization.
Application of the H/V Spectral Ratios for Earthquake Ground Motions at
K-NET Sites in Tohoku Region, Japan to Delineate Soil Nonlinearity
Kawase, H., DPRI, Kyoto Univeristy, Uji, Kyoto, Japan, kawase@zeisei.
dpri.kyoto-u.ac.jp; NAGSHIMA, F., DPRI, Kyoto Univeristy, Uji, Kyoto,
Japan, [email protected]; MATSUSHIMA, S., DPRI,
Kyoto Univeristy, Uji, Kyoto, Japan, [email protected];
SANCHEZ-SESMA, F. J., UNAM, Mexico City, D.F., Mexico.
We have proposed an optimal way to use horizontal-to-vertical (H/V) spectral
ratios for underground structure exploration, which is based on diffuse field concepts (Sánchez-Sesma et al., 2011; Kawase et al., 2011). This approach is applicable to earthquake and microtremor ground motions.
For seismic motions we assume that a set of incoming elastic plane waves
with various azimuths, incidences, and polarizations will form a spatially homogeneous wavefield. For microtremors we assume that randomly distributed
sources, mostly close to the surface, will generate them. In both cases the motions
are considered as belonging to multiple scattered diffuse fields. Then the stack of
normalized Fourier transformed autocorrelation functions, that is, the average of
spectral densities should correspond to the imaginary part of the Green’s function. The imaginary part of the Green’s function is proportional to the square of
the absolute value of the one-dimensional (1D) transfer function for normal incidence. Since seismic motions and microtremors illuminate different parts of the
ground around the site, we can invert velocity structures based on the observed
H/V ratios for either seismic motions or microtremors independently or both at
the same time.
We show here analysis on the observed data at two K-NET stations in Japan
where very large peak ground accelerations were observed. From seismic motions
we can constrain deeper part of the velocity structure by H/V ratios in the lower
frequency range, while we can constrain shallower part of the velocity structure
by those in the higher frequency range of seismic motions as well as microtremors.
After we determine detailed velocity structures based on the H/V ratios of the
seismic motions and microtremors, we then compare H/V ratios of the strong
motions during The 2011 Off the Pacific Coast of Tohoku Earthquake of 11
March 2011 with those averaged over several weak motions to see soil nonlinearity effects
Automatic Determination of Amplification for New Sites Within a Seismic
Network
Edwards, B., Swiss Seismological Service, ETH Zürich, Zürich, Switzerland,
[email protected]; FÄH, D., Swiss Seismological Service, ETH Zürich,
Zürich, Switzerland, [email protected]
We present a method for the automatic determination of site-amplification at
newly installed sensor locations within an existing seismic network. The method
empirically quantifies site amplification at the site immediately following the first
earthquake recording. Further recordings are then utilised, such that the amplification is dynamic; becoming more robust with time. Only small magnitude
events (MW>1) are required to estimate the linear response, so the method is
equally applicable in low or high seismicity regions, and can be used to obtain
reliable estimates of linear-amplification phenomena prior to larger events. As the
amplification is empirical, we observe 2- or 3D effects (e.g., basin edge generated
surface waves) in addition to simple 1D resonance phenomena. The method is
based on fitting the Brune far-field spectrum to recordings of small to moderate
earthquakes and analysing systematic deviations from expected shaking levels.
Absolute amplification estimation is possible through the use of a known generic
reference profile and the corresponding reference amplification condition.
Response spectra amplification functions are then computed for given magnitude-distance scenarios using a stochastic method. The method is automated at
the Swiss Seismological Service, with access through a web-interface, and is used
to assess the rapidly expanding Swiss Strong-Motion Network. We have observed
amplifications consistent with expectations from 1D modelling, with additional
insight into possible 2- or 3D effects, including amplification levels of up to 15x
in the city of Lucerne, thought to be due to the generation of surface waves at the
edge of the sedimentary basin.
Application of Microtremor Array Measurements and Three-Component
Microtremor Measurements to Estimate S-Wave Velocity Structure at San
Francisco Bay Area
Hayashi, K., Geometrics, San Jose, CA, [email protected];
UNDERWOOD, D., Geometrics, San Jose, CA, [email protected]
Active and passive surface wave methods have been increasingly getting popular in last 10 years. The passive method or microtremor array measurements in
which ambient noise is used as surface waves, is particularly attractive because
the method does not require any artificial source and the depth of investigation
can be increased easily. In order to evaluate the applicability of microtremor array
measurements in San Francisco Bay Area, we have performed the microtremor
array measurements and the three-component microtremor measurements at
several sites in South Bay of San Francisco Bay Area. A couple of seismographs
including three-component accelerometers were used for data acquisition.
Separations of two accelerometers vary from 5 to 4125m and several different
separations were used in the microtremor array measurements at one site. Length
of microtremor data for one separation is about 10 to 60 minutes and measurements of one site took several hours. A spatial autocorrelation was used for calculating phase-velocities and clear dispersion curves were obtained between 0.2
to 10 Hz. Maximum phase velocity is about 2300m/s at the frequency of 0.2Hz.
Same microtremor data was used for the calculation of horizontal and vertical
ratio (H/V) of spectra. There are two peak frequencies of H/V spectra. Higher
peaks vary from 1 to 2Hz and lower peaks vary from 0.2 to 1Hz. A joint inversion of an H/V spectrum and a dispersion curve is applied to observed data and
S-wave velocity models down to a depth of about two kilometers were obtained.
A low velocity layer with S-wave velocity lower than 500m/s existed down to a
depth of 50 to 100m at all sites. Intermediate bedrock with S-wave velocity higher
than 1000m/s existed at a depth of 500 to 1000m. Deepest bedrock with S-wave
velocity higher than 3000m/s seems to be existed at a depth of at least 1500m. It
seems that the lower peak frequency of 0.2 to 1Hz in the H/V spectra is mainly
due to the deepest bedrock.
Directions
Oral Session · Tuesday 2:15 pm, 17 April · Pacific Salon 1&2
Session Chairs: Youshun Sun, Michael Begnaud, Sidao Ni,
and Junmeng Zhao
High-Resolution Seismic-Reflection Imaging Profiles across the Grizzly
Valley Fault System, Northern Walker Lane, California
Gold, R. D., U.S. Geological Survey, Golden, CO, [email protected];
STEPHENSON, W. J., U.S. Geological Survey, Golden, CO, wstephens@
usgs.gov; ODUM, J. K., U.S. Geological Survey, Golden, CO, [email protected];
BRIGGS, R., U.S. Geological Survey, Golden, CO, [email protected]; CRONE,
A., U.S. Geological Survey, Golden, CO, [email protected]; WORLEY, D., U.S.
Geological Survey, Golden, CO, [email protected]; ALLEN, J., U.S. Geological
Survey, Golden, CO, [email protected]; Angster, S., U.S. Geological Survey,
Golden, CO, [email protected]; Bowden, D., U.S. Geological Survey,
Golden, CO, [email protected]
The Grizzly Valley fault system strikes northwestward across Sierra Valley,
CA and is part of a network of active dextral strike-slip faults in the northern
Walker Lane. To evaluate the recency of faulting along the Grizzly Valley fault,
we acquired six, high-resolution, P-wave, seismic-reflection profiles. The 0.5-to2.0-km long profiles were sited orthogonal to suspected tectonic lineaments
identified from previous mapping and our analysis of high-resolution airborne
LiDAR data. To image the upper 400–700 m of subsurface stratigraphy of Sierra
Valley we used a 230-kg accelerated weight drop with source and receiver spacings
of 2–5 m. The profiles reveal a highly reflective, deformed basal marker that we
interpret to be the top of Tertiary volcanic rocks and a 120- to 300-m-thick suite
of subhorizontal reflectors we interpret as basin-fill deposits composed of alternating alluvial and pluvial sand and silt. Three profiles that cross a structure along
the southwestern margin of the North Channel of Little Last Chance Creek
reveal a subvertical fault zone in both the volcanic rocks and the basin fill. We
interpret the Grizzly Valley fault system to have been active in Quaternary time
because: 1) the LiDAR data reveal a 1.7-m-high linear topographic ridge, which
may have been generated by recent faulting; 2) the seismic-reflection profiles doc-
ument shallow (≤400 m) faulting in the basin fill of Sierra Valley that coincides
with the topographic lineament, and 3) vegetation lineaments and drainage patterns visible on aerial and satellite imagery indicate that geologic structures control the distribution of surface and ground water coincident with the topographic
lineament. These results will guide future paleoseismic studies to determine the
times of recent earthquakes.
Seismic Tomography Structurally Constrained by a priori Model Based on a
Cross-Gradient Approach
Zhang, H., Univ. Science and Technology of China, Dept. of Geophysics,
Anhui, Hefei, China, [email protected]; NEWMAN, G. A., Lawrence
Berkeley National Laboratory, Geophysics Department, Berkeley, CA,
[email protected]; FEHLER, M., Massachusetts Institute of Technology,
EAPS, Cambridge, MA, [email protected]
It is known that seismic travel time tomography may be an ill-conditioned problem because of poor ray coverage over some model regions. To make the inversion
stable, damping and smoothing constraints are generally applied. In some cases,
a priori velocity model may also be used to constrain the inversion in such a way
that the inverted velocity model cannot be far away from the a priori model. In
our approach, the a priori model does not have to be a velocity model and it can
be any model available, such as the resistivity model or the local geological model.
The way that the a priori model is used to constrain the inverted model is also
different. In the inversion, we require the inverted model to be structurally similar to the a priori model, while at the same time to fit the travel time data. The
structural constraint is accomplished using the cross-gradient approach proposed
by Gallarado and Meju (2003), where the cross product of the spatial gradients of
the a priori model and the inverted model are forced to be zero.
We tested this method based on a synthetic model consisting of a series of
vertical reflectors. The events and stations are the same as those used in Zhang
et al. (2009a) around the SAFOD site. The synthetic test showed encouraging
results. When seismic tomography is constrained by the known priori model, the
inverted model better recovers the vertical reflectors. We will apply this method
to the real data set around the SAFOD site and the a priori model will be constructed from the structure imaging result using the scattered waveforms as
shown in Zhang et al. (2009b).
Adjoint Tomography Reveals European Upper Mantle Structure
Tromp, J., Princeton University, Princeton, NJ, [email protected]; ZHU,
H., Princeton University, Princeton, NJ, [email protected]; BOZDAG,
E., Princeton University, Princeton, NJ, [email protected]; PETER, D.,
Princeton University, Princeton, NJ, [email protected]
We determine a transversely isotropic tomographic model of the European upper
mantle based on an iterative preconditioned conjugate-gradient inversion strategy involving adjoint methods. Using three-component body- and surface-wave
phase measurements from ~200 earthquakes recorded by permanent seismographic stations and PASSCAL experiments in Iceland, Turkey and Spain, we
have thus far performed 26 tomographic iterations, requiring a total of ~16, 000
wavefield simulations and 2.4 million CPU hours. During the inversion, smaller
scale structures -such as slabs, upwellings, and delaminations- naturally emerge
from the smooth background of the 3D starting model, thereby bridging the gap
between high-resolution body-wave traveltime tomography and lower resolution
inversions based on long-period body waves, surface waves and free oscillations.
It is comforting to observe that many of these small-scale features are consistent
with existing high-resolution tomographic images of Europe, but encouraging to
simultaneously find hitherto unidentified structures, such as a fast wave speed
signature of northeastward subduction of the Adria plate, upper-mantle slow
wave speed anomalies related to Cenozoic volcanism in central Europe, and clear
examples of lithospheric drips associated with delamination.
Full-3D Waveform Tomography for Southern California
Chen, P., Department of Geology and Geophysics, University of Wyoming,
Laramie, WY, [email protected]; LEE, E., Department of
Geology and Geophysics, University of Wyoming, Laramie, WY; JORDAN,
T. H., Department of Earth Sciences, University of Southern California, Los
Angeles, CA; MAECHLING, P. J., Department of Earth Sciences, University
of Southern California, Los Angeles, CA; DENOLLE, M., Department of
Geophysics, Stanford University, Stanford, CA; BEROZA, G. C., Department
of Geophysics, Stanford University, Stanford, CA.
Our full-3D tomography (F3DT) uses 3D SCEC Community Velocity Model
Version 4.0 (CVM4) in Southern California as initial model, a staggered-grid
finite-difference code to simulate seismic wave propagation and the sensitivity
(Fréchet) kernels are calculated based on the scattering integral and adjoint meth-
ods to iteratively improve the model. We use both earthquake recordings and
ambient noise Green’s function data, stacking of station-to-station correlations
of ambient seismic noise, in our F3DT inversions. To reduce errors of earthquake
sources, the epicenters and source parameters of earthquakes used in our F3DT
are inverted based on full-wave method. In the first two iterations, we used scattering integral to construct sensitivity (Fréchet) kernels of broadband phase-delay
measurements and LSQR algorithm to invert 3D perturbations. In first iteration,
we only used waveforms from regional earthquakes and the waveforms of updated
model generally provide better fit to the observed waveforms. In second iteration,
we only used ambient noise Green’s function data in inversion and the synthetic
waveforms generated by updated model not only improved ambient noise Green’s
function waveform fittings but also earthquake waveform similarities. Since the
waveform fittings of earthquake waveforms and ambient noise Green’s function
data are improved after first two iterations, we start to combine frequency dependent measurements made on waveforms of earthquake and ambient noise Green’s
function data and to use adjoint method for structure perturbations. After nine
iterations, the current model (CVM4SI10) shows many features that relate to
the geological structures at shallow depth. In addition, the earthquake waveform
misfit and summation of square of ambient noise Green’s function group velocity
delay time between observed waveforms and updated synthetic waveforms both
reduced more than 50%.
Full-3D Waveform Tomography for Northern California Using Ambient-Noise
Cross-Correlation Green’s Functions
Lee, E., Department of Geology and Geophysics, University of Wyoming,
Laramie, WY, [email protected]; XU, Z., China Earthquake Networks Center,
Beijing, China; CHEN, P., Department of Geology and Geophysics, University
of Wyoming, Laramie, WY.
We cross-correlate the vertical components of ambient seismic noise data recorded
on USArray broadband stations in the northern California area to estimate interstation Green’s functions. Ambient noise Green’s function can take advantage
of the density of the USArrary station coverage and do not require earthquakes
and active sources. These ambient-noise Green’s functions are then compared
with synthetic Green’s functions computed using the finite-difference method in
a hybrid 3D reference model obtained by combining the California state-wide 3D
seismic velocity model provided by Lin et al. (2010) with the USGS 3D seismic
velocity model for the San Francisco Bay Region. The adjoint method is adopted
to construct the gradient of the misfit functional, which is defined in terms of the
frequency-dependent phase-delay measurements made on time-localized surface
waves on the ambient-noise Green’s functions and the synthetics computed using
our 3D starting model. The first iteration of our inversion involves nearly 3200
inter-station paths that provide good coverage of northern California. After the
first iteration, the updated 3D seismic velocity model provides nearly 50% reduction in the misfit functional. By carrying out more iterations and including more
waveforms from ambient-noise Green’s functions as well as waveforms from natural earthquakes, our studies will gradually improve the regional seismic velocity
model in northern California.
SALSA3D—Improving Event Locations Using a Global 3D P-Velocity Model of
the Earth’s Crust and Mantle
Ballard, S., Sandia National Laboratories, Albuquerque, NM, sballar@
sandia.gov; BEGNAUD, M. L., Los Alamos National Laboratory, Los Alamos,
NM, [email protected]; YOUNG, C. J., Sandia National Laboratories,
Albuquerque, NM, [email protected]; HIPP, J. R., Sandia National
Laboratories, Albuquerque, NM, [email protected]; ENCARNACAO, A.
V., Sandia National Laboratories, Albuquerque, NM, [email protected];
CHAEL, E. P., Sandia National Laboratories, Albuquerque, NM, epchael@
sandia.gov; PHILLIPS, W. S., Los Alamos National Laboratory, Los Alamos,
NM, [email protected]; Steck, L. K., Los Alamos National Laboratory, Los
Alamos, NM, [email protected]
To test the hypothesis that high quality 3D Earth models will produce seismic
event locations that are more accurate and more precise than currently used 1D
and 2/2.5D models, we are developing a global 3D P wave velocity model of the
Earth’s crust and mantle using seismic tomography. To obtain an optimal model
with as few nodes as possible, we use a progressive grid refinement methodology
based on the diagonal of the model resolution matrix, resulting in a grid with
spatial resolution that varies in both geographic and radial dimensions. To ensure
that our data is in synch with our final model, we iteratively perform tomography
and relocate the events in our catalog until the event locations stabilize. We use
the model covariance matrix computed from our final tomographic model to calculate path-dependent travel time prediction uncertainties.
We compare the location capabilities of SALSA3D with the new pathdependent travel-time uncertainties and with a simple distance-dependent
travel-time uncertainty model. We also compare SALSA3D against standard
1D and 2/2.5D models with simple distance-dependent travel time uncertainties. Location capability for each model is evaluated using a global event set with
GT of 5 km or better. These events generally possess hundreds of Pn and P picks
from which we generate different realizations of station distributions, yielding
a range of azimuthal coverage and ratios of teleseismic to regional arrivals. The
SALSA3D model reduces mislocation over the standard 1D ak135 model regardless of Pn to P ratio, with improvement most pronounced at higher azimuthal
gaps.
Receiver Functions on Ice: Crust and Mantle Properties from POLENET
Chaput, J. A., New Mexico Tech, Socorro NM, [email protected];
HANSEN, S., University of Alabama, Tuscaloosa, AL; ASTER, R., New Mexico
Tech, Socorro NM, [email protected]; NYBLADE, A., Penn State University,
State College, PA; WIENS, D., Washington University; HUERTA, A., Central
Washington University, Ellensburg, WA; WILSON, T., Ohio State University,
Columbus, OH; The POLENET group
We use of P-to-S and S-to-P receiver functions to study crustal thicknesses and
mantle transition zone depths across a wide extent of West Antarctica and the
Transantarctic Mountains (TAM) as a component of the POLENET project,
with a primary focus on the recently complete dataset from an 1000 km broadband seismic transect crossing the West Antarctic Rift System (WARS). The
presence of thick ice sheets and underlying sedimentary basins create complications in identifying basic (e.g., Moho) conversions that are normally readily visible
in continental settings in P-S receiver functions, though S-P receiver functions in
theory can circumvent some of these issues for a limited range of source ranges.
We investigate various approaches for deconvolving ice and shallow responses
using the entirety of available POLENET and other Antarctic stations, including selective filtering, multimode analysis and top-down building of synthetic
receiver function models. We will report on the best-constrained crustal thickness and other results in the context of Antarctic tectonics, and provide an early
geological interpretation pertaining to the lithosphere-scale structure of the
WARS, TAM front and the Marie Byrd Land volcanic province.
Onshore/Offshore Structure of the Northern Cascadia Subduction Zone
Obtained from Bayesian Receiver Function Inversion
Brillon, C., University of Victoria, Victoria, BC, Canada/Pacific Geoscience
Centre, Sidney, BC, Canada, [email protected]; CASSIDY, J. F.,
Pacific Geoscience Centre, Sidney, BC, Canada/University of Victoria, Victoria,
BC, Canada, [email protected]; DOSSO, S. E., University of Victoria,
Victoria, BC, Canada, [email protected]
This study applies Bayesian inversion to receiver functions (RFs) to solve for
local shear wave velocity (Vs) structure of the crust and upper mantle beneath
the northern Cascadia subduction zone at four sites from the Juan de Fuca Ridge
(JdFR) to Vancouver Island, B.C.. We use passive seismic data recorded on NC89,
a permanent NEPTUNE (North-East Pacific Time-series Undersea Networked
Experiments) ocean bottom seismometer (OBS) located on the continental slope,
and a temporary autonomous KECK foundation OBS, KEBB, located on the
Endeavour segment of the JdFR. The two land based seismometers (OZB and
PGC) are located on Vancouver Island and are part of the Canadian National
Seismograph Network (CNSN). The introduction of NEPTUNE has helped to
fill a gap in offshore seismic monitoring. However, due to high noise levels, few
events are useful (to date) for RF analysis. In this study, we utilize three-component, broadband recordings of large (M6+), distant (30°-100°) earthquakes
to compute RFs due to locally generated P to S converted waves. RFs are then
inverted using a non-linear Bayesian approach which yields optimal Vs, Vp, strike
and dip profiles, as well as rigorous uncertainty estimates of these parameters.
Near the JdFR a thin sediment layer (<1km) overlying the oceanic crust containing a large velocity contrast at the depth of an expected axial magma chamber
was resolved. The oceanic crust thickens to ~10km at the continental slope where
it is overlain by ~5km of sediments. At the coastal station a low velocity zone is
imaged at ~16km depth dipping approximately 12° NE. Evidence for this low
velocity zone is also seen beneath southern Vancouver Island at a depth consistent
with previous studies. Determining such models at a number of locations (from
the spreading ridge to the coast) will provide new information regarding local
structure and aid in hazard analysis.
A New Paradigm for Seismic Imaging: Transdimensional Inversion of
Receiver Functions and Surface Wave Dispersion with Hierarchical Bayes
Algorithm
Tkalcic, H., The Australian National University, Canberra, ACT, Australia,
[email protected]; BODIN, T., The Australian National University,
Canberra, ACT, Australia, [email protected]; SAMBRIDGE, M.,
The Australian National University, Canberra, ACT, Australia, Malcolm.
[email protected]; GALLAGHER, K., Université de Rennes, Rennes,
France, [email protected]; ARROUCAU, P., North Carolina
Central University, Durham, NC, [email protected]
Here we present a novel method for a joint inversion of receiver functions and surface wave dispersion data, in which trans-dimensional and hierarchical sampling
methods are used to produce a multidimensional posterior probability distribution. We use a trans-dimensional Bayesian inverse method, as it has an excellent
property that it treats the number of model parameters (e.g. number of layers) as
an unknown in the problem.
With a recent expansion of seismic instruments, the receiver-based approach
that combines receiver functions and surface wave dispersion has become a routine choice in Earth imaging in many parts of the world.
Some issues of traditional techniques for joint inversion that are addressed
here include treating an inaccurate approximation of data noise (i.e. the data
covariance matrix) and the inadequate definition of the misfit function, which
becomes even more important in the context of a joint inversion. The level of data
noise is crucial because it effectively quantifies the usable information present in
the data (a very noisy dataset does not contain much retrievable information) and
here it naturally controls the quantity of information that consequently should be
present in the model (i.e. the number of model parameters).
We show how the Hierarchical Bayes method can be used to solve the above
problems. First, we extend the Bayesian formulation to hierarchical models,
which are able to consider the lack of information that the user has on the data
errors. In other words, we let the data infer their own degree of uncertainty treating the magnitude and correlation of noise as unknowns in the inversion. Second,
we design a scheme that naturally weights the contribution of different data types
in the likelihood function thus removing the arbitrary choice of a weighting factor.
To demonstrate the applicability of the method, we show examples of joint
inversion of seismic data and argue that these methods are set to play a major in
the future.
Long-Period Surface-Wave Attenuation within the Mantle
Morozov, I. B., University of Saskatchewan, Saskatoon, SK, Canada, igor.
[email protected]
The existing forward models of surface-wave attenuation are based on the viscoelastic theory and correspondence principle. However, it is rarely noticed that
these methods do not completely agree with principles of solid- and fluid-state
physics, and consequently their results may be subject to certain limitations. For
example, the model of long-period Love-wave attenuation well known from the
60’s violates the total-energy balance and over-predicts energy dissipation by
about 20%. Here, we model Love- and Rayleigh-wave attenuation by using a firstprinciple physical approach based on Lagrangian mechanics. Three mechanisms
of dissipation are considered: 1) solid (rhelogical) viscosity, 2) thermoelasticity,
and 3) scattering. Kinetic effects (such as diffusion of dislocations) represent
another important mechanism, which is included empirically. For viscosity,
linear and non-linear rhelogical (stress to strain rate) relations are considered,
and non-linearity appears to be favored by the data. Thermoelastic dissipation
could be significant for Q levels above about 100, which is commonly observed
for surface waves within the mantle. Thermoelastic dissipation is also sensitive to
the scale lengths of heterogeneities. For heterogeneity scales (“grain” size) below
~5 mm, long-period thermoelastic Q increases with frequency, and for largerscale heterogeneity, this Q decreases with frequency. Scattering also appears to
be a viable mechanism for explaining the observed frequency dependences of
surface-wave Q’s. Unfortunately, differentiating between these three (or four)
mechanisms using only the frequency-dependent Q data appears difficult. At the
same time, compared to the conventional Q-based model, the described model is
significantly more specific about physical properties of the mantle, and it also provides correct quantitative predictions of mechanical-energy dissipation within
surface waves.
Inversion of Surface Waves Including Higher Modes of Propagation
Hosseini, S. M., The University of Memphis, Memphis, TN, shsseini@
memphis.edu; PEZESHK, S., The University of Memphis, Memphis, TN,
[email protected]; PUJOL, J., The University of Memphis, Memphis, TN,
[email protected]; STOVALL, S., U.S. Nuclear Regulatory Commission,
Rockville, MD, [email protected]
The correct estimation of the shear-wave velocity is of great interest in engineering and geophysics. Multi-channel analysis of surface waves is a non-invasive
seismic survey method based on the surface-wave propagation which captures
the phase velocity of Rayleigh waves versus the frequency (dispersion curve). The
inversion method is used to estimate the soil dynamic properties of the medium
through which the Rayleigh wave has been traveling. Regardless of the type of the
inversion method, the non-uniqueness is an important issue. The non-uniqueness
of the solution can be reduced by considering higher modes of propagation and
putting boundaries on the range of possible shear-wave velocities and/or on the
difference of shear-wave velocities between two consecutive layers. Furthermore,
the non-uniqueness problem can also be reduced by using time-domain synthetic
seismograms computed using the velocity models determined by inversion, which
are compared with actual seismograms. A genetic algorithm optimization procedure is used in the inversion process, and the comparison of actual and synthetic
seismograms is used to eliminate populations that do not produce a good match.
The resulting inverted profiles are compared with those obtained using the computer program SurSeis 3 (software from the Kansas Geological Survey) which is
a gradient-based Rayleigh wave inversion program. The inverted velocity profiles
are also compared with downhole seismic survey results to illustrate possible
strengths and limitations of the proposed inversion technique.
Performance of Geo-acoustic Parameter Estimation From Ambient Noise
Measurements: Aperture, SNR, and Information in Diffuse Wave Fields
Walker, S. C., Scripps Institution of Oceanography, La Jolla, CA, scwalker@
ucsd.edu
Recent experiments have focused on characterizing geoacoustic parameters of
interest from the spatial correlations (measured over a pair of spatially separated
passive sensors) associated with directionally diffuse ambient vibration fields. The
stochastic nature of the measurements introduces stochastic error in the parameter estimation process. Here Cramer Rao (CR)analysis is applied to set a lower
bound on the estimation error of the wave speed and attenuation parameters of
Rayleigh waves. The results provide information on the influence of the seismic
source distribution and sensor geometry on the estimate uncertainty. The analytic CR results are illustrated and verified through simulation.
Oral Session · Tuesday 8:30 am, 17 April · Pacific Salon 3
Session Chairs: Yehuda Bock, Shri Krishna Singh, and
Timothy Melbourne
GPS Earthquake Early Warning in Cascadia
Szeliga, W. M., Central Washington University, Ellensburg, WA, walter@
geology.cwu.edu; MELBOURNE, T. I., Central Washington University,
Ellensburg, WA, [email protected]; SANTILLAN, V. M., Central
Washington University, Ellensburg, WA, [email protected];
SCRIVNER, C., Central Washington University, Ellensburg, WA, scrivner@
geology.cwu.edu
Over 400 GPS receivers of the combined PANGA and PBO networks currently
operate along the Cascadia subduction zone, all of which are high-rate and telemetered in real-time. These receivers span the M9 megathrust, M7 crustal faults
beneath population centers, several active Cascades volcanoes, and a host of other
hazard sources, and together enable a host of new approaches towards hazards
mitigation. Data from the majority of the stations is received in real time at
CWU and processed into one-second position estimates using 1) relative positioning within several reference frames constrained by 2) absolute point positioning using streamed satellite orbit and clock corrections. While the former
produces lower-noise time series, for earthquakes greater than ~M7 and ground
displacements exceeding ~20 cm, point positioning alone is shown to provide
very rapid and robust estimates of the location and amplitude of both dynamic
strong ground motion and permanent deformation. We are now producing realtime point-positions using GIPSY5 and corrections to broadcast satellite clocks
and orbits streamed live from the DLR in Germany. We have also developed a
stream-editor to flag and fix cycle-slips and other data problems on the fly prior
to positioning. We are achieving < 3s latency and RMS scatter of under 4 cm.
For use in earthquake early warning, we have developed estimation routines that
derive products relevant to on-the-fly hazards response and mitigation: sidereal
position differences and triggering detectors; “ShakeMaps” and “ShiftMaps”
of maximum dynamic and permanent ground displacement, respectively, and
source magnitude and distribution of fault slip on known major faults. For
megathrust slip estimation, we also predict sea-floor uplift along the near-coastal
Cascadia region. Finally, a set of Java routines, meant for distribution, are under
development to allow streaming of these data products to the community for customized analyses and triggers.
Application of Real-Time GPS to Earthquake Alerts in Northern California
Allen, R. M., UC Berkeley, Berkeley, CA, [email protected]; JOHANSON,
I., UC Berkeley, Berkeley, CA, [email protected]; ZIV, A., Tel Aviv
University, Tel Aviv, Israel, [email protected]
The Bay Area Regional Deformation (BARD) network in Northern California
consists of a backbone of 32 stations continuously telemetered to the Berkeley
Seismological Lab (BSL). The extended BARD network also includes stations
run by other agencies, such as the USGS, PBO and those collected in the NGS
CORS network. Data from the backbone stations are processed using TrackRT.
We are in the process of investigating TrackRT’s various parameters and the
effect of network design. Our design goals for real-time BARD processing is to
obtain an accurate GPS seismogram preserving the full static offset after an earthquake has been detected.
As we implement real-time processing at BSL we are also developing methodologies to extract key information from real-time high-rate GPS displacement
data for earthquake early warning and other real-time earthquake information
products. We use 1 Hz displacement waveforms from the 4 April 2010, Mw 7.2
El Mayor-Cucapah earthquake and several large magnitude Japanese earthquakes
to explore what constraints can be placed on the seismic source as a function of
time. We also compare these data to those provided by broadband velocity and
accelerometer instrumentation. We find that the unique information provided
by the GPS-based displacement timeseries is the permanent/static displacement.
Using a simple algorithm that can be applied in real-time, we extract the static
offset shortly after the S-wave arrival, around the time of the observed peak shaking at the same site, and before shaking at more distant locations. These data can
be used, as they become available, to provide a robust estimate of the earthquake
magnitude. We therefore conclude that real-time high-rate GPS can provide a
useful and independent assessment of earthquake magnitude for the purpose of
earthquake early warning and real-time earthquake information systems in general including tsunami warning systems.
Earthquake Early Detection and Rapid Characterization in California Using
Real Time GPS and Accelerometer Data
BOCK, Y., Scripps Institution of Oceanography, La Jolla, CA, ybock@ucsd.
edu; CLAYTON, R., California Institute of Technology, Pasadena, CA, clay@
gps.caltech.edu; CROWELL, B., Scripps Institution of Oceanography, La Jolla,
CA, [email protected]; FANG, P., Scripps Institution of Oceanography, La
Jolla, CA, [email protected]; GENG, J., Scripps Institution of Oceanography,
La Jolla, CA, [email protected]; KEDAR, S., Jet Propulsion Laboratory,
Pasadena, CA, [email protected]; MELGAR, D., Scripps Institution
of Oceanography, La Jolla, CA, [email protected]; Squibb, M., Scripps
Institution of Oceanography, La Jolla, CA, [email protected]; Webb, F., Jet
Propulsion Laboratory, Pasadena, CA, [email protected]; Yu, E.,
California Institute of Technology, Pasadena, CA, [email protected].
With funding from NASA’s Advanced Information System Technologies
(AIST) program, we are developing a system for earthquake early detection and
rapid characterization in California based on an optimal real-time combination
of GPS displacements and accelerometer data as described in Bock et al. (2011).
We currently collect 1 Hz data from over 200 GPS stations in California operated by SOPAC, PBO, USGS, BSL, and Caltrans. The data are analyzed to provide 1 Hz on-the-fly broadband (static and dynamic) displacements with a latency
of 1-2 seconds and a precision of about 1-5 cm. The displacement waveforms
for stations in southern California are collected in RYO format, converted to
mSEED and SAC formats, and archived by the Southern California Earthquake
Data Center. We are currently in the process of collecting real-time very-highrate (100 Hz) accelerometer data from seismic stations that are within 1-2 km
of GPS stations. These data will be combined using a smoothing Kalman filter
to produce 100 Hz broadband displacements with a latency of about 5 seconds,
and stored at SCEDC for southern California. Using data from the 2003 Mw
8.3 Tokachi-oki, 2010 Mw 7.2 El Mayor-Cucapah, and 2011 Mw 9.0 Tohoku-oki
earthquakes, we have demonstrated that 100 Hz broadband displacements can be
estimated with an accuracy of about 1 mm in all three coordinate components so
that P-wave arrivals can be clearly detected, and false alarms can be minimized.
We are also implementing rapid characterization of earthquakes using a hierarchy
of rapid products, including earthquake early warnings (Crowell et al., 2009),
CMT solutions (Melgar et al., 2011), and finite fault inversions (Crowell et al.,
2012). Finally, we are improving our analysis of GPS displacements by integrating
precise point positioning with ambiguity resolution into our current approach of
network positioning
Determination of Tsunamigenic Potential of a Scenario Earthquake in the
Guerrero Seismic Gap Along the Mexican Subduction Zone
PÉREZ-CAMPOS, X., Instituto de Geofísica, Universidad Nacional Autónoma
de México, Mexico, DF, Mexico, [email protected]; SINGH, S. K.,
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico,
DF, Mexico, [email protected]; CRUZ-ATIENZA, V., Instituto
de Geofísica, Universidad Nacional Autónoma de México, Mexico, DF, Mexico,
[email protected]; MELGAR, D., Scripps Institution of Oceanography,
University of California, La Jolla, CA, [email protected]; IGLESIAS, A.,
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico,
DF, Mexico, [email protected]; HJÖRLEIFSDÓTTIR, V., Instituto
de Geofísica, Universidad Nacional Autónoma de México, Mexico, DF, Mexico,
[email protected]
From synthetic data generated for a postulated Mw8.2 earthquake in the
Guerrero seismic gap, we test the tools that are currently in operation or under
development at UNAM to determine the tsunamigenic potential of subduction
thrust earthquakes. The process includes three steps: (1) determination of the
rupture area and its location relative to the Pacific coast, (2) a quick estimate of
Mw, (3) determination of moment tensor using W-phase and final Mw. For the
first step, we use horizontal displacement data simulated at coastal GPS stations.
We test and calibrate the station selection algorithm and the estimation of the
rupture length following Singh et al. (2011). The vertical displacement data give
the downdip limit of the fault with respect to the coastline. With these data, we
estimate Mw (step 2) following Singh et al. (2011) using Okada’s (1992) model.
For the proposed scenario earthquake, with the data available in real time, these
source parameters are estimated within 3 minutes. These estimations may be used
for first alert. At the same time, an inversion for the seismic moment tensor using
W-phase is triggered. The outcome of this inversion may be used to confirm the
initial alert or to revise it if warranted. In addition, we assess the resolution of the
procedures for different event magnitudes depending on the available data and
propose an optimum station coverage along the Pacific coast region.
Seismic and Tsunami Monitoring in the Caribbean
Huerfano, V. A., Puerto Rico Seismic Network, Mayaguez, PR, victor@
prsn.uprm.edu; BAEZ, G., Puerto Rico Seismic Network, Mayaguez, PR,
[email protected]; VON HILLEBRANDT-ANDRADE, C., NOAA/
NWS CTWP, Mayaguez, PR, [email protected]; LOPEZ, A., UPRM
Geology, Mayaguez, PR, [email protected]
The Caribbean region has a documented history of large damaging earthquakes
and tsunamis that have affected coastal areas, including the events of Jamaica in
1692, VI in 1867, PR in 1918, DR in 1946 and the M 7.0 Haiti event in 2010.
There is evidence that tsunamis have been triggered by large tsunamigenic earthquakes that deformed the ocean floor around the Caribbean Plate (CP) boundaries. Local, Regional and Teleseismic earthquake sources have been identified and
are being modeled.
There are plans to establish a Caribbean Tsunami Warning Center
(CTWC). Caribbean seismic, sea level and geodetic networks are participating
in this initiative that consists in real time (RT) data sharing and the warning
center. Currently, more than 100 broad-band seismic and more than 20 sea levels
channels are received in the Puerto Rico Seismic Network (PRSN) in real time,
in addition to more than 10 GPS live stations. These RT streams are used by the
EW/EB/TideView/nTrip/rtkLib/PR-DANIS packages to locate and determine
the size of events in the Caribbean with magnitudes greater than 4.5 as well as the
sea level evaluation and static deformation of the crust, the solutions are provided
in a timely framework. This program is also the base of a broader Caribbean Early
Warning System (CEWS) with the added capability of estimating strong ground
shaking and tsunami forecast.
The need to establish such system in the Caribbean has been recognized by
the emergency agencies, scientific community and intergovernmental organizations (IOC). Presently, the PRSN of the UPRM jointly with NOAA/NWS are
working to establishing such system for PR/VI. Also, a protocol for exchanging
data and information on potentially tsunamigenic events in the PR/VI is currently in place. The goal of this presentation is to describe the CEWS, including tsunami modeling, real time ground shaking and tsunami data sharing and
monitoring as well as the specific protocols used to broadcast earthquake/tsunami messages.
Rapid Estimation of Damage to Tall Buildings Using Near Real-Time
Earthquake and Archived Structural Simulations
Krishnan, S., California Institute of Technology, Pasadena, CA,
[email protected]; CASAROTTI, E., Istituto Nazionale di Geofisica
e Vulcanologia, Italy, [email protected]; GOLTZ, J., California
Emergency Management Agency, Mather, CA, [email protected]; JI, C.,
University of California, Santa Barbara, Santa Barbara, CA, [email protected];
KOMATITSCH, D., Aix-Marseille University, France, [email protected]; MOURHATCH, R., California Institute of Technology, Pasadena, CA,
[email protected]; MUTO, M., California Institute of Technology, Pasadena,
CA, [email protected]; Shaw, J. H., Harvard University, Cambridge,
MA, [email protected]; Tape, C., University of Alaska, Fairbanks, AK,
[email protected]; Tromp, J., Princeton University, Princeton, NJ,
[email protected].
We will present a new approach to rapidly estimate the damage to tall buildings
immediately following a large earthquake. The pre-event groundwork involves
the creation of a database of structural responses to a suite of idealized ground
motion waveforms. The post-event action involves (i) rapid generation of an
earthquake source model, (ii) near real-time simulation of the earthquake using
a regional spectral-element model of the earth and computing synthetic seismograms at tall building sites, and (iii) estimation of tall building response (and
damage) by determining the best fitting idealized waveforms to the synthetically
generated ground motion at the site and directly extracting structural response
metrics from the database. Here, ground velocity waveforms are parameterized
using sawtooth-like wavetrains with a characteristic period (T), amplitude (peak
ground velocity, PGV), and duration (number of cycles, N). The proof-of-concept
is established using the case study of one tall building model. Nonlinear analyses
are performed on the model subjected to the idealized wavetrains, with T varying
from 0.5s to 6.0s, PGV varying from 0.125m/s to 2.5m/s, and N varying from 1
to 5. Databases of peak transient and residual interstory drift ratios (IDR), and
permanent roof drift are created. We demonstrate the effectiveness of the rapid
response approach by applying it to a suite of near-source records from the 1971
San Fernando, the 1978 Iran, the 1979 Imperial Valley, the 1987 Superstition
Hills, the 1989 Loma Prieta, the 1992 Cape Mendocino, the 1992 Landers, the
1994 Northridge, the 1995 Kobe, and the 1999 Chi-Chi earthquakes, and synthetic waveforms from a simulated 1857-like magnitude 7.9 San Andreas earthquake. The peak interstory drift ratio, a key measure of structural performance, is
predicted well enough for emergency response decision making.
Automated Real-Time Detection of Extended Fault Ruptures during Large
Earthquakes
BOESE, M., Caltech, Pasadena, CA, [email protected]; HEATON, T.
H., Caltech, Pasadena, CA, [email protected]; HAUKSSON, E., Caltech,
Pasadena, CA, [email protected]
Most algorithms for earthquake early warning (EEW) approximate earthquakes
as point sources and thus neglect source finiteness. Consequently, shaking intensities can be significantly underestimated during large earthquakes and warnings
not issued when necessary. Recently, this occurred during the 2011 M 9 Tohokuoki earthquake in Japan. Even though shaking in the Kanto region around Tokyo
was strong, users and people where not alerted by the Japanese JMA EEW system, because Kanto was several hundreds of kilometers far from the epicenter and
shaking in this region under predicted. We have developed an algorithm for automated real-time detection of extended fault ruptures using image recognition
techniques. This algorithm, called FinDer, detects and maps finite fault ruptures
in real-time by estimating their current centroid position, length, and azimuth
assuming a line source. The approach is based on a rapid (high-frequency) near/
far-source classification of ground motion amplitudes in a dense seismic network
(< 50 km), and comparison with a set of pre-calculated generic templates using
Matching by Correlation. For increased speed correlation is performed in the
wavenumber domain. FinDer keeps track of the current dimensions of a rupture
in progress without attempting to predict its future evolution. Errors in the estimated rupture lengths are typically in the same order as station spacing in the
network. The continuously updated estimates of source geometry make predicted
shaking intensities more accurate and thus more useful for EEW, ShakeMaps,
and related products. The algorithm is demonstrated for several recorded and
simulated earthquakes with different focal mechanisms.
A Rapid, Reliable, and Robust Method to Estimate Mw and Other Fault
Parameters for Early Tsunami Warning Based on Coastal GPS Networks
Singh, S. K., Instituto de Geofísica, Universidad Nacional Autónoma de
México, México, D.F., Mexico, [email protected]; PÉREZCAMPOS, X., Instituto de Geofísica, Universidad Nacional Autónoma de
México, México, D.F., Mexico, [email protected]; IGLESIAS, A.,
Instituto de Geofísica, Universidad Nacional Autónoma de México, México,
D.F., Mexico, [email protected]; MELGAR, D., Scripps Institution of
Oceanography, University of California, San Diego, La Jolla, CA, dmelgarm@
ucsd.edu
We show that rapid, reliable, and robust estimation of rupture length, location
of surface projection of the downdip edge of the rupture with respect to the
coast, and Mw of large subduction thrust earthquakes can be obtained from
near-source, coseismic static displacement vectors obtained from coastal GPS
stations, adjacent to the trenches. We assume that dip, and Ws (the width of seismogenic zone) and its maximum depth are a priori known. Our analysis is based
on Okada’s model (1992). The rupture length, L, is estimated from the amplitude
of the observed horizontal displacement along the coast and its fall off with distance. The downdip extent of the rupture is fixed by the sense of vertical displacement. The width W is estimated using the criteria: if L>Ws then W=Ws, but if
L< Ws then W=L. We assume a rake of 90°. The slip D on the fault is computed
using Okada’s model so that it agrees with the average of observed horizontal displacement along the coast over L. Finally, the seismic moment is computed from
M0 =µLWD.
We apply the proposed method to coseismic deformation reported for
nine subduction thrust earthquakes (7.3≤Mw≤9.2), including the 2011 Tohoku
(Mw9.1) event. The estimated Mw is within 0.2 of that reported in the GCMT
catalog in all cases and L and the location of the downdip edge of the rupture are
in rough agreement with those reported in detailed studies. With real-time tracking of displacement of GPS sites, it is possible to obtain a robust estimate the critical source parameters in <5 min even for Mw9 class of earthquakes. The method
is simple, robust, and does not assume a point source. It also provides length of the
rupture. Thus, it offers some advantages over the W-phase. An algorithm based of
the method has been tested on synthetic data from postulated large earthquakes
in the Guerrero seismic gap along the Mexican subduction zone (Pérez–Campos
et al., 2012). It yields results in excellent agreement with the input source parameters
Rapid Centroid Moment Tensor Computation for the Mw 9.0 Tohoku-oki
Earthquake from Local and Regional Displacement Records
Melgar, D., Scripps Inst. of Oceanography, La Jolla, CA, dmelgarm@ucsd.
edu; CROWELL, B. W., Scripps Inst. of Oceanography, La Jolla, CA, bwcrowel@
ucsd.edu; BOCK, Y., Scripps Inst. of Oceanography, La Jolla, CA, ybock@ucsd.
edu
We present here the results of rapid source modeling of the 2011 Mw 9.0 Tohokuoki earthquake. We compare and contrast the use of two data sets and two rapid
modeling techniques. The first data set is a simulated real-time mode analysis of 1
Hz GPS RINEX files using the method of instantaneous positioning of Bock et
al. (2000); these solutions are then referenced to a far away, stable station through
a network adjustment (Crowell et al. 2009). These GPS-only time series provide
1-2cm accurate displacements in the horizontal direction and ~5cm accurate displacements in the vertical direction. The second data set is from a simulated realtime combination of GPS and strong motion data via a Kalman filter (Bock et al.
2011), which yields 100Hz displacement waveforms with ~1-2mm accurate data
in the 3 directions of motion.
Modeling is performed using the fastCMT algorithm of Melgar et al.
(2012), which utilizes static offsets estimated from real-time data and combines
a formal inversion for the moment tensor with a grid search for the centroid location. We will show that due to the size of the Tohoku-oki event incorporating
near field data in this algorithm violates the point source assumption yielding
inaccurate centroid location and magnitude estimates. To alleviate this and given
that we are employing static field data with no time dependency we have expanded
the fastCMT algorithm to include multiple point sources. We show that in this
fashion it is possible to discern magnitude, event location, gross dimensions and
style of faulting within 2-3 minutes after rupture initiation. This information
can then be incorporated into further finite source modeling and near- field and
regional tsunami early warning algorithms.
Near Real-time Full-Wave Centroid Moment Tensor (CMT) Inversion for
Ground-Motion Forecast in 3D Earth Structure of Southern California
Lee, E., Department of Geology and Geophysics, University of Wyoming,
Laramie, WY, [email protected]; CHEN, P., Department of Geology and
Geophysics, University of Wyoming, Laramie, WY; JORDAN, T. H.,
Department of Earth Sciences, University of Southern California, Los Angeles,
CA; MAECHLING, P. J., Department of Earth Sciences, University of Southern
California, Los Angeles, CA.
Accurate and rapid CMT inversion is important for seismic hazard analysis.
We have developed an algorithm for very rapid full-wave CMT inversions in
a 3D Earth structure model and applied it on earthquakes recorded by the
Southern California Seismic Network (SCSN). The procedure relies on the use
of receiver-side Green tensors (RGTs), which comprise the spatial-temporal displacements produced by the three orthogonal unit impulsive point forces acting
at the receiver. We have constructed a RGT database for more than 200 broadband stations in Southern California using an updated version of the 3D SCEC
Community Velocity Model (CVM) version 4.0 and a staggered-grid finite-difference code. Finite-difference synthetic seismograms for any earthquake in our
modeling volume can be simply calculated by extracting a small, source-centered
volume from the RGT database and applying the reciprocity principle. We have
developed an automated algorithm that combines a grid-search for suitable epicenter and focal mechanisms. In this algorithm, the CMT solutions are inverted
near real-time by using waveform in a 3D Earth structure. Comparing with the
CMT solutions provided by the Southern California Seismic Network (SCSN)
shows that our solutions generally provide better fit to the observed waveforms.
Our algorithm may provide more robust CMT solutions for earthquakes in
Southern California. In addition, the rapid and accurate full-wave CMT inversion has potential to extent to accurate near real-time ground motion prediction
based on 3D structure model for earthquake early warning purpose. When combined with real-time telemetered waveform recordings, our algorithm can provide (near) real-time ground-motion forecast.
Rapid Magnitude and Fault Slip Determination from Combined GPS and
Accelerometer Data
Crowell, B. W., Scripps Institution of Oceanography, La Jolla, CA,
[email protected]; BOCK, Y., Scripps Institution of Oceanography, La Jolla,
CA, [email protected]; MELGAR, D., Scripps Institution of Oceanography, La
Jolla, CA, [email protected]
Real-time GPS networks provide the perfect complement to seismic networks,
which operate with lower noise and higher sampling rates than GPS networks,
but only measure accelerations or velocities, putting them at a disadvantage for
ascertaining the full extent of slip during a large earthquake in real-time. Here
we report on three examples of rapid modeling of recent large earthquakes near
large regional real-time GPS networks and combined GPS/seismic networks.
The first utilizes 416 stations in Japan’s GEONET during the 2003 Mw 8.3
Tokachi-Oki earthquake about 100 km offshore Hokkaido Island, the second
investigates the 2010 Mw 7.2 El Mayor-Cucapah earthquake recorded by 95 stations in the California Real Time Network and the final one examines the 2011
Mw 9.0 Tohoku-Oki earthquake recorded by over 800 stations in GEONET.
We leverage the improved accuracy of the combined GPS/accelerometer data to
rapidly compute magnitude through scaling between the hypocentral distance,
moment magnitude and the initial slip parallel displacements a few seconds after
the P-wave arrival. As the event continues, we add complexity by first computing
a centroid moment tensor (CMT—fastCMT in Melgar et al., 2012) and then performing a finite fault slip inversion, both from the static offsets obtained from the
GPS data in real-time. We utilize two inverse approaches to ascertain the extent
of fault-slip in a simulated real-time environment. The first inverse approach uses
predefined fault planes from a catalog of generalized faults while the second one
computes fault planes from the fastCMT inversion that operates once per second.
Overall, we are able to determine magnitude within a few seconds and roughly
characterize the slip distribution and manner of faulting for all three earthquakes
using a few minutes of data, greatly enhancing the time to obtain fault slip and
moment release during Mw 6.0+ earthquakes by almost an order of magnitude.
Newly Developed an Algorithm to Detect/Estimate Static Ground
Displacements for Near-Field Tsunami Forecasting Based on the RTK-GPS
Data
Ohta, Y., RCPEVE, Tohoku University, Sendai, Miyagi, Japan, ohta@
aob.gp.tohoku.ac.jp; KOBAYASHI, T., RCPEVE, Tohoku University,
Sendai, Miyagi, Japan, [email protected]; TSUSHIMA, H.,
Meteorological Research Institute, Tsukuba, Ibaraki, Japan, tsushima@mri-jma.
go.jp; MIURA, S., ERI, the University of Tokyo, Bunkyo-ku, Tokyo, Japan,
[email protected]; HINO, R., RCPEVE, Tohoku University, Sendai,
Miyagi, Japan, [email protected]; IINUMA, T., RCPEVE, Tohoku
University, Sendai, Miyagi, Japan, [email protected]; FUJIMOTO,
H., RCPEVE, Tohoku University, Sendai, Miyagi, Japan, fujimoto@aob.
gp.tohoku.ac.jp
Real-time crustal deformation monitoring is important for achieving rapid
understanding of actual earthquake scales. We have developed an algorithm to
detect/estimate static ground displacements due to earthquake from real-time
kinematic GPS (RTK-GPS) data, which named as the “Real-time Automatic
detection method for Permanent Displacement” (RAPiD). The algorithm identifies permanent displacements by monitoring the difference of a short-term
average (STA) to a long-term average (LTA) of the GPS time series. We applied
developed our algorithm to the 2011 Tohoku Oki earthquake (Mw 9.0) to check
the possibility of coseismic displacement detections. Furthermore, we estimated
the obtained displacement fields for a fault model. The estimated a fault model
with Mw 8.7, which is close to the actual Mw of 9.0, within five minutes from
the origin time. Once the fault model is estimated, tsunami waveforms can be
synthesized using pre-computed tsunami Green’s functions. The calculated waveforms showed agreement with the actual tsunami observations both in arrival
times and wave heights.
We also assessed the performance of the permanent displacement detection algorithm. Based on the long-term data, we calculated the false detection
rate which reached ~0.25% with 4-σ confidential limit at single baseline. We
modified permanent displacement detection algorithm for mitigation of the false
detection. The earthquake occurrence is defined as all neighboring GPS sites
must be detected the displacement including oneself. We applied this algorithm
to actual data. False detection rate clearly decreases with our improved algorithm.
When we use several reference sites for the RTK-GPS processing and compared
with each reference site results, the false detection rate will become almost zero.
These results suggesting that the RTK-GPS data by our algorithm can provide reliable rapid tsunami forecasting that can complement existing tsunami
forecasting systems based on seismic observations.
Oral Session · Tuesday 2:15 pm, 17 April · Pacific Salon 3
Session Chairs: Paul Davis, Freeman Gilbert, David Jackson,
and Thomas Jordan
The Burridge-Knopoff Slider Block Model: A Retrospective Analysis and
Future Outlook
Rundle, J. B., University of California, Davis, CA, [email protected];
TURCOTTE, D. L., University of California, Davis, CA, jbrundle@ucdavis.
edu
In 1967, Leon Knopoff and Robert Burridge published the paper “Model and
Theoretical Seismicity” in the Bulletin of SSA. As of 1 January 2012, that paper
has collected over 660 citations. Cast as a model of a single earthquake fault, the
array of sliding frictional blocks has been used to describe not only systems of
earthquake faults, but also neural network models of the human brain, evolutionary models in ecology, and the financial markets. Originally a fully mechanical
model using a train of weights on sandpaper, it was later adapted to computers
of the era and shown to give interesting results, specifically statistical distributions similar to the Gutenberg-Richter magnitude-frequency relation, and in
some cases, the Omori relation. However, because the mechanical model and
the computers of that time were so limited, only models with a few blocks (~10)
could be examined. Later models of the 1970’s included the first cellular automaton version of the model by JBR and DD Jackson. After the 1970’s, geophysical
research interest moved on to other areas until the Asilomar meeting in February,
1989, on Chaos and Earthquakes, organized by us together with Bruce Julian. In
pre-conference communications, JS Langer and J Carlson became aware of the
model and decided to bring modern computers to bear. They analyzed BK models
with hundreds to thousands of sliding blocks and proposed that the model was
an example of the recently-described Self-Organized Criticality model of Per Bak
et al. for driven dissipative systems such as sandpiles. As a result of the CarlsonLanger work, the BK model is now regarded as fundamental in physics, similar to
the well-known Ising model of magnetic systems. In this talk, we recount some
of the history of the BK model and its applications, together with recent results
as published in the seismological, physics, biological, and financial literatures. We
also discuss future directions for these interacting threshold models
Earthquake Prediction: The Scientific Heritage of Leon Knopoff
KEILIS-BOROK, V., UCLA, Los Angeles, CA; ZALIAPIN, I., University of
Nevada Reno, Reno, NV.
We review the Leon Knopoff’s works specifically dedicated to algorithmic earthquake prediction. Formulation of prediction problem follows the multidisciplinary framework, set up by the committee headed by Frank Press, in the wake
of the 1954 Alaskan earthquake. These works establish important connections
between parameters of premonitory seismicity patterns, and general statistical
scaling of seismicity in different tectonic environments.
Is the Global Sequence of Large Earthquakes, with Aftershocks Removed,
Poissonian?
Shearer, P. M., U.C. San Diego, La Jolla, CA, [email protected]; STARK,
P. B., U.C. Berkeley, Berkeley, CA, [email protected]
Yes.
The recent elevated rate of large earthquakes has fueled concern that the underlying global rate of earthquake activity has increased, which would have important
implications for assessments of seismic hazard and our understanding of how
faults interact. We examine the timing of large (magnitude M ≥ 7) earthquakes
from 1900 to the present, after removing local clustering related to aftershocks.
The global rate of M ≥ 8 earthquakes has been at a record high roughly since
2004, but rates have been almost as high before, and the rate of smaller earthquakes is close to its historical average. Some features of the global catalog are
improbable in retrospect, but so are some features of most random sequences—if
the features are selected after looking at the data. For a variety of magnitude cutoffs and three statistical tests, the global catalog, with local clusters removed, is
not distinguishable from a homogeneous Poisson process. Moreover, no plausible
physical mechanism predicts real changes in the underlying global rate of large
events. This suggests that the global risk of large earthquakes is no higher today
than it has been in the past.
Modulation of Tectonic Tremor by the Tides: Physical Models Descended
from Leon Knopoff with Application to the Deep San Andreas
Beeler, N. M., US Geological Survey—Cascades Observatory, Vancouver,
WA, [email protected]; THOMAS, A., University of California, Berkeley, CA,
[email protected]; BURGMANN, R., University of California, Berkeley,
CA, [email protected]; SHELLY, D., US Geological Survey—
Long Valley Observatory, Menlo Park, CA, [email protected]
Knopoff (BSSA, 1964) explained the absence of correlation between the tides
and earthquake occurrence by a delay between the onset of slip and the eventual
failure, a nucleation time. He concluded that if earthquake failure is delayed then
small stress perturbations with duration shorter than the nucleation time will
have a muted influence on earthquake occurrence. This has been verified in lab
experiments. The delay (from subcritical crack growth or contact plasticity) is a
key feature of rock friction theory and the essence of Dieterich’s (JGR, 1994) seismicity rate formulation. For tectonic stressing rates and stresses, lab data suggest
that the nucleation time is much longer than the daily tides and that a few percent
of earthquakes correlate with the tides, confirming Knopoff’s explanation. The
failure rate due to tidal stress is in phase with the tidal stress and depends on
stressing rate, effective normal stress, friction, and the shear and normal stress
tidal amplitudes resolved on to the fault plane (Thomas et al., EOS, 2011).
Families of recurring low-frequency earthquakes within tectonic tremor on
the San Andreas fault in central California show sensitivity to both shear and
normal stresses induced by the tides. In some cases the recurrence interval is less
than the daily tidal period, meaning that these are outside Knopoff’s regime.
However, occurrence rate is in phase with the tidal stress. To explain the tidal correlation we develop a failure model where loading results from the tides and fault
creep. Fault creep is assumed purely rate strengthening and the nominal creep
rate due to tectonic loading, is also modulated by the tides. Thus, the tremor rate
is driven by direct and indirect loading from the tides. There is an analytical solution for tremor rate as a function of the shear and normal components of the tidal
stress. We use the natural tremor rate to explore the model’s constraints on deep
effective normal stress and friction.
Physics of Q
Morozov, I. B., University of Saskatchewan, Saskatoon, SK, Canada, igor.
[email protected]
One of the most famous papers by Leon Knopoff was entitled “Q.” This symbol
has marked over half a century of studies of seismic attenuation. In his pioneering work continuing the efforts of Jeffreys and Ricker, Knopoff was looking for
physical mechanisms of attenuation. Today, there is still much to learn from the
breadth of his theoretical outlook and particularly from commitment to physical
principles shown in these studies.
Here, we revisit some of the first principles of the physics of Q. Is seismic
attenuation really described by a Q? What are the roles of physical principles, such
as Hamiltonian action and thermodynamics, in the theory of attenuation? How
do these principles relate to mathematical postulates, such as the correspondence
principle and analyticity? Is Q physically related to the viscoelastic moduli? What
are the roles of viscosity, thermoelastic, kinetic effects, and scattering, and how
can they be differentiated in the observations? Are solids and fluids strongly different in attenuation? What physical mechanisms can be behind the frequencydependent and frequency-independent Q’s? Answers to these questions come
from developing the early Knopoff’s views on mechanical friction within seismic
waves. As illustrations, we show a “near-dry” solid-viscosity model derived from
free oscillations of the Earth and a thermoelastic dissipation model for the Moon.
Probabilistic Earthquake Forecasts Based on Branching Models of
Seismicity: Tracing Leon Knopoff’s Contributions
Werner, M. J., Princeton University, Princeton, NJ, mwerner@princeton.
edu; HELMSTETTER, A., LGIT, Universite Joseph Fourier, CNRS, Grenoble,
France, [email protected]; JACKSON, D. D., UCLA, Los Angeles,
CA, [email protected]; KAGAN, Y. Y., UCLA, Los Angeles, CA,
[email protected]
Amongst his many accomplishments, Leon Knopoff was also a pioneer in the
application of stochastic modeling and probabilistic forecasting to earthquake
source dynamics and to seismicity. In this presentation, we highlight some of Leon
Knopoff’s contributions by presenting two recently published stochastic models
[Werner et al., BSSA, 2011] for estimating the probabilities of future earthquakes
in California, and by retracing his impact on the developments that led toward
the establishment of this class of models. The first model is a time-independent
model of adaptively smoothed seismicity and provides five-year forecasts for
earthquakes with magnitudes M > 4.95. We show that large earthquakes tend to
occur near the locations of small M > 2 events, so that a high-resolution estimate
of the spatial distribution of future large quakes is obtained from the locations of
the numerous small events. We further assume a universal Gutenberg–Richter
magnitude distribution. In retrospective tests, we show that a Poisson distribution does not fit the observed rate variability (see also Knopoff, BSSA, 1964), in
contrast to assumptions in current earthquake predictability experiments. We
therefore issued forecasts using a better-fitting negative binomial distribution for
the number of events. The second model is a time-dependent stochastic branching
model (similar to the one by Kagan and Knopoff, Science, 1987) that provides
next-day forecasts for magnitudes M > 3.95. In this model, the forecasted rate is
the sum of a background rate and of the expected rate of triggered events due to
all prior earthquakes. Each earthquake triggers events with a rate that increases
exponentially with its magnitude and decays in time according to the Omori–
Utsu law. We estimate parameter values by optimizing retrospective forecasts and
find that the short-term model realizes a probability gain (Kagan and Knopoff,
PEPI, 1977) of about 6.0 per earthquake over the time-independent model.
Triggering Cascades and Statistical Properties of Aftershocks
Davidsen, J., Complexity Science Group, University of Calgary, Calgary,
Canada, [email protected]; GU, C., Complexity Science Group,
University of Calgary, Calgary, Canada; BAIESI, M., Dipartimento di Fisica,
Universita degli Studi di Padova, Padova, Italy.
Applying a recently introduced general statistical procedure for identifying aftershocks, we investigate the statistical properties of aftershocks for a high-resolution earthquake catalog covering Southern California. We compare our results
with those obtained by using other definitions of aftershocks in order to show
that many features depend sensitively on how one exactly defines aftershocks and
whether one includes only directedly triggered aftershocks, or if one also takes all
indirectly triggered aftershocks into account. These variable features include the
temporal variation in the rate of aftershocks, for mainshocks of small magnitude
for short to intermediate times, and the spatial distribution of aftershocks at large
distances. We also discuss why the mean aftershock distance—often used in the
context of aftershock diffusion—is not a good descriptor of the seismic process.
Other features are, however, robust indicating that they truly characterize
aftershock sequences. These include the p-values in the Omori-Utsu law for large
mainshocks, Bath’s law, the productivity law with an exponent smaller than the
b-value in the Gutenberg-Richter law, and the identification of the most likely
distance of aftershocks from the main shock with the rupture length. We also
find that, for large mainshocks, the dependence of the parameters in the OmoriUtsu law on the lower magnitude cut-off are in excellent agreement with a recent
proposition based on Bath’s law and the Gutenberg-Richter law, giving rise to
a generalized Omori-Utsu law. Our analysis also provides evidence that (i) the
exponent p in the Omori-Utsu law does not vary significantly with mainshock
magnitude, and (ii) dynamic stress changes play a significant role for the triggering of aftershocks.
Velocities of Plate Motions, Fault Rupture, and Epicenter Migration: a Unified
Mesoscale Framework Based upon Statistical Mechanics of Cracks
BEN-MENAHEM, S., Carnegie Mellon University Silicon Valley, Mountain
View, CA, [email protected]; BEN-MENAHEM, A., Weizmann
Institute of Science, Rehovot, Israel, [email protected]
Traditional assumptions of infinitesimal strains and linear Hooke’s law are
invalid in the immediate vicinity of earthquake source regions in the tectosphere.
Additionally, the continuous damage mechanics due to fracture and healing of
cracks along and near a fault, result in further nonlinearities, creep, stochasticity, and also non-local dynamics due to the presence of the elastic bulk in nearby
plate regions. In this paper, we present a model which begins with the statistical
mechanics of mesoscale crack processes. We proceed to derive an approximate
macroscopic reaction-diffusion equation, which governs deformation, fracture,
flow and earthquake genesis along active faults. The model is shown to relate the
velocities of plate motions, epicenter migration, and fault rupture— which range
over some twelve orders of magnitude— via particular soliton solutions.
Ground Motion Prediction Using Virtual Earthquakes for Kinematic Rupture
Models
DENOLLE, M., Stanford, Stanford, CA, [email protected]; DUNHAM,
E. M., Stanford, Stanford, CA, [email protected]; PRIETO, G., Universidad
de los Andes, Bogota, Colombia, [email protected]; BEROZA, G. C.,
Stanford, Stanford, CA, [email protected]
Predicting ground motion for potential large earthquakes is a key factor in seismic
hazard analysis. Seismologists turn to physics-based simulations that account for
complexity of the source, propagation effects and site response. Our incomplete
knowledge of the crustal structure directly affects the reliability of those simulations. To validate the physics-based approach, we compute the Earth impulse
responses combining both ambient seismic field and coda-wave cross-correlations
in a way that preserves the amplitude information (elastic and inelastic). We correct the Green’s functions for both the source-depth dependence of surface-wave
excitation and the double-couple radiation pattern, and validate the result using
moderate earthquakes in southern California. We can combine these Green’s
functions with a realistic, kinematic source description using the representation
theorem to include directivity and other effects of source finiteness. We apply
this approach to estimate ground shaking in the Los Angeles area for M7+ scenario earthquakes on the southern San Andreas Fault using a temporary seismic
network of 10 stations to determine the requisite Green’s functions. We compare
these results with ground motion simulations for the same events.
Ambient-Field Green’s Functions From Asynchronous Seismic Observations
Ma, S., San Diego State University, San Diego, CA USA, [email protected].
edu; BEROZA, G. C., Stanford University, Stanford, CA USA, beroza@
stanford.edu
The past decade has seen tremendous success in obtaining station-to-station
Green’s functions from the ambient seismic wavefield. The method has relied
on data recorded at different stations at the same time, i.e., synchronously. Here
we demonstrate that it is possible to extract Green’s functions between stations
that operate asynchronously, through scattered waves as recorded by a network
of fiducial stations. This approach can extract Green’s functions across all seismic
stations occupied regardless of whether or not they are occupied simultaneously,
providing ray paths that can lead to orders of magnitude more information about
Earth structure. It also suggests a new mode in observational seismology and may
influence future experimental design.
Point Source Seismogram using 2D Staggered-Grid Finite Difference Method
Li, D., Seismological Lab, California Institute of Technology, Pasadena, CA;
HELMBERGER, D., Seismological Lab, California Institute of Technology,
Pasadena, CA, USA; CLAYTON, R., Seismological Lab, California Institute of
Technology, Pasadena, CA.
While considerable progress has been made in 3D modeling of longer period
waveforms, the shorter periods are still challenging due to large computing
demands. Thus 2D synthetics are widely used.
Helmberger and Vidale (1988) interfaced Cagniard-de Hoop analytical
solution with 2D FD code using a transparent source box. To correct for the
spreading differences between 2D and 3D, Vidale and Helmberger(1987) builds
an approximation into the source box for P-SV system which weights P and S
wave from line source differently. Such an approximation cause displacement to
grow as t2 for late time. We find this drift can be eliminated if we simulate a line
source without any correction first and save the correction for a later stage of postprocessing.
The line source can be generated using the source box approach, which
is complicated for staggered grid, or numerical momentum source approach
(Coutant, et al., 1995). Our tests show that they are in agreement.
For 2D lateral inhomogenous medium, the out of plane spreading needs
to be computed using ray tracing because the ray parameter changes along the
rays. But in many applications, the receiver side ray parameter pr(t) or the source
side ray parameter ps(t) can approximate the global average ray parameter p(t). By
processing the synthetics f 2D, we can obtain pr(t) f 2D; by modifying the source
box or momentum source, we can calculate ps(t) f 2D by an extra FD run. Then
we can linearly combine f 2D with p(t) f 2D (Stead, 1988), or take the signed square
root of [ p(t) f 2D f 2D ] to correct spreading ( square root of [p(t)/r], where r is the
epicentral distance).
We accelerate our code using multiple GPUs on a single desktop. Complete
seismograms for global scale can be generated in hours, and they are in good agreement with those generated by other point-source method, including core-phases.
Earthquake Source Physics Studied with Elastodynamic Modeling and
Laboratory Seismology
Mclaskey, G. C., United States Geological Survey, Menlo Park, CA,
[email protected]; KILGORE, B. D., United States Geological Survey,
Menlo Park, CA, [email protected]; BEELER, N. M., United States Geological
Survey, Menlo Park, CA, [email protected]
We have conducted laboratory experiments designed to explore dynamic rupture
propagation by measuring high frequency ground motions which are produced
during the rupture of a large-scale (2 m) laboratory fault. Our approach is to
merge the mathematics of wave propagation with observational seismology and
experimental rock mechanics. This allows us to better understand the physics of
fault rupture, the mechanisms involved in the production of earthquakes, and the
seismic signatures of these mechanisms. We apply this approach to stick-slip friction experiments in a large-scale biaxial apparatus. The sample is instrumented
with an array of slip and strain sensors that constrain source properties such as
stress drop, slip velocity, rupture speed, and precursory slip during the nucleation
phase. It is also instrumented with an array of piezoelectric sensors capable of
detecting high frequency (100 kHz) surface motions. At these frequencies, wavelengths are much smaller than the dimensions of the sample, so wave propagation in the granite test blocks can be modeled using elastodynamic solutions for
a thick slab. We detect very small amplitude impulsive precursory events which
occur tens of milliseconds before the dynamic rupture of the laboratory fault.
These events are located on the interface, and emanate from a fault patch only a
few cm in size in the interior of the fault. These highly localized events, only a few
microseconds in duration, are used to verify the wave propagation models. Using
seismic analysis techniques, we then map the production of seismic waves in space
and time from spontaneous nucleation to the dynamic propagation of rupture
along the length of the fault. This research facilitates a link between the rupture
characteristics of stick-slip friction observed in the laboratory and parameters
which can be observed seismically for earthquakes on natural faults.
Session Chairs: Yehuda Ben-Zion and Ilya Zaliapin
Elucidating Regional Tectonic and Secondary Causes of Seismicity in
Southern California: Application of Waveform Relocated Seismicity and High
Precision Focal Mechanisms and Other Geophysical Data Sets
Hauksson, E., California Institute of Technology, Pasadena, CA, hauksson@
gps.caltech.edu; YANG, W., California Institute of Technology, Pasadena, CA,
[email protected]; SHEARER, P. M., U.C. San Diego, Scripps, La
Jolla, CA, [email protected]
Seismicity reflects regional plate-boundary tectonics and other crustal deformation processes that are active in the southern California crust. The ongoing
seismic cycles along major late Quaternary fault zones or major principal slip
zones (PSZs), control the spatial and temporal distribution of both background
seismicity and aftershocks. Crustal properties such as temperature, thickness,
stress, fluids, and proximity of PSZs affect the seismicity processes. The magnitude distribution near the PSZs suggests that large earthquakes are more common close to the PSZs, and they are more likely to occur at greater depth than
small earthquakes. In contrast, small quakes can occur at any geographical location but tend to cluster at the top and bottom of the seismogenic zone. Localized
regions of constant seismicity rate such as along the San Jacinto fault suggest
the presence of fluids or low fault normal stress. Crustal temperature influences
the relative size distribution of earthquakes. Further, in high temperature crust
the late Quaternary faults are spread over distributed regions, such as the Salton
Trough, in part related to crustal thinning. In crust with average temperature,
plate motion is accommodated along the spatially narrow San Andreas Fault.
Seismicity processes are also associated with extreme variations in crustal thickness, from 22 to 45 km. The seismicity of the topographically high southern Sierra
Nevada reflects gravitational collapse of the range. The deep seismicity beneath
the Ventura basin and Banning Pass suggests the presence of crustal delamination processes. The stress within the crustal blocks, bound by PSZs, reflects the
regional stress. The PSZs are simply the surfaces that separate the blocks and are
surrounded by damage zones, but do not have their own stress fields. In some
cases, the damaged edges of the blocks may be more compliant than the interior
of the blocks, thus leading to an apparent effect of local compression.
Testing for Poisson Behavior
Stark, P. B., University of California, Berkeley, Berkeley, CA, stark@stat.
berkeley.edu; LUEN, B., [email protected]
Common tests of whether seismicity is consistent with a spatially inhomogeneous temporally homogeneous Poisson process (SITHP) ignore space, are insensitive to long-term rate variations, are relatively insensitive to seismicity rate fluctuations on the scale of weeks, and use an inaccurate approximation to the null
distribution of the test statistic. Better temporal tests and a novel spatio-temporal
test show that SITHP does not fit M ≥ 3.8 1932-1971 or 1932-2010 Southern
California Earthquake Center (SCEC) catalogs declustered using Gardner and
Knopoff’s (1974) windows in a linked-window or a mainshock-window algorithm. For M ≥ 4.0, SCEC catalogs declustered using the Gardner-Knopoff
windows in a linked-window method are far closer to SITHP, while catalogs
declustered using those windows in a mainshock-window method are inconsistent with SITHP. Reasenberg’s (1985) declustering method applied to southern
California seismicity produces catalogs inconsistent with SITHP, even for events
with M ≥ 4.0.
Deleting enough events will leave the remainder consistent with SITHP.
This suggests an optimization problem: Delete the fewest events such that those
left pass a particular test or suite of tests for SITHP. This optimization problem
is combinatorially complex, but inexpensive suboptimal methods are surprisingly
effective: Declustered catalogs can be consistent with temporal tests of SITHP
at significance level 0.05 and have 50% to 80% more events than window-declustered catalogs that fail those tests. Tests that incorporate spatial information
reject the SITHP hypothesis for those declustered catalogs, illustrating the power
of spatial information.
Estimating ETAS
Schoenberg, F. P., UCLA, Los Angeles, CA, [email protected]
Following a brief tutorial for the novice on how to use existing methods for estimating (inverting) ETAS models by maximum likelihood, we will discuss a new
trick that facilitates the computation enormously. The trick, which involves a
slight reparameterization of the model, is shown through simulations to result
in substantially decreased computation time and increased stability, with no discernable effect on accuracy. The main advantage, however, is a huge decrease in
programming time. Results for various earthquake catalogs are presented.
Supershear Ruptures and the Rock Strength
Shcherbakov, R., University of Western Ontario, London, ON, Canada,
[email protected]; BHATTACHARYA, P., Princeton University, Princeton,
NJ.
The Gutenberg-Richter law is a prominent statistical feature of natural seismicity.
Its parameter, the b-value, characterizes the distribution of magnitudes in a population of earthquakes following self-similar scaling. The b-value has been observed
to exhibit statistically significant variations in laboratory experiments, mines and
different tectonic regimes including aftershock zones and also with various levels
of crustal differential stresses. Simple physical models of seismicity show that the
b-value might also depend on varying material strength in the crust. We argue
that spatial variations of the b-value in the aftershock sequences of supershear
earthquakes support this hypothesis. We also attempt to verify whether this feature is robust and more general characteristics of natural seismicity by looking
at the occurrence of earthquakes on different faults across Southern California
and Alaska. In particular, we try to ascertain whether populations of earthquakes
occurring on the two sides of faults exhibiting bi-material contrast are statistically different in terms of their b-values.
Sequence Clustering in Earthquake Catalogs
Newman, W. I., UCLA, Los Angeles, CA, [email protected]; TURCOTTE, D.
L., UC Davis, Davis, CA, [email protected]; MALAMUD, B. D., KCL,
London, UK, [email protected]; HOLLIDAY, J. R., UC Davis, Davis,
CA, [email protected]; RUNDLE, J. B., UC Davis, Davis. CA.
Consider a catalog of earthquakes with magnitudes greater than m in a specified
region and time period. Further:
1) Consider the sequence of earthquakes in time. Attach each earthquake
to its nearest neighbor. The attached earthquakes form clusters. There are nm clusters that include m earthquakes in the sequence.
2) Consider the sequence of earthquake magnitudes as a time series. Define
a maximum magnitude earthquake to be an earthquake that is larger than the
two adjacent earthquakes. Determine the cluster size m of earthquakes that follow each maximum magnitude earthquake. There are n m clusters that include m
earthquakes in the sequence.
If the earthquake catalogs are random an anlytic expression can be derived
for the distribution of cluster sizes m applicable to both sequences. Specifically
the mean cluster size is m=3. As an example we have determined the magnitude
clusters from the global CMT catalog with m>5.5 for the period 1980-2011.
There were 14, 022 earthquakes and 4763 clusters so that the mean cluster size
is m=3.000642, very close to the value m=3 expected for a random sequence.
The observed value for m=2 was n2=1882, the analytic prediction is 1870. The
observed value for m=3 was n3=1539, the analytic prediction is 1558. Other
examples will be given. The mean value of m is a measure of long range correlations. For a Gaussian white noise the mean value of m is 3 as expected, for a
Brownian walk the mean value of m is 4.42.
Are Earthquake Magnitudes Clustered?
Davidsen, J., Complexity Science Group, University of Calgary, Calgary,
Canada, [email protected]
One of the hallmarks of our current understanding of seismicity as highlighted
by the epidemic-type-aftershock sequence model is that the magnitudes of earthquakes are independent of one another and can be considered as randomly drawn
from the Gutenberg-Richter distribution. This assumption forms the basis of
many approaches for forecasting seismicity rates and hazard assessment. Recently,
it has been suggested that the assumption of independent magnitudes is not valid.
It was subsequently argued that this conclusion was not supported by the original earthquake data from southern California. One of the main challenges is the
lack of completeness of earthquake catalogs and potential spatial and temporal
dependencies. In this talk, I will review these arguments and then present findings for an aftershock sequence of nano– and picoseismicity as observed at the
Mponeng mine, South Africa, for which the issue of incompleteness is much less
pronounced. Our results show that this sequence does not exhibit any significant
evidence of magnitude correlations.
High-Resolution Fault Tomography from Accurate Locations and Focal
Mechanisms of Swarm Earthquakes
Vavrycuk, V., Institute of Geophysics, Academy of Sciences, Prague, Czech
Republic, [email protected]; BOUCHAALA, F., Institute of Geophysics, Academy
of Sciences, Prague, Czech Republic, [email protected]
We analyze 463 microearthquakes in the magnitude range from 0.5 to 3.7 that
occurred during the 2008 earthquake swarm in West Bohemia, Czech Republic,
in order to image a detailed structure of the focal zone located at depths between
7 to 11 km. The double-difference location method was applied to records of 22
local stations in order to retrieve highly accurate locations of hypocenters with
accuracy less than 20 m. The hypocenters are well clustered and distinctly map
the system of activated faults. The fault geometry is surprisingly complex, the
fault being composed of several segments with different orientations. The orientation of segments coincides well with the focal mechanisms. The two principal
fault segments are optimally oriented with respect to the tectonic stress and the
associated microearthquakes are mainly double couple. The other fault segments
are slightly misoriented being associated with microearthquakes displaying nondouble couple mechanisms.
The statistical distribution of focal mechanisms is used for studying the
stress conditions and the failure criterion in the focal zone. The direction of
maximum compression is significantly inclined from the horizontal plane. The
activated fault planes concentrate in the area of validity of the Mohr-Coulomb
failure criterion. The distribution of the P/T axes reveals the ‘butterfly’ wing pattern. The average friction of faults is 0.5 and corresponds to a deviation of 32°
of the principal fault segments from the maximum compression. The observed
variability of focal mechanisms points to presence of a complex fault system with
mutual interactions of fault segments rather than to presence of small scale stress
heterogeneities or temporal changes of tectonic stress in the focal area.
Relations Between Seismic Clustering and Physical Properties of the
Lithosphere
Zaliapin, I., University of Nevada Reno, Reno, NV, [email protected]; BENZION, Y., University of Southern California, Los Angeles, CA, benzion@usc.
edu
We demonstrate quantitative connections between structures of seismic clusters
and physical properties of the crust in southern California using the relocated
catalog of Hauksson et al. [SCEC abstract, 2011]. The seismicity is represented
as a sequence of statistically significant spatio-temporal clusters using the nearestneighbor approach of Zaliapin et al. [PRL, 2008]. The multi-event clusters largely
correspond to individual foreshock-mainshock-aftershock sequences or swarms.
Each cluster is considered as a rooted tree with vertices representing earthquakes
and edges representing nearest-neighbor links. We demonstrate the existence
of a bimodal structure of earthquake clusters, with one mode corresponding
to aftershock-like sequences and the other to swarm-like sequences. Clusters of
different types are found generally in different spatial regions. Aftershock-like
clusters occur predominantly in regions characterized by relatively low heat flow
and mild-to-no geothermal activity. Such clusters tend to have higher mainshock
magnitude, larger difference between the mainshock and largest aftershock, localized distribution of events in time and space, low (graph-theoretical) tree depth,
and higher degree of branching within the tree. Swarm-like sequences occur predominantly in regions characterized by relatively high heat flow and geothermal
activity. Such clusters tend to have lower mainshock magnitude, lower difference
between the mainshock and largest aftershock, more uniform event distribution
in time and space, high tree depth, and low degree of branching within the tree.
The presented methodology and results contribute to better understanding of
detailed non-universal relations between time-space-size variations of seismicity
and physical properties of a region. The results can be used to develop improved
region-specific estimates of earthquake hazard assessment.
On the Relation of Stresses to Aftershock Decay
Gerstenberger, M. C., GNS Science, Lower Hutt, New Zealand; FRY,
B., GNS Science, Lower Hutt, New Zealand; ABERCROMBIE, R., Boston
University, Boston, MA; DOSER, D., University of Texas at El Paso, El Paso,
TX; RISTAU, J., GNS Science, Lower Hutt, New Zealand.
The rate of aftershock activity typically follows Omori’s Law, which describes
the rate of decay of the aftershock frequency with increasing time from the main
shock. In high seismicity areas, simple forecast models based on the Omori law
have been shown to contain significant information. In low strain rate and low
seismicity regions, such as Canterbury, New Zealand, the relationship may not
be so clear. The Canterbury earthquake sequence consists of a series of subsequences, separated by three to six months, each causing a significant increase
in aftershock activity. As of January, 2012, the total number of aftershocks is
roughly as would be expected based on Omori decay; however, the overall decay
rate is not well fit by a single Omori p-value.
Low-seismicity regions might have strong faults and high stress-drop earthquakes. The largest earthquakes in the Canterbury sequence have been relatively
high-stress drop events. It is possible that a lack of post-seismic relaxation or
smaller magnitude seismicity affects the decay of aftershocks by creating punctuated clustering. It is normal for aftershock sequences to have aberrations from a
smooth decay curve, as each larger aftershock triggers its own daughter earthquakes. However, in the Canterbury sequence, the clusters carry more moment
than in a typical Omori sequence. We speculate that this clustering behavior
might be more pronounced in low-strain rate regions with high-stress drop events.
The December 2011 swarm occurred in a region approximately 10km more distal
than most of the previous activity. Preliminary analysis of these events suggests
they are lower-stress drop events than other large earthquakes in the sequence.
Furthermore, it is possible that intraplate high-stress sequences in areas of lowstrain may more closely follow this type of punctuated, clustering behavior than
low-stress sequences that occur in high-strain areas.
Stress Driven Variations in Microseismicity during Laboratory Stick-Slip
Tests
GOEBEL, T. H. W., USC, Los Angeles, CA, [email protected];
SCHORLEMMER, D., Geoforschungs Zentrum, Potsdam, Germany, [email protected]; DRESEN, G., Geoforschungs Zentrum, Potsdam, Germany, dre@
gfz-potsdam.de; BECKER, T. W., USC, Los Angeles, CA, [email protected]
Microseismicity provides important insights into fracture and frictional processes at various scales. We investigated the connection between the occurrence
of microseismic events and cyclical stress changes during laboratory stick-slip
tests on fracture surfaces. Our experimental set-up enabled us to create series
of up to six stick-slips on a single fault plane allowing us to document temporal
changes in acoustic emissions statistics over several successive cycles. Our aim
was to detect recurring patterns in AE rate, seismic moment and b-values during
increasing stress level prior to the onset of slip events.
Slip events were preceded by a longer term acceleration in AE rates. The
frequency magnitude distributions (FMDs) of AEs followed a power-law similar
to the Gutenberg-Richter law with decreasing slopes (b-values) before slip events.
In addition to low b-values, we observed high seismic moments when approaching slip events. AEs that occurred after slip events were connected to an abrupt
increase in b-values and relatively low seismic moments.
Before the slip onsets we observed extended periods of b-value minima,
ranging from several minutes before, to several seconds after the onset of slip
events. b-values and differential stress showed a negative, linear relationship.
This linear relationship broke down at high differential stresses when the fault
approaches its critical strength. Here, we observed several small slip events, probably related to the failure of small scale asperities and grain comminution, which
led to perturbations of both stress and b-value curves. Our results support the
application of b-value variations as indicators for stress levels at loaded asperities
but also highlight the influence of fault complexity on local stress field variations.
A detailed understanding of microseismicity characteristics may provide important insights into preparatory processes before slip events.
Systematic Analysis of Foreshock Sequences in Southern California
Chen, X., U.C. San Diego, La Jolla, CA, [email protected]; SHEARER, P. M.,
U.C. San Diego, La Jolla, CA, [email protected]; HAUKSSON, E., California
Institute of Technology, Pasadena, CA, [email protected]
Foreshocks are one of the few recognized precursors to earthquakes, but they do
not precede every earthquake nor are foreshock sequences readily recognizable
as foreshocks until after the mainshock occurs. We examine all earthquakes of
M ≥ 5 in southern California between 1981 and 2010, using a recently updated
catalog with improved locations computed from waveform cross-correlation. 62
out of 131 M ≥ 5 mainshocks have one or more foreshocks occurring within 5
days and 2 km of the mainshock hypocenter. We examine these events to see if
their locations, focal mechanisms, and estimated stress drops are consistent with
earthquake-to-earthquake triggering or if they appear to result from an underlying physical process, such as fluid flow or slow slip, that might also have triggered
the mainshock. We also attempt to compare foreshock sequences with comparable sets of earthquakes, such as swarms or small groups of isolated events, that
do not produce mainshocks, to see if any distinguishing features can be resolved
in foreshocks compared to that seen in background seismic activity. These results
should help constrain earthquake triggering models and theories of earthquake
nucleation.
Advances in Local b-Value Imaging and New Insight on Physical Interpretation
Tormann, T., ETH Zurich, Switzerland, [email protected].
ch; WIEMER, S., ETH Zurich, Switzerland, [email protected];
HARDEBECK, J. L., U.S. Geological Survey, Menlo Park, CA, jhardebeck@
usgs.gov
Spatial heterogeneity in the distribution of Gutenberg-Richter b-values has been
interpreted as representing relative stress differences in the earth’s crust. We
study in unprecedented detail the b-value distributions along all major faults in
California.
Based on a semi-synthetic test environment we develop a new and more
physical seismicity sampling approach for high-resolution cross-sectional b-value
imaging along faults. Combining it with a significance and linearity filter we
present a consistent method to systematically analyze spatial variability of b-values and reliably identify significant anomalies in a large fault and seismicity dataset of varying quality.
For selected high data-quality sites, we investigate the temporal dimension
of b-value variation and resolve, among others, a strong correlation between fluctuations in the b-value time series and surface creep rates in Parkfield.
Overall, we provide new evidence that high-resolution b-value mapping in
space and time is a powerful tool to reach a deeper understanding of the stress
field and its evolution along fault segments, identify asperities and barriers, and
therewith reveal likely locations, estimate sizes and even resolve temporal variations in earthquake probabilities for future events. In cases in which we are able
to unravel the fault segmentation and understand its structure this allows an
improved assessment of the current likelihood of failure in a large event. We present the different estimates for selected locations in California.
In view of the solidly and physically meaningfully established variations
of b-values in space and time, the universality of the Gutenberg-Richter relation
between earthquake magnitudes transforms into a universal scaling between the
b-value and acting stresses.
Magnitude Dependent Seismic Quiescence Investigated with a Fault
Simulator that Incorporates Dilatancy and Hydrological Effects
Smith, D. E., Carnegie Institution of Washington, Department of Terrestrial
Magnetism, Washington, DC, [email protected]; SACKS, I. S., Carnegie
Institution of Washington, Department of Terrestrial Magnetism, Washington,
DC, [email protected]; RYDELEK, P. A., Carnegie Institution of Washington,
Department of Terrestrial Magnetism, Washington, DC.
Magnitude dependent seismic quiescence has been observed for a number major
events including, 1982 Urakawa-Oki earthquake, 1994 Hokkaido-Toho-Oki
earthquake, 1994 Northridge earthquake, 1995 Kobe earthquake, 1988 Spitak
earthquake, and 2011 Tohoku earthquake.
We add dilatant effects to a fault simulator to include physics consistent
with observations of seismic quiescence. We examine precursory statistics of
major events, changes in b-value, correlations between slip and static stress
changes, and temporal decay of aftershocks.
The physics of dilatancy theory, which we add to the simulator, may explain
seismic quiescence. As the fault is loaded toward failure and the stress increases,
if the stress is sufficiently high, the rock can begin to dilate. As dilation occurs,
the pore pressure decreases, the effective normal stress increases, and the fault
core also stiffens. Because the fault core can now support more of the stress, the
seismicity of the surrounding region will decrease as is observed. Over time (~220 years) the water will percolate back into the fault core from the surrounding region. The pore pressure in the fault core increases again, the normal stress
decreases, and failure is encouraged.
We simulate these observables, by modifying the fault simulator of Sacks
and Rydelek [1995]. This simulator, based on simple physics such as discrete
patches, Coulomb failure, and redistribution of stresses on a specified fault geometry, has already been shown to reproduce Gutenberg-Richter statistics, constant
average stress drops for larger events, and precursory increase of small earthquakes in the mainshock region. We add dilatancy and hydrological diffusion
to this simulator to reproduce quiescence, changes in b-values, and aftershock
behavior.
Cumulative Coulomb Stress Changes—What Influence do Small Events have
on Triggering and the Time to the Next Earthquake?
Woessner, J., Swiss Seismological Service, ETH Zurich, Zurich, Switzerland,
[email protected]; MEIER, M. A., Swiss Seismological Service, ETH
Zurich, Zurich, Switzerland, [email protected]; WERNER, M.
J., Princton University, Princeton, NJ, [email protected]; WIEMER, S.,
Swiss Seismological Service, ETH Zurich, Zurich, Switzerland, s.wiemer@sed.
ethz.ch
Earthquakes occur following changes in the crust’s stress state. To date, however,
the causative process for earthquake triggering remains unclear. To understand
this process, many researchers have employed Coulomb stress change theory,
which quantifies the static Coulomb stress changes (dCFS) from nearby ruptures.
This theory seems to at least partly explain the spatial patterns of triggered earthquakes, in particular during aftershock sequences and along faults.
Nevertheless, using dCFS alone does not allow an estimate of when the
next earthquake will occur. In addition, most studies compute dCFS for only the
largest earthquakes, owing either to the lack of information for smaller events
or an assumption that smaller earthquakes do not significantly affect triggering
(despite theoretical evidence to the contrary).
We use the recently updated southern California focal mechanism catalog to model the cumulative Coulomb stress changes on a receiver fault, i.e. an
earthquake with specified focal mechanism, from all previous earthquakes. We
use scaling relations to estimate source parameters and use finite-fault slip models when available. Our calculations suggest that small events dominate static
stress redistribution in almost all clusters; however, the dCFS from small events
are less important than the dCFS from large events to explain the overall spatial
occurrence of events. To examine the effect of uncertainties in the small event
focal mechanisms, we generate perturbed catalogs and attempt to quantify their
significance for the Coulomb stress change calculations. Finally, we analyze the
timing of events as a function of the triggering threshold and the size of the triggered events to investigate whether there is any valuable information available to
forecast the time of the next rupture.
Correlation Fractal Dimension Approach for Estimating Temporal and Spatial
Pattern of Seismicity in the Himalayan Region
SINGHA ROY, P. N., Indian School of Mines, Dhanbad, Dhanbad, Jharkhand,
India, [email protected]; MONDAL, S. K., Indian School of Mines,
Dhanbad, Dhanbad, Jharkhand, India, [email protected]
Himalayan seismicity is considered worlds one of the most complex one to be
studied. Especially the West of Nepal and Kumaon Himalaya surrounding seismicity gives clue for understanding the impending large earthquake in the region.
However conventional time series gives us to see how the seismicity has evolved
where as using the modern fractal approach gives more quantitative understanding of complex seismicity pattern temporal and spatial. Temporal fractal correlation dimension (D2(t)) has been obtained from inter occurrence time of events,
which gives value ranges from 0.2 to 0.7.Typically the value shows low of 0.2 when
we are having ideal clustering temporally which may be used as large earthquake
forecasting tool. Moreover when we see the equivalent spatial Correlation fractal
Dimension (Dc), b-value (Guttenberg Richter Approach) for the same set of hundred data of consecutive eight windows we get significant correlation. As all these
parameters are governed by the outcome of complex interaction related to faults
physics, hence this integrated approach of understanding seismicity of the region
helps to assess the impending large earthquake of the region.
Probabilistic Fault Displacement Hazard Analysis
Session Chairs: Robb Moss and Mark Petersen
Quantifying Surface Fault Displacement Hazard: What is the Status?
Schwartz, D. P., USGS, Menlo Park, CA, [email protected]; DAWSON,
T. E., CGS, Menlo Park, CA, Timothy Dawson <Timothy.Dawson@conservation.
ca.gov>
The effects of strong ground motion with respect to damage to the built environment are substantially broader than those of surface rupture. Paleoseismic
studies show that most faults of concern have surface rupture recurrence rates
of many hundreds to thousands, or even tens of thousands, of years, and worldwide only a handful of faults have had repeated surface rupture in the past 150
years. Nonetheless, surface faulting is an important design consideration for critical facilities such as power plants, repositories, dams, pipelines, and transportation systems. While surface rupture across such facilities is not common, it does
occur. Two recent examples are the 2002 Denali fault rupture beneath the TransAlaska Pipeline and the 1999 Chelungpu fault rupture beneath the Shih-Kang
dam in Taiwan. For the pipeline a 6m design offset had been developed, a 5m
offset occurred, and it continued to function. For the dam no design provision
was made for the fault, which resulted in the first failure of a concrete dam from
surface rupture.
While the best approach for accommodating surface rupture is avoidance
this is not always possible, especially for retrofitting existing infrastructure in
active fault corridors. Ideally, estimates of the amount of future slip should be
based on measurements of repeated past slip per event but these data are generally
unavailable. As a result, probabilistic surface fault displacement hazard analysis
(PSFDHA), which builds on approaches used for ground motion estimates, is
being developed. At present there is no uniform PSFDHA methodology. For
faults such as the Hayward this has led to variable estimates of coseismic slip
based on different models for the design of pipelines, tunnels, and rails that cross
the fault. These coseismic offset estimates range from almost 3m to only a few
10s of cm followed by extended afterslip. This illustrates the need for a consensus
approach and transparency in the continuing development and use of PSFDHA.
Fault Rupture Displacement at Caltrans Bridges
Shantz, T., Caltrans—Research and Innovation, Sacramento, CA, tom_
[email protected]; MERRIAM, M., Caltrans—Geotechnical Support,
Sacramento, CA, [email protected]; YASHINSKY, M., Caltrans—
Earthquake Engineering, Sacramento, CA, [email protected]
Caltrans has approximately 100 bridges that either cross known faults or are in
close proximity to mapped traces. Bridges require special design for fault rupture
when potential displacement demand exceeds ordinary design. For structural
evaluation, potential displacement demand resulting from fault rupture displacement is estimated using the largest of deterministic and probabilistic (5% in 50
yr) estimates.
Our probabilistic procedures are based on work done by Abrahamson
(2006), Petersen et al (2005), and Chen et al (2011). In instances where estimated
displacements are large and mitigating design costs are extreme, the preferential
use of probabilistic methods may be applied on a project specific basis. Typical
investigations include use of boring logs, air photos, maintenance records, previous fault studies, and field investigations including geophysics and trenching.
This presentation will provide an overview of the deterministic and probabilistic procedures used at Caltrans for fault rupture hazard evaluation. A casehistory demonstrating these procedures will also be presented.
Non-Ergodic Models for Probabilistic Fault Rupture Hazard
Abrahamson, N., Pacific Gas & Electrric Company, San Franciso, CA,
[email protected]
Traditionally, probabilistic seismic hazard analysis has used global models to
describe the amplitude fault rupture for a given earthquake. Using global models
assumes that the distribution (median and standard deviation) of the fault rupture at a specific site from a suite of future earthquakes is the same as the given
by the global model. This ergodic assumption is reasonable for ground motions
but is not reasonable for surface fault ruptures which are much more fault and
site specific.
At low probability levels, fault rupture hazard is controlled by the standard
deviation of the fault rupture model. Based on global models, the standard deviation of the average surface rupture for a given magnitude is about 0.74 natural log
units (e.g. Wells and Coppersmith, 1994). If the variability of the rupture along
strike is considered, then the standard deviation of the surface rupture at a specific site along the fault is about 1.0 natural log units. This large standard deviation leads to a significant flattening of the slopes on the hazard and, in many cases,
unrealistically large surface ruptures for low probability levels.
Hecker et al (2011) showed that the aleatory standard deviation of the surface rupture at a point on the fault, based on sites with rupture ruptures, is about
0.4 natural log units, much smaller than given by the global models. To use this
reduced site-specific standard deviation requires an estimate of the median surface rupture at the site. Without any site-specific or fault-specific data, the epistemic uncertainty in the median will be large, about 0.9 natural log units. This
leads to very wide uncertainty fractiles on the rupture hazard. Given even one
site-specific observation of surface slip from a past earthquake greatly reduces the
epistemic uncertainty due to the relatively small aleatory variability. An example
application to the surface rupture hazard along the Hayward fault is shown using
the ergodic and non-ergodic models.
Reverse Faulting and Probabilistic Surface Displacement Estimates
Moss, R., Cal Poly, San Luis Obispo, CA, [email protected]
Reverse faulting presents some unique challenges when a probabilistic forecast
of surface fault displacement is needed. The primary challenge has to do with the
probability of displacements reaching the ground surface; whether there will be
surface expression or it will be a blind thrust with no discrete surface expression.
Recent research on probabilistic forecasting of the surface rupture from a reverse
fault, how the probability distribution of displacement reaching the ground surface influences the estimate, and how material properties of the near surface geology is correlated to the probability of surface rupture will be presented. Examples
of past events reverse events will be used to illustrate.
Case Studies of Probabilistic Analysis of Fault Displacement and Related
Hazards
Thio, H. K., URS Corporation, Los Angeles, CA, [email protected];
SOMERVILLE, P. G., URS Corporation, Los Angeles, CA, paul.somerville@
urs.com
Over the last decade, we have carried out several probabilistic fault displacement
hazard analyses in a variety of environments. Whereas in some cases, the objective of the analysis is to determine the probabilistic amount of fault displacement
for a structure directly crossing an active fault, in other cases the analysis is carried out to account for deformation away from the actual fault plane. Examples
include surface deformation above a blind thrust, coseismic subsidence in graben
environments, and also the vertical deformation needed as input for probabilistic
tsunami hazard studies. In these cases, where little empirical data exists, we often
rely on tailor-made solutions that relate the slip on a rupture to the deformation at
the site. These solutions usually consist of a combination of an empirical analysis
of the fault slip with a numerical method that relates the fault slip with the type
of deformation of interest at the site. For simple ground displacements, simple
elastic deformation methods are adequate but in complex environments, we have
used FLAC to compute the comprehensive response of the ground surface to the
slip at depth.
We will present examples, from the Los Angeles area as well as other regions
of both the direct fault displacement hazard analysis and the more secondary
deformation analysis and discuss the various numerical approaches of extending
the empirical methods to analyze hazard in the vicinity of faults. We will also
discuss the importance of probabilistic fault displacement hazard analysis as an
element in the process of creating probabilistic tsunami hazard maps.
Surface Fault Displacement Hazards for the Long Valley Caldera–Mono Lake
Area
Chen, R., California Geological Survey, Sacramento, CA, rui.chen@
conservation.ca.gov; WILLS, C. J., California Geological Survey, Sacramento,
CA, [email protected]; BRANUM, D. M., California Geological
Survey, Sacramento, CA, [email protected]
As part of the United States Geological Survey (USGS) multi-hazards project
in the Long Valley Caldera–Mono Lake area, the California Geological Survey
(CGS) developed several earthquake scenarios. Potential surface fault displacement hazards associated with these scenario earthquakes were evaluated using
both deterministic and probabilistic approaches.
The Long Valley Caldera-Mono Lake area has numerous active faults.
Five of these faults or fault zones are considered capable of producing M ≥ 6.7
earthquakes by the 2007 Working Group of California Earthquake Probabilities
(WGCEP) and the USGS National Seismic Hazard Mapping Program
(NSHMP). CGS developed earthquake scenarios for all five of these potential
earthquake faults and for the White Mountains Fault to the east. The scenario
earthquakes were based on fault geometry and activity data developed by the
2007 WGCEP and NSHMP. In addition, for the Hilton Creek Fault, two alternative scenarios were developed to account for different opinions in the northern
extension of the fault into the Long Valley Caldera. Surface fault displacement
hazards were evaluated for each scenario using the Petersen et al. 2010 approach
supplemented by the Youngs et al. 2003 regression equations for normal faults.
The effect of surface fault displacements may be localized along surface traces of a
mapped earthquake fault if fault geometry is simple and the fault traces are accurately located. However, surface fault displacement hazards can spread over a few
hundred meters to a few kilometers if the earthquake fault has numerous splays or
branches, such as the Hilton Creek Fault. In the later case, evaluating the distribution of surface fault displacement is challenging. We applied an approach that
relies on a deterministic methodology to depict distribution of fault displacement
along fault strikes and a probabilistic methodology to evaluate displacement
amplitude and distribution across the fault.
Session Chairs: Delphine Fitzenz and Andrew Michael
Data Constraints on Models for Earthquake Physics and Forecasting
Rundle, J. B., University of California, Davis, CA, [email protected];
HOLLIDAY, J. R., University of California, Davis, CA, Holliday@physics.
ucdavis.edu; GRAVES, W. R., OpenHazards, Inc, Davis, CA, graveswr@gmail.
com; SACHS, M. K., University of California, Davis, CA, sachs@physics.
ucdavis.edu; HEIEN, E. M., University of California, Davis, CA, emheien@
ucdavis.edu; YIKILMAZ, M. B., University of California, Davis, CA,
[email protected]; TURCOTTE, D. L., University of California, Davis,
CA, [email protected]
Models for earthquake physics and forecasting require input data, along with
model parameters. The models we specifically consider are Virtual California, a
numerical model for driven interacting faults in California (and elsewhere; see
Heien and Sachs, in prep., 2012), and the Natural Time Weibull (NTW) model
for regional earthquake forecasting (e.g., JBR et al., PRL, submitted, 2012). We
have also considered models for activation and quiescence, and we have analyzed
their performance using Reliability/Attributes and standard Receiver Operating
Characteristic (ROC) tests. The input data that are used in these models consists of catalog data, in the case of the stochastic models, and paleoseismology
data in the case of the numerical simulations. The output data we fit are observed
frequencies and times of large events in the case of stochastic models, and spacetime patterns and statistics of large events (such as slip-magnitude, magnitudelength, magnitude-area, etc.) in the case of numerical simulations. Important
components of these fits include not only the mean values, but also correlations,
standard deviations, and other measures of statistical variability. An important
method to determine the usefulness of data is a sensitivity analysis, where changes
in the input data produce changes in the output data. The model is viewed essentially as a filter or transformation that maps the input data into the output data.
Typically the output can be compared directly with paleoseismic or catalog data.
In this type of analysis, the catalog data is divided into a training set and a “prediction set” that are disjoint in time. In this talk we consider aspects of these prob-
lems in the context of the VC and NTW models. We show how the Reliability
and ROC tests allow us to judge data completeness and estimate error. It is clear
from much of the analysis that data quality is a major limitation on the accurate
computation of earthquake probabilities.
Irregular Behavior of the Dead Sea Transform, Inferred from 3D Paleoseismic
Trenching
Wechsler, N., San Diego State University, San Diego, CA, nwechsler@
projects.sdsu.edu; ROCKWELL, T. K., San Diego State University, San Diego,
CA, [email protected]; KLINGER, Y., Institute de Physique de
Globe, Paris, France.
Understanding earthquake production along major plate-boundary faults is
critical for improving seismic hazard assessment and earthquake forecast models, which are based on limited observations of recurrent slip at a point along a
fault or on variations in recurrence times at multiple paleoseismic sites along a
fault. To better understand long-term earthquake recurrence there is a need for
comprehensive event records that include magnitude, location and displacement
data. The Beteiha site, located on the Dead-Sea Transform (DST), provides an
opportunity for constructing such a record for an active plate-boundary via highresolution 3D trenching. Previous trenches in the same locale exposed buried
paleo-channels which provided slip-per-event data for the last two historical
earthquakes (1202, 1759 CE) as well as a slip-rate estimate for the past 5ka. The
two events had different magnitudes (M7.5, M6.5, respectively) reflected by their
different amounts of slip (2.2m, 0.5m), and while rupturing the same segment
at their southern end, they ruptured through different segments to the north.
Returning to the site, we exposed upwards of seven additional buried channels to
be used as offset markers. The ages of the buried channels span the period between
the last large event of 1202 and over 4ka ago. By excavating fault-crossing and
-parallel trenches we were able to extend the event history on this segment, refine
slip-rate estimates, which are comparable to those from previous studies, and add
to the slip-per-event data. We found evidence for a moderate event (0.5m slip)
between 800-1200 CE and for 4-5 events between 100-400 CE, previously considered seismically quiet. The earthquake production seems to be bi-modal, perhaps due to the splaying of the DST into several faults in the Lebanese restraining
bend north of our site. Periods of activity and quiescence suggest a non-periodic
behavior of the fault, possibly due to its proximity to a convergence of several segments.
Stress Uncertainties of the San Andreas Fault System from 4-D Deformation
Modeling
SMITH-KONTER, B. R., University of Texas at El Paso, El Paso, TX, brkonter@
utep.edu
Interseismic stress rates of the San Andreas Fault System (SAFS), derived from
the present-day geodetic network spanning the North American-Pacific plate
boundary, range from 0.5–7 MPa/100yrs and vary as a function of fault locking
depth, slip rate, and fault geometry. Calculations of accumulated stress over several earthquake cycles, consistent with coseismic stress drops of ~1-7 MPa, also
largely depend on the rupture history of a fault over the past few thousand years.
However, uncertainties in paleoseismic slip history, geologic/geodetic slip rates,
and variable locking depths throughout the earthquake cycle, can introduce
uncertainties in stress rate and in present-day stress accumulation calculations.
For example, geodetic and geologic slip rates along the SAFS can vary by as much
as 25% of the total slip budget; geodetic locking depths, while within the bounds
of seismicity, typically have uncertainties that range from 0.5–5 km; uncertainties in paleoseismic chronologies can span several decades, with slip uncertainties on the order of a few meters. Here we assess the importance of paleoseismic
chronology, slip rate, and locking depth accuracies using a 3-D semi-analytic
time-dependent deformation and stress model of the SAFS. We perform a sensitivity analysis of stress rate and present-day accumulated stress by calculating
stress derivatives with respect to each model parameter over the estimated range
of uncertainty. Our results suggest that stress rates can vary by as much as 2-3
MPa/100yrs from variations in slip rates and fault locking depths. Uncertainties
in accumulated stress throughout the earthquake cycle on the order of ~0.5-3.0
MPa can be expected from associated uncertainties in paleoseismic data. Stress
variations of these magnitudes have critical implications for seismic hazard analyses given that modeled stress accumulation levels of the southern San Andreas
appear to be approaching those of historically great events (~7+ MPa).
Aftershock Statistics Constitute the Strongest Evidence for Elastic Relaxation
in Large Earthquakes—Take 2
Field, E. H., USGS, Golden, CO, [email protected]
The forecast models developed by the Working Groups on California Earthquake
Probabilities (WGCEPs) have constituted the most official statements of timedependent earthquake probabilities for California. The recurrence models used
in these studies have been based on elastic-rebound theory (and the related
seismic-gap hypothesis), while spatiotemporal clustering has been excluded as
negligible. However, the recent earthquake sequences in both New Zealand and
Japan are only the latest reminders that aftershocks can be large and damaging.
The 1999 debate on earthquake prediction in Nature identified consensus that “…
earthquake triggering leads to a transient, local increase in probability of future
earthquakes…”, whereas there remains “…a continuing debate on the applicability
of the seismic gap hypothesis…” (Main, week 7, http://www.nature.com/nature/
debates/earthquake). In other words, the influence of elastic rebound is still questionable for large events because long recurrence intervals preclude definitive
tests. Lack of spatiotemporal clustering was explicitly identified as a limitation in
the last WGCEP model (UCERF2), and has since been a priority for inclusion
in the next model (UCERF3). A presentation by this author at the 2011 AGU
Fall Meeting attempted to show that implementing spatiotemporal clustering via
ETAS statistics in UCERF3 indicates that elastic rebound must also be included;
otherwise large, triggered events will tend to occur close to the main shock, or
even re-rupture the same fault surface, much more frequently than is observed in
nature. Ironically, this implies that aftershock statistics may represent the strongest evidence for the influence of elastic relaxation in large earthquakes. However,
an informal poll following that AGU presentation made it clear that this simple
point was obscured by the necessity and difficulties of describing UCERF3 itself.
Here, the same point will be made using two very simple end-member models.
Under the Hood of the Earthquake Machine: IndentifyingImportant Constraints
for the Predictive Modeling of the Seismic Cycle
Barbot, S., Caltech, Pasadena, CA, [email protected]; LAPUSTA,
N., Caltech, Pasadena, CA, [email protected]; AVOUAC, J. P., Caltech,
Advances in observational, laboratory, and modeling techniques provide increasingly rich findings about the earthquake source behavior on various spatial and
temporal scales. Now the challenge is to develop unifying models capable of integrating a wide range of observations using realistic fault physics. Here, we build
the first fully dynamic model of a fault segment that quantitatively reproduces its
behavior over the entire earthquake cycle. In the model, a rate-and-state fault is
tuned to the wealth of data for the Parkfield segment of the San Andreas Fault.
The model succeeds in reproducing a realistic earthquake sequence of irregular
Mw~6 mainshocks—including events similar to the ones in 1966 and 2004—
and provides an excellent match to the detailed inter-, co-, and post-seismic observations during the most recent earthquake cycle. We discuss the implication for
earthquake source physics and the new observations that are needed to place new
important constraints on the seismic cycle. Such calibrated physical models may
be used in the future to assess seismic hazard and forecast seismicity response to
perturbations of natural or anthropogenic origins.
Integrating Seismicity and Potential Fields Data to Determine Structural
Controls on the Fairbanks and Salcha Seismic Zones, Interior Alaska
Doser, D. I., University of Texas at El Paso, El Paso, TX, [email protected];
SCHINAGEL, S. M., University of Texas at El Paso, El Paso, TX, smschinagel@
miners.utep.edu; DANKOFF, C. J., University of Texas at El Paso, El Paso, TX,
[email protected]
The Fairbanks and Salcha Seismic Zones (SSZ and FSZ) are located in a swampy,
densely vegetated region between Fairbanks and the foothills of the Alaska
Range where evidence for surficial faulting is difficult to observe. We compare
relocated historical (1899-1971) and recent (1996-2007) seismicity of the Salcha
and Fairbanks seismic zones (SSZ and FSZ), source processes of historical M>6
earthquakes from body waveform modeling, and filtered Bouguer gravity anomaly and magnetic data to determine how changes in bedrock geology may relate to
observed regional patterns in seismicity and fault rupture processes. The southern
SSZ bounds the edge of a magnetic high. A cluster of recent seismicity located
near the 1937 Salcha (M=7.3) epicenter is associated with a small gravity and
magnetic high. Rupture initiation near this high in 1937 and propagation to the
southwest would be consistent with both waveform modeling and intensity information. Potential fields data for the FSZ show considerably more complexity, in
accord with seismicity patterns that show at least 4 distinct bands of earthquakes
within the FSZ. Aeromagnetic anomalies indicate northeast-southwest trending
structures that appear related to the observed bands in seismicity. Two east-west
trending magnetic highs appearing to truncate parts of the FSZ with nucleation
of the 1947 (M=7.2) Fairbanks earthquake occurring near the southernmost
high. An intense seismic swarm occurring near Fairbanks in 1967 appears to
coincide with the edge of a Bouguer gravity high.
Do We Understand Stepovers Sufficiently to Model Them?
Michael, A. J., USGS, Menlo Park, CA, [email protected]
Wesnousky and Biasi (BSSA, 2011) showed that there is a 50% chance of an
earthquake rupturing through a fault stepover with a width of 1 to 4 km. Can
we learn enough about individual stepovers so that physical models provide
more specific information than their empirical result? The Cholame stepover
at Parkfield, California, is heavily studied but a challenge to model. A physical
model of a stepover requires knowing the fault geometry, stress state, and how
lithology and failure criteria vary (Harris, 2004). Knowing the fault geometry is
a challenge. Some fault stepovers have only been studied from surficial mapping
because there may be insufficient seismicity or other geophysical data to produce a
true three-dimensional image of the fault structure. Where there is sufficient data
to map the fault in three-dimensions, there is often a simpler fault plane at seismogenic depths than at the surface although it is difficult to image subsurface fault
structures in great detail. For instance, the surficial stepover in Cholame Valley
is underlain by a single fault plane at seismogenic depths (Eberhart-Phillips and
Michael, JGR, 1993; Thurber et al., BSSA, 2006). If we do know how a single fault
links across a stepover then Lozos et al. (BSSA, 2011) showed that modest, potentially unobservable, rotations of the stress axes have a major effect on dynamic
rupture models. Finally, the earthquake history at Parkfield and geologic analysis
of Simpson et al. (BSSA, 2006) suggest that the Cholame stepover has a lower
than 50% probability of being ruptured through despite the fact that there is no
actual stepover at seismogenic depths. The surficial stepover may be a symptom
of fault segmentation rather than its cause, which may be subsurface lithologic
variations imaged in geophysical models, but it is unclear how to include those
variations in physical models. When this heavily studied stepover is so perplexing
can we hope to properly model stepovers that present more unknowns?
What Can Surface Slip Distributions Tell Us About Fault Connectivity at
Depth?
Oglesby, D. D., University of California, Riverside, Riverside, CA, david.
[email protected]
Fault traces on the Earth’s surface are often discontinuous. In many earthquakes,
however, rupture propagates across numerous fault segments, leading to the question of whether these segments are connected by a single through-going fault at
depth. To help answer this question, it would be useful if the connectivity of fault
segments at depth were manifested as an observable feature of the surface slip
distribution, which could be mapped in the field. In the present research, I use
3D dynamic models to investigate the impact of fault connectivity at depth on
the surface slip distribution in an earthquake. In particular, I compare results
for faults with several coplanar segments that are disconnected by locked patches
on the surface but are connected to a through-going fault at varying depths, as
well as faults that are entirely disconnected or entirely connected. I find that the
deeper the depth of connection between the segments, the lower the slip on the
individual segments. Segments that are entirely disconnected produce roughly
elliptical surface slip profiles that are almost indistinguishable from those of
segments that are connected at depths below around 8 km. For segments that
are connected up to shallower depths, the surface slip distributions become flatter in the middle, with steeper slip gradients near the segment edges. However,
these differences are rather small, and might not be easily distinguished from
slip heterogeneity induced by other factors, such as heterogeneous stress, material properties, and fault geometry. Thus, I conclude that it may be quite difficult
under most circumstances to discern fault connectivity at depth from surface slip
mapping unless the connection is rather shallow (1-3 km); in such cases, high slip
gradients near the segment edges might be indicative of connection below the
surface. The results may have implications for the predictability of earthquake
size, ground motion, and seismic hazard.
Fault Interaction Deduced from Characteristic Geomorphic Offsets, Southern
San Andreas Fault
Williams, P. L., San Diego State University, San Diego, CA, plw3@earthlink.
net
LiDAR, Google satellite imagery and low-altitude aerial photography support a
systematic inventory of small geomorphic offsets for both major strands of the
100 km Coachella Valley segment (CVS) of the southern San Andreas fault zone
(SSAFZ). Goals of the work are characterization of recent displacement magnitudes, evaluation of displacement patterns along strike, and examination of the
mechanics and dimensions of the prominent Banning-Mission Creek fault step.
Sites recording multiple offsets from a single source stream were identified at a
small number of localities in the Mecca and Indio Hills. Field evaluation of all
the sites indicates predominance of moderate displacements and rare larger offsets. The pattern indicates a predominance of “characteristic” CVS behavior, i.e.
repeating similar offsets. The Banning fault (BF) of the SSAFZ branches 5° to
20° west of the Mission Creek fault (MCF). Northward, slip is transferred from
the MCF to the BF across a fault-parallel zone extending over 8km between the
faults. Kinematics of slip transfer can be deduced by tracking individual increments of geomorphic offset into the zone of fault overlap. Interpretation of the
locus of slip transfer is supported by a marked increase of deformation intensity
within the stepover, and patterns of fault linking across the northern Indio Hills.
These findings anticipate high rupture complexity within the stepover zone.
Characterization of the area and mechanics of the slip transfer zone could be
incorporated post-earthquake imaging to capture the full extent of surface deformation. Mapping the dramatic structural expression of the transfer zone will
inform studies of structures similar in topographic expression, but lacking the
excellent exposure and access of the northern Indio Hills.
Seemingly Minor Details of Fault Geometry May Strongly Affect Rupture
Propagation
Lozos, J. C., University of California, Riverside, Riverside, CA, jlozo001@ucr.
edu; OGLESBY, D. D., University of California, Riverside, Riverside, CA, david.
[email protected]
As numerical modeling techniques of earthquakes have become more advanced,
it has become possible to incorporate smaller details of fault geometry into these
models. Our recent work highlights that such details, some of which might be
tempting to remove from a model for the sake of computational efficiency, may
actually have a significant effect on rupture propagation and ground motion. In
particular, we will discuss how the presence of a small fault segment within a disconnected stepover may arrest or facilitate rupture jumping depending on the
length of the segment, how the exact angle of a fault bend determines whether
or not rupture will propagate through the bend, and how the maximum stepover
width through which rupture may propagate is strongly affected by whether or
not the primary segments of the stepover are joined by a linking segment. We will
make a case for more detailed field observations and descriptions of these smaller
details of fault geometry.
The Importance of the Orientation of the Maximum Remote Stress in QuasiStatic Triggering of Fault Slip in Multi-Fault Earthquakes
Madden, E. H., Dept. of Geological & Environmental Sciences, Stanford
University, Stanford, CA, [email protected]; MAERTEN, F.,
Schlumberger—MpTC, Grabels, FRANCE, [email protected]; POLLARD,
D. D., Dept. of Geological & Environmental Sciences, Stanford University,
Stanford, CA, [email protected]
Earthquakes that rupture multiple faults are of concern because they can be larger
than earthquakes predicted for any one fault involved. The width between faults
rupturing in the same event has been proposed as 3-4km from observations of
multi-fault events and up to 5km from dynamic models of en echelon strike-slip
faults. We explore the mechanical basis for quasi-static triggering of slip across a
step-over of 3-5km using 3D linear-elastic models and find it in accordance with
the extent of the 1MPa contour of Coulomb stress change (CSCH) on ‘receiver’
faults at constant depths and orientations, due to slip along a planar, vertical fault.
We test the sensitivity of this contour to the dimensions of the slipping fault,
calculation depth, receiver fault orientation, friction and the orientation of the
maximum remote compression (S1) driving fault slip. Results do not vary greatly
with fault dimension, but contour size decreases with fault slip for less optimal
fault orientations and higher friction. The relative sizes of lobes extending parallel
and perpendicular to fault strike are much less sensitive to receiver fault orientation than to S1 orientation. These calculations provide some constraint on the
influence of these variables on CSCH, but in nature faults are neither vertical
nor planar. We extend this analysis to faults involved in the 1992 Landers, CA
earthquake to study the influence of fault geometry on CSCH and constrain the
sequence of fault slip across the southern-most step-over. The Landers-Kickapoo
and the Homestead Valley faults are tested as receiver faults due to slip along the
Johnson Valley Fault in 3 structural models. CSCH changes with fault geometry,
friction, and S1 orientation. S1 has the largest influence on CSCH and therefore
on constraining the sequence of slip through the step-over. We review different
orientations of S1 from the literature and present new results for its orientation
from a mechanical inversion of Landers aftershocks.
Testing Segmentation Models
Jackson, D. D., UCLA, Los Angeles, CA, [email protected]
Segmentation, and the characteristic earthquake hypothesis that depends on it,
have no meaning unless they are testable. Most applications of the segmentation
hypothesis now use a weak form that assumes segment boundaries stop most but
not all ruptures. I developed a method for testing such models, both retrospectively and prospectively, based on the conditional stopping probability that if
rupture enters a segment boundary zone, it will stop before escaping. My test, like
all others I can imagine, requires that the segment boundary locations be defined
to within specified limits. A definitive outcome requires that the conditional
stopping probabilities be much higher than expected for a random model of
rupture termination. Reports of the Working Group on California Earthquake
Probabilities (WGCEP 2002, 2008) employed the segmentation hypothesis to
generate rupture scenarios. From the frequencies associated with these scenarios
I’ve computed the conditional stopping probabilities. A simple null hypothesis
assumes random locations, GR magnitudes, and length proportional to the cube
root of seismic moment. For magnitude 6.5+, the conditional stopping probability is about 0.009 per km of segment boundary. In a retrospective test on the 1906
and 1857 earthquakes, the WGCEP segmentation model beats the null hypothesis, but only because segment boundaries were drawn at the assumed ends of
those ruptures. I propose a prospective test for California, but if the WGCEP
model is correct, it could take up to 100 years to falsify the null hypothesis. A
faster definitive test will require application on many more segment boundaries.
Validation of Strong Ground Motion Simulations for
Session Chairs: Nicolas Luco, Sanaz Rezaeian, and Thomas H.
Jordan
Progress of the Southern California Earthquake Center Technical Activity
Group on Ground Motion Simulation Validation
Luco, N., United States Geological Survey, Golden, CO USA, nluco@usgs.
gov; JORDAN, T. H., University of Southern California, Los Angeles, CA USA,
[email protected]
Strong ground motion records are fundamental to engineering applications, such
as nonlinear response history analysis of geotechnical or structural (e.g. building,
bridge) systems for building code or risk assessments, and to the development of
prediction models for ground motion intensity measures (e.g. spectral acceleration). Despite the thousands of strong ground motion records readily available
online, there remains a shortage of records for large-magnitude earthquakes at
short distances, as well as records that sample specific combinations of source,
path, and site characteristics. Owing to the development of numerical sourceexcitation and wave-propagation codes, deterministic and stochastic simulations
of strong ground motions now offer increasingly realistic, physics-based models
of strong ground motions. In order to be useful in engineering applications, however, simulated records must first be statistically validated against available strong
ground motion data.
The development and implementation of validation methodologies requires
collaboration between ground motion modelers and engineering users. With this
goal, the Southern California Earthquake Center (SCEC) has recently established a Technical Activity Group (TAG) focused on Ground Motion Simulation
Validation (GMSV). An initial planning workshop was held in January of 2011
to prioritize the activities of the GSMV TAG, which resulted in a number of recommendations (http://collaborate.scec.org/gmsv/2011_Workshop). Building
on this outcome, a plenary session at the 2011 SCEC Annual Meeting identified
six priority activities and topics (http://www.scec.org/proposals/SCEC2012RFP.
pdf, pages 18-19). The presentation summarized here describes these initial priorities and the SCEC research projects subsequently undertaken to address them. It
also outlines plans for future work based on a workshop held to coordinate these
GMSV TAG projects.
Validation of Las Vegas Basin Response to the 1992 Little Skull Mtn.
Earthquake as Predicted by Physics-Based Nevada ShakeZoning
Computations
Flinchum, B. A., Nevada Seismological Laboratory, Reno, NV, flinchu4@
gmail.com; SAVRAN, W. H., Nevada Seismological Laboratory, Reno, NV,
[email protected]; SMITH, K. D., Nevada Seismological Laboratory, Reno,
NV, [email protected]; LOUIE, J. N., Nevada Seismological Laboratory,
Reno, NV, [email protected]; PULLAMMANAPPALLIL, S. K., Optim
Seismic Data Solutions, Reno, NV, [email protected]; PANCHA, A.,
Optim Seismic Data Solutions, Reno, NV, [email protected]
We have been developing and refining ``Nevada ShakeZoning’’ procedures to
define earthquake hazards in the Intermountain West. Nevada ShakeZoning
relies on physics and geology to estimate earthquake shaking hazards, rather than
statistics. In order to verify the results of ShakeZoning and the ground shaking it predicts for Las Vegas Valley (LVV), we simulated the M L 5.6-5.8 Little
Skull Mountain (LSM) earthquake. ShakeZoning uses a finite-difference code
to compute wave propagation through complex 3d models, so it limits us to lower
wave frequencies. For the extensive LSM-LVV model the limit is 0.1-0.3 Hz and
lower. The Clark County Parcel Map is a critical data set included in Nevada
ShakeZoning predictions for LVV. Though we use the Parcel Map only in the
upper 30 m of our models, it demonstrates amplifications of 120% to 300% even
at these low frequencies. A detailed model of the LVV basin-floor depth, and
regional basin-thickness models derived by the USGS are also important components in Nevada ShakeZoning. Before comparison, we integrated the groundmotion time histories recorded by accelerometers to particle velocity units. Then
we band-pass filtered the recorded time histories to corner frequencies of 0.1 and
0.6 Hz, in order to properly compare the recordings against our ShakeZoning
synthetics. We found that Rayleigh-wave minus P-wave (R-P) times and the pulse
shapes of Rayleigh waves correlate well between the data and synthetics. Most
importantly, the ShakeZoning predicted peak ground velocities matched what
was observed, to closer than a factor of two. Our models still need much development, since observed seismograms within LVV show longer durations of shaking,
caused by horizontally reverberating, 0.2-Hz longitudinal waves beyond 100 sec
after Rayleigh-wave arrival. Within the basins, our current velocity models are
homogeneous below 30 m depth, causing our LVV synthetics to show insufficient
shaking durations of only 30-40 s.
Validation of a 4-Hz Physics-Based Simulation of the 2008 Chino Hills
Earthquake
Taborda, R., Carnegie Mellon University, Pittsburgh, PA, rtaborda@cmu.
edu; BIELAK, J., Carnegie Mellon University, Pittsburgh, PA, [email protected]
Physics-based, deterministic earthquake simulations using numerical methods
and high-performance computing have gained increased acceptance within the
seismologic and earthquake engineering communities in recent years. Large-scale
simulations are used as a means for understanding ground motion characteristics
and seismic hazard of entire regions. Their level of detail, however, has been predominantly limited to long-periods, with most verification and validation studies
using maximum simulation frequencies lower than or equal to 1 Hz, and minimum shear wave velocities greater than or equal to 500 m/s. We present a simulation of the Mw 5.4 2008 Chino Hills earthquake for a maximum frequency up to
4 Hz and a minimum shear wave velocity down to 200 m/s, and perform a validation study comparing data obtained from seismic networks with simulation
synthetics on more than 300 recording stations. The simulation was done using
Hercules, the parallel octree-based finite-element earthquake simulator developed by the Quake Group at Carnegie Mellon University. The source model corresponds to that of an independent inversion study and the material model used is
a Community Velocity Model developed by the Southern California Earthquake
Center. Our results show (i) strong sensitivity of the ground motion to the velocities of the shallow layers, especially at the higher frequencies; (ii) that extending
the maximum frequency beyond 1 Hz for deterministic earthquake simulations
is an effort worth pursuing; and (iii) suggest areas where future improvement of
seismic velocity and source models is required.
A Method for Validation of Simulated Ground Motions Using Time-Domain
Cumulative Statistical Characteristics
Rezaeian, S., U.S. Geological Survey, Golden, CO, [email protected]
Response history analysis for assessment of existing structures or design of
new ones requires reliable accelerograms. Due to scarcity or lack of real ground
motions (GMs) for certain earthquake and site characteristics, engineers are
often forced to use simulated or scaled GMs. Numerous simulation and scaling
methods have been proposed. The general concern among engineers is that the
resulting artificial records may not be equivalent to real records in estimating the
seismic demand, and hence, the induced damage to structures.
This research proposes a new testing methodology to assess the validity of
artificial GMs against real GMs that were recorded during past earthquakes. The
validation is done by looking at three criteria that characterize and quantify the
evolution of the intensity, predominant frequency, and bandwidth of a GM over
time. These characteristics are known to influence the structural response. Since
earthquake GMs can be seen as stochastic processes that are nonstationary in
both time and frequency domains, the three criteria can be quantified by statisti-
cal characteristics of an equivalent stochastic process. The statistical characteristics of interest are the time-varying standard deviation of the process, the mean
zero-level up-crossing rate (i.e., the mean number of times per unit time that the
process crosses the level zero from below), and the rate of negative maxima and
positive minima (i.e., the number of local peaks and valleys per unit time). While
the first measure controls the evolving intensity of the process, the second and
third are surrogates for the predominant frequency and bandwidth, and together
control the frequency content of the process.
Using cumulative measures of the aforementioned statistical characteristics
provides us with relatively smooth vectors over the time domain. These vectors
and their plots versus time are used to compare the time-varying intensity and
frequency content of artificial and real records.
Ground Motion Simulations for the 2009 L’Aquila (Central Italy) Earthquake:
Modeling and Validation
AMERI, G., Istituto Nazionale di Geofisica e Vulcanologia, Milano, Italy,
[email protected]; PACOR, F., Istituto Nazionale di Geofisica e
Vulcanologia, Milano, Italy, [email protected]; GALLOVIC, F.,
Charles University, Department of Geophysics, Prague, Czech Republic,
[email protected]
On 6 April 2009 a Mw 6.3 earthquake struck the L‘Aquila city, one of the largest
urban centers in the Abruzzo region (Central Italy), causing a large number of
casualties and damage in the town and surrounding villages. The earthquake was
recorded by several digital stations of the Italian Strong-Motion Network. The
collected records represent a unique dataset in Italy in terms of number and quality of records, azimuthal coverage and presence of near-fault recordings. Soon
after the earthquake the damage in the epicentral area was also assessed providing
macroseismic intensity estimates, in MCS scale, for 314 localities (I ≥5).
Despite the moderate magnitude of the L‘Aquila earthquake, the strongmotion and macroseismic data in the vicinity of the fault depict a large variability
of the observed shaking and damage.
In this study we present broadband (0.1–10 Hz) ground motion simulations of the L’Aquila earthquake to be used for engineering purposes in the
region. The Hybrid Integral-Composite method is used and several features of
the source model are constrained by low-frequency slip inversion results.
We first model the recorded strong motions in order to calibrate some
source parameters and to assess the capabilities of the broadband simulation
model. The goodness-of-fit is evaluated in time (peak values and duration) and
frequency domains (elastic and inelastic response spectra) and shows a remarkable agreement between observed and simulated data at most of the stations.
Then, we simulate the ground motion at a grid of sites in the epicentral area
and compare the synthetic ground-motion parameters with estimates from several empirical ground motion prediction equations (GMPEs). The comparison
highlights potential drawbacks in using GMPEs to validate simulated motions.
Finally, we compare the observed macroseismic intensity distribution with
that obtained applying ground-motion-to-intensity conversion equations to the
synthetic parameters.
Comparison of Nonlinear Building Response Simulations Using Recorded
and Simulated Ground Motions
Goulet, C. A., Pacific Earthquake Engineering Research Center, Berkeley,
CA, [email protected]; HASELTON, C. B., California State University,
Chico, Chico, CA; BAYLESS, J., URS Corporation, Los Angeles, CA.
Although substantial progress has been made in physics-based ground motion
simulations in the recent years, the engineering community is still reluctant to
use simulated time series for design. One of the reasons for this is a lack of understanding of how simulated ground motions compare to recorded ground motions,
especially when it comes to their impact on nonlinear structural response. There
are on-going efforts of validation of simulated ground motions, but these tend to
be focused on record properties or on the response of single-degree-of-freedom
systems. We have used a different approach and compared the nonlinear structural response of building models subjected to both recorded and simulated
ground motions, with both sets exhibiting similar response spectral shapes. The
results are compared based on the maximum inter-story drift ratio (MIDR) for
three different reinforced concrete frame building models.
Results from our previous work show that for first-mode-dominated structures (such as the three buildings used), the response spectral shape tends to control the structural response. Other factors, such as distance, magnitude and site
type are considered to have secondary effects only. In order to capitalize on previous research, we compared the structural response to recorded and simulated
acceleration time series for three types of “target” spectral shapes conditioned
on a given earthquake scenario: 1) as-recorded shape, 2) 98th percentile uniform
hazard spectrum (UHS) shape and 3) 98th percentile conditional mean spectrum
(CMS) shape.
Our initial findings show that when time series are conditioned on response
spectral shape, there is no statistical difference in MIDR for recorded and simulated motions. Further analyses are needed to confirm that the results from our
study are applicable to broader applications but these results are promising.
Validation of Broadband Synthetic Seismograms with Earthquake
Engineering-Relevant Metrics
Olsen, K. B., San Diego State University, San Diego, CA, kbolsen@sciences.
sdsu.edu; JACOBSEN, B. H., University of Aarhus, Aarhus, Denmark, bo@
geo.au.dk; TAKEDATSU, R., San Diego State University, San Diego, CA,
[email protected]
We have used the goodness-of-fit (GOF) measure for broadband (0-10Hz)
ground motion time histories by Olsen and Mayhew (2010) to validate broadband ground motions for historical earthquakes, including the 1994 Northridge,
1992 Landers, and 1979 Imperial Valley events. The GOF method includes a set
of commonly used, user-weighted metrics, such as peak ground motions, response
spectrum, the Fourier spectrum, cross correlation, and energy release measures.
In addition, the method includes a metric with specific interest for structural
engineers, the ratios of inelastic/elastic displacements (IE ratios). The broadband
synthetics for the selected historical earthquakes are generated by combining
long-period deterministic synthetics with high-frequency scattering functions
using the method by Mai et al. (2010). Comparison of the earthquake engineering-relevant metrics derived from synthetic and recorded broadband time series
generally show a good fit at long periods, which, as expected, degrades at shorter
periods.
Shallow near-surface material plays a critical role in ground motion simulation validation. The modeling of the resultant small-scale amplification effects
requires a resolution of the shallow sediment velocities on the order of 100 m or
less. State-of-the-art area specific velocity models poorly resolve the near-surface
heterogeneities on such scales in most areas. Furthermore, due to the expensive
acquisition of the data, it may not in the foreseeable future be feasible to capture the likely rapid spatial variation of the near-surface material by deterministic
models. Toward characterizing the variability of shallow sediment amplification,
we have investigated the effects of modeling inhomogeneities with fractal distributions augmented onto the shallow seismic velocity structure. We demonstrate
the extent to which the statistical model of the near-surface heterogeneities may
affect the ground motions during the 2010 M7.2 El Mayor-Cucapah earthquake.
Nonlinear Response Potential Evaluation Using Stochastically Simulated
Accelerograms
Goda, K., University of Bristol, Bristol, Avon, United Kingdom, katsu.goda@
bristol.ac.uk; ATKINSON, G. M., University of Western Ontario, London, ON,
Simulated earthquake accelerograms have wide and important applications in
earthquake engineering, especially in cases where appropriate real accelerograms
are scarce. For generating simulated accelerograms, target earthquake scenarios
or elastic response spectra are often specified, and artificially-generated timehistory data are matched to the target spectrum or scenario conditions. Various
methods are available, including spectral modification of real records, simple
stochastic simulation methods, hybrid methods, and physics-based approaches.
From users’ viewpoints, key questions regarding the validity of such simulated
accelerograms are: (i) whether artificial accelerograms produce realistic nonlinear
structural responses in comparison with real accelerograms; and (ii) which methods are applicable (and under what circumstances).
We have conducted comparisons of the nonlinear response potential of
records simulated using finite-fault stochastic methods and hybrid methods with
that of real records. The use of finite-fault stochastic methods as a reference technique is motivated by their simplicity and versatility, which allows application in
a variety of situations where parameters for more detailed methods are lacking.
To draw generic conclusions on the response potential of records, inelastic singledegree-of-freedom systems with different hysteretic characteristics are employed.
We present results from two investigations: (i) response characteristics of finitefault stochastically-simulated records versus real records observed during the M9
March 11th 2011 Tohoku earthquake; and (ii) response characteristics of finitefault stochastic records versus hybrid broadband records for a M7.5 strike-slip
crustal earthquake. We conclude that peak nonlinear responses of accelerograms
generated using different approaches are similar if (and only if) they have similar
probabilistic features (same median and same variability) in terms of their elastic
response spectra.
Wood Frame Building Damage Prediction Using Broad-Band Synthetic
Ground Motions: A Comparative Study
Pei, S., South Dakota State University, Brookings, SD, [email protected];
VAN DE LINDT, J. W., University of Alabama, Tuscaloosa, AL, jwvandelindt@
eng.ua.edu; HARTZELL, S., USGS, Golden, CO, [email protected]; Luco,
N., USGS, Golden, CO, [email protected]
Light frame wood buildings are the vast majority of residential buildings in the
U.S. and Canada. Performance of this building category in historical earthquakes indicated that servere damage to residential buildings represents a threat
to infrastructure resiliency. Accurate prediction of damage to these buildings
using synthetic ground motions is desirable from a performance based seismic
design stand point. Based on a validated wood frame building damage index, a
damage potential indicator was developed and calibrated to quantitatively represent the damage potential of any given ground motion time history to typical
wood frame building design configurations. By comparing the damage potential
for four different broad-band synthetic ground motion models with the historically recorded ground motions at corresponding sites, the effectiveness of synthetic ground motions to reproduce realistic damage to residential buildings was
investigated. The factors that may impact the synthetic ground motion accuracy
in damage prediction were investigated. It was concluded that damage for sites
closer to the fault is over-predicted and far field damage is under-predicted for the
models considered in this study.
Assessment of Synthetic Ground Motion Records Obtained from Alternative
Simulation Methods in Dynamic Analyses of Multi-Storey Frame Buildings
KARIMZADEH-NAGHSHINEH, S., Middle East Technical University,
Ankara, Turkey, [email protected]; ASKAN, A., Middle East
Technical University, Ankara, Turkey, [email protected]; AMERI, G.,
Istituto Nazionale di Geofisica e Vulcanologia, Milano, Italy., gabriele.ameri@
mi.ingv.it; YAKUT, A., Middle East Technical University, Ankara, Turkey,
[email protected]
For seismic design purposes and dynamic response analyses of building structures, it is essential to estimate the hazard to which the structures will be exposed
during their lifetimes. Nonlinear time-history analysis, which requires full time
series of ground acceleration, is one of the alternative techniques to assess the
dynamic response of a structure. For regions with sparse ground motion data,
records from other regions are generally employed and averaged to obtain the
dynamic response of a structure. Ground motion simulations provide alternative
acceleration time series for this purpose. Alternative simulation methods provide
different levels of accuracy in terms of modeling any ground motion record. It
is thus critical to investigate the nonlinear response of structures to synthetic
records of alternative levels of accuracy. For this purpose, in this study, we present
nonlinear time history analyses of multi-storey frame buildings under real and
corresponding synthetic ground motions. Records of 2009 L’Aquila (Italy) earthquake are simulated using two alternative ground motion simulations methods:
Hybrid Integral-Composite method and stochastic finite-fault method. Results
of nonlinear time history analyses from real and alternative synthetic records of
this event are compared in terms of inter-storey drift ratios aiming to investigate
the ability of synthetic ground motions to predict the seismic responses of reinforced concrete frame structures.
A Statistical Analysis of the Response of Linear and Nonlinear Building
Systems to Observed and Simulated Ground Motions for Past Earthquakes
Galasso, C., University of California, Irvine, Irvine, CA, [email protected];
ZHONG, P., University of California, Irvine, Irvine, CA, [email protected];
ZAREIAN, F., University of California, Irvine, Irvine, CA, [email protected]
We compare seismic demands of multiple degree of freedom (MDOF) building
systems subjected to four past events using hybrid broadband simulations and
actual recordings. We select a number of linear elastic generalized MDOF systems with: (1) eighteen oscillation periods between 0.1s and 8s; (2) three shear
to flexural deformation ratios to represent respectively shear walls structures,
dual systems, and moment-resisting frames; (3) two stiffness distribution along
the height of the systems; i.e., uniform and linear. We derive median demand
spectra (and their intra-event variability) in terms of maximum interstory drift
ratio (IDR) and floor acceleration for Imperial Valley, Loma Prieta, Landers and
Northridge earthquakes. In addition, for two nonlinear selected case study structures, we compare the IDR distributions over the height and their statistics for
both recorded and simulated time histories. These structures are steel moment
frames (SMFs) designed for high seismic risk, 20-storey high-rise and a 6-storey
low-rise buildings, similar to many SMF structures in Los Angeles.
Results of this study show that simulation matches well the seismic demands
produced by recorded ground motions. Some differences between median esti-
mate of IDR and accelerations demand obtained by using real records and that
obtained by simulations are observed. The amount of these differences varies with
the considered event and the structural period while they are fairly independent
of the type of structure. These differences are generally statistical significant only
at short periods, where the simulation is semistochastic and where discrepancies
in elastic spectral shape may be significant. Moreover, the intra-event standard
deviation values of structural response calculated from the simulation are generally low compared to those given by recorded ground motions. Analyses’ results
are formally compared by statistical hypothesis test to assess the significance of
the differences found.
A Statistical Analysis of the Response of Tall Buildings to Recorded and
Simulated Ground Motions
Jayaram, N., Risk Management Solutions Inc., Newark, CA, nirmal.
[email protected]; SHOME, N., Risk Management Solutions Inc., Newark, CA,
[email protected]
Performance based earthquake engineering often involves dynamic structural
analysis of buildings using a set of input ground motions whose response spectra
match a target response spectrum. On occasions where recorded ground motions
are not sufficient, simulated ground motions are sometimes used to complete the
ground-motion set. In this study, we perform statistical analyses to evaluate the
level of similarity between the response of tall buildings to comparable recorded
and simulated ground motions. Structural response measures of a 40 story steel
moment frame building designed based on the 2006 IBC are estimated under 40
recorded and simulated ground motions selected from the NGA database and
the 2009 broadband San Andreas simulations by Dr. Rob Graves. The ground
motions are selected such that the mean and the variance of their spectra match a
pre-specified target mean and variance. In order to ensure that the recorded and
simulated ground motions are comparable, it is made sure that for each recorded
ground motion, a simulated ground motion is selected so that the response spectra and durations of both ground motions match. The response measures considered are peak story drift ratio, peak floor acceleration, residual drift ratio and
beam plastic rotation—measures that are commonly used to assess building performance. This study provides a statistical basis to test simulated ground motions
and identify applications where simulated ground motions can be used.
Poster Session · Tuesday am, 17 April · Golden Ballroom
New Active Fault Map for the Inner Continental Borderland, Southern
California, Santa Monica Bay to the Mexican Border
Conrad, J. E., U.S. Geological Survey, Menlo Park, CA, jconrad@usgs.
gov; RYAN, H. F., U.S. Geological Survey, Menlo Park, CA, [email protected];
PAULL, C. K., Monterey Bay Aquarium Research Institute, Moss Landing, CA,
[email protected]; MCGANN, M., U.S. Geological Survey, Menlo Park, CA,
[email protected]; EDWARDS, B. D., U.S. Geological Survey, Menlo Park,
Seismic hazards of faults offshore southern California between Santa Monica Bay
and the Mexican border are not well understood because the slip rate and rupture
frequency of offshore faults are difficult to determine. Approximately 5-8 mm/
yr of right-lateral slip between the North American and Pacific plates is accommodated in the Inner Borderland, mainly on high-angle faults that strike about
N30°W. From east to west, these faults include the Newport-Inglewood-Rose
Canyon, the San Mateo-Carlsbad (SMC), Coronado Bank (CB), Palos Verdes
(PV), San Diego Trough (SDT), San Pedro Basin fault (SPB), and San Clemente
fault zones.
We present a new map of active faults offshore southern California based
on recently acquired high-resolution multibeam bathymetry and a combination
of existing multichannel seismic reflection data and new high-resolution minisparker and CHIRP seismic reflection data. Sediment cores collected near faults
were used to determine recency of offset. Ultra-high resolution bathymetry and
CHIRP seismic reflection profiles were collected by autonomous underwater
vehicle (AUV) in key areas along the PV and SDT fault zones to calculate slip
rates.
A prime focus of the fault studies was to determine linkages between the
various fault zones. Our data show that the PV and CB fault zones are not linked
as has been shown on previous fault maps. However, the northern part of the
SMC fault trends WNW north of Lasuen Knoll and appears to end near, and
perhaps connect to, the southern PV fault zone. Slip on the CB fault zone is most
likely linked to the southern end of the SMC fault via a NE-trending fault imaged
in multibeam bathymetry. A newly mapped segment of the SDT fault zone
extends NW from Crespi Knoll through a restraining bend where it connects to
the SPB fault zone, which continues across a releasing bend in San Pedro Basin,
north to Point Dume. An offset submarine channel wall along the SDT-SPB fault
zone indicates a slip rate of about 1-2 mm/yr.
Kinematics of Displacement on the Central and Western Agua Blanca and
Santo Tomas Faults, Baja California, Mexico
Wetmore, P. H., University of South Florida, Tampa, FL, wetmore@usf.
edu; MALSERVISI, R., University of South Florida, Tampa, FL, [email protected];
WILSON, J., University of South Florida, Tampa, FL, [email protected];
FERWERDA, B., University of South Florida, Tampa, FL, [email protected].
edu; ALSLEBEN, H., Texas Christian Universiyt, Fort Worth, TX, h.alsleben@
tcu.edu
The Agua Blanca Fault (ABF) of northern Baja California, Mexico transfers plate
boundary strain from the Gulf of California into the Continental Borderlands,
circumventing the “Big Bend” on the San Andreas Fault. The ABF is characterized by a single fault trending east-west in eastern and central portions but, splits
into two branches (northern ABF and the Santo Tomas fault (STF)) with northwest trends in the western third of the fault. Bedrock and geomorphic mapping
demonstrate that the central ABF is characterized by ~10+ 2 km of dextral displacement based on offset of the San Marcos Dike Swarm in Cañon Dolores. Slip
on the central ABF appears to be almost purely strike-slip based on the observation that the elevation of the Agua Blanca fan in Valle Agua Blanca is equivalent
on both sides of the fault despite ~5km of offset. The lack of a dip-slip component
for the central ABF is further supported by the presence of subhorizontal lineations on exposures of the fault in Cañon Dolores.
The two strands of the ABF in the western third of the fault both exhibit
structural and geomorphological evidence for a subordinate component of dipslip motion. The STF along the southern margin of Valle Santo Tomas is characterized by a steep mountain front with triangular facets, 1 to ~4 meter high
scarps, and gently plunging (10-20°) striations on north-dipping surfaces of the
fault. Modeling of gravity data from the region suggests a maximum of ~1 km of
total dip-slip displacement on the STF. There are no constraints for the dextral
component of slip on the STF. The northern ABF exhibits little to no evidence
for a component of dip-slip motion in the section of the fault that overlaps the
STF, but exhibits clear evidence in the northwest along the northeastern foothills of the Punta Banda Ridge. Mapping near the southwestern corner of Valle
Maneadero reveals a sequence of fluvial terraces with an offset of approximately
seven to one dextral to normal dip-slip.
Evidence for Quaternary Faulting along the Gales Creek Fault Zone, Northwest
Oregon
Bemis, S. P., University of Kentucky, Lexington, KY, [email protected];
WELLS, R. E., U.S. Geological Survey, Menlo Park, CA, [email protected]
Despite significant offsets and deformation of the mid-Miocene Columbia
River Basalt Group (CRBG) across major bedrock fault zones in NW Oregon,
evidence for Quaternary displacement on these faults is lacking. In particular,
the NW-striking Gales Creek fault zone (GCFZ) may have up to 6 km of postCRBG right-lateral offset with significant vertical deformation. Using LiDAR
data from the Oregon LiDAR Consortium, we compared bedrock geologic mapping of the GCFZ with high-resolution topography to map neotectonic landforms. Northwest of Hagg Lake, the fault is characterized by a narrow, relatively
continuous, 15 km-long lineament along the steep east flank of the Coast Range,
where the drainages are offset right-laterally up to 2 km. This lineament appears
to be an expression of the GCFZ in soil-mantled bedrock, but we identified two
sites where the fault may offset Quaternary deposits. South of Hagg Lake, landslides, Missoula Flood deposits below ~120 m, and loess appear to obscure much
of the fault trace. However, a 6 km-long lineament SW of the GCFZ has a distinct scarp that suggests recent offset. Our two sites NW of Hagg Lake proved
inconclusive for Quaternary activity. Paleoseismic excavations on the 6 km lineament at WillaKenzie Estate south of Hagg Lake uncovered a thrust fault, displacing Eocene Yamhill Formation bedrock SW-ward over a clayey silt horizon of
likely Pleistocene age. Unfaulted likely Missoula Flood silt and pebbles at the top
of the stratigraphic section suggests a pre-Holocene age. Slickenlines within fault
gouge indicate offset nearly perpendicular to the fault trace. The buried clayey silt
is devoid of visible organics for 14C dating, but we have submitted two samples
for OSL dating to constrain the deposit age. Late Quaternary activity on the
GCFZ may have significant hazard implications, as fault activity may extend >60
km northwest of the source of the 1993 M5.6 Scotts Mills earthquake, along the
margin of the N Willamette Valley.
Where are the Quaternary Strike-Slip Faults in Northwestern Montana?
Stickney, M. C., Montana Bureau of Mines and Geology, Butte, MT,
[email protected]
The USGS Quaternary fault and fold database lists 83 faults in western Montana
with a combined length of over 1800 km. Only one of these mapped faults, with
a length of 3 km, is classified as a strike-slip fault; the rest are classified as normal
faults. In northwestern Montana (north of 46°N and west of 111.5°W), earthquake focal mechanisms compiled from publications, moment tensor catalogs,
and the Montana Bureau of Mines and Geology fault plane solution catalog
reveal that strike-slip faulting is the most prevalent type. Fifty-one of 114 focal
mechanisms (45%) show strike-slip faulting while 31 (27%) show normal faulting. Eight mechanisms (7%) show normal-oblique (combination of normal and
strike-slip) faulting, while only two (2%) show reverse-oblique faulting, and two
show reverse faulting. Twenty mechanisms (18%) fall outside the above five categories (Zoback 1992, JGR 11703-11728). Strike-slip events also account for the
majority of seismic moment release; 15 strike-slip events have magnitudes ranging
from 3.0 to 6.3 but only seven normal events have magnitudes ranging from 3.0
to 3.7. The prevalence of strike-slip faulting events begs the question: are there
unrecognized strike-slip faults with Quaternary displacement in northwestern
Montana? The Lewis and Clark Zone, an ancient WNW-trending fault zone,
transects west-central Montana and contains at least a dozen strike-slip faults, but
none have recognized Quaternary displacement. Failure to recognize Quaternary
strike-slip displacement on low-slip-rate faults, if they exist, may result from 1)
forested terrain underlain by young glacial and lacustrine deposits, 2) poor scarp
preservation as compared to 1-2 m scarps produced by normal faulting, and 3)
minimal topographic expression owing to their existence within and parallel to
stream valleys with active fluvial systems. If such faults exist, seismic hazard levels
are understated. Regional LiDAR coverage is needed to help identify and assess
these faults.
Multi-Scale Study of Quaternary Deformation in the Sevier Desert Basin
(Central Utah): Clear Lake Fault Zone
Mcbride, J. H., Brigham Young University, Provo, UT, john_mcbride@byu.
edu; NELSON, S. T., Brigham Young University, Provo, UT, steve_nelson@byu.
edu; TINGEY, D. G., Brigham Young University, Provo, UT, david_tingey@
byu.edu; HEINER, B. D., Brigham Young University, Provo, UT, bdh_pete@
yahoo.com
The Clear Lake fault zone is a major region of Quaternary deformation composed
of faults that strike more or less north-south through the Sevier Desert of central Utah, along the western margin of the Colorado Plateau-Basin and Range
Transition Zone. The longest continuously mapped strand is located near the
western flank of the Sevier Desert basin and covers a straight-line end-to-end
distance of over 26 km, making it one of the longest Quaternary faults in the
region. This strand has been implicated to be kinematically related to the Sevier
Desert detachment, which putatively underlies the basin and is thought to have
accommodated crustal extension along the margin of the Transition Zone. In
order to obtain a more complete understanding of the fault zone geometry and
kinematics, we have acquired and/or reprocessed a suite of geophysical profiles
across the western strand of the Clear Lake fault zone. The data span a range of
scales from 200-MHz ground-penetrating radar profiles with vertical resolution
close to a decimeter to reprocessed deep seismic reflection data with a resolution
of 10s of meters. In between these two extremes, we have also acquired horizontally polarized shear (SH) wave reflection profiles and reprocessed previously
surveyed P-wave reflection data acquired by the U.S.G.S. Because the latter were
collected with a common mid-point (cmp) spacing of ~8 m (and a Mini-Sosie
vibrator source) and the former with a cmp spacing of 0.38 m (with a 1-kg mallet
struck horizontally against a solid metal cylinder), we are able to relate coarsely
defined fault deformation features at depth with ultrashallow fine-scale deformation. The integration of the data with various levels of resolution permits nearsurface deformation to be geometrically associated with deeper structures that
are potentially seismogenic. The use of such a multi-scale strategy can be used to
inform seismic hazard estimates for this region.
The Blue Ridge Fault, a Newly Discovered Holocene Fault near Mt. Hood,
Oregon
Madin, I. P., Oregon Department of Geology and Mineral Industries,
Portland, OR; MA, L., Oregon Department of Geology and Mineral Industries,
Portland, OR.
The Blue Ridge Fault was discovered in 2007 when high resolution lidar imagery became available for the area. The fault consists of discontinuous scarps that
stretch NNW for 11-17 km across glaciated terrain north of Mt Hood, a dormant
3400 m volcano in NW Oregon. The scarps are only preserved where the fault
crosses broad gentle ridgetops. The longest and best preserved scarp is almost 5
km long, and cuts lateral moraines from the most recent glaciations, indicating
Holocene age. Numerous scarp profiles extracted from the lidar data all show a
simple scarp, ranging in height from 1.2 to 2.1 m, surface offset ranging from 1.2
to 1.8m and calculated diffusion ages ranging from 2.3 to 9 ka. Two trenches were
excavated across the scarp in 2011 and both exposed till offset by a west-dipping
normal fault. The till in Trench BR-1 is offset vertically by 1.8 m and has a fissure
6 m wide at the foot of the scarp. The bottom of the fissure is filled with loose
cobbles and boulders of platy lava, which are overlain by a wedge of muddy cobble
colluvium containing detrital charcoal fragments. Cobble colluvium with a silty
sandy matrix overlies the muddy colluvium, and also contains detrital charcoal.
It is in turn overlain by sandy silty colluvium that fills a depression that persists
above the fissure and which also contains charcoal. 14C dating of the charcoal is
pending.
North of the Blue Ridge Fault, the Gate Creek Fault was discovered using
the new lidar. The Gate Creek Fault is an east-dipping normal fault with wellpreserved scarps in bouldery talus, till and colluvium. and extends at least 12 km
almost reaching the Columbia River near the community of Carson. The Blue
Ridge Fault is the first Holocene fault scarp to be documented in NW Oregon,
and with the Gate Creek Fault comprises an active fault zone extending over 30
km. The Blue Ridge Fault projects directly beneath Mt Hood, and may play a part
in the location of the Mt Hood vent.
Splay-Fault Origin for the Yakima Fold-and-Thrust Belt, Washington State
Pratt, T. L., U. S. Geological Survey, Seattle, WA, [email protected].
edu
The Yakima fold and thrust belt (YFTB) is a set of anticlines above reverse faults
in the Miocene Columbia River Basalt flows of Washington State. The YFTB
is bisected by the ~1100-km-long Olympic-Wallowa geomorphic lineament
(OWL). There is considerable debate about the origin and earthquake potential
of the YFTB and OWL, which lie near six major dams and a large nuclear waste
storage site. Here I show that the trends of the YFTB anticlines relative to the
OWL match remarkably well the trends of the principal stresses determined from
Linear Elastic Fracture Mechanics modeling of the end of a vertical strike-slip
fault. From this comparison and the termination of some YFTB anticlines at the
OWL, I argue that the YFTB formed as splay faults caused by an abrupt decrease
in the amount of strike-slip motion along the OWL. If this hypothesis is correct,
the OWL and YFTB are likely interconnected, deeply-rooted structures capable
of large earthquakes.
Morphotectonic Segmentation Along the Nicoya Peninsula Seismic Gap,
Costa Rica, Central America
Marshall, J., Geological Sciences Dept, Cal Poly Pomona, Pomona, CA,
[email protected]; MORRISH, S., Cal Poly Pomona, Pomona, CA;
LAFROMBOISE, E., Cal State Northridge, Northridge, CA; BUTCHER, A.,
Cal Poly Pomona, Pomona, CA; RITZINGER, B., Cal Poly Pomona, Pomona,
CA; WELLINGTON, K., Cal Poly Pomona, Pomona, CA; BARNHART,
A., Cal Poly Pomona, Pomona, CA; Kinder, K., Cal Poly Pomona, Pomona,
CA; Utick, J., Cal Poly Pomona, Pomona, CA; Protti, M., OVSICORI,
Universidad Nacional, Heredia, Costa Rica; Gardner, T., Trinity University,
San Antonio, TX; Fisher, D., Penn State University, University Park, PA;
Simila, G., Cal State Northridge, Northridge, CA; Spotila, J., Virginia
Tech University, Blacksburg, VA; Owen, L., University of Cincinnati,
Cincinnati, OH; Murari, M., University of Cincinnati, Cincinnati, OH;
Cupper, M., University of Melbourne, Melbourne, Victoria, Australia.
The Nicoya Peninsula, Costa Rica forms a prominent forearc high along the erosive Middle America convergent margin. This emergent landmass overlies the
seismogenic zone and occupies a seismic gap that last ruptured in 1950 (M7.7).
The edges of both the Nicoya gap and the peninsula’s abrupt shorelines correspond with aftershock limits of recent earthquakes to the north (1992 M7.2) and
south (1990 M7.0). The coincidence of emergent topography and historic rupture
zones suggests persistence of the Nicoya segment through multiple seismic cycles.
Uplift along the Nicoya coast is recorded by emergent Quaternary strandlines,
marine terraces, and incised valley-fill alluvium. Field mapping, surveying, and
isotopic dating reveal uplift variations along the Nicoya margin that coincide
with three contrasting domains of subducting seafloor (EPR, CNS-1, CNS-2).
Variable uplift may reflect along-strike differences in subducting-plate roughness, thermal structure, fluid flow, and seismogenic-zone locking. Based on convergence rate (9 cm/yr) and historic seismicity, the repeat time for large Nicoya
earthquakes is estimated at 50 ±10 years. The most recent event (1950) generated
>1m of coseismic uplift along the central Nicoya coast. Since then, most of this
has been recovered by gradual interseismic subsidence, reflecting strain accumulation toward the next event. While elastic seismic-cycle strain produces high
frequency shoreline fluctuations, long-term net uplift results in gradual coastal
emergence and the growth of topographic relief. We suggest that net uplift along
the Nicoya segment is the product of irrecoverable upper plate shortening associated with the seismic cycle, coupled with tectonic erosion at the trench and
underplating of eroded material at depth beneath the peninsula. The persistence
of the Nicoya segment may result from a feedback between subduction generated
upper plate thickening and increased coupling along the plate interface due to
isostatic loading.
Progress in Linking Earthquakes to Seismogenic Faults in the Lake TahoeTruckee Area, California and Nevada
Reed, T. H., Baylor University, Waco, TX, [email protected];
LINDSAY, R. D., Baylor University, Waco, TX, [email protected]; CRONIN,
V. S., Baylor University, Waco, TX, [email protected]; SVERDRUP, K.
A., University of Wisconsin-Milwaukee, Milwaukee, WI, [email protected]
Preliminary work by Lindsay and Cronin used the Seismo-Lineament Analysis
Method (SLAM; Cronin and others, 2008, Env & Eng Geol 14[3], 199-219) and
focal mechanism solutions from 29 earthquakes in an effort to spatially correlate
earthquakes with the faults that generated them in the northern Lake TahoeTruckee area of California and Nevada. The earthquakes used in the preliminary
study included the largest reported from the area (1966 Truckee M 6.0) and
earthquakes with magnitudes of 3 or greater that occurred between 1980 and
late 2009. Tentative spatial correlation was noted between one or more earthquakes and several known or suspected faults, including the Dog Valley fault zone
(fz), Stateline-North Tahoe fz, West Tahoe-Dollar Point fz, Incline Village fault,
Polaris fault and the hypothetical Agate Bay fault. Two other trends were identified along which seismo-lineaments coincide with geomorphic lineaments that
might have developed during Quaternary displacement along previously unrecognized faults.
The current study includes additional earthquakes, uses improved focalmechanism solutions when available, includes spatial trend analysis of hypocenters for events that lack focal mechanism solutions, utilizes an improved version
of the SLAM computer code operating on higher-resolution DEM data, and references additional known/suspected Quaternary faults compared with the initial study. The initial study used single-event focal locations; the current study is
using relocated foci (e.g., Jordan and Sverdrup, 1981, BSSA 71, 1105-1130). We
also use GPS geodetic data from EarthScope’s Plate Boundary Observatory to
better understand the current horizontal strain field in the North Tahoe area.
Synthesis of preliminary results with prior work indicates that the study area is
subject to earthquakes on N-striking E-dipping normal faults, NW-striking dextral faults and their conjugates–NE-striking sinistral faults.
Ground Penetrating Radar as a Tool for Paleoseismic Site Evaluation: A Case
Study on the Calabasas and Vallecitos Faults of Northern Baja California
Wilson, J. A., University of South Florida, Tampa, FL, [email protected].
edu; WETMORE, P. H., University of South Florida, Tampa, FL, wetmore@
usf.edu; KRUSE, S., University of South Florida, Tampa, FL, skruse@usf.
edu; FLETCHER, J., C.I.C.E.S.E., Ensenada, Baja California Norte, Mexico,
[email protected]; TERAN, O., C.I.C.E.S.E., Ensenada, Baja California
Norte, Mexico, [email protected]; YELIL, R., C.I.C.E.S.E., Ensenada, Baja
California Norte, Mexico.
Excavation of trenches for the purposes of paleoseismic assessment is an expensive
and time intensive exercise that can produce varied results and ultimately destroy
the depositional/paleoseismological record in the trenched area. Geophysical
methods that can remotely characterize potential trench sites without disrupting the geology (e.g. ground penetrating radar (GPR) and shallow seismic experiments) represent an important tool to paleoseismologists in aiding their efforts
to locate productive sites to collect data on past surface rupturing events. The
purpose of this study is to identify potential paleoseismic sites for studying the
slip history and long term slip rate of the Calabasas and Vallecitos members of the
San Miguel-Vallecitos-Calabasas fault zone of northern Baja California, Mexico.
Site selection was limited because the faults primarily cut bedrock and mountainous terrain. The two sites we selected are on alluvial fans where the fault can be
either 1) projected across the fan as in the case of the Calabasas site, near Rancho
Santa Clara or 2) located to within meters based upon a 75 cm high scarp at the
Vallecitos site, near Carmen Serdan. We chose GPR survey sites with a relatively
smooth surface and limited vegetation. A PulseEKKO1000 GPR system with 50,
100 and 200 MHz antennas was used for this study. Transects were oriented parallel and perpendicular to the fault to constrain the offset of stream channels and
the width of the fault zone. Radar data collection along each transect included
those from each of the available antennas, to maximize the amount of data collected and determine which antenna(s) were best suited for the soil profiles in
each area. Our results suggest that the combination of 50 MHz and 100 MHz
antennas is best suited for our application due to the complementary relationship
between the 5-15 meter penetration of the 50 MHz antenna and the increased
near surface resolution provided by the 100 MHz antenna.
Paleoseismic Study of the San Andreas Fault at the Crystal Springs South
Site, San Mateo County, California
Prentice, C. S., US Geological Survey, Menlo Park, CA, cprentice@usgs.
gov; ZACHARIASEN, J., URS Corporation, Oakland, CA, judy.zachariasen@
urs.com; KOZACI, O., Fugro-William Lettis and Associa, Walnut Creek, CA,
[email protected]; SANQUINI, A., Stanford University, Stanford, CA,
[email protected]; WOLF, E., University of California Los Ang, Los Angeles,
CA, [email protected]; SICKLER, R., US Geological Survey, Menlo Park
CA, [email protected]; FEIGELSON, L., US Geological Survey, Menlo Park,
CA, [email protected]; Crankshaw, I., US Geological Survey, Menlo
Park, CA, [email protected]; Rosa, C., San Francisco State University,
San Francisco, CA, [email protected]; Baldwin, J., Lettis Consultants
International, Walnut Creek, CA, [email protected]
We excavated four paleoseismic trenches at the Crystal Springs South site, which
is about 1.2 km southeast of Crystal Springs Reservoir on the Peninsula section
of San Andreas Fault. Our analysis of LiDAR data shows that young fluvial sediments have been deposited across the fault in this location, indicating it is a suitable site to evaluate the fault’s late Holocene behavior. We excavated two trenches
across and two trenches parallel to the fault. The fluvial gravel and overbank
deposits exposed in the trenches are cut by two distinct sets of faults. The younger
set extends nearly to the ground surface, and we interpret these to be the 1906
surface faulting that is buried by post-1906 sediment. The older faults terminate
at the base of a colluvial deposit that is derived from fluvial gravel. This scarpderived colluvium buries faulted, fine-grained overbank sediment that, in turn,
rests on the channel gravel; we interpret the overbank deposit to be the ground
surface at the time of the older earthquake. Preliminary radiocarbon ages suggest
that this surface rupture occurred approximately 800 years BP. We are obtaining additional radiocarbon ages from fragments of fragile stems and grasses to
determine if our preliminary ages from charcoal samples might be significantly
older than the time of sediment deposition, and thus yield an erroneously old
age estimate for the penultimate earthquake. In our fault-parallel trenches, we
recognized a unique channel deposit that has been laterally offset about 7–11 m
by both sets of faults. We plan to more accurately trace this channel across the
fault zone and more precisely measure the amount of slip since its formation. In
addition, new radiocarbon analyses will allow us to refine the age of this channel. Our preliminary results suggest that the 1838 earthquake that affected the
San Francisco Peninsula did not produce surface rupture at the Crystal Springs
South site.
Paleoseismic Results from 2011 SSA Fieldtrip Trench across the Southeastern
Reelfoot Rift Margin
Cox, R. T., University of Memphis, Memphis, TN, randycox@memphis.
edu; VANARSDALE, R., University of Memphis, Memphis, TN, rvanrsdl@
memphis.edu; CLARK, D., Geoscience Australia, Canberra, ACT, Australia,
[email protected]; LUMSDEN, D., University of Memphis, Memphis, TN,
[email protected]; HILL, A., University of Memphis, Memphis, TN,
[email protected]
A trench was excavated across the southeastern Reelfoot Rift margin 20 km
northwest of Memphis, Tennessee, for paleoseismic research purposes and for the
2011 Seismological Society of America national meeting field trip. The trench
was parallel to and 6 m southwest of the Oldham trench of Cox et al. (2006).
In this 2011 trench, faulted alluvial fan stratigraphy and liquefaction deposits
less than 4000 year old were exposed. In contrast to the conclusion of Cox et al.
(2006) of one (and possibly a second) paleoseismic event at the study site, this
new trench revealed evidence for three paleoseismic events. The first event (formation of a small graben) and the second event (sand blow, minor faulting, and
injection of sand dikes) both post-date a paleosol circa 4000 yr B.P. and pre-date
a surficial colluvial soil deposit circa 2000 yr B.P. The third event (minor shallow liquefaction) post-dates a surficial colluvial soil dated at “post-bomb” in this
trench but more accurately dated as 2120 to 1800 yr B.P. at a deeper level in this
soil in the previous Oldham trench. Our second event can be correlated to the
faulting event reported by Cox et al. (2006). On the basis of proximity to the
northeast-trending Mississippi River bluff lineament and of northeast strikes of
structures observed in the trench, we conclude that the seismic source of these
events may be a bluff-lineament fault directly below the trench site, as imaged by
shallow seismic reflection.
Rupture Driving Force for Interlocking Heterogeneous Plate Coupling and the
Recent Megathrust Earthquake
Tajima, F., LMU, Munich, Germany, [email protected]
Leon Knopoff introduced me to the concept of rupture driving force in a heterogeneous plate coupling region. We carried out simple numerical experiments
with a condition that the balance between the stress drop (tectonic stress level
minus dynamic friction) and the fault coupling strength controls rupture propagation. We generated a catalog of “seismic rupture lengths” that show temporal
variations. Later an asperity model characterized the ruptures of large shallow
subduction zone earthquakes in context of plate coupling strength. The asperity model suggested regional variations of the size of the largest earthquakes
among the major subduction zones while it also indicated temporal variations
of rupture extents in the same subduction zones [Ruff and Kanamori, 1980,
1983; Lay and Kanamori, 1981]. The 2011 Tohoku-Oki earthquake (Mw9)
ruptured a large portion of the boundary between the Pacific and the Okhotsk
plates where the coupling was considered weak and represented by sparsely distributed small asperities [e.g., Tajima and Kanamori, 1985 a, b], and such a great
earthquake had not been anticipated. In this region a typical asperity break was
expected to produce an event of about Mw7.5 to lower 8 with a recurrence interval of 30-40 years that is in contrast to the subduction zone which is characterized by a uniform, large asperity and has a record of a megathrust event, e.g., the
1964 Mw9.2 Alaskan earthquake. When the 2011 megathust event took place,
I recalled Leon’s instruction given almost four decades ago. When the rupture
was initiated, the tectonic stress levels should have been close to the maximum
shear strength in the past distinct source areas that were interlocked to produce,
in total, an Mw9 event. We had tested the intuition that a heterogeneous plate
coupling zone could produce an interlocked megathrust event using the simple
numerical experiments. It is still a challenge, however, to detect such conditions
using advanced modern data and techniques.
The Effects of Static Coulomb, Normal and Shear Stress Changes on
Earthquake Occurrence in Southern California
Strader, A. E., UCLA, Los Angeles, CA, [email protected]; JACKSON, D.
D., UCLA, Los Angeles, CA, [email protected]
Deng & Sykes (1997) found a strong correlation between receiver earthquake
location and positive increase in Coulomb stress (∆CFF). Assuming a coefficient
of friction of 0.6, and resolving stresses onto assumed fault planes with uniform orientation parallel to average Pacific-North American plate motion, they
found that only 15% of receiver earthquakes occur in “stress shadows” where the
Coulomb stress change should impede faulting. We extended their study by adding two source earthquakes (Hector Mine, 1999 and El Mayor-Cucupah, 2010),
and calculating the stress changes at the locations of 134 receiver earthquakes
with magnitude 4.4 and greater after 1999. We examined shear, normal and
Coulomb stress, resolving stresses onto five different hypothetical fault planes:
uniformly oriented planes, a weighted average of nearby fault-plane orientations, planes interpolated from smoothed seismicity, and both nodal planes. We
also computed shear, normal, and Coulomb stress histories oriented according
to each fault orientation and tested the effect of total stress change on receiver
earthquake magnitude.
Our chi square test results indicate that, with 95% confidence, receiver
earthquakes do not tend to avoid stress shadows, and that the choice of plane
onto which stress is resolved does not affect the result; however, when the amount
of stress is not taken into account earthquakes tend to occur in areas of increased
Coulomb and shear stress when resolving stress onto uniformly oriented planes.
On average, 39% of earthquakes occur at the time of maximum stress at the event
location, with no significant variation depending on the choice of rupture plane
or type of stress change. We found a correlation between earthquake magnitude
and total stress change at the events’ locations, indicating that modeled Coulomb
stress change may control the size of earthquakes once they nucleate, although it
does not strongly control the location of future earthquakes.
Interpreting Tsunami Source Clustering in Terms of a Branching Process
Geist, E. L., USGS, Menlo Park, CA, [email protected]
Stochastic branching models provide a framework for understanding temporal
clustering of tsunami sources. Analysis of the global tsunami catalog indicates
that the detection rate for tsunamis >1m has been approximately constant since
1890. The empirical distribution of tsunami source inter-event times contains
more short inter-event times than expected from a stationary Poisson process.
Examination of the tsunami source data indicate that there are short sequences
of events in close spatial proximity, but aftershocks make up only a small fraction
of these sequences. A fit to several theoretical distributions is performed using
both chi-square and C-statistic minimization. Of the several clustering distributions that fit the tsunami data, one is derived from an Epidemic Aftershock-Type
Sequence (ETAS) branching model. One of the distribution parameters in the
ETAS-related inter-event distribution is a branching parameter that indicates
the fertility in producing offspring events. Stochastic branching models (e.g.,
Kagan and Knopoff, 1981) have been successful in replicating key characteristics
of earthquake occurrence such as Omori’s Law. The apparent branching parameter associated with tsunamis is significantly smaller than for global earthquakes.
This might be expected, owing to the fact that earthquakes make up the majority of tsunami sources and only earthquakes above a certain threshold trigger
detectable tsunamis. Thus, the true branching parameter maybe higher, but many
offspring events produce tsunamis that are not detectable. Only earthquakes
under certain conditions generate observable tsunamis: if the magnitude is large
enough, if the earthquakes (and seismically-triggered landslides) are beneath the
ocean, and if the earthquakes are not very deep. Interpretation of the tsunami
inter-event distribution is the first step in developing a theoretical branching
model for tsunami sources.
Dominant Roles of a Possible Subducting Seamount in the 2011 Mw 9.0
Tohoku-Oki Earthquake
Duan, B., Texas A&M University, College Station, TX, [email protected]
Effects of subducting seamounts on earthquake ruptures have been revealed by
kinematic inversions of some recent subduction zone events. Stalling rupture
propagation for tens of seconds and producing a large slip patch are commonly
observed features associated with subducting seamounts in these events. In this
study, we use spontaneous rupture models to explore effects of subducting seamounts on dynamic rupture propagation and seismic radiations. In particular, we
investigate roles of a possible subducting seamount in the 2011 Mw 9.0 TohokuOki earthquake. Some kinematic inversions suggest the up-dip rupture in the
event was stalled for about 40 seconds. Although nearly all kinematic inversions
agree that large slip occurred up-dip of the hypocenter in the event, the exact
location of most of large slip (i.e., near the trench vs. near the hypocenter) is under
debate. Resolving this question has important implications for frictional behavior of the shallow portion of the subduction zone. We parameterize a seamount
just up-dip of the hypocenter with higher static friction, lower pore fluid pressure,
and higher initial shear stress than surround areas in our models. Using parallel
computing on supercomputers, we perform a large set of numerical experiments
on spontaneous rupture models for the 2011 event. We find that the seamount
not only stalls the up-dip rupture propagation and produces the largest slip, but
also drives the rupture to penetrate into the likely velocity-strengthening shallow
portion and to propagate into the low stress-drop deep portion on the subduction plane. Significant slip near the trench can occur, but within a limited region
up-dip of the seamount. Failure of the seamount also likely generates strong highfrequency seismic radiations. If the seamount is larger and stronger, it would not
fail and the rupture would be confined within a much smaller region, resulting
an Mw 7~8 event.
Earthquakes with Anomalously Steep Dip in the Source Region of the 2011
Tohoku-Oki Earthquake—Possible Indicators for Enhanced Plate Coupling
Zhan, Z., Caltech, Pasadena, CA, [email protected]; HELMBERGER,
D. V., Caltech, Pasadena, CA, [email protected]; SIMONS, M., Caltech,
Pasadena, CA, [email protected]; KANAMORI, H., Caltech, Pasadena,
CA, [email protected]; WU, W., University of Science and Technology
of China, Hefei, Anhui, China, [email protected]; HUDNUT, K. W., U.
S. Geological Survey, Pasadena, CA, [email protected]; CHU, R., Caltech,
Pasadena, CA, [email protected]; Ni, S., University of Science and
Technology of China, Hefei, Anhui, China, [email protected]; Hetland,
E. A., University of Michigan, Ann Arbor, MI, [email protected];
CULACIATI, F. H. O., Caltech, Pasadena, CA, [email protected]
The 2011 Mw 9.0 Tohoku-Oki earthquake occurred with unusually large slip
(over 50 m) concentrated in a relatively small region with the inferred local stress
drop 5-10 times larger than found for typical megathrust earthquakes. By applying a new high-resolution seismic waveform analysis approach, we determine that
smaller earthquakes occurring in the region that experienced large-slip during
the Mw 9.0 event had steeper dip angles than the surrounding plate interface.
3D SEM synthetic tests with realistic velocity model show that these differences
in dip angles can not be explained by bias due to 3D source-side structure. This
observation is suggestive of a rough plate interface, which in turn may be the
underlying cause for such large and concentrated energy-release. The physical
origin of this local fault topography is uncertain. We note that the dimension of
these smaller earthquakes is comparable to those of small seamounts. The correlation between a rough plate interface and anomalously large coseismic slip underscores the potential importance of estimating fault roughness when estimating
seismic hazard at other subduction zones.
Effects of Subducted Seamounts on Megathrust Earthquakes
Yang, H., Woods Hole Oceanographic Institution, Woods Hole, MA,
[email protected]; LIU, Y., McGill University, Montreal, QC, Canada, yajing.
[email protected]; LIN, J., Woods Hole Oceanographic Institution, Woods Hole,
MA, [email protected]
Large seamounts riding on a subducting plate may play a critical role in controlling the characteristics of earthquakes in a subduction zone, including the maximum sizes of the potential mega-earthquakes. However, it is not well understood
under what conditions subducted seamounts will generate megathrust earthquakes and there is no quantitative analysis so far. Here we show results from a
series of numerical experiments in the framework of rate- and state-dependent
friction law, in which seamount is characterized as elevated effective normal
stress. We find that subducted seamounts do not always cause large megathrust
earthquakes. Rather, subducted seamounts sitting up-dip to the megathrust
nucleation zone act as rupture barrier which may completely stop a coseismic rupture and may lead to smaller earthquake nucleation at the shallow part of the fault
because of stress transfer. More interestingly, we observe that the “barrier” could
turn into an “asperity” that initiates megathrust earthquakes if it is preceded by
a smaller event, owing to the accumulation of shear stress on the seamount. We
conclude that whether the subducted seamounts generate or stop large megathrust earthquakes is critically dependent on their relative locations to the megathrust nucleation zone and the stress history on the fault. Our results have implications for evaluating the effects of general “barriers” on rupture nucleation and
propagation on a heterogenous fault.
Examples of Seismic Behavior in Areas of Seamount Subduction
BILEK, S. L., Earth and Environmental Science Dept., New Mexico Tech,
Socorro, NM, [email protected]; WANG, K., Pacific Geoscience Centre,
Geological Survey of Canada, Sidney, BC, Canada, Kelin.Wang@NRCan-RNCan.
gc.ca
Seamount subduction is a common process in subduction zone tectonics, yet its
relationship to earthquake occurrence and rupture behavior is not completely
clear. In many previous studies, large earthquakes have been spatially linked to
past seamount subduction, even with the uncertainties in defining the spatial
extent of the subducted seamount and uncertainties in earthquake locations.
However, detailed study offshore Japan provides an example of high earthquake
slip away from an area of subducted seamount. Our model suggests a lack of great
or large earthquakes in regions of seamount subduction, allowing it to subduct
nearly aseismically. Deformation and small magnitude earthquakes would be
concentrated within fracture networks in the upper plate. The complex structure
and heterogeneous stresses of this network provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation
and propagation of large ruptures. Here we show examples of this seismic behavior along several subduction zones where seamounts have subducted, such as in
Central America, Java, Japan, and Alaska. We explore detailed seismicity catalogs
where available (such as in Central America) and slip distributions of large earthquakes in other regions. In most of these cases, where moderate magnitude earthquakes have occurred, rupture behavior has been complex, with heterogeneous
patches of moment release.
Cascadia in western North America, Jalisco/Colima in Mexico, and southern
Chile. Striations in the tremor source distribution are apparent in Nankai, as
well as in Mexico and southern Chile, though clear striations are not visible in
Cascadia where tremor zone is the widest in the slab dip direction. Short-term
(< 30 min.) migration directions of tremor sources show high probability near
the subduction direction (along slip) in all regions, while tremor sources tend to
migrate in the trench axis direction (along strike) between 1-10 days. The difference of short- and long-term migration directions can be explained by anisotropic
distribution of small brittle patches embedded in the viscous plate interface as
suggested by Ando et al. (2010). Brittle patches may increase as subduction continues and construct a wide tremor zone, in which striations are obscure if the
subduction direction changes. Thus the geometry and heterogeneity of tremor
zones may provide information on the maturity of the plate interface, and potentially control the characteristics of megathrust earthquakes.
Seismic Strong Motion Array Project (SSMAP) to Record Future Large
Earthquakes in the Nicoya Peninsula Area, Costa Rica
Simila, G., CSU Northridge, Northridge, CA, [email protected];
QUINTERO, R., OVSICORI, Universidad Nacional of Costa Rica, Heredia,
Costa Rica, [email protected]; MCNALLY, K., UC Santa Cruz, Santa Cruz,
CA, [email protected]; LAFROMBOISE, E., CSU Northridge,
Northridge, CA, [email protected]; MOHAMMAD EBRAHIM, E.,
CSU Northridge, Northridge, CA, [email protected].
edu; SEGURO, J., OVSICORI, Universidad Nacional of Costa Rica, Heredia,
Costa Rica.
The seismic strong motion array project (SSMAP) for the Nicoya Peninsula in
northwestern Costa Rica is composed of 10 sites with Geotech A900/A800
accelerographs (three-component) and GPS timing. Since 2006, the main objectives of the array are to: 1) record and locate strong subduction zone mainshocks
[and foreshocks, “early aftershocks”, and preshocks] in Nicoya Peninsula, at the
entrance of the Nicoya Gulf, and in the Papagayo Gulf regions of Costa Rica,
and 2) record and locate any moderate to strong upper plate earthquakes triggered by a large subduction zone earthquake in the above regions. Our digital
accelerograph array has been deployed as part of our ongoing research on large
earthquakes in conjunction with the Earthquake and Volcano Observatory
(OVSICORI) at the Universidad Nacional in Costa Rica. The country wide
seismographic network has been operating continuously since the 1980’s, and
has been upgrade with broad-band seismometers and Episensors. The recording of seismicity and strong motion data for large earthquakes along the Middle
America Trench (MAT) has been a major research project priority over these
years, and this network spans nearly half the time of a “repeat cycle” (~ 50 years)
for large (Ms ~ 7.5–7.75) earthquakes beneath the Nicoya Peninsula, with the
last event in 1950. The major goal of our project is to contribute unique scientific
information pertaining to a large subduction zone earthquake and its related seismic activity in Nicoya. We are now collecting a database of strong motion records
for moderate sized events (M=4.0-4.9) to document this last stage prior to the
next large earthquake. Recent M=5.1 events have occurred in the Gulf of Nicoya
rupture area of the 1990 Mw=7.0 which was associated with the subduction of
a seamount. In addition, we have recorded M=5.0 events in the Central Valley
region and the northern volcanic chain. Relocation solutions in the Nicoya region
define the subducting Cocos plate.
Directions
Short-Term Migration of Deep Tectonic Tremor along Subduction Direction:
Striations Due to Seamounts Subduction?
Ide, S., Dept. EPS, Univ. Tokyo, Hongo, Bunkyo, Tokyo, Japan, [email protected]
3D Depth Migrations from Networks of 2D Seismic Lines for Fault Imaging in
Western Nevada
Frary, R. N., University of Nevada, Reno, NV, rfrary0615@gmail.
com; LOUIE, J. N., University of Nevada, Reno, NV, [email protected];
PULLAMMANAPPALLIL, S., Optim, Inc., Reno, NV, [email protected];
EISSES, A., University of Nevada, Reno, NV, [email protected]
Deep tectonic tremor occurs at various sites worldwide and the source characteristics are spatially heterogeneous, even at small scales. Ide (2010) proposed that
spatial heterogeneities in tremor activity may be controlled by the heterogeneous
frictional properties of the plate interface due to the long-term subduction of
heterogeneous structures such as seamounts, based on the fact that old (>5 Ma)
and current subduction directions correspond with two directions of lineation in
tremor hypocenters in western Shikoku of Nankai. Here I present the results of
similar investigation using tremor catalogs in subduction zones at Nankai, Japan,
Many of the current geothermal power plants in Nevada are found in regimes
that are associated with faults and fault intersections. We have 38 km of seismic
reflection data in a “wide azimuth” network of 16 2D lines of various orientations
intersecting northwest of Pyramid Lake, Nevada. The survey used three vibrators,
and recorded 10-100 Hz sweeps. Source-receiver spacing varied from 17-67 m,
with up to 240 channels live. Preliminary 2D processing with first-arrival velocity optimization shows strong fault-plane reflections and sets of stratigraphic
terminations against faults. We interpret three sets of faults, which appear to
intersect at about 1.3 km depth. Despite the three fault sets each appearing on
tokyo.ac.jp
several lines, only the lines trending perpendicular to strike show direct imaging
of fault-plane reflections. We hypothesize that a 3D depth migration will reveal
additional direct images of the faults. We are testing this with a 3D Kirchhoff
prestack migration of the data from this network of 2D lines. The migration takes
account of lateral velocity changes. This migration should directly image steeply
dipping fault planes at a wider range of orientations than the 2D imaging. The
Pyramid Lake Paiute Tribe will use this information to build 3D hydrogeologic
models for geothermal power development. We also have a network of 8 2D seismic lines in Reno, with north-south and east-west orientations. In collaboration
with Lee Liberty of Boise State and Bill Stephenson and Jack Odum of the USGS,
we collected 15 km of 2D reflection data, using an accelerated weight drop source
and the nees@UTexas minivib I vibrator source. Source-receiver spacing varied
from 3-5 m. Preliminary 2D processing of these data shows stratigraphic terminations against suspected faults at 10-200 m depths. We believe a similar 3D migration of this network of lines will let us interpret additional fault planes in Reno,
which will have significant implications on the seismic hazard there.
Characterization of Shallow S-Wave Velocities across the Tacoma Basin,
Washington State, from SPAC and HVSR Microtremor Analyses
Stephenson, W. J., U.S. Geological Survey, Golden, CO, wstephens@
usgs.gov; ODUM, J. K., U.S. Geological Survey, Golden, CO, [email protected];
DART, R. L., U.S. Geological Survey, Golden, CO, [email protected]; ANGSTER,
S. J., U.S. Geological Survey, Golden, CO; WORLEY, D. M., U.S. Geological
Survey, Golden, CO, [email protected]
Spatial-autocorrelation (SPAC) and horizontal-to-vertical spectral ratio (HVSR)
analyses of microtremor array data, acquired at 20 sites across the Tacoma Basin,
Washington State, were used to characterize S-wave velocities (Vs) as part of
ongoing earthquake hazards investigations in the Puget Lowland. We simultaneously recorded one hour of data with ten Nanometrics Trillium Compact
sensors at each site, using three nested equilateral triangular arrays with sensors
deployed at 33.3-m, 100-m, and 300-m inter-station distances, respectively. Of
the 20 sites, four were acquired in close proximity to seismograph stations of the
local U. S. Geological Survey urban seismic array or Pacific Northwest Seismic
Network. The remaining 16 sites were located within and around the basin, both
to obtain reasonable spatial coverage and to sample representative mapped soil
deposits. We developed one-dimensional Vs models first by forward modeling to
match observed spectral coherency, then we constrained high-impedance boundary depths by jointly modeling SPAC dispersion and HVSR spectral peaks. The
HVSR data generally corroborate the SPAC microtremor results based on good
alignment of theoretical Rayleigh ellipticity and HVSR peak frequencies. Our
preliminary interpretations suggest that soil Vs within the basin generally ranges
between 250 m/s and 650 m/s in the upper 150 m, with Vs as low as 110 m/s in the
upper 10 m at one site in the Tacoma Harbor area that we interpret to be artificial fill over fluvial deposits. At many of the investigation sites, SPAC and HVSR
modeling results can be interpreted confidently to more than 200 m depth, with
depths as great as 300 m obtained at some sites. A high-velocity layer interpreted
between 120 and 340 m depth, with Vs generally between 760 and 1000 m/s, is
present at most of the sites and may represent a common geologic deposit across
the basin.
Time-Resolved Velocity Tomography at Mount Etna Volcano (Italy) during
2000–2008
Barberi, G., I.N.G.V.—Osservatorio Etneo—Sezione di Catania, Catania,
Italy, [email protected]; COCINA, O., I.N.G.V.—Osservatorio
Etneo—Sezione di Catania, Catania, Italy, [email protected];
CHIARABBA, C., I.N.G.V.—CNT—Roma, Roma, Italy, claudio.chiarabba@
ingv.it; DE GORI, P., I.N.G.V.—CNT—Roma, Roma, Italy, pasquale.degori@
ingv.it; PATANÈ, D., I.N.G.V.—Osservatorio Etneo—Sezione di Catania,
Catania, Italy, [email protected]
The continuous volcanic and seismic activity at Mount Etna makes this volcano
an important laboratory for seismological and geophysical studies. We used
repeated three-dimensional tomography (4D tomography) to detect variations
in elastic parameters during different volcanic cycles in the period November
2000–May 2008, that includes several flank eruptions.
The use of a large number of permanent seismic stations and the abundance of local earthquakes, occurring both before and during the eruptions,
guarantee consistent and high-resolution velocity models. First, we performed
a tomographic inversion of the whole data set to define the 3D P-wave velocity
(VP) and the structure of the P- to S-wave velocity ratio (VP/VS). A total of ca.
3, 000 well constrained earthquakes (root mean square time residuals ≤ 0.4 s;
horizontal and vertical hypocentral location errors ≤ 1.5 km; azimuthal gap of
the stations ≤ 180°), ca. 40, 000 P-wave arrivals, and ca. 9, 000 S-wave arrivals
were inverted to model a grid, 2 km by 2 km by 1 km spaced, with the use of
SIMULPS-14 software. Then, on the basis of geophysical and geochemical observations indicating some cyclic recharging and discharging (eruptions) phases, we
inverted different sub-periods to investigate time variations in the elastic parameters.
The observed time changes of velocity-oriented anomalies suggest that
four-dimensional tomography could provide a basis for more efficient volcano
monitoring and short- and midterm eruption forecasting.
Evidence for a Bimaterial Interface along the Mudurnu Segment of the North
Anatolian Fault Zone from P Wave Arrival Times and Polarization Analysis
Bulut, F., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany; BENZION, Y., University of Southern California, Los Angeles, CA; BOHNHOFF,
M., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany.
We present results on imaging the contrast of seismic velocities across the
Mudurnu segment of the North Anatolian Fault Zone (NAFZ) in northwestern
Turkey with two new basic techniques using signals in P waveforms generated
by near-fault seismicity and recorded by near-fault stations. The first technique
uses changes in motion polarity from fault-normal to source-receiver directions
to identify early-arriving fault zone head waves on the slow side of the fault, and
measure the arrival times of the head and direct P waves. The moveout between
the head and direct waves with increasing source-receiver distance along the fault
provides an estimate of the average contrast of seismic velocities across the fault.
The second technique involves measuring travel times from near-fault earthquakes to a pair of stations located at similar distances across the fault, and using
the results to estimate average velocities associated with the different ray paths.
The results from both techniques indicate that the average contrast of P wave
velocities across the Mudurnu segment of the NAFZ is at least 6%, with the south
block being the faster side. The findings provide a basis for deriving improved
event locations, focal mechanisms and estimated shaking hazard associated with
earthquakes on the fault. The analysis techniques can be used in other fault zones
monitored using sparse seismic instrumentation.
The LLNL-G3D Global P-Wave Velocity Model and the Significance of the
BayesLoc Multiple-Event Location Procedure
Simmons, N. A., Lawerence Livermore National Lab, Livermore, CA,
[email protected]; MYERS, S. C., Lawrence Livermore National Lab,
Livermore, CA, [email protected]; JOHANNESSON, G., Lawrence Livermore
National Lab, Livermore, CA, [email protected]; MATZEL, E., Lawrence
Livermore National Lab, Livermore, CA, [email protected]
LLNL-G3D is a global-scale model of P-wave velocity designed to accurately predict seismic travel times at regional and teleseismic distances simultaneously. The
underlying goal of the model is to provide enhanced seismic event location capabilities. Previous versions of LLNL-G3D (versions 1 and 2) provide substantial
improvements in event location accuracy via 3-D ray tracing. The latest models
are based on ~2.7 million P and Pn arrivals that are re-processed using our global
multi-event locator known as BayesLoc. Bayesloc is a formulation of the joint
probability distribution across multiple-event location parameters, including
hypocenters, travel time corrections, pick precision, and phase labels. Modeling
the whole multiple-event system results in accurate locations and an internally
consistent data set that is ideal for tomography. Our recently developed inversion approach (called Progressive Multi-level Tessellation Inversion or PMTI)
captures regional trends and fine details where data warrant. Using PMTI, we
model multiple heterogeneity scale lengths without defining parameter grids
with variable densities based on some ad hoc criteria. LLNL-G3Dv3 (version 3) is
produced with data generated with the BayesLoc procedure, recently modified to
account for localized travel time trends via a multiple event clustering technique.
We demonstrate the significance of BayesLoc processing and the impact on the
resulting tomographic images. This work performed under the auspices of the
U.S. Department of Energy by Lawrence Livermore National Laboratory under
Contract DE-AC52-07NA27344. LLNL-ABS-491805.
Shear Wave Velocity-Depth from IMASW Measurements in Teton County,
Idaho: Updated NEHRP Site-Response Classification and Seismic
Amplification Maps
Turner, J. P., Fugro Consultants, Inc., Golden, CO, [email protected];
PHILLIPS, W. M., Idaho Geologic Survey, Moscow, ID, phillips@uidaho.
edu; ZELLMAN, M. S., Fugro Consultants, Inc., Golden, CO, m.zellman@
fugro.com; O’CONNELL, D. R. H., Fugro Consultants, Inc., Golden, CO,
[email protected]
Interferometric Multichannel Analysis of Surface Waves (IMASW) shallow
S-wave velocity profiles were acquired in July 2011 at 31 new sites in Teton
County, Idaho, to characterize 30-meter average S-wave velocity (Vs30) of sur-
ficial deposits. Vs-depth profiles and existing geologic maps are combined to
develop Vs30 NEHRP Site Class maps to delineate seismic ground shaking hazards in Teton County, located adjacent to the Teton fault, which has an assigned
slip rate of 1.3 mm/yr and characteristic rate of 9.96 × 10-4/yr, the 6th most seismically active Holocene fault in the Intermountain West region. NGA ground
motion equations and the International Building Code commonly use Vs30 to
characterize ground shaking hazards.
IMASW processing provides Vs-depth estimates at 0.5m resolution
allowing calculation of depth-averaged Vs at any interval of interest within the
Vs-depth data constraints. Assessment of individual or composite unit-averaged
Vs profiles provides bases for 1st-order interpretations of unit thickness and bedrock depths using Vs structure which is useful for regional Vs-structure extrapolations, particularly where additional geologic constraints (i.e. borehole, CPT
data, soil profile data) are available. In addition to Vs30, we present a suite of
Vs maps at 5m depth intervals (Vs5, Vs10, ... Vs25). Vs-depth values are applied
to existing surficial geologic maps to make a suite of incremental Vs-depth maps
that illuminate regional subsurface unit geometries where Vs30 alone would not
(e.g. comparing Vs10, Vs15, and Vs20 maps would show 10m thick 200 m/s soil
deposits overlying 1000 m/s bedrock). This is important because unconsolidated
alluvium overlying bedrock can produce strong ground motion amplification. In
addition to illuminating regional soil thickness, Vs-depth maps are used to define
and calculate empirical amplification functions based on characteristic soil and
bedrock Vs and thickness to define zones of strong ground motion amplification.
Virtual Seismic Receiver Array
ALHUKAIL, I. A., Texas A&M University, College Station, TX; IKELLE, L.
T., Texas A&M University, College Station, TX.
We are presenting a new way of improving seismic receiver array responses. By
analyzing the relationship between the covariance matrix of the real sensors of
the seismic receiver arrays and the fourth-order crosscumulants from the same
sensors, we find that artificial sensors can be constructed from the real sensors.
We have called these artificial sensors “virtual sensors”. Furthermore, we have
called the combination of the real and virtual sensors a “virtual seismic receiver
array”. For example, for an equally linear-weighted receiver array of five sensors, a
weighted virtual receiver array of nine sensors can be constructed.
The basic idea behind this concept is that seismic data, like many real-life
signals and processes, are non-Gaussian rather than Gaussian. Therefore, the
fourth-order crosscumulants of the real sensors’ responses are nonzero. In other
words, the analyses of seismic responses are not limited to the classical secondorder statistics tools like covariances. We could also consider higher-order statistics tools like cross-cumulants and auto-cumulants.
This concept has wide applications in geophysics and remote sensing,
including earthquake seismology. The aim could be to further improve the signalto-noise ratio of the recorded seismograms in any particular recording station
by adding additional seismograms to the existing seismograms, creating virtual
recording stations in areas that do not have recording stations, or both.
The mathematical formulation of the virtual seismic receiver array will be
presented, followed by some examples that illustrate the improvement in the seismic receiver array responses, as a result of creating the virtual sensors and adding
them to the real sensors.
Anisotropy of the Mexico Subduction Zone Based on Shear-Wave Splitting
Analysis
Stubailo, I., UCLA, Los Angeles, CA, [email protected]; DAVIS, P.
M., UCLA, Los Angeles, CA, [email protected]
The Mexico subduction zone is an important region to investigate since it is
characterized by both steep and flat subduction, a volcanic arc that appears to
be oblique to the trench, and an excellent data coverage due to the 2005-2007
Middle America Subduction Experiment (MASE). Here, we study the anisotropy of the region using shear-wave splitting measurements. Our goal is to verify
and complement the three-dimensional model of shear-wave velocity and anisotropy in the region constructed using Rayleigh wave phase velocity dispersion
measurements (Stubailo, Beghein, and Davis, submitted to JGR, 2011). That
model contains lateral variations in shear wave velocity consistent with the presence of flat and steep subduction as well as variations in azimuthal anisotropy that
suggest a tear between the flat and steep portions of the slab. Shear-wave splitting
is effective for studying upper mantle anisotropy beneath the receivers and has a
better lateral resolution than the Rayleigh wave phase velocity dispersion measurements. We will report on our shear-wave splitting results and their comparison with the existing model.
The Use of Direct Shear Waves in Quantifying Seismic Anisotropy: Results
from the Northeastern Tibet
Eken, T., Seismology Section (2.4), GeoForschungZentrum (GFZ), Potsdam,
Germany, [email protected]; TILMANN, F., Seismology Section (2.4),
GeoForschungZentrum (GFZ), Potsdam, Germany, tilmann@gfz-potsdam.
de; NUNN, C., Department of Earth Sciences, University of Cambridge, UK,
[email protected]
The distribution of earthquake foci with SKS phase provides a limited azimuthal
coverage with steep incidence angles which is modeling the 3-D orientation of
anisotropic structures. Another type of waves which are theoretically suitable
for splitting analyses is direct shear waves. The most common reason for the rare
usage of teleseismic direct shear waves in splitting analyses is the contamination
by source-side splitting. Thus the processing of direct shear waves is much more
complicated. Here we introduce a direct S wave-based method in the estimation of shear-waves splitting parameters. The method depends on maximizing
the correlation between the seismic traces at reference station (with well-known
SKS splitting parameters) and target stations after correcting the reference station for the receiver side anisotropy effect. The procedure effectively assumes the
same source side anisotropy affecting the two stations for the same seismic event.
Synthetic tests performed using various hypothetical anisotropic models show
sufficient stability of direct S-based splitting parameters with those obtained
from a SKS method even where variability in near surface properties (i.e. thickness and velocity of sediment layer) exists. In the final stage, we applied the reference station technique to the real data obtained from the INDEPTH IV and
ASCENT seismic experiments at the northern margin of Tibet. Average splitting
parameters obtained from the analysis of direct shear waves recorded at possible
station pairs within a range of interstation distance less than 300 km are mostly
similar to the analysis previously carried out using the SKS method. Where differences exist, the resolved shear waves fast polarization azimuths (FPA) indicate
a higher degree of internal consistency for closely spaced stations where we do not
expect clear lateral variation. This is probably due to the much larger number of S
waves available for splitting measurements compared to SKS.
Body Wave Attenuation Heralds Surfacing Magma at Mount Etna (Italy): The
2001–2003 and 2007–2008 Case Studies
Giampiccolo, E., I.N.G.V.—Osservatorio Etneo—Sezione di Catania,
Catania, Italy, [email protected]; DE GORI, P., I.N.G.V.—
CNT—Roma, Roma, Italy, [email protected]; CHIARABBA, C.,
I.N.G.V.—CNT—Roma, Roma, Italy, [email protected]; COCINA,
O., I.N.G.V.—Osservatorio Etneo—Sezione di Catania, Catania, Italy, ornella.
[email protected]; PATANÈ, D., I.N.G.V.—Osservatorio Etneo—Sezione di
Catania, Catania, Italy, [email protected]
During magma emplacement in the shallow crust, transient variations of physical
properties underneath active volcanoes are expected and in a few cases observed.
The predictability of such changes strongly depends on how fast this process
is, compared to our ability to handle geophysical data and consistently resolve
transient anomalies in the physical properties of the medium. The velocity of the
magma upwelling depends on the local conditions of the volcanic conduit and
rheology of the magma. Mt Etna is a perfect natural laboratory to investigate
such issues, due to the almost continuous magmatic activity and the high quality
of seismologic and geodetic data. Our experience with the most recent eruptive
activity at Etna volcano (1989, 1991-1993, 1999, 2001, 2002–2003, 2004, 2006–
2007, 2008–2009) has indicated that most of these eruptions were preceded by
changes in several geophysical parameters, the most evident being: i) increase
of seismicity; ii) deformation and iii) stress field variations. Changes in seismic
attenuation properties in the region of magma intrusion can be also detected, and
the 3D tomography by using a set of earthquakes recorded just before an eruption provides an image of such changes. Thus, to recognize if any change in the
attenuation parameters, QP and/or QS, was produced by intrusive processes at
Mt Etna, we analyzed the seismicity occurred in two different periods (20012003 and 2007-2008) during which three eruptive episodes occurred. Here we
show that seismic attenuation of local earthquakes strongly increases due to the
emplacement of magma within the crust, forecasting eruptions.
Crust and Upper Mantle Structure of Iran from the Simultaneous Inversion of
Complementary Geophysical Observations
Maceira, M., Los Alamos National Laboratory, Los Alamos, NM,
[email protected]; BERGMAN, E. A., University of Colorado, Boulder, CO,
[email protected]; ROWE, C. A., Los Alamos National Laboratory,
Los Alamos, NM, [email protected]; ZHANG, H., University of Science and
Technology of China, Anhui, China, [email protected]
We present a preliminary model of the three-dimensional seismic-structure of the
Iran region obtained via simultaneous, joint inversion of body wave travel time
measurements and gravity observations. The body wave data set is derived from
previous and on-going work on location calibration and includes a large (>1000
events) subset of events that qualify as GT5. The associated arrival time data sets
for these events include many readings of direct crustal P and S phases, as well
as regional (Pn and Sn) and teleseismic phases. The data set has been carefully
groomed to identify and remove outlier readings and empirical reading errors
are estimated for most arrivals from a multiple event relocation analysis. We use
Bouguer gravity anomalies derived from the global gravity model extracted from
the GRACE satellite mission. The gravity data provide information on broadwavenumber shallow density variations and long-wavenumber components of
deeper density structures. To increase the usefulness of gravity data, we entail
high-pass gravity filtering. Filtered gravity anomalies possess highest resolving
power at short wavelengths and thus enhance resolution of lithospheric structure.
We use a simple, approximate relationship between density and seismic velocities
so that both data sets may be combined in a single inversion. Final results of the
simultaneous inversion will help us to better understand one of the most prominent examples of continental collision. Such models also provide an important
starting model for computationally more expensive and time-consuming fully
3D waveform inversions.
Crust and Upper Mantle Structure of the Western US from Simultaneous
Inversion of Surface-Wave Dispersion, Gravity, and Receiver Functions
Steck, L. K., Los Alamos National Laboratory, Los Alamos, NM, lsteck@
lanl.gov; MACEIRA, M., Los Alamos National Laboratory, Los Alamos, NM,
[email protected]; HERRMANN, R. B., Saint Louis University, St. Louis,
MO, [email protected]; AMMON, C. J., Penn State University, University
Park, PA, [email protected]; STEAD, R. J., Los Alamos National Laboratory, Los
Due to excellent data density, the Western United States presents an ideal location for testing advanced imaging methods for Earth structure. Our goal is to
produce a high-resolution image of the crust and upper mantle structure for
this region through simultaneous inversion of surface wave dispersion, gravity
data, receiver functions and, ultimately, other body waveforms. In this paper we
focus on imaging using the first three of these data types. In our initial analysis we will employ grid sizes of 0.5 to 1 degree in latitude and longitude, with
variable layering in depth down to about 200 km. Rayleigh and Love dispersion data come from multiple filter analysis of regional earthquakes, while the
PACES and GRACE campaigns provide the gravity measurements. We complement these datasets with receiver functions from the EarthScope Automated
Receiver Survey (EARS) automated system, which provides data for upwards
of 1500 sites. Initial comparisons suggest that the EARS receiver functions are
consistent with both previously published receiver functions and our spot check
analysis in southern California. However, in some cases they suffer from high
noise levels and excessive reverberation, and implementation of quality control
is needed before including them into the inversion. We also explore noise reduction through receiver function stacking over azimuth and ray parameter bins.
Imaging algorithms for this work are in continued development, and due to the
large data quantity we will employ simple parallelization and other schemes to
improve code performance. Preliminary results for the crust and upper mantle of
the western United States will be presented.
A New 3D P-Wave Velocity Model of Mount Rainier Using Double-Difference
Local Earthquake Tomography
Feenstra, J. P., University of Wisconsin-Madison, Madison, WI, jpfeens@
geology.wisc.edu; THURBER, C. H., University of Wisconsin-Madison,
Madison, WI, [email protected]; MORAN, S. C., USGS CVO,
Vancouver, WA, [email protected]
We have developed a new 3D P-wave velocity model of a 200x150 km area centered on Mount Rainier using a greatly expanded dataset and improved tomography and relocation methods. We integrate local earthquake data collected on
various networks for the last 31 years into a robust dataset so as to develop a more
complete, updated velocity model. Our dataset includes picks from 5, 413 events
recorded by 93 stations of the Pacific Northwest Seismic Network (PNSN),
479 events recorded by 102 temporary stations from the Cascadia Array For
Earthscope (CAFÉ) experiment during 2006-2008, and additional data from
various refraction experiments. We perform double-difference local earthquake
tomography (DD LET) with these data, utilizing absolute and differential times
from catalog and waveform cross-correlation data to precisely relocate earth-
quakes and solve for the velocity model with 4 to 6 km horizontal and 2 to 11 km
vertical grid spacing. Our preliminary model is consistent with some features of
the LET-derived velocity model of the greater Mount Rainier area produced by
Moran et al. (1999; 2000). The two models show similar low velocity anomalies
to depths of ~15 km directly beneath Mount Rainier, which is suspected to reflect
the presence of magma and/or fluids. The new model produces slightly greater
depths for earthquakes occurring beneath the summit, and sharpens seismicity
features in the western Rainier seismic zone, suggesting that this zone is characterized by low velocities down to 10 km depth. The expanded dataset and new
model also better resolve structures below 10 km depth, revealing anomalies not
present in the previous model.
3D Seismic Models and Finite-Frequency vs Ray Theoretical Approaches
Maceira, M., Los Alamos National Laboratory, Los Alamos, NM, mmaceira@
lanl.gov; LARMAT, C., Los Alamos National Laboratory, Los Alamos, NM,
[email protected]; ALLEN, R. M., UC Berkeley, Berkeley, CA, rallen@berkeley.
edu; PORRITT, R., UC Berkeley, Berkeley, CA, [email protected];
ROWE, C. A., Los Alamos National Laboratory, Los Alamos, NM, char@lanl.
gov; OBREBSKI, M., Ifremer, France.
For the last decade, several research institutions have been addressing the Earth’s
3D heterogeneities and complexities by improving tomographic methods.
Utilizing dense array datasets, these efforts have led to 3D seismic models with
the best resolution thus far, but little is done to provide any absolute assessment
of the model uncertainty. Model validation is typically limited to resolution
tests that assume the imaging theory used is accurate and thus only considers the
impact of the data coverage on resolution. We present the results of a more rigorous approach to model validation based on the Spectral Element Method (SEM).
SEM makes no assumptions about the velocity structure and allows computation
of full waveform seismograms with unprecedented accuracy independent of the
theory used to generate the velocity models.
We focus on validating 3D tomographic models for the Western USA
(DNA models) generated using both ray-theoretical and finite-frequency methods in order to get insight into the merit of these two imaging techniques. We
investigate the models performance using different measurement techniques for
different parts of the signal contained in the synthetic seismograms. Preliminary
results for DNA09 and four moderate-size events show no perceptible difference in performance between models obtained with the finite-frequency or raytheory at intermediate periods (50-200s). Differences start to appear, however,
at higher frequencies (<15s). For the four events considered and for the period
band between 50-200s, both finite-frequency and ray-theoretical DNA09 models fit the observations well. The largest correlation coefficient values are for the
horizontal components and smaller epicentral distances; the fit degrades as we go
farther from the event within the model. We are performing farther research to
interpret this results by looking for systematic path or radiation pattern effects.
Shear Velocity Structure of the Iberian Peninsula Using Seismic and Gravity
Observations
Villasenor, A., Institute of Earth Sciences Jaume Almera, Barcelona, Spain,
[email protected]; MACEIRA, M., Los Alamos National Laboratory, Los
Alamos, NM, [email protected]; AMMON, C. J., Penn State University,
University Park, PA.
We present the 3D shear wave velocity structure underneath the Iberian
Peninsula and northern Moroco obtained via simultaneous, joint inversion of
surface-wave dispersion measurements and gravity observations. Surface-wave
dispersion measurements are sensitive to smooth and average seismic shear-wave
velocities; gravity measurements provide broad-wavenumber shallow density
variations and long-wavenumber components of deeper density structures. We
use a simple, approximate relationship between density and seismic velocities so
that both data sets may be used in a single inversion. By combining these two
independent data sets, we obtain a 3D shear-velocity model with increased resolution of shallow geologic structures. We use high-resolution group and phase
velocity maps of Rayleigh waves at periods from 6 to 30s. The maps were obtained
by cross-correlation of ambient noise data recorded by stations of the seismic
broadband IberArray experiment complemented with other permanent stations
from local and regional networks. Gravity observations are extracted from the
global gravity model derived from the GRACE satellite mission as well as gravity anomalies provided by regional studies by Corchette. Preliminary results
show the main structural elements of the Iberian upper crust, including the
Iberian Massif, Alpine orogens and major sedimentary basins. The Pyrenees and
the Iberian Chain are imaged as relatively high velocities, in contrast with the
Betic Cordillera, which is characterized by low velocities. The most prominent
low velocity anomalies in the Iberian Peninsula are related to the Guadalquivir
Basin, the flysch units of the Campo de Gibraltar, and the sediments of the Gulf
of Cadiz. Final results of the simultaneous inversion will help us to better answer
the questions related to the interaction of tectonic plates in the Ibero-Magrebi
area. Such models also provide an important starting model for time-consuming
and fully 3D waveform inversions.
Attenuation and Source Parameters for the Western US Using Automated
Amplitude Measurements
Phillips, W. S., Los Alamos National Laboratory, Los Alamos, NM, wsp@
lanl.gov; MAYEDA, K. M., Weston Geophysical, Berkeley, CA, kmayeda@
yahoo.com; MALAGNINI, L., INGV, Rome, Italy, [email protected]
We inverted for 2-D attenuation, site terms, moments and apparent stress using
over 460, 000 Lg amplitudes recorded by the USArray for frequencies between
0.5 and 16 Hz. Corner frequencies of Wells, Nevada, aftershocks, obtained by
analysis of coda spectral ratios, controlled the tradeoff between attenuation and
stress, while independently determined moments constrained absolute levels.
We used no manually determined arrival times to set amplitude measurement
windows, and relied on quality control procedures to filter out poor data. The
most important of these was fitting 1-D propagation models to regional subsets
of magnitude-based, source-corrected amplitudes. This eliminated noise bursts,
secondary events, and coda measurements that passed our signal-to-noise criteria.
2-D results showed the quality factor, Q, to be low for coastal regions and interior
volcanic and tectonic areas, and high for stable regions such as the Great Plains,
and Colorado and Columbia Plateaus. Q increased with frequency, and the rate
of increase correlated inversely with 1-Hz Q. Apparent stress ranged from below
0.01 to above 1 MPa, with means of 0.1 MPa for smaller events, and 0.3 MPa
for larger events. Stress was observed to be spatially coherent in some areas, for
example, stress was lower along the San Andreas fault through central and northern California, and higher in the Walker Lane, and for isolated sequences such
as Wells. Variance reduction relative to 1-D models ranged from 50% to 90%.
Power-law Q models produced little misfit relative to individual frequency dependent Q models, and performed better than omega-square source models in that
sense. The derived models can be used for broad area source spectra, magnitude
and yield estimation, and, in combination with models for all regional phases,
can be used to improve discrimination, in particular for intermediate bands that
allow coverage to be extended beyond that available for high frequency P-to-S
discriminants.
Teleseismic Imaging of the Eastern Tibetan Plateau
Ge, C., Institute of Geodesy and Geophysics, Chinese Academy of Sciences,
Wuhan, Hubei Province, China, [email protected]; SUN, Y., Massachusetts
Institute of Technology, Cambridge, MA, [email protected]; ZHENG, Y.,
Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan,
Hubei Province, China, [email protected]; XIONG, X., Institute
of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, Hubei
Province, China, [email protected]; TOKSOZ, M. N., Massachusetts
Institute of Techn, Cambridge, MA; ZHENG, Y., Massachusetts Institute of
Techn, Cambridge, MA.
A three-dimensional Kirchhoff depth migration method in local dip angle
domain is proposed to image the Earth’s interior structure using teleseismic
receiver functions. This 3D migration method is useful for imaging complex
structures such as the Eastern Tibetan plateau with sparse station distribution. More than one hundred stations have been deployed between the Yarlung
Tsangpo Suture and the Kunlun faults in different time spans. The distribution
of these stations is not suitable to use common conversion point (CCP) stacking method. Application of our imaging technique to the Eastern Tibertan plateau yields fruitful results as many localized crust and mantle discontinuities are
imaged in this continental collision zone. Our results are helpful to understand
the mechanism of lithospheric mantle shortening and can be used to test competing models of plateau building and deformation.
Upper Mantle Structure around the Mid-Ocean Ridge of the Pacific Ocean
with the Precursors of SS and PP
Sui, Y., Graduate University, Chinese Academy of Sciences, Beijing, China,
[email protected]; ZHENG, Y., Massachusetts Institute of Technology,
Cambridge, MA; ZHOU, Y., Graduate University, Chinese Academy of
Sciences, Beijing, China, [email protected]; SUN, Y., Massachusetts Institute
of Technology, Cambridge, MA.
The distribution of the partial melting around the mid ocean ridge of the Pacific
Ocean is helpful for understanding the dynamic process of mantle convection.
Seismic precursors of PP and SS are important tools for studying the velocity
structures beneath the mid ocean ridge. Beneath the Tonga-Fiji region, plenty of
earthquakes are recorded by the dense network of stations in western US includ-
ing US array stations. In order to get fine precursors related to the seismic interfaces or scatterers, we have used more than 500 earthquakes, with Mb between
5.0 and 6.4 and depths ranging from 100 km to 300 km, and the events have high
signal-to-noise ratios and relatively simple source time functions. The waveforms
from the stations are processed with the 3D Kirchhoff migration method (Zheng,
2007) to retrieve the crustal and upper mantle structures. The primary results
show that there are some seismic interfaces related to the Moho and LAB and
some scatterers which may relate to the partial melting.
Poster Session · Tuesday pm, 17 April · Golden Ballroom
Quick-and-Dirty Earthquake Parametrizations: Why Short Analysis Times
with Big Azimuth Gaps suffice for Initial Tsunami Warning Operations
SARDINA, V. H. R., Pacific Tsunami Warning Center, NOAA, NWS, Ewa
Beach, HI, [email protected]; BECKER, N. C., Pacific Tsunami
Warning Center, NOAA, NWS, Ewa Beach, HI, [email protected];
WEINSTEIN, S. A., Pacific Tsunami Warning Center, NOAA, NWS, Ewa
Beach, HI, [email protected]; FRYER, G., Pacific Tsunami Warning
Center, NOAA, NWS, Ewa Beach, HI, [email protected]; KOYANAGI,
K., Pacific Tsunami Warning Center, NOAA, NWS, Ewa Beach, HI, Kanoa.
[email protected]; WANG, D., Pacific Tsunami Warning Center, NOAA,
NWS, Ewa Beach, HI, [email protected]; WALSH, D., Pacific Tsunami
Warning Center, NOAA, NWS, Ewa Beach, HI, [email protected];
Mccreery, C., Pacific Tsunami Warning Center, NOAA, NWS, Ewa Beach,
HI, [email protected]
The two US tsunami warning centers (TWCs) rapidly analyze earthquakes in
real time to assess their tsunami-generating potential before issuing initial warning messages based on location and magnitude criteria. To evaluate the quality of
the TWCs’ fast earthquake parametrizations we compiled and analyzed 6, 031
observatory messages issued by the TWCs from 2003 to 2011. We then crossvalidated the TWCs hypocentral locations with those issued by the USGS’s
National Earthquake Information Center (NEIC), and the TWCs’ earthquake
magnitudes with the moment magnitudes released by the Global Centroid
Moment Tensor (GCMT) project. The results show that both, hypocenter locations and magnitude values remain rather insensitive to the maximum azimuth
gap incurred in the earthquake parametrizations. The average lateral offsets
between the TWCs’ and NEIC’s epicenters remain under 60 km, well within the
range acceptable for tsunami warning purposes, even for azimuth gaps as wide
as 240 degrees. Likewise, making use of additional processing time to include
more than five seismic stations in the analyses does not appear to significantly
improve the accuracy of the preliminary magnitude estimates that, on average,
do not vary from GCMT values by more than 0.2 magnitude units for azimuth
gaps as wide as 280 degrees. Given the TWC’s mission to protect lives and property, these findings make it difficult to justify longer seismic data analyses that
use the already limited time available for coastal evacuations, particularly in the
earthquake’s near field. Furthermore, the results demonstrate that current procedures at the US TWCs routinely generate quick earthquake parameters with
sufficient accuracy for most initial tsunami warning operations. Some regional
seismic observatories could consider applying the TWCs’ methods to expedite
the release of their preliminary earthquake parameters as well.
Caltech/USGS Southern California Seismic Network: Recent Upgrades of
Instrumentation and Operational Capabilities
Crummey, J., California Institute of Technology, Pasadena, CA, jcrummey@
gps.caltech.edu; BHADHA, R., California Institute of Technology, Pasadena,
CA, [email protected]; DEVORA, A., California Institute of Technology,
Pasadena, CA, [email protected]; GUIWITS, S., California Institute of
Technology, Pasadena, CA, [email protected]; JOHNSON, D., California
Institute of Technology, Pasadena, CA, [email protected]; WATKINS,
M., California Institute of Technology, Pasadena, CA, [email protected].
edu; HAUKSSON, E., California Institute of Technology, Pasadena, CA,
[email protected]; Thomas, V., US Geological Survey, Pasadena,
The Caltech/USGS Southern California Seismic Network (SCSN) consists
of more than 335 stations, including 175 broadband, 100 short-period, and 55
strong motion stations. In addition the SCSN imports real-time data streams
from more than 100 partner stations. The SCSN records and provides rapid
notifications for more than 15, 000 local earthquakes per year. We are actively
improving the data quality, data latency and network diversity for the SCSN by
improving instrumentation and operational procedures. The five projects that are
in progress include the rehabilitation of our STS-1 seismometers, development of
auto-recentering scripts for broadband seismometers, modification and deployment of the ISTI RockToSLink module, automated data recovery, and installation and operation of cell modems for real-time telemetry. The aging STS-1 seismometers are being refurbished in collaboration with the Albuquerque Seismic
Lab (ASL). We have been able to identify and repair problems with sensors, cables
and Feed Back Electronics (FBE). This effort has enabled us to keep these aging
seismometers running and generating high quality broadband data. The automatic re-centering script is being developed to automate the re-centering of sensors. With this added capability we are able to keep broadband sensors on scale as
well as to notify the Earthquake Early Warning (EEW) algorithms before re-centering, avoiding false triggering of the EEW system. We have modified the ISTI
RockToSLink module to lower the latency of data received from Basalt dataloggers. For the Q330/Baler44 stations we are developing an automated data recovery process to minimize gaps in the waveform data. The addition of cell modems
into our network has increased telemetry diversity and prepared us for the loss of
aging communications technology such as frame relay.
A Systematic Investigation of the “Nucleation Phase” of Large Global
Earthquakes Using Broadband Teleseismic Data
BURKHART, E. T., University of California, Santa Barbara, Santa Barbara,
CA, [email protected]; JI, C., University of California, Santa Barbara, Santa
Barbara, CA, [email protected]
Earthquake’s dynamic motion starts suddenly but often with an interval of relatively weak motion, which was coined the “nucleation phase” by Ellsworth and
Beroza (1995). Ellsworth and Beroza (1995, 1996) found that the nucleation phase
existed in the near-source records of all 41 earthquakes they studied, spanning a
magnitude range from M 1 to M 8. On average the nucleation phase accounts for
~0.5% of the total moment but exists for about 1/6 of the total duration. Ji et al.
(2010) investigated the initiations of 19 Mw 8.0 earthquakes since 1994 using a
new approach applied to teleseismic broadband data. They found that about fifty
percent of the earthquakes had a weak initiation phase; the durations of the weak
initiation phases are consistent with the dataset based on near-source records in
terms of their correlation with final seismic moments. We use the same method
to study the rupture initiation of 60 Mw 7.5-8.0 earthquakes since 1994. Our
preliminary result indicates that the rate at which weak nucleations are observed
is about the same as that for Mw 8.0 earthquakes. Interestingly we more often
observe the weak nucleation phases in strike-slip earthquakes than thrust or normal earthquakes. Here we will further estimate magnitude of nucleation phases
by waveform matching the stacked waveforms with 1D synthetic seismograms.
Rapid Estimation of Tsunami Waveheights after Large Earthquakes: Examples
from the 2011 Tohoku and 2010 Maule Earthquakes
Thio, H. K., URS Corporation, Los Angeles, CA, [email protected];
POLET, J., Cal Poly Pomona, Pomona, CA, [email protected]
We have developed a system for tsunami early warning at regional and larger
distances which leverages existing capabilities in automated rapid moment tensor inversions and a library of pre-computed tsunami Green’s functions that was
originally developed for tsunami hazard analysis. An early version of this method
was applied immediately after the 2011 Tohoku earthquake, where the automated research CMT system yielded a solution with a moment magnitude of 8.9
within 23 minutes after the origin time using data from worldwide seismic stations. Based on the CMT results, and an existing library of tsunami Green’s functions, we predicted shoreline tsunami waveheights for a suite of rupture models
consistent with the CMT solution within three hours, even though the process at
the time was not automated or even streamlined. In an automatic environment,
the predicted waveheights can be made available within a few minutes after the
CMT is determined.
Because of the rapid waveheight computation, we are able to produce a distribution of waveheights for any point along the coast, using a range of geometries, dimensions and their probabilities derived from scaling relations and consistent with the CMT. Initially, these distributions can be very wide, but they can
subsequently be narrowed down as more constraints are added to the earthquake
source model. The automated CMT system uses a jack-knifing method to explore
the range of plausible solutions, and this can automatically be extended to the
tsunami waveheights as well. We thus produce a range of predicted tsunami waveheights that are consistent with the uncertainties in the initial CMT parameters,
variability in rupture location and scaling, and which can be efficiently updated
as better constraints become available.
We will discuss the application of this method to the 2011 Tohoku and
2010 Maule earthquakes, and potential developments, which make use of backprojection methods to further improve the response times.
Radial Decay of Coseismic Displacement Amplitudes from Thrust
Earthquakes
Marrett, R., University of Texas at Austin, Austin, TX, marrett@mail.
utexas.edu
The most widely used models for understanding spatial patterns of coseismic
ground displacements are based on elasticity theory. The models provide important tools for constraining source parameters and quantifying mechanical interaction among faults. Elasticity predicts that the amplitude of coseismic displacement decreases with distance from the source as a power law. However, data from
large to moderate thrust events show exponential decay of displacement with
distance, from tens to more than a thousand kilometers.
Using published GPS data from a variety of thrust earthquakes, I have
ignored the azimuths between source and receiver, as well as the directions of
coseismic displacement. These parameters are critical to establishing earthquake
focal mechanisms, but are unnecessary to quantify radial decay patterns of displacement amplitude. A simple three-parameter model (assuming known slip
centroid) is sufficient to describe the spatial pattern of coseismic displacement
decay. Two parameters characterize exponential decay of data from proximal
stations. Physically, the parameters represent coseismic displacement at the centroid and the characteristic distance for exponential decay (in part, a function of
rupture area), and appear to be useful for estimation of moment magnitude. The
third parameter represents 1/R decay from distal stations.
A mechanical explanation for observed exponential decay of coseismic displacement with radial distance is that it reflects coupling of an elastic seismogenic
zone with underlying viscous rock. A model for cyclic episodes of fault slip in such
material predicts exponential decay (Turcotte and Schubert, 1982). Due to longterm viscous flow, differential stress in the viscous lower crust is minimal at the
time of an earthquake. Although short-term behavior might be approximately
elastic, the lower crust dissipates coseismic energy rather than releasing it.
Rapid Determination of Earthquake Source Parameters Using an Earthquake
Search Engine
Zhang, J., Univ. Science and Technology of China, Dept. of Geophysics,
Hefei, Anhui, China, [email protected]; ZHANG, H., Univ. Science and
Technology of China, Dept. of Geophysics, Hefei, Anhui, China, zhang11@ustc.
edu.cn; CHEN, E., Univ. Science and Technology of China, Dept. of Geophysics,
Hefei, Anhui, China, [email protected]; ZHENG, Y., Univ. Science and
Technology of China, Dept of Computer Sciences, Hefei, Anhui, China, xiaoe@
mail.ustc.edu.cn; KUANG, W., Univ. Science and Technology of China. Dept of
Geophysics, Hefei, Anhui, China, [email protected]
We have developed an earthquake search engine that integrates seismology
and computer sciences to search for similar earthquakes from a large database.
Advanced computer image search technology allows finding the best seismogram
matches in seconds among billions of events in database. Our database includes
historic earthquake events with known source solutions and also synthetic seismograms calculated with a global earth model for a large range of earthquake
source parameters. When an earthquake takes place, recorded seismograms are
fed into the search engine automatically, and similar real and theoretical earthquakes are found in a couple of seconds from database by applying the multiple
randomized k-d tree algorithm developed in computer sciences. From the search
results, we can immediately obtain the earthquake source parameters such as epicenter distance, depth, focal mechanism, and magnitude of the entry event. With
search results from three or more seismic stations, we are also able to determine
the earthquake location as well. We demonstrate the approach and the benefits
of the method by searching an earthquake that took place on 26 December 2004
in the Sumatra region using this system. This earthquake search engine can be
routinely applied in any seismic station for real-time earthquake monitoring as a
supplementary system to current standard practice.
Rapid Estimation of Slip Models for Large Shallow Earthquakes using
Teleseismic P Waves
Mendoza, C., Centro de Geociencias UNAM, Juriquilla, Queretaro,
Mexico, [email protected]; HARTZELL, S., U.S. Geological
Survey, Denver, CO, [email protected]; BENZ, H., U.S. Geological Survey,
Denver, CO, [email protected]; HERRMANN, R., St. Louis University, St. Louis,
MO, [email protected]
We have developed a single-step, finite-fault (SSFF) inversion procedure to
recover preliminary models of subsurface slip for large (Mw > 6.5) shallow
(h < 50 km) earthquakes within 5 minutes following the realtime collection of
broadband teleseismic P waves. The analysis is based on the finite-fault inversion
scheme of Hartzell and Heaton (1983) but uses an automatically-derived stabilization constraint that spatially smooths the fault slip and minimizes the seismic
moment to identify the simplest solution that fits the observed records. The SSFF
procedure uses a database of teleseismic P-wave Green’s functions precomputed
at 1-deg distance and 1-km depth intervals using the AK135 velocity model. For
rapid response, we use the moment magnitude of the earthquake to define the
fault dimensions, the initial dislocation duration, and the length of record to
invert. A rectangular fault is assumed with orientation based on the earthquake
source mechanism. The rake can be fixed or allowed to vary as part of the solution vector. The fault is divided into 200 subfaults with the hypocenter placed at
the center of the fault and synthetic waveforms constructed for each subfault at
the teleseismic stations assuming a specified rupture velocity. The synthetics form
the coefficient matrix of a linear system that is solved to identify the amount of
fault slip required to reproduce the data. In the inversion, the dislocation duration is discretized to allow for a variable rise time. The amount of spatial smoothing and moment minimization to apply is calculated from the average absolute
value of the elements in the coefficient matrix using a linear relationship previously observed in the analysis of several large earthquakes using the Hartzell and
Heaton (1983) formulation. Application of the SSFF procedure to several large
worldwide earthquakes yields preliminary slip models similar to the finite-fault
solutions obtained by the USGS/NEIC using body- and surface-wave data.
Developments in Earthquake Early Warning at UCB: CISN ShakeAlert
Hellweg, M., UC Berkeley Seismological Laboratory, Berkeley, CA, peggy@
seismo.berkeley.edu; ALLEN, R. M., UC Berkeley Seismological Laboratory,
Berkeley, CA, [email protected]; BROWN, H., UC Berkeley Seismological
Laboratory, Berkeley, CA, [email protected]; HENSON, I., UC
Berkeley Seismological Laboratory, Berkeley, CA, [email protected];
KONG, Q., UC Berkeley Seismological Laboratory, Berkeley, CA, kongqk@
berkeley.edu; KUYUK, S., UC Berkeley Seismological Laboratory, Berkeley,
CA, [email protected]; NEUHAUSER, D. S., UC Berkeley Seismological
Laboratory, Berkeley, CA, [email protected]
As part of a USGS-funded project, UC Berkeley’s Seismological Laboratory
(BSL) is participating in the implementation and testing of a prototype, endto-end earthquake early warning system using reatime data from the California
Integrated Seismic Network (CISN), the CISN ShakeAlert system. Having a
alert of shaking just before it starts can improve resilience if the recipient of the
alert has developed plans for responding to it and acts on them. The end-to-end
processing system is currently operational. Alerts are being received by scientists,
and we are working with a suite of perspective users from critical industries and
institutions throughout California, such as the Bay Area Rapid Transit District,
to identify information necessary for ShakeAlert users, as well as delivery mechanisms, procedures and products. For the entire CISN ShakeAlert system, and for
the BSL elements in particular, we continue to evaluate and improve reliability of
alert information and the speed with which they are produced. For earthquakes
in the Bay Area, initial alerts are available an average of 15 s after the origin time.
Over the past 6 months, 75% of the events with M>3 have been detected, and
ElarmS has an overall false alarm rate of 20%. We have taken the first steps to
include information from GPS data streams and to improve the estimation of
event magnitudes and finite rupture for large earthquakes.
Seismic Source Studies at the Berkeley Seismological Laboratory
Dreger, D. S., Berkeley Seismological Laboratory, Berkeley, CA, dreger@
seismo.berkeley.edu; GUILHEM, A., Lawrence Berkeley National Laboratory,
Livermore, CA, [email protected]; BOYD, O. S., Berkeley
Seismological Laboratory, Berkeley, CA, [email protected]; CHIANG,
A., Berkeley Seismological Laboratory, Berkeley, CA, [email protected];
HELLWEG, M., Berkeley Seismological Laboratory, Berkeley, CA, peggy@
seismo.berkeley.edu
Characterization of seismic sources is an important research effort at the Berkeley
Seismological Laboratory, with new tools and results in several directions. We
have refined the GridMT method to account for extended sources using quasifinite-source Green’s functions. Application of the approach to the 11 March
2011 Tohoku-oki earthquake indicates that it is possible to autonomously detect,
locate and obtain robust estimates of seismic moment within 8 minutes of the
origin time using streaming waveform data. We are now implementing the methodology to detect and characterize great earthquakes in the Mendocino region
in realtime processing. Continued analysis of seismic moment tensors for earthquakes occurring at the Geysers geothermal field indicate that some events have
statistically significant non-double-couple components. In several cases, the
sources have volumetric terms indicating a complementary tensile process. We
present the analysis of these events, and the methods we have developed to assess
solutions stability, uncertainties and significance. We are developing regional
distance seismic moment tensor methods for nuclear explosion discrimination
and have investigated the free-surface effects on recovery of the seismic moment
tensor and scalar seismic moment. Finally, the Berkeley Seismological Laboratory
has implemented automated seismic moment tensors as part of our joint monitoring systems. We have updated our analyst interface to allow for analysis of full
moment tensor solutions, and we are investigating methods for utilizing both
weak motion velocity for moderate earthquakes, and strong motion acceleration
data streams for large earthquakes.
Tohoku-Oki Tsunami Simulations Reveal Importance of Sophisticated
Seismic Source Parameters
Watts, P., Applied Fluids Engineering, Inc., 6216 E. PCH #237, Long Beach,
CA, 90803, [email protected]
Detailed tsunami simulations of the 2011 Tohoku-Oki tsunami carried out
with varied tsunami sources reveal a wide range of potential skill and accuracy.
More sophisticated tsunami sources do a markedly better job of reproducing
tsunami observations and records. All tsunami simulations are carried out with
the well validated 4th order Boussinesq wave model Geowave. The Boussinesq
model retains seismic source information in the wave physics of propagation
and inundation. The simulations involve 50 m uniform grids at fishing villages,
and 10 m uniform grids at the Fukushima Daiichi nuclear power plant. These
locations provide the relevant observations and records for a tsunami source to
reproduce, assuming a Boussinesq model is used. A sensitivity analysis shows dramatic simulation differences between: 1) Typical tsunami science moment tensor source (a rectangular fault), 2) Slip patch reconstruction of coseismic source
(semi-realistic), 3) GPS and seismic inversion based coseismic source (Simons et
al.), and 4) Dynamic, time sensitive GPS and seismic source (Avouac and Wei).
The first source gives poor results when compared to observations, and is sensitive
to many source factors, including hypocenter depth, water depth, fault length,
etc. The fourth source reproduces observations sufficiently well to issue highly
accurate tsunami warnings. Seismic source details matter. GPS measurements
constrain the seismic source location and improve the seismic source for large
subduction zone events. The simplistic tsunami models and seismic sources from
the recent past do not contain sufficient information for accurate tsunami warnings. Without a substantial upgrade, real time tsunami simulations and accurate
tsunami warning systems are flawed from the outset. More instrumentation is
needed to distinguish smaller earthquake magnitude events, more unusually rupture characteristics (e.g., soft sediment or splay faults), and landslide tsunamis.
What about the Influence of the Nature of the Pore Fluid on Long-Term or
Triggered Faulting Behavior?
Fitzenz, D. D., Universidade de Evora-CGE, Evora, Portugal, delphine@
uevora.pt; CROVISIER, M., Universidade de Evora-CGE, Evora, Portugal,
[email protected]; MAURY, V., IFPEN School / Maury consultant, Paris
/ Idron, France, [email protected]
Gas may appear in a fault zone through dilatant deformation of the zones adjacent to the core fault (Kuo, 2006 ), due to fluid depressurization and degassing.
Other sources of gas e.g., mantle degassing, devolitization of coal or other organic
matter during frictional sliding (O’Hara et al., 2006), may be remote, and diffuse
through a fracture network, or local.
The mechanisms that have been investigated to predict the impact of these
compressible phases (whether supercritical or gas) on faulting are 1) those related
to fluid flow and the effects of a rapid access of a fault to a source of overpressured
fluids on effective stress and failure criterion (Miller et al., 2004), and 2) dynamic
pressurization.
However, the presence of compressible pore fluids also impacts the response
of the porous medium to stress changes, i.e., the poroelastic and poroplastic
effects. Maury et al. 2011 presented both the case of the appearance/disappearance of a compressible phase in the pore fluid, and its effects on the loading path
in the framework of a Coulomb failure criterion, and the impact of the fluid compressibility itself on the size of the instability domain in the framework of an
interface Cam-Clay poroplastic behavior.
If indeed important, first order faulting characteristics, such as apparent
strong fault versus apparent weak fault, or stable versus unstable faulting, may be
controlled by pore fluid compressibility, more information is needed.
We would therefore like to point to the need for an increased communication namely between earthquake seismologists and modelers and communities
who can address the following questions: 1) can we detect the spatial variability in
fluid compressibility in fault systems (in various environments and depth-ranges:
for hydrothermal, geothermal, CO2 sequestration, crustal faults), 2) can we con-
strain the proposed end-cap interface models in the lab using samples from fault
cores, including the effect of pore fluid compressibility?
Earthquake Scaling Relationships Estimated from a 16 Year Catalog of
Published InSAR Studies
Funning, G. J., University of California, Riverside, CA, [email protected];
WESTON, J., University of East Anglia, Norwich, UK, [email protected];
ELLIOTT, J., University of Oxford, Oxford, UK, [email protected];
FERREIRA, A. M. G., University of East Anglia, Norwich, UK, a.ferreira@uea.
ac.uk; RICHARDS-DINGER, K. B., University of California, Riverside, CA,
[email protected]
The question of how moment release in earthquakes scales to other source parameters, such as fault length and average slip, is a long-standing controversy in
earthquake science. The question has wide practical implications (e.g. in estimating seismic hazard due to known unruptured fault segments) and also theoretical implications (e.g. in the debate about self-similarity of earthquakes across all
magnitudes). Here we use a catalog of earthquake source parameters derived from
published InSAR earthquake studies to address this question. InSAR data may
be considered preferable for this purpose over traditional sources such as aftershock data and seismic inversion models, as several key source parameters—in
particular, the fault length—can in many cases be measured directly from the
data.
We have compiled fault length, width, average slip and seismic moment
estimates from published studies of over 70 individual earthquakes. Using linear
regressions, we find the best best-fitting trends and their uncertainties between
these quantities, treating all events together and also separately by mechanism
type (strike-slip, thrust and normal). Our results suggest: 1) The best-fitting single scaling relationship between moment and length has a slope of 1.76 in log-log
space. This is more consistent with the ‘L model’ scaling which predicts a slope
of 2. This relationship does not vary significantly with earthquake mechanism.
2) The data do not require a change of scaling regime around M7.2 as suggested
previously (e.g. Romanowicz, 1992). 3) Ratios of average slip to length fall broadly
into two fields—high slip-to-length events (1–3 × 10^-4) and low slip-to-length
events (0.4–4 × 10^-5). The low slip-to-length category includes subduction
earthquakes and events occurring on strike-slip faults with fast slip rates (> 2
mm/yr); the high slip-to-length category includes several blind faulting earthquakes, typically occurring on faults with low slip rates (<2 mm/yr).
The Impact of Space-Geodetic Data on California Earthquake Risk
Nyst, M., RMS, Inc., Newark, CA, [email protected]; MAK, L., RMS, Inc,
Newark, CA.
Traditionally, Probabilistic Seismic Hazard Assessment (PSHA) studies have
been based on earthquake and paleoseismic observations. Recent research focuses
on the inclusion of space-geodetic observations (like GPS and INSAR) to contribute to estimates of slip rates on active faults, but also to complement presentday crustal deformation rates that are purely based on earthquake data.
California is monitored by a dense network of GPS stations, producing a
high resolution velocity field of the Earth’s surface. One way of translating this
velocity field into crustal deformation parameters that can be used in PSHA is
the ‘block model’. In the block model the crust is parameterized as a number of
elastically deforming blocks, bounded by surfaces that represent the major active
faults. A number of these block models has been published for California. Based
on differences in underlying methods and assumptions they produce significant
differences in terms of fault slip rates, geometry of the building blocks and location of the faults.
This study focuses on the impact of the inclusion of block models on earthquake risk in California. Earthquake risk combines earthquake hazard and
building vulnerability to estimate the probable damage and loss of property and/
or life. We look at the impact of space-geodetic data on risk by comparing loss
results from traditional risk models, based on earthquake and geology data, with
loss results from block models. In addition, we compare risk results from the various block models to develop an idea of the sensitivity of damage and loss to the
differences in underlying assumptions.
Earthquake Forecasts for California Based on Adaptive Space-Time
Smoothing of Seismicity and Rate-and-State Friction
Helmstetter, A., Universite Joseph Fourier, CNRS, Grenoble, France,
[email protected]; WERNER, M. J., Princeton University,
Princeton, NJ, [email protected]
We present new methods for time-independent and time-dependent earthquake
forecasting, based on adaptive space-time smoothing of seismicity. The models
exclusively use modern high-quality earthquake catalogs as input data, providing
objective, simple, testable and yet skillful benchmarks against which other forecasts can be tested that derive from models that might use less certain or systematic input data. In our models, past earthquakes are smoothed in space and time
using adaptive Gaussian kernels. The bandwidths in space and time associated
with each event are a decreasing function of the seismicity rate at the time and
location of each earthquake, in order to obtain higher resolution in space-time
volumes of intense seismicity and a smoother density otherwise. For time-independent forecasts, we take the long-term rate in each cell as the median value of
the temporal history of the (smoothed) seismicity rate in this cell. When tested
on Californian data, this model is slightly more skillful than a previous method
based on spatial smoothing of declustered catalogs (Helmstetter et al., 2006,
2007; Werner et al., 2011) and is much simpler (no declustering, fewer parameters). To generate time-dependent forecasts, we assume that the seismicity rate in
the future will be constant in time and equal to its present (smoothed) value. The
method’s 24h forecasts for California are almost as skillful as the ETAS model’s
forecasts (Helmstetter et al., 2006; Werner et al., 2011). Finally, we developed
a (slightly) more physical model based on the rate-and-state model of Dieterich
(1994), which we use to extrapolate the rate beyond its present value, without
reverting to stress calculations. At least two major uncertainties exist in the input
data: the short duration of high-quality catalogs and the incomplete recording of
small (M<2) earthquakes. We investigate the latter by computing the predictive
skill of the models for different input magnitude thresholds.
A Stochastic Earthquake Source Model Combining Fault Geometry, Slip
Rates, and Smoothed Seismicity: California
Hiemer, S., Swiss Seismological Service, Institute of Geophysics, ETH
Zurich, Zurich, Switzerland, [email protected]; JACKSON, D. D.,
Department of Earth and Space Sciences, UCLA, Los Angeles, CA, djackson@
ucla.edu; WANG, Q., AIR-Worldwide Corporation, Boston, MA, qiwang@
stat.ucla.edu; KAGAN, Y. Y., Department of Earth and Space Sciences, UCLA,
Los Angeles, CA, [email protected]; WOESSNER, J., Swiss Seismological
Service, Institute of Geophysics, ETH Zurich, Zurich, Switzerland, jochen.
[email protected]; ZECHAR, J. D., Swiss Seismological Service, Institute
of Geophysics, ETH Zurich, Zurich, Switzerland, [email protected].
ch; WIEMER, S., Swiss Seismological Service, Institute of Geophysics, ETH
Zurich, Zurich, Switzerland, [email protected]
We present a stochastic forecast model based on the frequency-magnitude distribution, slip rates on major faults, long-term strain rates, and source parameter
values of instrumentally-recorded and historic earthquakes. The basic building
blocks are two pairs of probability density maps. The first consists of smoothed
seismicity and weighted focal mechanisms of past earthquakes. The second pair
contains the same information for faults. We prescribed rectangular fault elements, computed moment rate tensors from their area, slip rate, and orientation,
then smoothed their locations and interpolated their focal mechanisms. We then
simulate a “stochastic event set” for hazard calculations and model testing.
Random magnitudes are drawn from a tapered Gutenberg-Richter.
Random epicentral locations of spontaneous events are assigned from a magnitude dependent probability density map based on past earthquakes and strain
rate. Moment tensors are then estimated as weighted averages of nearby earthquake and fault moment tensors. The length, displacement, and width are determined from the magnitude using a simple scaling relationship.
We assign times to the spontaneous events from a negative-binomial distribution, and from that catalog simulate locations, times, and focal mechanisms
for triggered events using a clustering model. We subdivide the rupture length of
each simulated event into 15 km intervals, divide its total seismic moment into
proportional intervals, and treat the total as a simultaneous rupture of each of the
fault patches. This avoids treating a large event as a single point source. Locations
of all spontaneous sources, including the centers of fault patches, are smoothed
with a magnitude-dependent spatial kernel to give a new spatial density map from
which locations of triggered events are drawn. We apply the model to California
and Europe to illustrate its features.
Three Historical Earthquakes on the Southern Santa Cruz Mountains Section
of the San Andreas Fault: Insights from Three Paleoseismic Sites
Dawson, T. E., California Geological Survey, Menlo Park, CA; STREIG, A.
R., University of Oregon, Eugene, OR, [email protected]; WELDON, R. J.,
University of Oregon, Eugene, OR, [email protected]
The Hazel Dell (HD) site, on the Santa Cruz section of the San Andreas fault
(SAF), has yielded good evidence of the 1906 surface rupture, and three to four
earlier earthquakes in the form of filled fault bounded depressions, upward terminations, and stratigraphic thickness changes. We found cut wood stratigraphically below the pre-penultimate earthquake horizon, and because logging likely
began in this area sometime around 1832, this suggests that earthquakes E2 and
E3 are historical. Multiple exposures of offset deposits and modeling of the relative amounts of vertical deformation suggest minimum lateral displacements of
1-2 meters per earthquake.
Recent paleoseismic investigations at Mill Canyon (MC) (Fumal, in press),
located ~8 km south of HD, show the penultimate event likely occurred during
the 19th Century, prior to ~A.D. 1854, and an average recurrence of 125 years
during the past ~500 years.
At Grizzly Flat (GF), 6 km northwest of HD, Schwartz et al. (1998) found
evidence for 1906 and an earthquake dated A.D. 1632-1659. This implies that the
fault south of GF ruptures more frequently. However, a reinterpretation of trench
logs identifies two possible additional events and an OxCal model using the available radiocarbon data suggests these earthquakes occurred between A.D. 17331906, and may be historical (Fumal, in press). We use Biasi and Weldon (2009)
to calculate that there is a >90% probability of correlation between HD and GF
using the inferred >1-2 m offsets at HD for the two pre-1906 earthquakes, supporting the hypothesis that the additional GF earthquakes are historical.
Historical earthquakes in 1838, 1865, and 1890 have been located in the
Santa Cruz Mts. (e.g. Tuttle and Sykes, 1992), and our data provide evidence from
event timing and probable extent of surface ruptures for one of these earthquakes
rupturing through all three sites, plus suggestive evidence for an additional earthquake prior to 1906 having ruptured the SAF at HD and GF.
Major Earthquakes on a Nascent Fault Zone: Lenwood Fault, Eastern
California
Strane, M. D., Altadena, CA, [email protected]; OSKIN, M. E.,
Department of Geology, University of California, Davis, Davis, CA, meoskin@
ucdavis.edu; KHATIB, F., Allied Geotechnical Engineers, Santee, CA;
LINDVALL, S. C., Lettis Consultants International, Valencia, CA, lindvall@
lettisci.com; ROCKWELL, T. K., Department of Geological Sciences, San Diego
State University, San Diego, CA, [email protected]; BLISNIUK, K.
N., Earth and Planetary Science. University of California, Berkeley, Berkeley,
CA; IRIONDO, A., Centro de Geociencias, Universidad Nacional Autónoma
de México, Juriquilla, Querétaro. Mexico, [email protected]
That major earthquakes may occur on faults that are in a nascent stage of development presents a significant challenge for quantifying seismic hazard. Historic
earthquake activity of the eastern California shear zone (ECSZ) across the
Mojave Desert highlights the complexity of major earthquake ruptures on a
nascent fault system. The 1992 Mw 7.3 Landers earthquake, in particular, served
as a case study of how a several seemingly distinct faults could link to produce
a large earthquake (e.g. Sieh et al., 1993). We examine total offset, segmentation, slip rate, and paleoseismicity along the Lenwood fault—a dextral strike
slip fault that lies 15-20 km west of the Landers rupture. Similar to other faults
of the Mojave Desert ECSZ, paleoseismic data show that the Lenwood fault is
characterized by infrequent, large earthquakes. These earthquakes were likely
to be ≥Mw 7 in order to sustain the slip per event and slip rates we document
for the Lenwood fault. Offset of pre-faulting markers consistently record ~1
km of dextral slip across the Lenwood fault. Similar offsets occur along most of
the 65 km length of the fault, despite the presence of multiple stepovers and, in
places, incomplete linkage of en echelon fault strands. High resolution airborne
laser swath mapping (ALSM) topography of three of these linkage zones reveals
coseismically formed scarps on disconnected, en echelon, faults. These short fault
segments link otherwise distinct segments of the Lenwood fault, and reveal how
distributed coseismic displacement occurs across linkage zones to generate larger,
multi-segment earthquake ruptures.
Rupture Dynamics on Parallel Faults at a Restraining Double-Bend and
Corroboration with the Natural Earthquake Record on the Altyn Tagh Fault,
Western China
Elliott, A. J., University of California Davis, Davis, CA, ajelliott@ucdavis.
edu; DUAN, B. C., Texas A & M University, College Station, TX, bduan@
tamu.edu; OSKIN, M. E., University of California Davis, Davis, CA, meoskin@
ucdavis.edu; LIU-ZHENG, J., China Earthquake Administration, Beijing,
China, [email protected]
Field evidence and numerical modeling suggest that restraining bends impede
strike-slip earthquake ruptures. In order to evaluate the extent to which fault
geometry indeed controls earthquake behavior, we analyze parameters of numerical, multi-cycle rupture simulations that we can also directly observe in the field.
We compare model outputs with observations of rupture extent, magnitude
of slip, offset kinematics, and recurrence interval for sinistral faults within the
Aksay restraining double-bend of the Tibetan Plateau-bounding Altyn Tagh
fault. Geomorphic observations at the Aksay double-bend demonstrate that slip
is transferred kinematically between two subparallel fault strands. Numerical
modeling of multiple earthquake cycles within this system indicates that strike-
slip deficits accrue where ruptures are halted by high fault-normal stress in the
most transpressive portion of the bend. Residual stresses accumulate at these rupture terminations and support smaller earthquakes within the bend. The heterogeneous distribution of stress after multiple earthquake cycles enables dynamic
triggering of earthquakes on one fault by some incoming ruptures on the other.
Our field observations corroborate the termination of at least one major (~M8)
rupture within the most transpressive portion of the bend. Preliminary paleoseismic investigations reveal a record of few, large, infrequent ruptures along the fault
outside of the bend, and smaller, more numerous, and perhaps more frequent ruptures within the bend. Full interpretation of this earthquake history awaits pending radiocarbon and optically stimulated luminescence dates. The size, extent,
and frequency of earthquakes can be compared directly between model output
and observational data, and preliminary results suggest compatibility between
the two. However, the limits of geochronologic analysis preclude positive identification of simultaneous rupture on both strands as identified in the models.
Scaling for Fault Models toward Ground Motion Prediction of Earthquakes in
Taiwan Region
Ma, K. F., Department of Earth Sciences, National Central University, Taiwan.
We characterized the seismic sources for earthquakes in Taiwan, investigated the
historical instrumental earthquakes, and source scaling of earthquakes (Mw4.68.9) from Taiwan Orogenic belt to build up the fault model toward ground motion
prediction. Our studies on source scaling from recent earthquakes suggest that
for future ground motion prediction program the stress drop, and seismogenic
depth are two important factors in the parameter setting for fault model. The
seismic sources from active faults suggest the possible length of the fault, but, the
width of the fault would be related to the thickness of the seismogenic depth. For
fold-and-belt collision environment of Taiwan, several earthquakes from blind
faults show high stress drops, thus, yielding regional high PGA. Rather than the
site effect, these high stress drop events from possible blind faults would need
to be addressed in the evaluation of seismic hazard potential. Our studies also
examine and discuss the use of “distance” to the hypocenters, or asperities for
the ground motion prediction equation (GMPE). We also made several ground
motion predictions using the method of empirical Green’s functions for the
crustal, inter- and intra-plate earthquakes in and around Taiwan region and made
the comparison to the Next Generation Attenuation (NGA) modle for GMPE.
The results show that the deep focus of the intra-plate events gives the high PGA
comparing to the shallow inter-plate event. Regardless the deep focus of the intraplate event, we need to pay special attentions to these events, especially the possible influence to the metropolitan city, where many high-rise modern buildings
had been built. Thus, for more exploration on the construction of fault model in
Taiwan, in addition to the association of earthquakes to the active faults, we also
investigate the historical intra-plate event as of 1909 Taipei earthquake, and 1920
M8.0 offshore Taiwan earthquakes.
Site Response
A New Empirically Based GMPE for Subduction Zone Earthquakes
Gregor, N., Bechtel, San Francisco, CA, [email protected];
ABRAHAMSON, N., U.C. Berkeley, Berkeley, CA, [email protected];
ADDO, K., BC Hydro, Burnaby, BC, Canada, [email protected]
Seismic design studies in the Pacific Northwest need to consider ground motions
from both crustal and subduction zone earthquakes. During the last decade,
the development of ground motion prediction equations (GMPEs) for subduction zone earthquakes has significantly fallen behind the development of crustal
GMPEs, partially due to the lack of strong ground motion recordings from large
interface events along the Cascadia subduction zone in the Pacific Northwest.
On a global scale, however, two recently recorded large shallow interface subduction zone earthquakes (i.e., 2010 Chile (M8.8) and 2011 Tohoku (M9) events)
has significantly increased the available database of empirical recordings.
A new GMPE for both interface and intraslab subduction zone earthquakes
has been developed for the seismic hazard study performed by BC Hydro for sites
located through out British Columbia Canada. As part of this development, several subduction zone databases from different authors were compiled along with
a substantial amount with new data from events in Taiwan and Japan. A quality check was performed for the associated metadata information. Although the
data from the two recent events were not used directly in the development of the
GMPE due to the cut off date for the database, a recommended magnitude scal-
ing adjustment for large interface earthquakes for the GMPE model was developed based on residual analyses.
This new GMPE is applicable for both interface earthquakes and the intraslab earthquakes observed in subduction zones through out the world. The model
is defined for spectral periods from PGA to 10.0s and includes a non-linear site
response component based on a defined Vs30m value. As additional subudction
zone data becomes available, this model will be updated as deemed necessary. In
addition, future modifications may be warranted for a new distance metric for
large shallow events with large rupture planes and sites being located off the ends
of these fault planes.
Investigation of Spatial Correlation of Single-Station Ground Motion
Residuals
Hollenback, J. C., UC Berkeley, Berkeley, CA, [email protected];
ABRAHAMSON, N., Pacific Gas and Electric Company, San Francisco, CA,
[email protected]
Probabilistic estimates of losses to spatially distributed infrastructure caused by
earthquakes are important on a city, state, and federal level. These estimates are
sensitive to the correlation of ground motion at multiple sites during a single event
(Park et al 2007). Previous studies have focused on the correlation of withinevent residuals from empirically based ground motion prediction equations
(Wang and Takada 2005, Goda and Atkinson 2010). Modern empirically based
ground motion prediction equations are being developed that implement singlestation sigma, a more representative standard deviation for ground motion prediction at a given site. In order to implement these type of models in estimates of
spatially distributed seismic loss, models of spatial correlation structure must be
compatible. Here, the spatial correlation structure of single-station within-event
residuals is investigated. Additionally, the spatial correlation structure of the site
terms, a necessary component for the use of single-station sigma ground motion
models, is evaluated. Three different data sets are used: events from California,
events from Taiwan, and events from Japan. Semi-variograms are used to quantify the correlation structure of each data set. The correlation of the traditional
within-event residuals for each data set is compared with previous studies. The
correlation of single-station within-event residuals and site terms is contrasted
against that of the traditional within-event residuals. Single-station within-event
residuals appear to have a longer correlation length than traditional within-event
residuals and site terms a smaller. An example of seismic loss estimates is given to
show how inclusion of single-station sigma ground motion prediction equations
and compatible correlation structure can effect estimates of spatially distributed
losses.
An Update of the Spudich and Chiou Directivity Model Using the NGA-West 2
Dataset
Spudich, P., US Geological Survey, Menlo Park, CA, [email protected];
CHIOU, B. S. J., California Department of Transportation, Sacramento, CA,
[email protected]
We have updated the Spudich and Chiou (Earthq. Spectra, 2008) directivity
model as part of the NGA-West 2 project. One deficiency of our previous model
was that all earthquakes regardless of magnitude had their maximum directivity effect at 10 sec period, which was the longest period that we considered. In
our new model we have corrected this deficiency. We retain the predictor IDP
(isochrone directivity parameter) from our previous work. The main change has
been to convert our original ‘broadband’ model, in which the scaling of directivity amplification with IDP (specifically, the coefficient b of the linear predictor
term) was an increasing function of period, independent of magnitude, into a
‘narrowband’ model in which the coefficient is a function of both magnitude and
period. For a particular magnitude earthquake b is modeled by a Gaussian function of log period, with the function peaking at a period which increases with
increasing magnitude. The peak of the Gaussian function is at about 0.7 sec for
M 5.5 and rises to about 8.5 sec for M 7.5. The width parameter of the Gaussian
function is about 0.4 in common log units for all magnitudes. This new model
was derived from 21 earthquakes (ranging in magnitude from 5.7 to 7.9) having
detectable and stable directivity (in other words a positive b for most periods of a
specific earthquake).
Ground-Motion Prediction Equations for Southeastern Australia Assuming
Variable Stress Parameters
Allen, T. I., Geoscience Australia, Canberra, ACT, Australia, trevor.allen@
ga.gov.au
Stochastic finite-fault ground-motion prediction equations (GMPEs) are developed for the stable continental region of southeastern Australia (SEA). The
models are applicable for horizontal-component ground-motion for earthquakes
4.0 ≤ MW ≤ 7.5 and at distances less than 400 km. The models are calibrated
with updated source and attenuation parameters derived from SEA groundmotion data.
Careful analysis of well-constrained earthquake stress parameters against
other source parameters (i.e., magnitude, depth, main-shock/aftershock dependence) indicates a strong dependence on hypocentral depth. It is speculated that
this is the result of an increasing crustal stress profile with depth. However, rather
than a continuous increase, the change in stress parameter appears to indicate a
discrete step near 10 km depth. Average stress parameters for SEA earthquakes
shallower and deeper than 10 km are estimated to be 23 MPa and 50 MPa, respectively. The stress parameters are subsequently input into the stochastic groundmotion simulations for the development of two discrete GMPEs for shallow and
deep events.
The GMPEs developed estimate response spectral accelerations comparable
to the Atkinson and Boore (2006) GMPE for eastern North America (ENA)
at short rupture distances (less than approximately 100 km). However, owing to
higher attenuation observed in the SEA crust (Allen and Atkinson, 2007), the
SEA GMPEs estimate lower ground-motions than ENA models at larger distances.
The response spectral models are validated against moderate-magnitude
4.0 ≤ MW ≤ 5.3 earthquakes from eastern Australia. Overall the SEA GMPEs
show low median residuals across the full range of period and distance. In contrast, Eastern North American models tend to overestimate response spectra at
larger distances. Because of these differences, the present analysis justifies the
need to develop Australian-specific GMPEs where ground-motion hazard from
a distant seismic source may become important.
Ground Motion Amplification at the Mexicali Valley, Baja California, México
VIDAL-VILLEGAS, J. A., Department of Seismology, Earth Sciences Division,
CICESE, Ensenada, Baja California, México, [email protected]; VEGAGUZMÁN, F. J., Department of Seismology, Earth Sciences Division, CICESE,
Ensenada, Baja California, México; HUERTA-LÓPEZ, C. I., Department
of Seismology, Earth Sciences Division, CICESE, Ensenada, Baja California,
México, [email protected]
This study was motivated because of the high amplifications of the seismic signal
recorded at some sites of the Mexicali valley. As an example we have the acceleration values recorded at the GEO station, which is located at the Cerro Prieto
Geothermal Field (492 gals, generated by an earthquake of magnitude 5.4). Our
goal was to find an explanation to the high seismic amplitudes and to determine a
shallow structure (0-50 m) at 5 specific sites. First, we gathered seismic noise along
a N180E profile that crosses the Cerro Prieto volcano (next to the Geothermal
field). Instrumentation used was short and intermediate period seismometers
in combination with 16-bit digital recorders. Furthermore, we analyzed records
from 24-bit accelerographs corresponding to earthquakes occurred from 2004
to 2006. Next, we calculated the H/V spectral ratios with both types of data.
To estimate the shallow structure we modeled the H/V ratios, based on onedimensional model, using the stiffness matrix propagation method. Concerning
the Cerro Prieto volcano, the H/V ratios confirm the existence of amplification
at its top (6.3 at 1.2 Hz) regarding the lower surrounding zone (no amplification
was observed at sites located along the aforementioned profile). In the case of the
GEO site, the H/V ratios are different by a factor of 2.15 between noise (8.6) and
acceleration (4). However, the fundamental frequency (0.8 Hz) is well defined.
Sites located at villages of Mexicali valley (DEL, CGG and CHI) show H/V
ratios between 5 and 17. Based on a structure of three horizontal layers lying over
a half-space, results of modeling the H/V ratios show that the physical properties
of the 5 sites are different. These properties: S-wave velocity, density, and Poisson’s
ratio, have values of 90 to 680 m/s, 1.0 to 2.3 g/cm3, and 0.20 to 0.35; respectively.
Explanatory Variables in Terrain-Based VS30 Model
Yong, A., U.S. Geological Survey, Pasadena, CA, [email protected];
IWAHASHI, J., Geospatial Information Authority of Japan, Tsukuba, Ibaraki,
Japan, [email protected]
The time-averaged shear-wave velocity to a depth of 30 meters, VS30, is a key index
adopted by the earthquake engineering community to account for seismic site
conditions. Ideally, VS30 should be based on direct or indirect measurements at
sites of interest. However, due to cost considerations, as well as logistical and
environmental considerations, VS30 data are often sparse or not available. To
augment these sparse observations, a number of proxy map-based models have
been developed to estimate VS30, including the terrain-based model (Yong et al.,
2012). Originally developed by Iwahashi and Pike (2007) to automatically classify global landforms at the 30-arc-sec scale, the terrain-based model describes 16
classes of terrain types on the basis of three geometric signatures: slope gradient,
local convexity and surface texture. In this study we evaluate the signatures and
their correlation with VS30. We calculate the correlation coefficient (r) for the log
of VS30 as described by slope gradient (r = 0.43), local convexity (r = 0.25) and
surface texture (r = 0.43) for 853 sites in California. The values for slope gradient and surface texture meet the criteria (0.3 to 0.5) for medium correlation. We
next perform multivariate regression on all three signatures and find the resultant r value (0.53) to fall marginally within the strong correlation criteria (0.5 to
1). Regressing VS30 on pairs of geometric signatures yields r values between 0.44
and 0.53. Our preliminary results are consistent with observations from a similar
study conducted by Iwahashi et al. (2010) for 1646 K-NET and KiK-net sites in
Japan. Hence, we expect that—individually and combined—slope gradient and
surface texture to be reliable explanatory variables for characterizing seismic site
conditions.
A Hybrid Slope-Geology VS30 Mapping Strategy
Thompson, E. M., Tufts University, Medford, MA, eric.thompson@tufts.
edu; WALD, D. J., US Geological Survey, Golden, CO, [email protected]
Despite obvious limitations as a proxy for site amplification, the use of time-averaged shear-wave velocity over the top 30 m (VS30) is useful and widely practiced,
most notably through its use as an explanatory variable in ground motion prediction equations (and thus hazard maps and ShakeMaps, among other applications). Local, regional, and global VS30 maps thus have diverse and fundamental
uses in earthquake and engineering seismology. As such, we are developing an
improved strategy for producing VS30 maps given the common observational
constraints available in any region for various spatial scales. Using the abundant
VS30 measurements in Taiwan as an example, we compare alternative mapping
methods that combine topographic slope, surface geology, and spatial correlation structure. We apply the kriging-with-a-trend mathematical framework to
combine these alternative predictive variables and assess the predictive accuracy
of the different methods through the k-fold cross validation procedure. The different VS30 mapping algorithms are distinguished by the definition of the terms
in the regression equation, representing the “trend” in the kriging-with-a-trend
procedure. We consider the globally applicable slope-only model, a locally refined
slope-only model, a geology-only model, and a series of models that include both
slope and geology. The cross validation allows us to quantify the uncertainty of
the alternative VS30 mapping algorithms, thereby illustrating the improvement of
the hybrid slope-geology model over the simpler and more widely applicable correlations with only geology or topographic slope that are currently employed by
ShakeMap and in other analyses that require site amplification maps.
Sea-floor Marine Site Characterization Using Earthquake Data Recorded at
the Gulf of California, México
HUERTA-LOPEZ, C. I., CICESE, Ensenada, Baja California, Mexico,
[email protected]; CASTRO-ESCAMILLA, R. R., CICESE,
Ensenada, Baja California, Mexico, [email protected]; GAHERTY, J. B., LamontDoherty Earth Observatory of Columbia University, Palisades, NY, gaherty@
ldeo.columbia.edu; COLLINS, J. A., Woods Hole Oceanographic Institution,
Woods Hole, MA, [email protected]
Regional and local earthquakes recorded by Ocean Bottom Seismometers (OBS)
deployed during the Sea of Cortez Ocean Bottom Array (SCoOBA) seismic
experiment were used to characterize the local site conditions of the shallow seafloor marine sediments in the Gulf of California (GoC).
The local site characterization of sea-floor marine sediments on the centralsouth portion of the GoC was carried out by means of H/V spectral ratio (H/VSPR) method to estimate the transfer functions. The stiffness matrix method
was used to characterize the theoretical site response and to estimate the marine
sediments properties. The data used come from OBS’s very-broad-band velocity sensors deployed in the central and southern portion of the GoC, during the
SCoOBA seismic experiment. The instruments recorded marine ambient noise
and earthquake signals during October 2005 to October 2006 in continuous
recording mode.
In order to compare the obtained results when using earthquake signals, the
Nakamura method was used to estimate H/V spectral ratios using only signals
of background noise. The results of both ways of estimating H/V spectral ratios
were consistent between them, in addition, it was also shown that in the northern sites the shallow portion of marine sediments have small thicknesses than
the sediment thickness of the stations located at the south. The velocities of the
southern sites were smaller than those of the northern sites, and the sites located
between northern and southern arrays. Site fundamental vibration frequency
variations from 1 to 0.32-Hz were clearly evident, decreasing from northern to
the southern sites, respectively.
Analysis of Joint Time-Frequency Spectral Decomposition of Acceleration
Time Series from the 17 December 2011 Mw 5.1 Puerto Rico Earthquake
UPEGUI-BOTERO, F. M., Puerto Rico Strong Motion Program-UPR
Mayaguez, Mayaguez, PR, [email protected]; HUERTA-LOPEZ, C. I.,
PRSMP-UPR Mayaguez—CICESE, Mayaguez, PR & Ensenada, Mexico,
[email protected]; CARO-CORTES, J. A., Puerto Rico Strong Motion
Program-UPR Mayaguez, Mayaguez, PR, [email protected]; MARTINEZCRUZADO, J. A., Puerto Rico Strong Motion Program-UPR Mayaguez,
Mayaguez, PR, [email protected]; SUAREZ COLCHE, L. E., Puerto
Rico Strong Motion Program-UPR Mayaguez, Mayaguez, PR, luis.suarez3@
upr.edu; Puerto Rico Strong Motion University (PRSMP) of Puerto Rico at
Mayaguez Campus
A joint time-frequency spectral decomposition analysis of time series from the 17
December 2011 moderate-sized (Mw=5.1) earthquake that occurred at 06:09:09
(UTC) in the west area of the Puerto Rico Island was conducted. The earthquake
epicenter was located at latitude 18.172° N, longitude 67.371° W, with a focal
depth of 17 Km. The epicentral distances ranged from 29 to 150 Km from the
nearest to the farthest stations, respectively. The earthquake was recorded by 50
strong motions stations of the Puerto Rico Strong Motion Program (PRSMP)
distributed around the island. In the analysis several time-frequency distribution
(TFD’s) were obtained, mapping a one-dimension signal into a two-dimensional
function of time and frequency showing the energy content of the signal in the
joint time-frequency domain simultaneously. The joint time-frequency spectral
decomposition is an appropriate tool for analysis of non-stationary signals whose
spectral characteristics change in time. Joint time-frequency distributions represent in some way the extension of stationary spectral functions with respect to the
time. The following Cohen class linear and quadratic distributions were applied:
(i) Short Time Fourier Transform (STFT), (ii) Wigner-Ville Distribution
(WVD), (iii) Choi-Williams Distribution (CWD), (iv) Reduced Interference
Distribution (RID), and (v) Adaptive Optimal Kernel (AOK). Each of these
distributions was applied to the recorded strong motion data and a comparison
among them was analyzed. The variation of the joint time-frequency characteristics of each record and the spatial distribution of these characteristics among the
stations are here presented as well.
Seismic Site Response in Christchurch (New Zealand) from Dense Aftershock
Recordings
Kaiser, A. E., GNS Science, Lower Hutt, New Zealand, [email protected];
BENITES, R. A., GNS Science, Lower Hutt, New Zealand, [email protected].
nz; CHUNG, A. I., Stanford University, Stanford, CA, angelaichung@gmail.
com; OTH, A., European Center for Geodynamics and Seismology, Walferdange,
Luxembourg, [email protected]; COCHRAN, E. S., USGS, Pasaden, CA,
[email protected]; FRY, B., GNS Science, Lower Hutt, New Zealand, b.fry@
gns.cri.nz; HAINES, A. J., GNS Science, Dunedin, New Zealand, j.haines@gns.
cri.nz
The Canterbury earthquake sequence began with the Mw 7.1 September 2010
Darfield earthquake and has included the destructive Mw 6.2 February 2011
earthquake and two further Mw > 6 aftershocks. The sequence has produced
widespread damage and multiple liquefaction events in Christchurch city. Strong
motion data suggest that site effects caused by localised soft soils, basin effects,
topographic amplification and liquefaction contributed to observed variations in
ground motion. Understanding site effects on ground motion is therefore crucial
in assessing the ongoing seismic hazard in the region and informing the rebuild
process.
We use the wealth of densely-spaced recordings from the Canterbury earthquake sequence to investigate variations in local seismic site response within the
Christchurch urban area. Seismic data are sourced from research-grade GeoNet
stations and a dense aftershock array of low-cost MEMS accelerometers linked to
the global Quake-Catcher Network (QCN). Spectral ratios are calculated relative to observed motion at a local reference station on Miocene basalt and also trialled with respect to input synthetic acceleration modelled with a finite, extended
fault. For noisier QCN stations, a maximum likelihood estimate of soil-to-rock
spectral ratio amplitude was needed to produce meaningful results. Results from
adjacent GeoNet and QCN stations are comparable, suggesting that dense lowcost aftershock arrays such as the QCN network can provide useful information
on local-scale ground motion properties. Results define an area of high amplification north of the city centre and strong high-frequency amplification in the
shallow basin of Heathcote Valley. In addition, we present preliminary observations using a spectral inversion method applied to GeoNet data. This method also
allows us to quantitatively separate site effects from source and path contributions to ground motion, further increasing our understanding of future hazard
in the region.
In-Situ Measurement of Velocity Change under Induced Strong Ground
Motion
Larmat, C., Los Alamos National Laboratory, Los Alamos, NM, carene@
lanl.gov; GUYER, R. A., Los Alamos National Laboratory, Los Alamos,
NM, [email protected]; LEE, R., Los Alamos National Laboratory,
Los Alamos, NM, [email protected]; RUTLEDGE, J. T., Los Alamos National
Laboratory, Los Alamos, NM, [email protected]; JOHNSON, P. A., Los
Alamos National Laboratory, Los Alamos, NM, [email protected]; STOKOE, K.,
University of Texas at Austin, Austin, TX.
Predicting ground motion from large earthquakes is a key ingredient for safe
design of critical facilities. Many approaches exist but the most common are to
test samples from boreholes, and to make predictions based on the elastic nonlinear properties of the samples. In this paper we present a field demonstration
of a new technique that has been previously demonstrated in laboratory studies
(Renaud et al., 2009; 2012). Our experimental concept is to dynamically stress
a large volume of soil with a low-frequency strain wavefield using a large vibrator truck (T-Rex), while simultaneously measuring the travel-times of high frequency pulses. Compared to existing methods such as measurement of resonance
frequency by John-son et al. (2009), the approach described here is capable of providing local and complete non-linear be-havior including stress-strain hysteresis
The experimental layout consisted of three 0.3 m diameter cased holes
augured to 1-, 2- and 3-m depth. Two vertical component accelerometers were
carefully driven into the soil a distance of 1 m and 2 m be-low the high-frequency
source to minimize disturbance of in-situ conditions. Sinusoidal cycles at 30Hz
were driven from T-rex with varying load levels ranging from 2000 to 50, 000 lbs
to simulate varying in-situ strain levels.
Two sets of propagation times were measured corresponding to the low- and
high-frequency content of the signal. The low-frequency signals show the local
velocity increasing corresponding to increasing T-Rex load (15% over a 10-fold
increase of strain). The high-frequency content shows a relative decrease of the
local velocity with increasing strain imposed by T-Rex, indicating that material
softening takes place with larger strain amplitudes. These results are consistent
with previous studies of static and dynamic be-havior in glass bead packs (e.g.,
Johnson and Jia, 2005) and in rock (Zinszner et al., 1997)) and they show that the
method may ultimately work for site characterization.
Analysis of Micro-Seismicity and Site Response Using Waveform Data from
a Small Broadband Deployment on Cal Poly Pomona Campus
Lino, S. I., California State Polytechnic University, Pomona, CA, silino@
csupomona.edu; HO, K. K., California State Polytechnic University, Pomona,
CA, [email protected]; POLET, J., California State Polytechnic
University, Pomona, CA, [email protected]
We present the results of a broadband study of the seismicity and site response of
Cal Poly Pomona campus using a small array of seismometers that were deployed
to promote undergraduate research in seismology. The campus is crossed by the
San Jose fault, which is considered to be an active reverse structure, but is not well
understood both in terms of location and tectonic activity. The focus of our study
is on the interpretation of waveform data from three Guralp CMG-6TD seismometers that were deployed for several months at three locations around campus. Our motivation for this research is twofold: to use ambient noise measurements to contribute to a map of site response for Cal Poly Pomona campus, and
to detect any micro-earthquakes on faults in the immediate vicinity, in particular
the San Jose Fault. An examination of the last few decades of seismicity of the area
as determined by the Southern California Seismic Network yields very few earthquakes consistent with the geometry of the San Jose fault, but it does show a trend
of magnitude 2 earthquakes leading North perpendicular to the San Jose Fault
just west of campus that does not appear to correspond to any mapped fault. Our
detailed analysis of micro-earthquakes will contribute to the assessment of the
seismic hazard of local faults and of the complexity of the fault systems. We will
determine earthquake locations from arrival time picks of P and S waves using the
HYPOINVERSE2000 software. We will also show our results of the analysis of
the ambient noise waveforms using the H/V Spectral Ratio Method, to determine site amplification and the fundamental frequency of the sites.
Seismic Wave Propagation Profiles and Response Spectra of Kuala Lumpur
City Center under the Far Field Earthquake Effects from Sumatra
Adnan, A. B., University of Technology Malaysia, Johor Bahru, Johor,
Malaysia, [email protected]; SUHATRIL, M., University of
Malaya, Kuala Lumpur Malaysia, [email protected]; HENDRIYAWAN,
Institute of Technology Bandung, Bandung, Indonesia, [email protected];
MASYUR, I., Institute of Technology Bandung, Bandung, Indonesia, masyur.
[email protected]
Local soil conditions greatly affect the behavior of ground motion during earthquakes and more significantly when the distance is far away. Studies have been
conducted to identify their effects to the largest city in Malaysia, Kuala Lumpur,
on earthquake hazards related to geotechnical factors in the form of microzonation maps and response spectra. Mapping of seismic hazard at local scales is
translated through the seismic wave propagation profiles. Since Kuala Lumpur is
about 250 to 350 km away from the most active seismic region in the world, the
great Sumatra Subduction Zone Faults and Sumatra Faults, the effect of the long
distant earthquake is vey much critical to the mainly soft soil profiles of the Kuala
Lumpur city center. The Kuala Lumpur city center sites are applied with the
500 years return period, bedrock peak ground acceleration (PGA), ranges from
0.046g to 0.093g for periods of 0.2 seconds and 1.0 second which are derived from
different fault sources. It is based on the latest Seismic Hazard Map of Malaysia
(2011) employing Next Generation Attenuations (NGA). The shear wave velocity of 1000 m/sec is utilised for the bedrock. The site tends to amplify the ground
motion at bedrock up to 3.1 times using the site synthetic time history ground
motions whereas in average, this site amplifies the wave to about 2.0 times. The
mean +1 standard deviation, peak response spectra acceleration reaches 0.8g in
the period of 0.4 seconds. The results from the ground motion analysis show shifting of the response spectra periods from 0.075 sec to 1.10 sec at 0.45g levels. The
peaks in the envelope shape of the spectra is dominantly placed within the range
of 0.1 to 1.1 sec at 0.045g to 0.08g ranges. In conclusion, the far field earthquake
effects from Sumatra provided large ground amplification factors (about 2 times)
compared to the results using soil factor recommended in the design specification
and shifted the response spectra to a longer period of about 15% more.
Seismic Noise in Antarctica
Anthony, R., New Mexico Institute of Mining and Technology, Socorro,
NM, [email protected]; ASTER, R., New Mexico Institute of Mining and
Technology, Socorro, NM, [email protected]; ROWE, C., Los Alamos
National Laboratory, Los Alamos, NM; WIENS, D., Washington University, St.
Louis, MO; NYBLADE, A., Pennsylvania State University, State College, PA.
We analyze recently recovered Polar Earth Observing Network (POLENET)
and Antarctica’s Gamburtsev Province (AGAP) seismic data, along with date
from prior long-term networks (Including GSN stations), to characterize background seismic noise across large sectors of Antarctica for the first time. The
power spectral density (PSD) at each broadband station is calculated over 1-hour,
continuous, overlapping time series segments sampled at 40 Hz and binned into
1/8 octave intervals between periods of 0.05 and 100 s. Statistical analysis over
month-to-decadal time periods allows for the calculation of probability density
functions that quantitatively characterize the likelihood of noise power levels
within each period bin, at each seismic station, as a function of time. Noise and
its geographic and temporal variability across Antarctica is of interest in directing the design of future seismic networks, including proposed backbone systems.
Additionally, seasonal variation in the power of the primary (~16 s) and secondary (~8 s) microseism spectral peaks provides insight into the microseism source
and on the annually evolving integrity of Antarctic sea ice. Finally, these observations provide key Southern Ocean components of a broader effort to globally
characterize extreme storm intensity/frequency and other ocean wave state statistics.
Investigating the 2011 Rumblings in Windsor, Ontario through Seismology
Bent, A. L., Geological Survey of Canada, Ottawa, ON, Canada, bent@
seismo.nrcan.gc.ca; WOODGOLD, C. R. D., Geological Survey of Canada,
Ottawa, ON, Canada, [email protected]
Since March 2011 many residents of the Windsor, Ontario region have been
reporting rumblings described as a low frequency sound and/or vibration sometimes continuing for several hours. The Ontario Ministry of the Environment
investigated several local industries and ruled them out as the source of the rumblings. Natural Resources Canada, who had previously eliminated earthquakes
as the cause, was asked for assistance. In June 2011 four three-component seismometers were installed in the western part of the city of Windsor where the
largest number of noise complaints originated. The stations ran until late August
2011. Examination of the data revealed a signal on two of the stations that was
consistent in character with the reported rumblings in terms of time, duration
and behavior. Further analysis of the signals primarily based on spectrograms
and particle motions revealed that they were propagating as acoustic waves in
the atmosphere and that they originated from the general vicinity of Zug Island,
Michigan. The findings of this study have been passed to the appropriate authori-
ties for consideration on the best course of action for further investigation to pinpoint the exact source of the noise.
An Experimental Study on Rock Physical Property Based on Binary code
Excitation
Wu, H. Z., Institute of Geophysics, China Earthquake Administration, Beijing,
China, [email protected]
The theories researching of numeric encoding ultrasound technique and rock’s
physical properties testing experiments are key points of this research. We brought
principle of coded excitation into rock testing and use rock’s physical properties
testing experiments to verify. With the ultrasound encoding observation system
set before, data collected by code launching and ultrasound transducer; the effect
of code types and code’s length on SNR, detecting distance and testing accuracy
of travel time are compared and analyzed by using decoding analytical method.
By the Coded excitation experiment platform set before, different coded
(mainly Barker and Golay code) were selected to excite the wideband transducer,
and effects of different modulation methods on excitation signals and theirs pulse
were researched, and then modulation parameters were also optimized. Observes
from the single pulse excitation and echo signal which from Barker, Golay code
excitation signal that passes through transducer, it can be seen that all of the
power of different excitation signals has weaken after the function of equivalent land pass filter. The improvement of signal’s SNR after pulse compression is
depended on the power of signal. The output SNR gain is down and its compression performance is lower under the influence of the transducer.
Unit code element has the Baker code with 1 cycle of carrier frequency that
after passed through pulse compression of the transducer, its loss of SNR gain is
relatively bigger. While Unit code element has the Baker code signal with 3 cycles
of carrier frequency that after passed through transducer, its power is wicked due
to the equivalent filter function of transducer, but the extent of it is relatively
small and the loss of SNR gain is relatively small too. Normally, for a best effect,
it uses a modulating signal of a Barker code with 3 cycles of carrier frequency to
excite the pulse compression of a transducer.
Observations and Models
Interpreting the 11th March 2011 Tohoku, Japan Earthquake Ground-Motions
Using Stochastic Finite-Fault Simulations
Ghofrani, H., University of Western Ontario, London, ON, Canada,
[email protected]; ATKINSON, G. M., University of Western Ontario,
London, ON, Canada, [email protected]; GODA, K., University of Bristol,
Bristol, United Kingdom, [email protected]; ASSATOURIANS, K.,
University of Western Ontario, London, ON, Canada, karenassatourians@
yahoo.com
We performed stochastic finite-fault simulations to obtain a source and attenuation model to match the Tohoku motions, accounting for the effects of site
response at each station. In the simulations we accommodated the expected
fore-arc/back-arc attenuation and Q, along with appropriate average regional site
conditions and their amplification effects. Linear site amplification is estimated
using cross-spectral spectral ratios of pairs of borehole-surface stations from the
KiK-net network (Aoi et al. 2004). The nonlinearity of the soil column is studied using a moving window technique that determines how the amplification
changes with signal strength within each record (Wu et al. 2010). We have found
that there was localized nonlinearity, but the effects of nonlinearity were not
pervasive. Stochastic finite-fault simulations generated by EXSIM (Atkinson et
al. 2009) are used to calculate the average predicted response spectra at different
distance ranges, and are compared with observed ground motions. The simulated
spectra are normalized based on an acceleration normalization scheme, considering a stress drop of 200bars. We used a modified version of the GSI’s model
for the fault parameters. The high-frequency decay of ground motions is modeled using a kappa value of 0.044. Geometrical spreading has a slope of -1 for all
distance ranges, and the duration of time series is modeled using: T=T0+0.09R.
For each simulation, random numbers are generated for point-source simulations,
hypocenter location, and slip weights. We simulated the double shock feature of
the Tohoku earthquake by joining two sets of simulations with different nucleation points. Overall, the predicted ground motions are in good agreement with
the observed ground motions. The calibrated simulation model for Tohoku can
be modified for use in predicting ground motions in other regions (e.g. Cascadia
region of North America) by suitable modifications of the regional attenuation
and site parameters.
Long-term Change of Site Response and High-Frequency Radiations
Associated with the Mw9.0 Tohoku-Oki Earthquake in Japan
Wu, C., Georgia Institute of Technology, Atlanta, GA, chunquanwu@gatech.
edu; PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng@gatech.
edu; ASSIMAKI, D., Georgia Institute of Technology, Atlanta, GA, dominic@
gatech.edu
The recent Mw9.0 Tohoku-Oki earthquake and its aftershocks generated widespread strong shakings as large as ~3000 gal along the east coast of Japan. Wu and
Peng (2011) found clear drop of resonant frequency of up to 70% during the main
shock at 6 sites and correlation of resonance (peak) frequency and peak ground
acceleration (PGA) during the main shock. Here we follow that study and systematically analyze long-term changes of material properties in the shallow crust
from one year before to 5 months after the main shock. We use sliding window
spectral ratios computed from KiK-Net surface and borehole station pairs to
track the temporal changes in the site response of 6 sites. Our results show two
stages of logarithmic recovery after a sharp drop of resonance frequency during
the Tohoku main shock. The first stage is a rapid recovery within several hundred
seconds to several hours, and the second stage is a slow recovery of more than
five months. We also investigate whether the damage caused by the Tohoku main
shock could make the near surface layers more susceptible to further damages,
but we do not observe clear changes in susceptibility to further damage before
and after the main shock. In addition, we identify high-frequency radiations during the large-amplitude main shock recordings and large aftershocks from many
K-Net and KiK-Net sites. These signals are characterized as very-short durations
(< 1 s) and ultra high-frequency contents (> 20 Hz), and only recorded at single
station. A notable example is station MYG004, which recorded a high-frequency
spike at ~90 s after the main shock that produced the highest peak ground acceleration of up to 3000 gal. Our next step is to classify the high-frequency bursts
into different categories based on their different behaviors, and to understand
the physical mechanisms of burst generation and their relationships to nonlinear
site responses.
Ground Motions in the Triggered Fukushima Hamadori Normal-Faulting
Earthquake Following the 2011 Tohoku Earthquake
BRUNE, J. N., Nevada Seismological Laboratory, Reno, NV, [email protected].
edu; BIASI, G., Nevada Seismological Laboratory, Reno, NV, [email protected],
Presented by ANDERSON, J.
A large crustal earthquake (MJMA=7.0; MW=6.69) with a normal mechanism
occurred in eastern Tohoku following the 11 March 2011 (MW=9.0) Tohoku,
Japan, earthquake. The strong motion recordings of this event, on 11 April 2011,
are by far the most extensive for any large normal-faulting earthquake. We consider this new data in the context of other data from normal faulting earthquakes,
including geological evidence. In total there are 731 strong motion recordings
from the K-NET and KiK-net stations operated by the National Institute for
Earth Science and Disaster Prevention (NIED). The most distant about 890 km
from the fault, and 82 records were obtained within 100 km.
Peak accelerations and peak velocities are compared with several ground
motion prediction equations (GMPEs). For distances less than 100 km, the peak
velocity observations are relatively consistent with these GMPEs. However, for
distances smaller than 100 km, peak accelerations are consistently significantly
larger. For instance, the distance dependence of the Boore and Atkinson (2008)
model best matches the observations, but within ~50 km the data are approximated by the amplitude of their mean plus one sigma curve. Furthermore, over
96% of the stations closer than 100 km had peak accelerations greater than the
median prediction of Abrahamson and Silva (2008), Campbell and Bozorgnia
(2008), and Chiou and Youngs (2008).
These observations raise concerns about the current state-of-the-art estimates of high-frequency amplitudes of ground motions during large normalfaulting earthquakes. Obviously, one alternative is to argue that the observed
motions are abnormal considering the circumstances surrounding this event.
However, the arguments that this earthquake should be considered abnormal are,
in our judgment, weak. We conclude that these data will be critical, and inappropriate to ignore, in future improvements of ground motion prediction equations.
Onshore Surface Fault Rupture and Crustal Deformation from the 11 April 2011
Mw 6.6 Hamadoori Earthquake, Japan (an Aftershock of the 11 March 2011
Tohoku Offshore Earthquake, Japan)
Kelson, K. I., Fugro Consultants, Inc., Walnut Creek, CA, kikelson@gmail.
com; RYDER, I., University of Liverpool, Liverpool, United Kingdom, i.ryder@
liv.ac.uk; STREIG, A. R., University of Oregon, Eugene, OR, streig@uoregon.
edu; BRAY, J. D., University of California, Berkeley, Berkeley, CA, bray@
ce.berkeley.edu; KONAGAI, K., University of Tokyo, Japan, [email protected]
tokyo.ac.jp; HARDER, L., HDR Engineering, Folsom, CA, les.harder@hdrinc.
com; KISHIDA, T., Chiba University, Japan, [email protected]
Soon after the great Mw9.0 Tohoku earthquake, several moderate to large aftershocks occurred at crustal depths of about 12 km in southeastern Fukushima
Prefecture. The April 11 Mw6.6 Hamadoori aftershock produced west-down
normal surface rupture along at least 11 km of the previously mapped N10W
Shionohira fault, and along at least 5 km of the N45W Idosawa North fault.
Rupture on the Shionohira fault has a right-stepping en echelon pattern, with
vertical displacement of 0.8 to 2.3 m and dextral offset of 0 to 0.3 m. Where present in shallow bedrock, the fault rupture is distinct and linear; where present in
unconsolidated alluvium the rupture is characterized by a fold scarp and hanging-wall cracking. Buildings and other structures were tilted as much as about 3
degrees westward but did not experience structural failure.
The pattern of surface deformation observed in the field is consistent
with satellite-based definition of regional crustal block re-adjustments after the
mainshock. Coseismic ALOS PALSAR interferograms were processed to assess
the locations and patterns of surface deformation resulting from the onshore
aftershocks. Wrapped interferograms show many distinct, and in some cases
overlapping, sets of phase fringes, which can be associated with post-March 11
aftershocks. Discrete deformations defined by the interferograms coincide with
observed surface ruptures along the Shionohira and Idosawa North faults, and
suggest that southeastern Fukushima Prefecture experienced normal faulting,
block tilting, and discrete surface rupture in the shallow crust following the mainshock. The deformation may represent a response of the upper crust to changes in
local stress fields resulting from the mainshock and subsequent aftershocks. The
pattern of deformation interpreted from satellite and field data provides evidence
of post-mainshock, distributed re-adjustments of the shallow crust along or near
previously mapped faults in the hanging wall of the subduction zone.
High-Frequency Back-Propagation Applied to the Strong-Motion Data from
the 2011 Tohoku Mw 9.1 Earthquake
Yano, T. E., University of California, Santa Barbara, CA, [email protected].
edu; SHAO, G., University of California, Santa Barbara, CA, [email protected].
edu; JI, C., University of California, Santa Barbara, CA, [email protected]
We propose improving the resolution of spatio-temporal evolution of the sources
of high-frequency radiation during earthquakes. This allow a better understanding of how the source produces a broad spectrum of frequencies. For example, the
rupture process of the 2011 Mw 9.1 Tohoku earthquake has been studied using
various methods, frequencies, and data sets. However, the slip models constrained
by low- and high-frequency data appear to be inconsistent with each other. This
inconsistency may be real and that the mechanical differences in the generation of low- and high-frequency radiation. However, it is also possible that the
high-frequency sources found by conventional back-projection might be strongly
affected by its resolution due to two basic assumptions—the Earth response is
a delta function for the direct arrival and the fault is at a constant depth. These
assumptions make it difficult to reduce the effect of the free surface such as surface reflection phases (pP, sP, etc.). We propose a back-propagation method that
mitigates the effects resulting from these assumptions.
Although it has been challenging to use strong-motion data because they
contain strong reverberations and depth phases, our method can take advantage
of these data. For each point on the fault, the new approach cross-correlates theoretical and empirical Green’s functions with observations to consider the realistic
propagation and radiation differences among seismic stations, and then stacks the
results together to capture the robust features of spatio-temporal revolution of
high-frequency radiation. The 3D velocity structure corrections can be crucial for
resolution. However, the calibration of the travel time for paths between sources
and stations can be done by cross-correlating S-waves of Green’s functions with
waveforms of foreshocks and aftershocks. We will apply our back-propagation
method to the KiK-net strong motion data recorded during the Mw 9.1 Tohoku
earthquake.
Propagation Through Complex Media
Oral Session · Wednesday 8:30 am, April 18· Pacific Salon
1&2
Session Chairs: Robert Abbott, Tarabay Antoun, Howard
Patton, Chandan Saikia, and Catherine Snelson
The Source Physics Experiments (SPE) at the Nevada National Security Site
(NNSS)
Snelson, C. M., National Security Technologies, LLC, North Las Vegas,
NV, [email protected]; CHIMPAN, V. D., National Security Technologies,
LLC, North Las Vegas, NV, [email protected]; WHITE, R. L., National
Security Technologies, LLC, North Las Vegas, NV, [email protected];
EMMITT, R. F., National Security Technologies, LLC, North Las Vegas, NV,
[email protected]; TOWNSEND, M. J., National Security Technologies,
LLC, North Las Vegas, NV, [email protected]
In order to detect low-yield nuclear explosions under the Comprehensive Nuclear
Test-Ban Treaty (CTBT), the United States must be able to understand and model
the explosive source in settings beyond where there is empirical data. Previously,
the modeling of explosion phenomenology has been primarily empirically based.
The Source Physics Experiments (SPE) at the Nevada National Security Site
(NNSS) are the first step in an endeavor to link the empirically based with the
physics-based modeling to develop this predictive capability. The current series
of tests is being conducted in the Climax stock in a fairly homogeneous granite
body on the NNSS, where data are available from previous underground nuclear
tests and the geology has been well documented. Among the project goals for the
SPE are to provide fully coupled seismic energy so that the transition between
the near and far-field data can be observed and we can begin to understand how
non-linear effects and anisotropy control seismic energy transmission and partitioning. Two shots have been conducted thus far out of a series of eight. SPE1
was a calibration shot of 100 kg at 55 m depth and SPE2 was a 1000 kg shot
at 46 m depth utilizing the same shot hole. An array of instruments recorded
the shot data, including accelerometers, geophones, rotational sensors, shortperiod, broadband seismic sensors, and infrasound sensors. Diagnostics included
Continuous Reflectometry for Radius vs. Time EXperiment (CORRTEX),
Time of Arrival (TOA), and Velocity of Detonation (VOD). Over 400 data channels were recorded for SPE1 and 2, and data recovery was about 95% with a high
signal to noise ratio. The utilization of this test bed will provide an opportunity
to develop a modeling capability that can be used to understand the generation
of S-waves from an explosive source. This work was done by National Security
Technologies, LLC, under Contract No. DE AC52 06NA25946 with the U.S.
Department of Energy.
Analysis of Near-Field Ground Motions from the Source Physics Experiment
Vorobiev, O., Lawrence Livermore National Laboratory, Livermore, CA USA,
[email protected]; ANTOUN, T., Lawrence Livermore National Laboratory,
Livermore, CA USA, [email protected]; XU, H., Lawrence Livermore National
Laboratory, Livermore, CA USA, [email protected]; HERBOLD, E., Lawrence
Livermore National Laboratory, Livermore, CA USA, [email protected];
GLENN, L., Lawrence Livermore National Laboratory, Livermore, CA USA,
[email protected]; LOMOV, I., Lawrence Livermore National Laboratory,
Livermore, CA USA, [email protected]
The Source Physics Experiment (SPE) at the Nevada National Security Site
(NNSS) is planned as a series of chemical explosions under a variety of emplacement conditions. The goal of the SPE is to improve our physical understanding
and ability to model explosively generated seismic waves, particularly S-waves.
The first two SPE explosions (a 100 kg shot at a depth of 60 m, and a 1000 kg
shot at a depth of 50 m) were performed recently in the Climax Stock granitic
outcrop at NNSS. The shots were well-recorded by an array of over 150 instruments, including both near-field wave motion measurements as well as far-field
seismic measurements. This paper focuses on measurements and modeling of the
near-field data, which included triaxial acceleration measurements at eighteen
different locations azimuthally distributed around the explosive charge. A review
of the data shows that the peak radial velocity as a function of scaled range is
consistent with previous nuclear explosion data but exhibits greater variability.
The scaled peak radial displacement also exhibits greater variability but the mean
values are significantly higher than exhibited in previous nuclear explosion data.
Preliminary modeling of the SPE shots shows that continuum simulations that
do not explicitly account for the effect of joints will not successfully reproduce the
observed directional variations in the recorded data. However, 2D and 3D simu-
lations that explicitly account for joints and pre-existing fractures show that a low
friction angle, derived with water-filled joints, may account for the observed variation in peak velocity and displacement. Waves appear to propagate more readily
in the direction of persistent joints, as opposed to staggered joints. Furthermore,
the anisotropy associated with wave propagation seems to be more pronounced
when the friction angle was lowered to account for the effect of saturation.
Near Field Modeling of High Explosive Sources: Use of Abaqus Coupled
Euler-Lagrange Capability for Modeling the Source Physics Experiment
Bradley, C., Los Alamos National Laboratory, Los Alamos, NM, cbradley@
lanl.gov; STEEDMAN, D., Los Alamos National Laboratory, Los Alamos, NM,
[email protected]; GREENING, D., Los Alamos National Laboratory, Los
Alamos, NM.
Los Alamos National Laboratory participated in the development of the fully
coupled Euler-Lagrange (CEL) version of the Abaqus Finite Element code to support hydrodynamic penetration studies. Our Earth and Environmental Sciences
Division has been using this code to perform successful modeling of high explosive events including response of aircraft to explosive loading and coupling of buried explosive sources to complex geologic settings.
We use Abaqus/CEL to model the second in a series of planned Source
Physics Experiments (SPE-2) at the Nevada National Security Site. The SPE is
in support of the Nations verification efforts with nuclear treaty monitoring.
An Eulerian regime was used to model the high-deformation explosive source
in granite, while the coupling performed automatically within the code models
the transfer of energy to a Lagrange regime populated with complex material
response. The Lagrange scheme applied to the surrounding rock matrix allows
that the known faults in the shot vicinity can be explicitly modeled using existing,
proven contact algorithms. Our familiarity with the user material capability of
Abaqus provides that we can use our site-specific non-linear constitutive models.
We will describe our computation approach and provide some results in comparison to recorded data.
Factors Affecting the Spallation Signature for the Source Physics Experiment
(SPE-1)
Rougier, E., Los Alamos National Laboratory, Los Alamos, NM, erougier@
lanl.gov; KNIGHT, E. E., Los Alamos National Laboratory, Los Alamos, NM,
[email protected]; SUSSMAN, A. J., Los Alamos National Laboratory, Los
Alamos, NM, [email protected]; BROOME, S. T., Sandia National Laboratory,
Albuquerque, NM, [email protected]
The Source Physics Experiment (SPE) project comprises a series of underground
high explosive (HE) detonations designed to provide a carefully controlled seismic and strong motion data at the Nevada National Security Site (NNSS). The
first experiment in the series (SPE-1) was conducted in May, 2011 and it consisted of a 100 kg HE stemmed for coupling at a depth of burial of 180 feet. The
response of the free surface after the experiment was recorded by a number of
accelerometers. The readings from these accelerometers allow to establish spallation ranges that can be predicted quite well by an empirical scaling relationship
developed for nuclear explosions with nominal scaled depths of burial (~120 m/
kt1/3). However, this correlation is unordinary because the actual scaled depth
of burial of the SPE-1 experiment was 940 m/kt1/3. The presence of a water table
that almost reached the free surface at shot time, potential fault interactions and
the existence of layers of weathered material close to the free surface could provide the explanation for this striking discrepancy on the predicted vs. observed
spallation ranges. A series of hydrodynamic calculations with different saturation
levels and geophysical structures were conducted and the results will be presented
at the meeting. The material models used in the hydrodynamic models were populated with the help of lab experimental results for NNSS granite obtained by
Sandia National Laboratory under drained and fully saturated conditions.
Nonlinear Simulation of Explosion Sources with Gravity and Propagation to
Regional and Teleseismic Distances
Stevens, J. L., SAIC, San Diego, CA, [email protected]; O’BRIEN,
M. S., SAIC, San Diego, CA, Michael.S.O’[email protected]
The techniques for numerical modeling of underground explosions are well developed thanks to years of calculations performed for the nuclear containment and
nuclear monitoring programs. In addition techniques have been developed using
the representation theorem to propagate the near source solution to regional
and teleseismic distances. These calculations have allowed us to infer the dominant mechanisms operating in the explosion source, and the equivalent sources
that generate seismic waves. The most important mechanisms operating in an
underground explosion that affect seismic waves are: the approximately spherical
explosion energy source; the variation of overburden pressure with depth and free
surface above the source; tectonic strain release; and material properties in the
source region and variation in those properties with location, with shear strength
being the most important property. The first mechanism can be modeled with
one-dimensional spherically symmetric calculations, and is a monopole source.
Two-dimensional axisymmetric calculations with gravity can simulate the effect
of variable overburden pressure and spall, as well as tectonic release states of uniform horizontal compression or tension. These sources are represented by a monopole plus a complex linear vector dipole (CLVD) source, and a possible vertical
dipole source. Three dimensional calculations are required to simulate horizontal
variation in strength and material properties as well as non-isotropic tectonic
release. The extra degree of freedom provided in three dimensions makes generation of shear waves much easier than with the restriction to axisymmetric geometry. A three dimensional explosion source can be represented by a full moment
tensor source plus dipoles in any direction.
Modeling Far-Field Seismic Ground Motions from the Source Physics
Experiment Explosions with Three-Dimensional Simulations, Including
Hydrodynamic Modeling of the Source
Pitarka, A., Lawrence Livermore National Laboratory, Livermore, CA,
[email protected]; MELLORS, R. J., Lawrence Livermore National Laboratory,
Livermore, CA; RODGERS, A. J., Lawrence Livermore National Laboratory,
Livermore, CA; HARBEN, P. E., Lawrence Livermore National Laboratory,
Livermore, CA; WAGONER, J. L., Lawrence Livermore National Laboratory,
Livermore, CA; WALTER, W. R., Lawrence Livermore National Laboratory,
Livermore, CA; PASYANOS, M. E., Lawrence Livermore National Laboratory,
Livermore, CA; Petersson, A., Lawrence Livermore National Laboratory,
Livermore, CA; Xu, H., Lawrence Livermore National Laboratory Livermore,
CA
The Source Physics Experiment (SPE) at the National Nuclear Security Site
(NNSS) provides excellent new data for investigating the excitation and propagation of seismic waves by buried explosions. The far-field ground motions recorded
along five radial lines during the first two SPE explosions reveal complex features,
such as variations in P- and S-wave arrival times, amplitudes and scattered energy,
as well as substantial energy on the tangential component. These features cannot
be fully explained by simple models of the source and underground structure.
Complex waveform signatures are also observed in the near-field (< 20 m) suggesting some complexities are imprinted very close to the source, however these
features become more pronounced as the waves propagate away from the source
to due path-specific structure. In this study we analyze the effects of three-dimensional (3D) structure and scattering on wave propagation with the SPE data by
examining synthetic seismograms calculated with 3D seismic models representing different features of the underground structure and surface topography. By
progressively including several geological features into the 3D model we are able
to analyze separately the effects on wave propagation and scattering as well as
their contributions to S-wave generation. The 3D model is based on a regional
geological model developed in Earth Vision, with material properties constrained
by shallow borehole data. We will show results of broadband simulations performed with WPP, an anelastic 3D finite-difference code and compare synthetic
and observed waveforms. We will also show preliminary results of WPP simulations that use near-field ground motion calculated with GEODYN, a hydrodynamic code for modeling the response of earth materials to explosion loading.
The GEODYN-WPP coupling allows for a more complete representation of the
physics of seismic energy generation and its propagation in the earth’s crust.
Seismic P and S Source Functions of Underground Chemical Explosions
(SPE)
Xu, H., Lawrence Livermore National Laboratory, Livermore, CA, xu10@llnl.
gov; ANTOUN, T., Lawrence Livermore National Laboratory, Livermore, CA,
[email protected]; RODGERS, A., Lawrence Livermore National Laboratory,
Livermore, CA, [email protected]; GLENN, L., Lawrence Livermore National
Laboratory, Livermore, CA, [email protected]; VOROBIEV, O., Lawrence
Livermore National Laboratory, Livermore, CA, [email protected]; LOMOV,
I., Lawrence Livermore National Laboratory, Livermore, CA, [email protected];
HERBOLD, E., Lawrence Livermore National Laboratory, Livermore, CA,
[email protected]; Walter, W., Lawrence Livermore National Laboratory,
Livermore, CA, [email protected]; Ford, S., Lawrence Livermore National
Laboratory, Livermore, CA, [email protected]
Identifications and characterizations of the shear waves generated by the underground events are a challenging topic in monitoring and discriminating earthquakes and underground explosions. The Source Physics Experiment (SPE-N)
at the Nevada National Security Site (NNSS) is planned as a series of chemical
explosions under a variety of emplacement conditions and provides an excellent
opportunity for investigating the wave characteristics both in the close-in region
and at local distances. This study examines the strong motions recorded at 3
depths in the 6 boreholes in the initial two chemical events, SPE 1 (100kg) and
SPE 2 (1169kg) in granite, and derives the seismic source functions for P waves
from the radial motions using the reduced velocity potentials. The elastic radius is
chosen at 220m/(kt)^(1/3) and is consistent with that obtained by Perret (1972)
for HARD HAT, SHOAL and PILEDRIVER events. The results show that the
source spectra derived from the borehole recordings are in good agreement with
the Mueller-Murphy (1971) model (P wave) for these two SPE events in form of
seismic moment, corner frequency and high-frequency roll-off slope.
For the transverse motions recorded in the two events, similar methodology is utilized to obtain the analogous source spectra for SV and SH waves in
the same manner as for P waves by substituting S wave speed for P wave speed
and assuming the transverse components are roughly distance-dependent only.
The empirical Mueller-Murphy S wave model is written in the same functional
form with the S wave speed instead of the P wave speed. The results demonstrate
that the analogous source spectra for both SV and SH waves derived from both
the SPE explosions have some consistency with the empirical Mueller-Murphy S
model in form of the high-frequency roll-off slope though the corner frequencies
are higher than predicted and the analogous seismic moments in general show
more variations than for P waves.
Investigating How and Why P/S Ratios Discriminate Explosions from
Earthquakes Using the Source Physics Experiment at the NNSS
Walter, W. R., Lawrence Livermore National Lab, Livermore, CA, walter5@
llnl.gov; FORD, S., LLNL, Livermore, CA, [email protected]; MELLORS, R.,
LLNL, Livermore, CA, [email protected]; PASYANOS, M., LLNL, Livermore,
CA, [email protected]; MATZEL, D., LLNL, Livermore, CA, matzel1@llnl.
gov; RODGERS, A., LLNL, Livermore, CA, [email protected]; PITARKA,
A., LLNL, Livermore, CA, [email protected]; Xu, H., LLNL, Livermore,
CA, [email protected]; Antoun, T., LLNL, Livermore, CA, antoun1@llnl.
gov; Vorobiev, O., LLNL, Livermore, CA, [email protected]; Lomov,
I., LLNL, Livermore, CA, [email protected]; Glenn, L., LLNL, Livermore,
CA, [email protected]; Myers, S., LLNL, Livermore, CA, [email protected];
Hauk, T., LLNL, Livermore, CA, [email protected]; Dodge, D., LLNL,
Livermore, CA, [email protected]; and Ruppert, S., LLNL, Livermore, CA,
[email protected].
It is well established that regional distance (200-1600 km) amplitude ratios of
seismic P-to-S waves at sufficiently high frequencies (~>2 Hz) can discriminate
explosions from earthquakes. However the physical basis for the generation of
explosion S-waves, and therefore the predictability of the P/S discriminant as
a function of event properties such as size, depth, geology and range, remains
incompletely understood. A goal of the Source Physics Experiments (SPE) at
the Nevada National Security Site (NNSS, formerly the Nevada Test Site) is to
improve our physical understanding of the mechanisms of explosion S-wave generation and improve our ability to numerically model and predict them.
Here we take advantage of the natural seismicity at the NNSS to record
nearby earthquakes at stations in common with those recording the SPE chemical explosions. We demonstrate that at local distances (0-200 km) P/S ratios in
the 2-100 Hz range can discriminate the small chemical SPE explosions (100 and
1000 kg) from small (magnitude 0-3) earthquakes. We compare the earthquake
P and S waves to modified Brune (1970) spectral models and the explosions to
several P and S-wave models. In particular we are examining the frequency dependent behavior of the P/S ratios as a function of explosion size, depth, geology and
path. Finally we compare our empirical observations with extensive numerical
modeling results for the SPE shots that couple the non-linear to elastic regimes.
SPE Source Characterization Using Hydrodynamic-to-Seismic Coupling and
Moment-Tensor Inversion
Yang, X., Los Alamos National Laboratory, Los Alamos, NM, xyang@lanl.
gov; PATTON, H. J., Los Alamos National Laboratory, Los Alamos, NM,
[email protected]; ROUGIER, E., Los Alamos National Laboratory, Los Alamos,
NM, [email protected]; ROWE, C. A., Los Alamos National Laboratory, Los
The Source Physics Experiment (SPE) being conducted at the Nevada National
Security Site (NNSS, formerly NTS) consists of a series of explosions detonated
or to be detonated in different emplacement and geologic environments. Sensors
deployed at near-source, local and near-regional distances record signals from
these explosions. To characterize SPE explosions and to validate new explosion
source models, we have developed capabilities to propagate hydrodynamic explosion simulations to seismic distances by coupling hydrodynamic and seismic
codes. We use a frequency-domain moment-tensor inversion method to invert
simulated seismograms from the coupling for time-dependent source moment
tensors. Initial results indicate that reasonable source moment tensors, including
both component strength and time histories, can be recovered. In addition, we
also observe interesting phenomena from the results. For example, the recovered
source spectrum shows more overshoot and a faster high-frequency decay than
what the Muller-Murphy model predicts. We are developing inversion techniques
to better resolve the source as well as to better quantify both the explosion and
the damage sources it induces. Using the inversion technique developed from
simulated data, we will construct time-dependent source moment tensors for
SPE explosions by inverting observed data. Preliminary results will be presented
at the meeting.
Moment Tensor Analysis of SPE-1 and -2
Ford, S. R., LLNL, Livermore, CA, [email protected]; MELLORS, R. J., LLNL,
Livermore, CA, [email protected]; WALTER, W. R., LLNL, Livermore, CA,
[email protected]
We calculate the seismic moment tensors of the Source Physics Experiment (SPE)
100 kg (SPE-1) and 1000 kg (SPE-2) explosions. Greens functions are obtained
from the response of a halfspace, and layer-over-a-halfspace via a 1-D f-k calculation (FKRPROG), and a full three-dimensional velocity model via a finitedifference calculation (WPP). Empirical Greens functions are obtained via the
deconvolution of SPE-1 from SPE-2. We investigate the relative contribution
of isotropic and deviatoric moment, and interpret the contributions in terms
of possible source models. A moment tensor description of the SPE source can
aid in the interpretation of farfield measurements. This research was performed
under the auspices of the U.S. Department of Energy by the Lawrence Livermore
National Laboratory under contract number DE-AC52-07NA27344. LLNLABS-522595.
Analysis of the Influence of Topography and Local Wave Propagation Model
on Waveforms Recorded During the Source Physics Experiments
Saikia, C. K., Air Force Technical Applications Center, Patrick, FL,
[email protected]; WOODS, M., Air Force Technical Applications
Center, Patrick, FL, [email protected]; MILLER, J., BAE System, Patrick,
FL; NGUYEN, B., Air Force Technical Applications Center, Patrick, FL;
SNELSON, C., National Center for Nuclear Security/NSTec, Las Vegas,
NV, [email protected]; TOWNSEND, M., National Center for Nuclear
Security/NSTec, Las Vegas, NV; DWYER, J. J., Air Force Technical Applications
Center, Patrick, FL.
We are investigating waveforms recorded by our local stations including those
deployed by the national laboratories and stations operated by IRIS, DMC within
150 km of the SPE shot point in granite of Climax Stock, NNSS. Objectives are
to explore whether (i) the Mueller-Murphy source can explain the observed spectra ratios computed for both P-wave and the entire seismogram, (ii) the amplitude
variation of the P and Rg wave, including the time-domain characteristics of the
Rg waves propagating along the linear profiles are related to the station elevation
or to the interaction of seismic waves with the topography, topography with the
faults, surface geology or all these effects combined, and (iii) the estimated mb
values and their uncertainties compare with the known values of source parameters. This study suggests that the amplitude of the P wave onsets depends on the
station elevation and structure along the wave propagation path. The amplitude
of the direct P wave varies along the same profile and is probably due to the shadowing of seismic rays. We found that a factor of 10-15 is necessary for the first shot
to match the amplitude and the spectra of the SPEs. This observation is consistent
even for stations of other networks that surrounded the SPE and recorded both
SPE-I and SPE-II, and does not bear well with the analysis using the MuellerMurphy source function. A preliminary simulation of 3D finite-difference seismograms using 1D, a 3D model only with the topography, and a 3D topography
model that also included two-fault model suggested waveforms are marginally
distinguishable for the majority of stations, and failed to produce good agreement
in the Rg waves. We expect the agreement to become better in our continuation
study by including a complex geology model. At this stage, the uncertainty in the
empirical mb estimates is high, and is probably due to the influence of either the
wave propagation or a poor instrument coupling on amplitude.
Generation and Propagation of Shear Waves from the HUMBLE REDWOOD
Explosions
Bonner, J. L., Weston Geophysical Corp., Lufkin, TX, bonner@
westongeophysical.com; LEIDIG, M., Weston Geophysical Corp., Houston,
TX, [email protected]; REINKE, R., Defense Threat Reduction
Agency, Albuquerque, NM, [email protected]; LENOX, E., Defense
Threat Reduction Agency, Albuquerque, NM, [email protected]
The HUMBLE REDWOOD (HR) I and II experiments (Foxall et al., 2008,
2010) provide a unique opportunity to study local phase generation, in particular
S-waves, from above- and below-ground explosions. We have identified P-waves,
higher and fundamental-mode Rayleigh (Rg) waves, and Love (SH) waves from
656 kg ANFO explosions detonated above and in alluvium in the Albuquerque
Basin, New Mexico. Identification of P and Rg was relatively simple based on
arrival times and rectilinear and retrograde elliptical particle motion, respectively.
Identification of higher mode Rayleigh waves required particle motion (prograde
elliptical) and synthetic modeling. The candidate shear (SH) arrivals from the
above-ground shots are difficult to positively identify due to small amplitudes
and complex particle motion. Conversely, the SH arrivals for most of the belowground explosions are positively identified as Love waves with transverse particle
motion and group velocity dispersion curves that match the theoretical curves for
a local velocity model based only on Rg. We have modeled the S-waves using the
Fisk (2006) conjecture and the Mueller and Murphy (1971) source, and we have
formed P/S ratios for the explosions for comparison to 13 earthquakes within
100 km of the HR test site. We explore possible sources for Love wave generation
from these explosions ranging from asymmetries in the source region to damage/
crack generation in low-strength media. Using high speed videography, we have
been able to digitally map the crack generation for one of the underground shots.
Oral Session · Wednesday 1:30 pm, 18 April · Pacific Salon
1&2
Session Chairs: Danijel Schorlemmer, David Jackson, Matt C.
Gerstenberger, and Matthias Holschneider
Segment Boundaries: It May Be a Matter of Time
Goldfinger, C., Oregon State University, Corvallis, OR, gold@coas.
oregonstate.edu
Our view of earthquake phenomenon is highly influenced by the timescale of the
observations. We may assign segment boundaries to faults based on actual behavior of the fault in past earthquakes, from interpretation of structural barriers,
and from geodetic observables. Rarely though do we have records long enough to
assess the consistency of the observations very well. The ~ 100 year instrumental
record can only rarely capture multiple earthquake cycles. Geodetic observations
only capture part of one cycle typically. For the most part, we do not have observations spanning a long enough period to define segmentation of a fault based on
actual performance, so a proxy of some sort is used. The record from NE Japan,
even with ~ 1000 years of historical record, was not sufficient to illuminate the
apparent cycling of very large events every ~ 1000 years or so, with many smaller
events scattered in the submarine forearc. Some interpreted these smaller events
as evidence of a segmented system. In Cascadia, for some time it was thought that
full-length M9 ruptures were the norm. Long paleoseismic records have revealed
segmented ruptures that could consistently be assigned to the southern margin.
The Haiyaun fault has very large ruptures that violate shorter segment boundaries,
but at intervals of ~ 5000 years. Were it not for the devastating 1920 earthquake,
and extensive 3D trenching, this would not be known. The Himalayan front may
have a similar history. Where long records are available, segment boundaries are
present, and are sometimes violated at variable time scales. Understanding the
phenomenon is for the most part not within the realm of seismology, and our
ability to model it from first principles is limited by poorly constrained parameterization and lack of a stress history (supercycles?). We require records much
longer than currently available, but long records are currently the best tool for
assessing the importance of segment boundaries.
Evidence Against the Hypothesis of Fault Segmentation
Hardebeck, J. L., US Geological Survey, Menlo Park, CA, jhardebeck@
usgs.gov
The segmentation model proposes that faults are divided into segments, each of
which fails as a whole in large earthquakes. Segment boundaries, usually defined
by surface trace irregularities and/or the ends of prior earthquakes, are taken to
be persistent barriers to earthquake rupture. The 2011 M9 Tohoku earthquake
ruptured across what was thought to be multiple segments limited to M8 events,
marking the failure of one particular segmentation model. Another recent earthquake more clearly contradicts a strong version of the segmentation hypothesis,
that segment boundaries are impenetrable barriers to earthquake rupture. The
2007 M8.1 Solomon Islands megathrust event spanned a tectonic triple junction,
where the Australia and Solomon Sea Plates subduct beneath the Pacific Plate
(Furlong et al., Science 2009.) This earthquake shows that not even a tectonic
plate boundary poses an impassable barrier to earthquake rupture, so it seems
unlikely that the smaller fault junctions and irregularities that are often proposed
as segment boundaries would be significant persistent rupture barriers. A weaker
version of the segmentation model proposes that faults fail in a limited number
of single- or multi-segment scenarios, often defined from past events. However,
random processes can create apparent patterns in small samples, so one must also
consider whether the past events are consistent with an unsegmented rupture process, as for the San Andreas Fault (Biasi & Weldon, BSSA 2009) and the Nankai
Trough (Parsons et al., in review). Earthquake occurrence is more likely controlled by stress at seismogenic depths. The Parkfield section of the San Andreas
consists of a long-lived high stress zone (Tormann et al., in review) likely related
to material properties (Michael & Eberhart-Phillips, JGR 1993). Persistent zones
of stress and slip may become expressed at the surface (e.g. Simpson et al., BSSA
2006; Wells et al., JGR 2003), creating the appearance of fault segmentation.
Earthquake Debate #2: PSHA Methodology
1&2
Session Chairs: Danijel Schorlemmer, David Jackson, Matt C.
Gerstenberger, and Matthias Holschneider
Has PSHA Done Its Time? The Hazard Mapper’s Perspective
Stirling, M. W., GNS Science, Lower Hutt, New Zealand, m.stirling@gns.
cri.nz
It has recently been suggested that probabilistic seismic hazard (PSH) modeling
has “done its time” and needs to be updated. Two bases for this perspective are
that many recent model updates have shown relatively minor changes to estimated hazard, and that PSH models have been inadequate for forecasting recent
devastating earthquakes.
The reduced changes to PSH models in recent versus earlier model iterations could be seen positively as the models having achieved some degree of stability, or negatively as PSH methodology having reached the point of diminishing
returns. I argue for the positive in the context of the PSH models being used correctly. Much of the issues associated with PSH models result from the misuse of
the models as short-term forecasting tools. The models are developed to provide
estimates of hazard for long return times (e.g. hundreds to thousands of years),
rather than to provide short-term (e.g. months to years) probabilities for impending earthquakes. PSH maps for long return times typically show large differences
in hazard across countries like the USA and New Zealand, reflecting differences
in the expected future activity of earthquake sources across the countries. The
PSH-derived hazard estimates can also be disaggregated to identify the most
likely (or most unlikely) earthquake scenarios for the site or region in question.
To replace PSH methodology requires the development of reliable and versatile
short-term-to-long-term forecasting methods. Promising efforts have been happening in California, New Zealand and elsewhere, but it is still early-days in
terms of a substantial update to PSH methodology. Until that time it seems that
PSH methodology is here to stay, with tangible “toolbox” improvements being
made wherever possible (e.g. ground motion prediction equations, epistemic
uncertainty, probabilistic versus deterministic treatment, testing methods, incorporation of time dependence).
Probabilistic Seismic Hazard Assessment and the Hazards of Overconfidence
Werner, M. J., Princeton University, Princeton, NJ, [email protected]
Probabilistic Seismic Hazard Assessment (PSHA) has been instrumental in
guiding the design of building codes, setting earthquake insurance rates, and
mitigating seismic hazard and risk. But recent—and not so recent—earthquakes
around the globe have brought shortcomings in the classical methodology to
light that suggest a fundamental rethinking of PSHA towards a validation-based
endeavor. Some shortcomings are a result of continued confidence in assumptions
that are untested, only valid in special circumstances, or demonstrably wrong.
These include, amongst others, (1) fault segments that determine maximum magnitudes and recurrence intervals, (2) a lack of space-time clustering, (3) quasiperiodic characteristic earthquakes, and (4) a small set of “allowed” large earthquakes on an incomplete set of faults. Several alternatives to traditional PSHA
are (or are becoming) available. Physics-based hazard calculations, which might
eventually generate broad-frequency end-to-end ground motion simulations of
earthquake ruptures probabilistically forecast by physics-based earthquake simulators, provide an attractive research avenue. At the moment, however, many
interesting scientific questions remain about the validity of the modeled physics
to large regions, and, moreover, about the calibration and validation of the models. Meanwhile, stochastic-empirical seismicity and earthquake rupture models,
which encode physical principles of earthquake processes in a statistical manner,
are available now, and, because of their simplicity and flexibility, have been and
continue to be under validation in experiments of the global Collaboratory for
the Study of Earthquake Predictability (CSEP). PSHA assumptions should be
continuously and globally tested in the same manner. CSEP already provides
basic cyber-infrastructure for such a validation-based PSHA, presenting an
opportunity for mitigating the hazards of overconfidence.
Wave Propagation
Oral Session · Wednesday 8:30 am, 18 April · Pacific Salon 3
Session Chairs: Emmanuel Chaljub, Steven Day, and Peter
Moczo
FD Modeling of Seismic Motion with a Stable Arbitrarily Discontinuous
Staggered Grid
Kristek, J., Comenius University Bratislava, Slovakia, kristek@fmph.
uniba.sk; MOCZO, P., Comenius University Bratislava, Slovakia; GALIS, M.,
Comenius University Bratislava, Slovakia.
Recent E2VP-Cashima numerical modeling of earthquake motion in the
Mygdonian basin, Greece, included 5 km × 15 km sediments with maximum
thickness 400 m, minimum VS=200 m/s, VP/VS=7.5, and VS=2600 m/s in the
bedrock. Consequently, the finite-difference (FD) modeling of 30 s time window
in the frequency range [0.3, 6 ] Hz was heavily depending on the computational
efficiency of the applied finite-difference scheme. The key aspect of the efficiency
was the use of a discontinuous staggered grid for the 4th-order velocity-stress
scheme.
We present an algorithm of the spatial discontinuous staggered grid. The
ratio between the grid spacings of the coarser and finer grids can be an arbitrary
odd number. We numerically tested ratios up to 25.
Relatively many algorithms for different kinds of discontinuous grids have
been developed and published. They focused on the problem how to interpolate
values at missing grid positions in order to update wavefield in the finer grid. As
we found out, the interpolation, in fact, neither poses a real problem nor solves
the key aspect of a contact between the finer and coarser grids. As far as we know
the other algorithms did not address this aspect and consequently and inevitably
had problems with stability.
The key aspect of a contact between the finer and coarser grids is what values at grid positions of a finer grid should enter the update in the coarser grid.
We solve this aspect by the application of the Lanczos downsampling filter. Our
algorithm is sufficiently accurate and stable.
Increasing the Frequency Resolution in Realistic Seismic Wave Simulations
by Using a 4th Order Accurate Summation by Parts Finite Difference Method
Petersson, N. A., Lawrence Livermore National Lab, Livermore, CA;
SJOGREEN, B., Lawrence Livermore National Lab, Livermore, CA.
Increasing the frequency resolution in seismic wave simulations is very important, e.g. in seismic monitoring applications, geophysical exploration, and for coupling the ground motion to engineering structures. There are two basic ways of
accomplishing this goal: a) buying a faster/bigger computer to increase the number of grid points, or b) finding a more efficient numerical method. Optimally, a)
and b) should be used together. This presentation will address b) by developing
a 4th order accurate, energy conserving, finite difference method for the elastic
wave equation.
The 4th order accurate method solves the elastic wave equation in second
order displacement formulation, which reduces the memory requirements compared to the first order velocity-stress formulation because the number of dependent variables is smaller. 4th order accuracy holds in both space and time. The
stability of the method is mathematically established through discrete energy
estimates using the summation by parts properties of the boundary modified
difference stencils. The stability holds for arbitrary heterogeneous material properties, on 2-D and 3-D spatial domains with Dirichlet or free surface (traction)
boundary conditions. The 4th order method satisfies the same fundamental
properties as our 2nd order accurate method, currently implemented in the open
source code WPP. These properties enable the basic 4th order method to be generalized to curvilinear grids allowing for realistic topography, mesh refinement
interfaces with hanging nodes, and visco-elastic material models.
Numerical examples show that the 4th order scheme is stable for CFLnumbers up to 1.3, and demonstrate a significant improvement in efficiency over
the 2nd order accurate method. Results are presented for the notoriously difficult
test problem of propagating Rayleigh surface waves in an almost incompressible
elastic half-space, i.e., a material where the compressional wave speed is much
larger than the shear speed.
Accuracy of Numerical Schemes with Respect to the P-Wave to S-Wave
Speed Ratio
Moczo, P., Comenius University Bratislava, Slovakia, [email protected];
KRISTEK, J., Comenius University Bratislava, Slovakia, [email protected].
sk; GALIS, M., Comenius University Bratislava, Slovakia, martin.galis@fmph.
uniba.sk; CHALJUB, E., ISTerre, Grenoble, France, [email protected]; CHEN, X., University of Science and Technology of China, Hefei,
Anhui, China, [email protected]; ZHANG, Z., University of Science and
Technology of China, Hefei, Anhui, China, [email protected]
Numerical modeling of earthquake ground motion in sedimentary basins and
valleys often has to account for the P-wave to S-wave speed ratios (VP/VS) as large
as five and even larger, mainly in sediments below groundwater level. The ratio
can attain values larger than 10—the unconsolidated lake sediments in Ciudad
de México are a good example. At the same time, accuracy of the numerical
schemes with respect to VP/VS has not been sufficiently analyzed. The numerical
schemes are often applied without adequate check of the accuracy.
We present theoretical analysis and numerical comparison of 18 3D numerical time-domain explicit schemes for modeling seismic motion for their accuracy
with the varying VP/VS. The schemes are based on the finite-difference, spectral-element, finite-element and discontinuous-Galerkin methods. All schemes
are presented in a unified form. Theoretical analysis compares accuracy of the
schemes in terms of local errors in amplitude and vector difference. In addition to
the analysis we compare numerically simulated seismograms with exact solutions
for canonical configurations.
We compare accuracy of the schemes in terms of the local errors, grid dispersion and full wavefield simulations with respect to the structure of the numerical schemes.
Modeling of Wave Propagation in Nonlinear Media for Inversion of Dynamic
Soil Properties from Earthquake Records
Roten, D., ETH Zürich, Zürich, Switzerland, [email protected];
FÄH, D., ETH Zürich, Zürich, Switzerland, [email protected]; LAUE,
J., ETH Zürich, Zürich, Switzerland, [email protected]; BONILLA, L. F.,
Universite Paris-Est, Paris, France, [email protected]
The rapid development of computer resources and the introduction of broadband
methods has enabled physics-based models of wave propagation to advance into
the frequency domain where nonlinear soil behavior is important (> 1 Hz). Even
though multiple constitutive models exist that predict the nonlinear stress-strain
behavior in soils including pore pressure generation and effective stress reduction,
modeling of nonlinear site response is often impeded by insufficient knowledge
about dynamic soil properties. Calibration of soil models from laboratory tests
remains costly and is aggravated by the difficulty to obtain undisturbed samples.
In this study we aim to invert vertical array records of strong ground motion for
the dilatancy parameters in the Iai et al. (1990) cyclic mobility model. The forward problem is represented by vertical SH wave propagation inside a horizontally layered medium with known low-strain geophysical properties but unknown
dilatancy parameters. We use the finite difference (FD), nonlinear effective stress
code NOAH to solve the forward problem and take the measured borehole accelerogram as input at the bottom of the model. We sample the parameter space
with the neighborhood algorithm (NA) and seek for a model that minimizes the
misfit between simulated and observed free-surface acceleration time series and,
if applicable, simulated and observed excess pore pressures. The NA takes advantage of parallel computing by distributing the FD simulations for the ensemble
of solutions over multiple CPU cores during each iteration. Application of the
method to the Wildlife refuge records of the 1987 Elmore ranch and Superstition
Hills earthquakes yields dilatancy parameters that are consistent with those
reported from a previous study. With the increasing volume of strong motion
data acquired on vertical arrays worldwide, this approach may contribute to a
more comprehensive characterization of nonlinear soil behavior during strong
ground motion.
Modeling Long Period (T > 4 sec) Strong Ground Motions for the 2011 Mw 9
Tohoku-Oki Earthquake using an Enhanced Source Representation and 3D
Seismic Velocity Models
Graves, R. W., US Geological Survey, Pasadena, CA, [email protected];
WEI, S., Caltech, Pasadena, CA; HELMBERGER, D., Caltech, Pasadena, CA.
Recent work by Wei et al (2012) inverted static GPS, ocean bottom geodetic measurements, and strong motion waveforms to derive a rupture model of the 2011
Mw 9 Tohoku-Oki earthquake. The inversion shows the large displacement rup-
ture close to the trench was dominated by relatively long period (>20 sec) radiation and led to the generation of the devastating tsunami. On the other hand,
the strong shaking came primarily from deeper rupture (>30 km) having relatively small displacements radiating at relatively short periods (<20 sec). Detailed
resolution of shorter period features using the current inversion methodology
is limited by several factors including smoothing constraints and modeling
assumptions on subfault size and shape of the slip rate function. Consequently,
the derived rupture model is relatively deficient at shorter periods (4–10 sec), and
tends to under-predict the observed waveforms in this period range. Additionally,
3D wave propagation effects further modify the observed ground motion
response, particularly in the deep sedimentary basin regions around Tokyo and
Niigata. In order to better model the observed ground motions, we first enhance
the source radiation at shorter periods by adding shorter length scale (<40 km)
stochastic features to the inverted rupture model and by replacing the slip rate
function with a Kostrov-like representation following the procedure outlined by
Graves and Pitarka (2010). Next we run forward simulations using this enhanced
rupture description using two recently developed Japan-wide 3D seismic velocity
models (NIED and JIVSM). The combination of the enhanced source and 3D
structure models significantly improves the fit to the observed ground motion
response. The response simulated using the JIVSM model does somewhat better
than NIED at matching the observed pattern and levels of amplification, as well
as in matching the waveform character and duration of later arriving phases.
Why Should Stress Drop in Dynamic Earthquake Source Models Be
Heterogeneous with a Power-Law Spatial Fourier Transform with Exponent
–1?
Andrews, D. J., USGS, emeritus, Menlo Park, CA.
A random function on a 2D plane with a power-law Fourier transform proportional to 1/k, where k is magnitude of the 2D wavenumber, is self-similar in the
sense that it is statistically the same at different length scales. Its power spectral
density is the square of the transform times 2πk, which is again proportional to
1/k. There is equal power in equal logarithmic wavenumber intervals. The variance of the function grows as the bandwidth is increased.
If a fault is idealized to be a plane, there are reasons to believe that stress
on the fault is self-similar, at depths within the seismogenic zone. Earthquake
stress drops have a distribution that is independent of magnitude or length scale.
The Gutenberg-Richter distribution of earthquake sizes with b=1 implies that
the number of events with rupture area greater than A is proportional to 1/A.
This is a self-similar distribution. The sum of stress changes from such a distribution of events at random locations is self-similar. It is a reasonable supposition for
dynamic simulations that stress drop is self-similar; with stress drop fluctuations
at wavelengths shorter than the rupture length determining high-frequency radiation, and fluctuations at larger scales determining the stopping of the rupture.
Spontaneous dynamic rupture with heterogeneous stress drop will have variable
rupture velocity. It is necessary to do such dynamic calculations in order to verify
whether self-similar stress drop will produce the observed flat acceleration spectrum at high frequencies. If that is the case, then dynamic spontaneous rupture
calculations will become a valuable simulation tool.
The unlimited variance of the self-similar function as the bandwidth is
increased in the Gaussian case can be avoided by using the asperity model of
Andrews and Barall (2011), in which stress is large but finite in a self-similar set
of asperities.
Constraints on Strong Ground Motion from Complex Dynamic Rupture
Simulations in Elastic and Plastic Media
Gabriel, A. A., ETH Zurich, Zurich, Switzerland, [email protected];
AMPUERO, J. P., Caltech, Pasadena, CA; MAI, P. M., KAUST, Thuwal,
Kingdom of Saudi Arabia; DALGUER, L. A., ETH Zurich, Zurich, Switzerland.
Ruptures can propagate with a variety of “styles” (spatio-temporal patterns),
which can be classified by several criteria: stability (decaying, steady or growing
behavior of peak slip rate), rise time (pulses or cracks), rupture speed (subshear or
supershear), and complexity (single or multiple rupture fronts). In an intrinsically
heterogeneous natural environment, earthquakes may not be restricted to a single
rupture style but rather involve complex rupture patterns with multiple rupture
fronts and multiple styles. The detection of rupture style and its transitions may
help elucidating the state of stress and strength of active fault zones.
High stress concentrations at earthquake rupture fronts may generate an
inelastic off-fault response at the rupture tip, leading to increased energy absorption in the damage zone. Furthermore, the induced asymmetric plastic strain field
in in-plane rupture modes may produce bimaterial interfaces that can increase
radiation efficiency and reduce frictional dissipation. Off-fault inelasticity thus
plays an important role for realistic predictions of near-fault ground motion.
This presentation focuses on the effects of rupture style and off-fault plasticity on the resulting ground motion patterns on measurable earthquake source
properties, especially on characteristic slip velocity function signatures.
We perform rupture dynamics simulations including rate-and-state friction
and off-fault plasticity to analyze quantitatively macroscopic source properties for
different rupture styles and their transitional mechanisms. The energy dissipation
due to off-fault inelasticity modifies the conditions to obtain each rupture style
and alters macroscopic source properties. We examine apparent fracture energy,
rupture and healing front speed, peak rupture and healing front speed, peak slip
and peak slip velocity, dynamic stress drop, slip and plastic seismic moment, size
of the process and plastic zones and their connection to ground motion.
Earthquake Source Dynamics of the 2011 Mw 9.0 Tohoku Earthquake
Constrained with Kinematic Source Inversion Results
Galvez, P., Swiss Seismological Service, ETH-Zurich, Zurich, Switzerland,
[email protected]; DALGUER, L. A., Swiss Seismological Service,
ETH-Zurich, Zurich, Switzerland, [email protected]; AMPUERO, J. P.,
California Institute of Technology, Pasadena, CA, [email protected].
edu; NISSEN-MEYER, T., Institute of Geophysics, ETH-Zurich, Zurich,
Switzerland, [email protected]
The 2011 Mw 9.0 Tohoku earthquake and its induced tsunami stroke the east
cost of the main island of Japan causing severe damage in cities. Kinematic source
models inverted from seismological, geodetic and tsunami observations, including source images from back-projection, indicate that the earthquake featured
complex rupture patterns, with multiple rupture fronts and rupture styles. The
compilation of these studies reveals distinct regions of low and high frequency
radiation: the regions of large slip in the shallower part of the fault dominate the
low frequency radiation and the bottom part dominates the high frequency radiation.
We investigate the features of this earthquake by developing spontaneous rupture models constrained by kinematic source slip derived from source
inversion. We estimate the stress drop distribution from the kinematic source
models to calculate the initial stress, constrained by a frictional strength profile
with depth dependent normal stress distribution of a realistic non-planar fault
geometry. Surface rupture is allowed. The shallow part of the fault is considered
as a stable zone that operates during rupture with an enhanced energy absorption
mechanism. We model this zone by assuming negative stress drop and large critical slip distance. Guided by conceptual dynamic rupture models developed by
Huang et. al. (2011 EPS) in 2D and Galvez et al (2012 in preparation) in 3D, we
incorporate small patches of asperities at the bottom of the fault to account for
the strong high frequency radiation.
We use the unstructured 3D spectral element open source code
SPECFEM3D, in which we recently implemented the dynamic fault boundary
conditions. In our models, we examine the frequency content of the slip velocity
pulse as a measure of ground-motion excitation, to define low and high frequency
radiation regions compatible with the source models derived from observed data
described above.
Computation of H/V Spectral Ratios of Microtremors at Sites with Strong
Lateral Heterogeneity using Diffuse Field Theory and IBEM
MOLINA-VILLEGAS, J. C., Instituto de Ingeniería, UNAM, Cd Universitaria,
Coyoacán DF, Mexico, [email protected]; PEREZ-GAVILAN, J. J., Instituto
de Ingeniería, UNAM, Cd Universitaria, Coyoacán DF, Mexico, jjpge@
pumas.iingen.unam.mx; SUAREZ, M., Instituto de Ingeniería, UNAM, Cd
Universitaria, Coyoacán DF, Mexico, [email protected]; FRANCO-CRUZ, P.,
Instituto de Ingeniería, UNAM, Cd Universitaria, Coyoacán DF, Mexico,
[email protected]; CHAVEZ-ZAMORATE, N., Instituto de
Ingeniería, UNAM, Cd Universitaria, Coyoacán DF, Mexico, nchavezz@
iingen.unam.mx; SANCHEZ-SESMA, F. J., Instituto de Ingeniería, UNAM, Cd
Universitaria, Coyoacán DF, Mexico, [email protected]; MATSUSHIMA, S.,
Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto
611-0011, Japan, [email protected]; Kawase, H., Disaster
Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011,
Japan, [email protected]; Luzon, F., Departamento de Física
Aplicada, Universidad de Almería, Cañada de San Urbano s/n; 04120-Almería;
Spain, [email protected].
It is well known that horizontal-to-vertical (H/V) spectral ratios of microtremors
are useful to identify the dominant shear frequency. In some cases H/V is considered to be either the S wave amplification or the Rayleigh wave ellipticity although
there are little theoretical support despite certain resemblance of results.
It has been recently proposed a theory for microtremor H/V spectral ratios
based on the diffuse field assumption (Sánchez-Sesma et al., 2011). In this theory
H/V corresponds to the square root of the ratio of the sum of horizontal energy
densities with respect to the vertical one. The directional energy densities are
proportional to the imaginary parts of the corresponding components of Green’s
tensor when both source and receiver are the same point.
For horizontally layered medium, we can easily calculate the theoretical Green function. Thus, by observing microtremors we can assess the underground structure below by using the theoretical point source solution. On the
other hand, for a laterally heterogeneous structure, the horizontal responses are
different. In that case, to interpret microtremor H/V spectral ratios, a numerical
approach is needed. In this communication the 3D indirect boundary element
method (IBEM) is used to study laterally heterogeneous elastic layers over a halfspace. In order to overcome the singularity within the IBEM the reference solutions correspond to the classical half-space problems by Lamb (1904) and Chao
(1960), for normal and tangential loads, respectively. A large number of cases are
analyzed for which we compute the H/V in 3D settings.
References
Chao, C. C. (1960). J. Appl. Mech. 27, 559–567.
Lamb, H. (1904). Phil. Trans. Roy. Soc. Lond. Ser. A 203, 1–42.
Sanchez-Sesma, F J. (2011). Geophys. J. Int. 186, 221–225.
On Numerical Solving the Complex Eikonal Equation using Ray Tracing
Methods
Vavrycuk, V., Institute of Geophysics, Academy of Sciences, Prague, Czech
Republic, [email protected]
The complex eikonal equation in isotropic or anisotropic viscoelastic media is
solved using three alternative ray-tracing methods: the complex ray tracing, the
real viscoelastic ray tracing, and the real elastic ray tracing. The complex ray tracing is complicated but yields the most accurate results, which serve as the reference solution. The real ray-tracing approaches are simpler but approximate.
Two models of a smoothly inhomogeneous viscoelastic medium with high
velocity gradients and with strong attenuation are used to check the robustness
of the approximate methods. The numerical modelling reveals that the real viscoelastic ray tracing is unequivocally preferable to the elastic ray tracing. It is
more accurate and works even in situations when the elastic ray tracing fail. In
the studied models, the errors in the complex travel time produced by the real viscoelastic ray tracing were 15 to 30 times less than those of the elastic ray tracing.
Also the ray fields calculated by the real viscoelastic ray tracing were excellently
reproduced even in the case when the elastic ray tracing yielded completely distorted results. Compared with the complex ray tracing, which is limited to simple
types of media, the real viscoelastic ray tracing offers a fast and computationally
undemanding procedure for calculating the complex travel times in complicated
3-D inhomogeneous attenuating structures.
Development and Optimizations of a SCEC Community Anelastic Wave
Propagation Platform for Multicore Systems and GPU-based Accelerators
Cui, Y., San Diego Supercomputer Center, La Jolla, CA, [email protected];
OLSEN, K. B., San Diego State University, San Diego, CA, kbolsen@sciences.
sdsu.edu; ZHOU, J., UC San Diego, La Jolla, CA, [email protected]; SMALL,
P., University of Southern California, Los Angeles, CA, [email protected];
CHOURASIA, A., San Diego Supercomputer Center, La Jolla, CA, amit@
sdsc.edu; DAY, S. M., San Diego State University, San Diego, CA, steven.day@
geology.sdsu.edu; MAECHLING, P. J., University of Southern California, Los
Angeles, CA, [email protected]; Jordan, T. H., University of Southern
California, Los Angeles, CA, [email protected]
AWP-ODC is a scalable finite-difference application package, involving collaborative development coordinated by the SCEC Community Modeling
Environment. This platform has undergone many optimizations in recent years,
transformed from Olsen’s personal research code into a community code for
large-scale dynamic rupture and wave propagation modeling. The code recently
achieved “M8”, a full dynamical simulation of a magnitude-8 earthquake on the
southern San Andreas fault up to 2-Hz using 223, 074 cores with a sustained performance of 220 TFlops. Current SCEC efforts involving AWP-ODC include
computation of strain Green’s tensors, as part of SCEC CyberShake 3.0 effort to
compute deterministic and probabilistic seismic hazard in California.
This presentation will describe the software capabilities and components
from mesh generation to post-processing. Optimization problems tend to emerge
at large-scale that are not significant in smaller scale simulations. Multicore
NUMA architectures and many-core co-processors have further increased complexity that has pushed the burden of obtaining good performance to the application level. We will summarize the optimization techniques that have allowed our
application to run efficiently on petascale supercomputers: efficient algorithms
for load balancing, effective intra-node and inter-node communications, optimal
cache utilization, scalable IO, fault tolerance, and understanding the underlying characteristics of the parallel file system involved. Recently, AWP-ODC has
been ported to CUDA-MPI preparing for GPU-based acceleration, where we
will introduce the benchmarks of performance on NVIDIA Tesla M2090 and
C2050 graphics cards. The presentation will conclude with a discussion on how
the seismology community can prepare for the challenges of Exascale computing.
Topography Effects on a Single Slope: The Effects of SV Incidence Angle
Mohammadi, K., Georgia Institute of Technology, Atlanta, GA,
[email protected]; ASSIMAKI, D., Georgia Institute of Technology,
Atlanta, GA, [email protected]
We study the effects of surface topography on the aggravation of seismic motion
for non-vertical SV wave incidence in the near field of an oblique-slip fault,
and compare results to our previous findings on vertically propagating seismic
wave amplification in the vicinity of topographic features. Compared to vertically propagated wave incidence, inclined waves lead to the generation of surface
waves upon incidence on flat ground, an effect further aggravated by the presence of irregular surface topography. To capture the effects of angle of incidence,
we develop a novel numerical simulation scheme using an explicit finite difference method. Instead of applying transformed stress on the boundaries of the
numerical model, we define an internal (truncated) domain and employ delayed
velocity components of the inclined waves on its boundaries. The nodes on which
velocity boundary conditions are initially imposed, are relaxed shortly after the
incident wave passage to allow far-field attenuation of the reflected waveforms,
a time-marching scheme in prescribing boundary conditions hereby referred to
as ‘fix-release’. Uniformly varying absorbing layers (referred to as sponge boundaries) are used outside the truncated numerical domain to trap any backward
scattered reflections. Using this numerical model, multiple slope geometries are
subjected to the direct SV wave incidence, which is isolated from the surface wave
reflections through a virtual obstacle, and the ground response components are
computed for various wave incidence angles (each positive and negative relative to
the vertical axes). Results show the additive effects of topography on the inclined
wave incidence amplification compared to those for flat ground conditions and
vertical wave incidence.
Oral Session · Wednesday 13:30 pm, 18 April · Pacific Salon 3
Session Chairs: Victor Wong and Raul Castro
The Importance of Geologic Coupling in Understanding the Complexities of
the 2010 El Mayor-Cucapah Earthquake: Use of a Buried High-Density
Broadband Geophone Network
Taylor, O. D. S., US Army Corps of Engineers ERDC, Vicksburg, MS USA,
[email protected] ; MCKENNA, M., US Army Corps of Engineers
ERDC, Vicksburg, MS USA, [email protected]; LESTER, A.,
US Army Corps of Engineers ERDC, Vicksburg, MS USA, alanna.p.lester@
usace.army.mil
On 4 April 2010, a Mw 7.2 earthquake occurred 51 km south of Calexico, CA in
the Baja California, Mexico region and is the result of a series of deep, complex
fault ruptures within a young fault system. This event was one of the larger in
recent years and occurred within 160 km from an existing linear, high-density,
broadband, 192-geophone network in southern San Diego County. The array is
part of an urban infrastructure heath monitoring research program and while
not its intended use, recorded the El Mayor-Cucapah Earthquake very well, on
all of its channels for the duration of the rupture, at a 2 kHz sampling rate. The
10-Hz geophones were buried near the surface, deep within the alluvium sediment or coupled with competent rock and were evenly spaced over a 1.2 km linear
distance. The geologic media across the array spans three distinct formations: the
remnants of the Santiago Peak Volcanics; competent volcanic sandstone of the
Otay Formation; and the San Diego Formation. The loose sands of the San Diego
Formation act as a natural filter reducing much of the elastic ground response.
The result is a clearly defined P-S interval that yields a specific rupture sequence
that is not depicted within the teleseismic and strong-motion accelerometers,
kinematic modeling, and geological investigation of this event and is critical to
the understanding of complexity of the subsurface faulting, true nature of energy
release, nucleation, or final magnitude of an earthquake.
The focus of this research is on the signal processing methodologies and
interpretations of data recorded by this high-density geophone network. The
direct coupling of these instruments to various geologic media allows for more
accurate understanding of wave propagation, ground motion response, and rupture characteristics, thereby adding another sensing modality to conventional
earthquake monitoring procedures.
Permission to publish and release granted by the GSL Director; distribution is unlimited.
Coseismic Deformation for the 2010 El Mayor-Cucapah Earthquake Estimated
from Cross-Correlation of Pre- and Post-Event Airborne Lidar Surveys
Borsa, A. A., UNAVCO, Boulder, CO, [email protected]; MINSTER, J. B.,
Scripps Institution of Oceanography, La Jolla, CA, [email protected]
The 4 April 2010 El Mayor-Cucapah earthquake has provided researchers an
opportunity to use post-event airborne LiDAR to scan comprehensively and
densely a fresh surface rupture in a well-exposed, arid environment. This is also
the first instance where pre-event LiDAR data are available over an entire rupture zone. Despite the dramatic resolution contrast between the pre- and postevent data sets, simple elevation differencing has illuminated details of near-field
ground deformation and its relationship to the complex surface faulting that
occurred in this earthquake (Oskin et al., in review).
Since lateral offsets in sloped topography result in apparent vertical deformation, it is essential to estimate the full 3-dimensional surface deformation field
in order to understand the actual coseismic deformation. We use a technique
of simultaneous cross correlation of both topography and backscatter intensity
from the pre- and post-earthquake lidar datasets (Borsa and Minster, in review)
to estimate deformation in areas where field measurements of coseismic slip from
the El Mayor quake provide an independent estimate of relative motion across
the fault plane. This technique is applied directly to the lidar point clouds and
has yielded dm-level horizontal and cm-level vertical recovery of synthetic slip in
tests using lidar data from a similar desert environment 100 km north of the El
Mayor rupture.
UAVSAR Observations of Slip on Faults in the Salton Trough Associated with
the 2010 M 7.2 El Mayor-Cucapah Earthquake
Donnellan, A., Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, CA, [email protected]; PARKER, J. W.,
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,
[email protected]
UAVSAR Repeat Pass Interferometry indicates that the 4 April 2010 M 7.2 El
Mayor-Cucapah earthquake triggered slip on several faults north of the mainshock rupture. The left-lateral conjugate Yuha fault slipped at the north of the
rupture during the event, but continued to slip for several months following the
earthquake. The UAVSAR observations show a lineation indicating that the M
5.7 aftershock that occurred on 15 June 2010 produced right slip on a fault patch
buried from 2-10 km. Both the Imperial and Superstition Hills had creep events
at the time of the El Mayor-Cucapah earthquake. The Imperial fault crept 4.3 cm
along a 25 km long segment of the fault. The Superstition Hills fault has a 2 cm
creep event along 30 km of the fault. Analysis of GPS position time series spanning these two faults indicates that the creep events occurred at the time of the
mainshock rupture. Furthermore, the GPS stations, located roughly 10 km apart
also show similar amounts of slip of 2 and 4.3 cm on the Superstition Hills and
Imperial faults respectively. Earthquakes ranging in magnitude from 1.4–2.5 km
tend to cluster on specific days on depths ranging from 0-25 km on the faults with
one such cluster of earthquakes occurring on 4 April 2010, the day of the mainshock. The average magnitude of the events is 1.9. The event size is consistent with
4.3 cm of slip on 25x25 m asperities on the Imperial fault.
Fault Rupture Associated With the 14 June 2010 Mw 5.7 Aftershock of the El
Mayor-Cucapah Earthquake
Treiman, J. A., California Geological Survey, Los Angeles, CA, Jerry.
[email protected]; RYMER, M. J., U.S. Geological Survey, Menlo
Park, CA, [email protected]; KENDRICK, K. J., U.S. Geological Survey,
Pasadena, CA, [email protected]; FIELDING, E. J., Jet Propulsion Laboratory/
Caltech, Pasadena, CA, [email protected]
The El Mayor-Cucapah earthquake was accompanied by an energetic aftershock
sequence at the northern end of the rupture, in the Yuha Desert, straddling the
U.S.-Mexico border region. The largest aftershock (Mw 5.7) of the earthquake
occurred on 14 June 2010 (local time) within the Yuha Desert area. This aftershock was associated with displacement on a buried northwest-trending fault
zone and accompanied, or triggered, a northwestward shift in local aftershock
activity. The event was significant because it, and concurrent fault rupture,
occurred within a seismic and structural gap between the Laguna Salada Fault
Zone and the Elsinore Fault Zone.
We present data from UAVSAR and other InSAR data that highlight
faulting and deformation associated with this aftershock. Up to 1.5 m of slip,
at a depth of 4-10 km, accumulated along a northwest extension of the Laguna
Salada Fault Zone over the two months following the event. We also present field
data documenting surface rupture associated with the aftershock, although not
all rupture inferred from remote sensing has been verified by direct observation.
A range of effects, including surface faulting, ground-surface fracturing, and triggered slip occurred on the Laguna Salada Fault, the Ocotillo Fault, the Elsinore
Fault, the Painted Gorge Wash Fault and several unnamed faults.
Precise Relocation of the Northern Aftershock Sequence Following the
4 April 2010 Mw 7.2 El Mayor-Cucapah Earthquake
Kroll, K. A., UC Riverside, Riverside, CA, [email protected]; COCHRAN,
E. S., United States Geological Survey, Pasadena, CA, [email protected];
RICHARDS-DINGER, K. B., UC Riverside, Riverside, CA, [email protected]
Following the 4 April 2010 Mw 7.2 El Mayor-Cucapah earthquake, eight temporary seismometers were installed in the Yuha Desert region north of the Mexican
border. During the deployment period, between 6 April and 14 June 2010, over
4, 300 aftershocks ranging in magnitude from M 0.1 to M 4.85, within a 20 km
by 14 km study area are reported in the Southern California Earthquake Data
Center catalog. We compute the double difference hypocenter relocations using
hypoDD with both manually picked P and S phase arrivals and waveform crosscorrelations. We initially locate the events with Hypoinverse using manual phase
picks and the Southern California Earthquake Center Community Velocity
Model, Version 4 (SCEC CVM-S4), Imperial Valley model. We improve the
locations by jointly inverting for a new velocity model, station corrections and
locations with the VELEST algorithm. To assess absolute location errors, we
relocate again with Hypoinverse, incorporating the output station corrections
and velocity model from VELEST, which result in mean horizontal and vertical errors of 549 m and 1830 m, respectively. Relative relocations are determined
with hypoDD, using both the manually picked arrival times and waveform
cross-correlation delay times. The mean horizontal and vertical relative relocation errors were reduced to 23 m and 82 m, respectively. Relocated seismicity is
highly correlated with faults observed to have surface slip as mapped by Rymer et
al., (2011) (i.e. Laguna Salada-East, Yuha Well Fault, Yuha Fault, Vista de Anza
Fault, and several normal faults). We identify spatio-temporal event migration
patterns that may relate to observed triggered slip, with some faults active for
short durations during the observation period. We propose that the dense cluster
of aftershocks in the Yuha Desert region is the result of increased stress at the end
of the mainshock rupture in region of complex, crosscutting, immature faults.
Observations of Isotropic Radiation from Aftershocks of the 4 April 2010 (Mw
7.2) El Mayor-Cucapah Earthquake, Baja California, Mexico
Castro, R. R., CICESE, Dep. Sismología, Ensenada, Baja California, Mexico,
[email protected]; BEN-ZION, Y., University of Southern CA, Los Angeles,
CA, [email protected]; Wong, V., CICESE, Dep. Sismologia, Ensenada, Baja
California, Mexico, [email protected]
We present observations of enhanced high-frequency radiation of P waves in the
source region of the 4 April 2010 (Mw 7.2), El Mayor-Cucapah, Baja California
earthquake that may reflect isotropic radiation generated by rock damage. We
analyze the best located aftershocks of the sequence that were recorded by a local
seismic network installed in the epicenter area. We examine source spectra properties of these events in an effort to detect seismic radiation that may be generated by rock damage during the brittle failure process and contribute additional
seismic energy to that associated with displacement discontinuities. To evaluate
the contribution to seismic motion from rock damage, we compare the radiation
between events located in the same source region that occurred within short time
intervals (less than 24 hrs). To eliminate path effects, we searched for collocated
aftershocks of the sequence with similar magnitude. Then we look for events having similar focal mechanism to minimize differences due to P and S radiation pattern effects. We found 4 pairs of events with magnitudes ranging between 2.5 and
3.7 and with focal mechanisms predominantly strike-slip with a small normal
component of motion. The P/P and the S/S spectral ratios calculated between the
pairs of events selected show that events with similar magnitude may have differences of high-frequency radiation up to a factor of 4 at 8 Hz and up to a factor of
5 at 16 Hz for P and S waves, respectively. To evaluate the differences between
P- and S-wave energy radiated at high frequencies, we calculated the P/S ratio of
the ratios at high frequencies (f >1.5 Hz) in a band where the signal-to noise ratio
is adequate. Since the pairs of events selected have approximately the same magnitude (± 0.2 at the most), the ratio of ratios is expected to be unity. We observed
high P/S spectral ratios at high frequencies (f > 6 Hz), up to a factor of 9, that may
reflect isotropic radiation associated with rock damage.
Stress Drop Spatial Variability and Magnitude Dependence for the 2010 El
Mayor Aftershocks 3.5 < Mw < 5.7
CREMPIEN, J. G. F., University of California, Santa Barbara, Santa Barbara,
CA, [email protected]; ARCHULETA, R. J., University of California,
Santa Barbara, Santa Barbara, CA.
SCEC deployed 8 portable stations to record ground motion produced by aftershocks of the El Mayor earthquake. We focus on aftershocks that are north of the
US-Mexico border. Five of the stations had instrumental problems resulting in
noisy data. The three useable stations—COON, OYSB and SHCM— recorded
91 MW ≥ 3.5 earthquakes north of the border. These stations are nearly directly
above these 91 aftershocks. With most of the earthquakes having strike-slip
mechanisms, these stations are ideally suited to record SH motion, providing an
excellent signal for determining the source spectrum.
From these data we computed the Fourier amplitude spectrum (FAS) for
the horizontal components of the recorded S-phase acceleration at each station.
The FAS is corrected for anelastic attenuation (Boatwright & Seekins, 2011).
We assumed Q values consistent with those reported by Hauksson & Shearer
(2006). With a kappa value of 0.02 s we corrected for site conditions using the
approach of Anderson & Hough (1984). We fit an omega-square model to the
FAS using Boatwright’s (1978) spectral model for each station and earthquake.
From the computed corner frequencies, we inverted for a source radius using
Dong & Papageorgiou’s (2003) azimuthally dependent corner frequency-source
radius relation using all 3 stations simultaneously, for each aftershock. This radius
is used to determine stress drop for the seismic moment corresponding to the
assigned magnitude. We computed the 1D power spectrum based on 2D Fourier
transform to see the spatial correlation of stress drops. With this we can obtain
the best fitting power law function following method of Lavallée et al. (2006).
Preliminary results suggest an average stress drop of 4.9 MPa, a value ~8 times
larger than the stress drops reported by Shearer et al. (2006) for the same region.
The stress drop results also hint at a possible magnitude dependence for seismic
moments less than 10^16 Nm.
Preliminary Estimate of Shallow Crustal Anisotropy in the Yuha Desert,
California From Aftershocks of the 2010 M 7.2 El Mayor-Cucapah Earthquake
Cochran, E. S., U.S. Geological Survey, Pasadena, CA, escochran@gmail.
com; KROLL, K. A., University of California, Riverside, CA, [email protected]
Following the 4 April 2010 M7.2 El Mayor-Cucapah earthquake, eight temporary seismic stations were deployed in the Yuha Desert region in California
to record aftershocks. These stations were installed to augment the Southern
California Seismic Network and provide near-source records of a vigorous cluster
of aftershocks. Relocations of over 4, 300 aftershocks (Kroll et al., 2011) coupled
with geologic observations (Rymer et al., 2011) in the Yuha Desert region show
that these events occur on sets of geometrically complex structures consisting of a
series of right- and left-lateral conjugate faults, and possibly, also on several steeply
dipping normal faults. We employ this unique aftershock dataset to estimate the
shallow crustal anisotropy in this data poor region of California. To estimate
anisotropy, we use the automated shear-wave splitting analysis program MFAST
outlined in Savage et al. (2010). Our preliminary analyses indicate that the average fast direction, between north-south and northwest-southeast, estimated at
the stations is quite uniform across the region. These fast directions are consistent with previous reports of maximum regional compressive stress directions
(SHmax) estimated from focal mechanisms that is oriented approximately northsouth as (e.g. Townand and Zoback, 2004; Heidback et al., 2008) as well as shearwave splitting measurements estimated at nearby stations with approximately
north-south to northwest-southeast fast directions (e.g. Boness and Zoback,
2006; Yang et al., 2011). Further analyses include a more comprehensive exploration of the spatial and temporal variations, if any, in the measured anisotropy.
Coupling of Pore Pressure and Ground Motion Data Recorded During the 2010
El Mayor-Cucapah (Baja California) Earthquake at the NEES@UCSB Wildlife
Station
SEALE, S. W. H., Earth Research Institute, UCSB, Santa Barbara, CA, sandy@
eri.ucsb.edu; LAVALLEE, D., Earth Research Institute, UCSB, Santa Barbara,
CA, [email protected]; STEIDL, J. H., Earth Research Institute, UCSB,
Santa Barbara, CA, [email protected]; HEGARTY, P., Earth Research
Institute, UCSB, Santa Barbara, CA, [email protected]
Pore pressure built up during an earthquake and the hazard associated with soil
liquefaction present a major challenge for our society, as has been dramatically
illustrated by recent large events. There is consensus among scientists that a better
assessment of the liquefaction risk requires a better understanding of the coupling between pore pressure and ground motion time histories. There is a basic
need to investigate coupling as a function of the frequency content of the ground
motion.
The 2010 M7.2 El Mayor-Cucapah event provides a remarkable opportunity to investigate and model the coupling. The event was well recorded at the
NEES@UCSB Wildlife station located 110 km from the hypocenter. The station
is equipped with three-component strong-motion accelerometers at the surface
and in boreholes at various depths and with pore pressure transducers located in
a saturated, liquefiable layer.
The recorded pore pressure and ground motion time histories both have
frequency content that is a function of time. A wavelet representation is a natural approach to investigate non-stationary time signals. We have used the following procedure: We first compute the wavelet coefficients associated with the
two signals. Then we compute the correlation between the wavelet coefficients of
the two signals as a function of the frequency. Correlation coefficients provide
information about the linear dependence between the two signals. We then compare the square norm of the wavelet coefficients of the two signals in the available frequency range. The distribution of the square norm of the wavelet coefficients allows the identification of the dominant wavelet coefficients necessary to
reconstruct the signal. We discuss the results for the following cases: two ground
motion time histories located at different depths; two pore pressure time histories
located at different depths; and a ground motion and a pore pressure time history
both (approximately) recorded at the same depth.
Electrical Resistivity Change in the Upper Crust of Mexicali Valley after El
Mayor-Cucapah M 7.2 Earthquake: From Magnetotelluric Data
Cortes, O. J., CICESE, Ensenada, Baja California, Mexico, ocortes@cicese.
edu.mx; ROMO, J. M., CICESE, Ensenada, Baja California, Mexico, jromo@
cicese.mx
The distribution of electrical conductivity in the north of Baja California peninsula has been investigated using the magnetotelluric method in a profile with 42
observation sites measured across some of the most important active structures in
the area. In March 2010, eight of these magnetotelluric soundings were measured
along a 20 km profile across the Mexicali valley. The data were processed with a
two-dimensional inversion algorithm to obtain a model of the electrical resistivity distribution in the upper crust of this zone. In May 2010, after the M7.2 earthquake of April 4th, a second measurement campaign was conducted to investigate
any possible change in the ground resistivity. The same measuring positions were
occupied and the same processing applied to the new data set. The results indicate
a drop in the electrical resistivity of about 9% in the central part of the profile
after the seismic event. This result is consistent with a possible increase of permeability caused by microfractures associated to the principal seismic event and its
aftershocks.
Detecting Triggered Earthquakes around Salton Sea Following the 2010 Mw
7.2 El Mayor-Cucapah Earthquake Using GPU Parallel Computing
Meng, X., EAS, Georgia Tech, Atlanta, GA, [email protected]; PENG, Z.,
EAS, Georgia Tech, Atlanta, GA, [email protected]; YU, X., ECE, Georgia
Tech, Atlanta, GA, [email protected]; HONG, B., CSE, Georgia Tech, Atlanta,
GA, [email protected]
Previous studies on earthquake triggering mostly examined seismicity rate
changes around the occurrence time of large earthquakes based on existing earthquake catalogs. However, such catalogs could be incomplete immediately after the
mainshock, which may cause apparent seismicity rate changes that are unrelated
to stress changes. In this study, we focus on the Salton Sea geothermal region following the 2010 Mw7.2 El Mayor-Cucapah earthquake According to the SCSN
catalog, the seismicity rate near Salton Sea increased immediately after the mainshock, but dropped below the pre-shocklevel within ~20 days and remained low
for a few months. This is qualitatively consistent with a combined effort of shortterm dynamic triggering and long-term stress shallow effect. To check whether
such pattern is caused by catalog incompleteness, we apply matched filter technique to detect missing events around Salton Sea. We use waveforms of ~2000
templates recorded by 6 borehole stations of the EN network, and scan through
the continuous data ~30 days before and ~60 days after the mainshock. Because
of the massive data set, we apply GPU computing to accelerate the matched filter technique. By dividing the computation into several routines and processing
them in parallel on GPU cards, we can achieve ~40x speedup for one Nvidia
GPU card compared to sequential CPU code. So far we have detected a total of
~24000 earthquakes, about ~70 times more than listed in the relocated catalog
of Hauksson et al. [2011]. The seismicity rate has a significant increase immediately after the mainshock, and followed by a rapid decrease in the following days,
except on the 15th and 18th day after the mainshock, when two bursts of seismic
activity occurred. The seismicity rate dropped below the pre-shock level at about
50 days after the mainshock. We are currently applying the same technique to a
longer time period to check the duration of the reduction of seismicity rate long
after the mainshock.
Evaluation of Predominant Site Periods of Ground Motion Stations During the
2010 El Mayor-Cucapah Earthquake Using H/V Response Spectral Ratio
Method
Liao, Y., Kleinfelder, Oakland, CA, [email protected]; MENESES, J.,
Kleinfelder, San Diego, CA, [email protected]
Predominant site period is an important parameter for assessing building damage. Predominant site periods of ground motion stations during the 2010 El
Mayor-Cucapah Earthquake are evaluated using horizontal-to-vertical (H/V)
spectral ratio technique (Zhao et al., 2006) which has been demonstrated to provide reliable estimates of predominate site periods.
The 4 April 2010 El Mayor-Cucapah Earthquake was recorded by 168
strong motion instruments within 200 km from the fault rupture. The majority
of the stations in the Imperial and Mexicali Valleys is located on young soft sediments with Vs30 less than 200 m/s. Vs30 values were measured at 23 of the 168 stations. Vs30 values of the remaining stations are inferred from the local geological
conditions. These stations are grouped into three site categories, namely stiff soil
sites with Vs30 between 180 and 366 m/s, very dense soil sites with Vs30 ranging
from 366 to 600 m/s, and rock sites with Vs30 greater than 600 m/s.
The results indicate that the mean H/V ratios for the stiff soil sites show a
sharp peak at 0.9 seconds. Interestingly, a sharp peak at 1.2 seconds is observed
for the sites with Vs30 between 180 and 200 m/s, indicating that these softer sites
show more pronounced nonlinear behavior during the shaking, which leads to a
lengthened predominant period. The mean H/V ratio curves for the rock sites
have a peak at 0.2 seconds.
However, the H/V ratio curves for the very dense soil sites do not show a
pronounced peak. Further investigation results indicate that some of these sites
assigned with a Vs30 of about 378 m/s show double peaks with a first peak at 0.5
seconds followed by a second one beyond 2 seconds, which suggests the presence
of two strong impedance contrasts in the geological deposits. It is interesting to
note that these sites are all located in the area of San Diego.
Oral Session · Wednesday 8:30 am, 18 April · Pacific Salon
4&5
Session Chairs: Darcy Ogden and Eric Dunham
Migrating Swarms of Brittle-Failure Earthquakes in the Lower Crust Beneath
Mammoth Mountain, California
Shelly, D. R., U.S. Geological Survey, Menlo Park, CA, [email protected];
HILL, D. P., U.S. Geological Survey, Menlo Park, CA, [email protected]
Brittle-failure earthquakes in the lower crust, where high pressures and temperatures would typically promote ductile deformation, are relatively rare but occasionally observed beneath active volcanic centers. When they occur, these earthquakes provide a rare opportunity to constrain volcanic processes in the lower
crust, such as fluid injection and migration. Here, we examine recent brief earthquakes swarms occurring in 2006, 2008, and 2009, deep beneath Mammoth
Mountain, located on the southwestern margin of Long Valley Caldera. These
brittle-failure earthquakes at depths of 19 to 30 km are likely occurring within
the more mafic mid to lower crust, which can remain in the brittle domain to
temperatures as high as ~700 degrees C.
To maximally illuminate the spatial-temporal progression of seismicity, we
supplement the earthquake catalog by identifying additional small events with
similar waveforms in the continuous data, achieving up to a 10-fold increase in
the number of locatable events. We then relocate all events, using cross-correlation and a double-difference algorithm. We find that the best-recorded 2009
swarm exhibits systematically decelerating upward migration, with hypocenters
shallowing from 21 to 19 km depth over approximately 12 hours. We also observe
substantial diversity in the pattern of P-wave first motions, where events with very
similar hypocenters and origin times exhibit nearly opposite patterns of compressional and dilational first motions at network seismometers.
Compared with other lower-crustal earthquake swarms, the 2009
Mammoth sequence is relatively short duration, fast migrating, and has no
detectible geodetic signal. A likely trigger may be CO2-rich fluid, given its low
viscosity, high buoyancy, and abundant release in the area at the surface. Thus the
swarm may reflect slip on pre-existing fractures triggered by increased fluid pressure and correspondingly reduced effective normal stress.
The Utility of Tracking Multiplets Across Several Eruptive Episodes at
Kilauea Volcano, Hawaiì
Thelen, W. A., USGS Hawaiian Volcano Observatory, Hawaiì National
Park, HI, [email protected]
Multiplets, or repeating earthquakes, are commonly observed at volcanoes, and
have been shown to be useful in tracking different volcanic processes. I constructed a multiplet catalog of volcano-tectonic earthquakes recorded during
three eruptive episodes in Kīlauea’s East Rift Zone between September 2010 and
August 2011. I define multiplets as a set of at least two earthquakes with arrivals
that are similar at a cross-correlation coefficient of 0.7 on two or more stations.
Multiplet behavior differs significantly on either side of an aseismic zone located
between Mauna Ulu and Makaopuhi Crater. Uprift of Mauna Ulu, multiplets
have longer lifespans, smaller recurrence intervals, and more member events than
multiplets downrift of Makaopuhi. In addition, the uprift seismicity is almost
entirely composed of multiplets, while the seismicity downrift is evenly composed
of multiplets and non-multiplet sequences. Further, the uprift multiplets continued to occur through all three episodes, while the multiplets, as well as non-correlating seismicity near Makaopuhi were only present prior to the Kamoamoa eruption. The differing behavior of the multiplets reflects different source processes
that drive multiplet development. Uprift of Mauna Ulu, the highly repeatable
nature of the seismicity over different eruptive episodes suggests a non-destructive source process, such as pressurization and subsequent elastic dilation of the
conduit connecting Kīlauea’s summit to Puù Òò. Absolute changes in pressure of the magmatic system, as reflected by the changing lava level prior to each
eruptive episode, are proportional to the seismic energy release during that time
period. Downrift of Makaopuhi, multiplets are confined to the time period prior
to the Kamoamoa eruption and are in a location between a dike intruded in 2007
and the modeled Kamoamoa dike. This suggests a largely non-repeatable process,
such as rock breakage associated with formation of the Kamoamoa dike.
Locating a Microseism Source in Southern Peru from Ambient Noise CrossCorrelation
Ma, Y., California Institute of Technology, Pasadena, CA; CLAYTON, R.
W., California Institute of Technology, Pasadena, CA; ZHAN, Z., California
Institute of Technology, Pasadena, CA.
The Green’s function between two stations can be obtained from the cross-correlation of ambient noise recordings by the stations[Lobkis and Weaver, 2001;
Shapiro and Campillo, 2004]. The surface wave part is the strongest and most easily extracted for the subsequent tomographic inversion[Lin et al., 2008; Shapiro
et al., 2005; Yao et al., 2006]. However, the surface wave precursors which have
larger apparent velocities compared with the same period Rayleigh wave may also
be expected if the contributions from noise sources out of the Fresnel zones cannot cancel out[Zeng and Ni, 2010; Zhan et al., 2010]. In this work, we will report
the observation of a strong surface wave precursor persistent in every month’s
noise cross-correlations in southern Peru. This is clearly recorded by two sides of
a box-like array, and is strongest in 5 s to 8 s period. It appears to be generated by
a noise source anomaly which is located at the active volcanic area by grid search
using a uniform surface wave group velocity model of 2.7 km/s at 6 s period. It is
inside of the array which enables us to locate it more accurately using a 0.3 × 0.3
degree group velocity tomography calculated from the dispersion of the normal
speed surface wave. The location is 71.6°W/16.1°S, which is less than 0.5 degree
from the active volcanoes El Misti and Sabancaya whose last eruptions are in 1985
and 2003 respectively. This anomaly can be caused by the microseism induced by
the active volcanoes, or very strong scattering of the oceanic source by the volcanoes. We are investigating more properties of this signal (e.g. spatial and temporal
variation of its amplitude) in order to better understand its source mechanism
and relationship with the volcanic activities.
Local Micro-Seismic Study the Menengai Geothermal Prospect in the Central
Kenya Domes
Patlan, E., University of Texas at El Paso, El Paso, TX, [email protected].
edu; WAMALWA, A., Geothermal Development Company (GDC), Nakuru,
Kenya, [email protected]; THOMPSON, L. E., University of Texas at El
Paso, El Paso, TX, [email protected]; KAIP, G., University of Texas
at El Paso, El Paso, TX, [email protected]; VELASCO, A. A., University of Texas
at El Paso, El Paso, TX, [email protected]
The Menengai Caldera is one of the major Quaternary volcanoes found along
the Kenya rift system within the Kenyan domes in a region marked with high
elevation, crustal thickening and magma under-plating and an underlying mantle
plume. The composition of volcanic rocks found around Menengai are mainly
trachytes, trachyphonolites and phonolites, and the hot springs, fumaroles and
hydrothermally altered surfaces in the caldera region suggest the existence of a
geothermal resource at depth. In addition, geophysical analyses over this region
have indicated the presence of dense high velocity material beneath the Menengai
caldera. Recent exploration drilling by the Geothermal Development Company
(GDC) within the caldera has proven the existence of geothermal resource. To
further target high producing wells in this field to be used for electricity generation, the GDC and the University of Texas at El Paso (UTEP) have deployed
fourteen seismic stations to monitor the seismicity around the volcano to help
identify active faults and fracture systems that may contain hydrothermal fluids
and favorable drilling targets. Here, we present our initial analysis of the data
collected from March to December 2011. We employed the double difference
relocation to image the margin of the caldera and calculated the SKS Shear Wave
Splitting to locate the orientation of the fault event in order to locate the active
hydrothermal system using teleseismic events for potential hydrothermal exploration for the GDC Company.
Practical Considerations for Applying Neural Network Classification
Techniques to Volcanic Earthquakes
West, E., Geophysical Institute, University of Alaska Fairbanks, Fairbanks,
AK, [email protected]; BRUTON, P., Geophysical Institute, University of
Alaska Fairbanks, Fairbanks, AK, [email protected]
Automated earthquake characterization is an unequivocal need in volcano
monitoring and research. We are fortunate that many volcanic processes have
seismic signatures that allow direct interpretation—shallow vs. deep, rockfalls
vs. earthquakes, brittle failure vs. non-destructive, and so forth. Though many
researchers have demonstrated the potential to automate these characterizations
using trained algorithms (mostly neural networks and hidden Markov models),
few organizations actually use these techniques for active monitoring. This presentation addresses hurdles that are faced by all such algorithms when applied to
earthquake classification. Our examples are based on an approach that utilizes
time delay neural networks. However we focus on challenges that are common to
many automated classification schemes.
One of the most significant considerations is whether the scheme should
detect events in the continuous seismic record or focus on classifying previously
identified events. We demonstrate the operational merits of focusing on events
that have been flagged previously by another system. Perhaps the biggest limitation in the adoption of trained algorithms is the frequent need to base the training, benchmarking and implementation on just one data channel. Not only does
this sidestep the richness and density of a typical volcano seismic network, it also
entrusts the entire system to the integrity of a single data channel—a dubious
practice in volcanic terrain. We present a approach that utilizes the full network
and provides some ability to weather data outages and changes in network configuration. We demonstrate these approaches using case studies from several volcanoes.
Volcanic Seismic Earthquakes at Mount St. Helens Exhibit Constant
Seismically Radiated Energy per Unit Size
Harrington, R. M., Karlsruhe Institute of Technology, Karlsruhe,
Germany, [email protected]; KWIATEK, G., GFZ German Research
Centre for Geosciences, Potsdam, Germany, [email protected]
The destructive nature of volcanic eruptions and the attenuating properties of the
volcanic edifice make inferring the source properties of volcanic seismic events
from waveforms a daunting task. Here we exploit the short source-receiver distances of a temporary deployment in September 2006 at Mount St. Helens to estimate the size-duration scaling of the earthquakes associated with the 2004-2008
eruption. We find that the size-duration scaling resembles that of similarly sized
tectonic earthquakes observed in other shallow fault zones. We cross-correlate
waveforms recorded on 11 broadband stations located less than 2 km from the
crater and classify roughly 500 events into 9 families. We observe a size-duration
scaling suggesting that the amount of seismically radiated energy per unit seismic
moment (scaled energy) is constant within event families, as well as between 7 of
9 event families. Cases where constant scaled energy values vary between families
may result from a lack of resolution in the velocity model.
Much of the seismicity from late 2004-2008 occurred on nascent faulting surfaces at the base of several Dacite rock spines extruded over the course
of the eruption. The nascent faults exhibited many features commonly observed
in shallow faulting zones, such as gouge, striations, and fault-zone Cataclasite.
The physical fault features and the similarity of the size-duration scaling with
that of tectonic earthquakes suggests that the mechanical failure processes of
the Mount St. Helens events are consistent with that of typical earthquakes, i.e.,
stick-slip. However, lower than expected corner frequency values relative to event
size suggest that the rupture velocities may be low compared to that of tectonic
earthquakes (< 2.5-3 km/s). The low corner frequencies likely result from low
shear wave velocities in the volcanic edifice (assuming that the rupture velocity is
0.9*shear-wave velocity), rather than low static stress drop values.
A Mechanism for Sustained, Energetic Tremor Heralding Rapid Onset of the
2004–2008 Eruption of Mount Saint Helens, Washington
Denlinger, R. P., US Geological Survey, Vancouver, WA, [email protected];
MORAN, S., US Geological Survey, Vancouver, WA.
The 2004-2008 eruption of Mount St. Helens (MSH), Washington began with
an increase in seismicity coincident with onset of down and south movement of
GPS station JRO, 9 km north of the crater. Seismic intensity and the velocity at
JRO increased through Oct 1st, when a large phreatic explosion on the southwest end of the new dome was followed by a short burst of tremor. The maximum
velocity of JRO towards the crater on Oct 2nd indicates maximum rate of flow
out of the subsurface reservoir at a depth of 7 km. About noon on Oct 2nd, a
shallow earthquake near the conduit was immediately followed by 45 minutes
of increasingly energetic tremor, with no gas or ash. Our analysis of the tremor
data shows that this tremor imparted the largest forces normal to the conduit
walls at 1 to 2 km depth, produced Love and Rayleigh waves, and excited harmonic resonance over a bandwidth of nearly 5 Hz. Full waveform analysis shows
that the observed tremor can be produced by a broad-spectrum vibration of the
conduit margins that then excites the natural resonant frequencies of the conduit
structure. Given the paucity of gas during eruption, and 3-5 m of cataclasite and
gouge mapped along margins of spines extruded from the conduit, we consider
vibration mechanisms that could result from progressive cataclastic deformation
along the conduit margins during simple shear of crystal-rich conduit magma.
Simple shear experiments by others suggest formation of cataclasite at rates of
sliding comparable to observed rates of conduit extrusion, and also produce large,
rapid fluctuations in force normal to shear margins. These experiments suggest
these forces come from jamming and unjamming of crystals within the magma
as it is pushed through the conduit. Even with a small flow rate, these forces can
be of sufficient frequency and magnitude that, if distributed along the conduit,
would generate the observed tremor on Oct 2nd.
A Comparison of Tremor Before, During, and After the Explosive Eruption of
Redoubt Volcano, Alaska in 2009
Hotovec, A. J., University of Washington, Seattle, WA, ahotovec@
uw.edu; PREJEAN, S. G., U.S. Geological Survey, Alaska Volcano Observatory,
Anchorage, AK, [email protected]; VIDALE, J. E., University of Washington,
Seattle, WA, [email protected]; GOMBERG, J. S., U.S. Geological Survey, Seattle,
WA, [email protected]
The most recent eruption of Redoubt Volcano, Alaska, produced a wide variety
of earthquake and tremor behavior. Seismic activity in the months leading up to
the onset of eruption was often dominated by sustained periods of tremor lasting
up to 3 weeks at a time in the 1-10 Hz frequency band. Because little activity was
observed at the surface, this pre-eruptive tremor was initially interpreted to be
due to boiling of the hydrothermal system. Indeed, this tremor’s behavior appears
to be markedly different than the spectacular upward gliding harmonic tremor
that occurred prominently before six nearly consecutive explosions during the
latter half of the eruptive sequence. Harmonic tremor is a signal characterized by
several narrow, evenly spaced peaks in the frequency spectrum that often change,
or glide, with time. The fundamental frequency, or lowest spectral peak, for the
pre-explosive tremor repeatedly glided upward from <1 Hz to as high as 30 Hz
in less than ten minutes, followed by a relative seismic quiescence of 10 to 60 seconds immediately prior to explosion. High frequency (5 to 20 Hz) gliding then
returned during the extrusive phase, and lasted from 20 minutes to 3 hours at a
time. Swarms of repeating high-frequency earthquakes immediately preceded the
first and third instances of pre-explosion gliding harmonic tremor on Redoubt
Volcano. We favor the explanation that the gliding harmonic tremor during and
after the explosive phase of eruption is created by the superposition of increasingly frequent, repeating stick-slip earthquakes, and further investigate the possible causes of the non-harmonic pre-eruptive tremor.
Modeling of Volcanic Tremor as Repeating Earthquakes
Dmitrieva, K., Stanford University, Stanford, CA, [email protected];
DUNHAM, E. M., Stanford University, Stanford, CA, [email protected]
Harmonic tremor preceded about twenty explosions during the 2009 eruption
of Redoubt Volcano, Alaska. Periodically repeating earthquakes were observed
beginning a few hours before each explosion, with events becoming more frequent prior to the explosions. Several minutes before each explosion the individual earthquake waveforms merged into a continuous tremor signal with fundamental frequency (interpreted as the reciprocal of earthquake interevent time)
that glided from ~1 to over 20 Hz. Seismicity then ceased for ~30 s before each
explosion. We explain these observations by modeling earthquake cycles on faults
governed by rate-and-state friction loaded by conduit processes leading up to the
explosions. Faults respond to applied shear stressing with either stable aseismic
sliding at a constant slip velocity or stick-slip oscillations (earthquakes). Linear
stability analysis of steady sliding shows that faults that are unstable to oscillations at low stressing rates can be stabilized, at sufficiently high stressing rates, by
inertial effects associated with seismic wave radiation. We interpret the Redoubt
observations as follows. An increasing stressing rate causes the earthquake recurrence interval to decrease (explaining the increasing tremor frequency). When the
stressing rate exceeds a critical value, sliding is stabilized (explaining the aseismic
interval prior to the explosions). The predicted critical stressing rate is ~(stress
drop)/(earthquake duration) and the corresponding maximum frequency is of
order the earthquake corner frequency. We invert the Redoubt data using our
model to infer the shear stressing rate history, which reaches a maximum ~10
MPa/s when seismicity ceases prior to the explosions. The duration of the aseismic period emerges naturally in our model. The high stressing rates suggest that
the fault is located close to the conduit.
Very-Long-Period Earthquakes and Cycles of Conduit Sealing and Puffing at
Fuego Volcano, Guatemala
Waite, G. P., Michigan Tech, Houghton, MI, [email protected]; LYONS, J.
J., Michigan Tech, Houghton, MI, [email protected]; NADEAU, P. A., Michigan
Tech, Houghton, MI, [email protected]; BRILL, K. A., Michigan Tech,
Houghton, MI, [email protected]
Fuego volcano, Guatemala is an open-vent basaltic-andesite stratovolcano characterized by varied low-level eruptive activity since 1999. In January 2008 and
2009, we recorded explosions with broadband seismic and acoustic sensors
approximately once per hour. In each deployment the nearest stations were 900
m north of the crater. In 2008, explosions were ash rich, and had emergent onsets,
low amplitudes (peak excess pressures reduced to 1 km were < 10 Pa) and long
durations (30–120 s). On the other hand, the explosions in 2009 had impulsive
onsets, high amplitudes (pressures > 100 Pa), and shorter durations with only a
single infrasound pulse. However, both types of explosions were accompanied by
very similar very-long-period (VLP) events. The 2008 network was not sufficient
for a full waveform inversion, but modeling the 2009 VLP data showed that they
were largely explained by volume changes within a crack dipping about 35° SW.
When compared on stations that were nearly co-located 900 m north of the vent,
the ratios of radial to vertical particle velocities are almost identical. This suggests
the same crack mechanism was responsible for the 2008 VLPs. We interpret this
mechanism using high-rate SO2 emission data from a UV camera system. Because
the 2008 explosions are ash rich, SO2 emission cannot be quantified. We focus
instead on a period of gas puffing and VLPs that lasted for more than an hour.
After each of the VLPs that occurred when the camera was operating, SO2 emission sharply increased and peaked within 2-6 minutes. The emission then sharply
decreased prior to the next VLP. These observations suggest cycles of partial sealing and conduit pressurization, followed by rapid gas release and conduit deflation, occurred in the shallow conduit and may be a common mechanism at Fuego
and elsewhere. We continue to investigate the nature of explosions at Fuego and
will also discuss new field observations from January 2012.
Santiaguito 2012: Lower Explosion Rate, Higher Intensity
Lees, J. M., Geological Sciences, University Of North Carolina, Chapel Hill,
NC, [email protected]; JOHNSON, J. B., New Mexico Inst. Of Mining
& Technology, Soccoro, NM, [email protected]; LYONS, J.,
Instituto Geofisico, Escuela Politecnica Nacional, Quito, Ecuador, jlyons@mtu.
edu; ANDERSON, J., New Mexico Inst. Of Mining & Technology, Soccoro,
NM, [email protected]; NIES, A., Geological Sciences, University Of North
Carolina, Chapel Hill, NC, [email protected]
Santiaguito Volcano, Guatemala, has been erupting since 1922, following the
cataclysmic eruption of Santa Maria Volcano in 1902. In 2007 and 2009 we
recorded data using campaign-style seismo-acoustic networks to monitor the
dome explosions that occurred once per hour, on average, on the active (Caliente)
dome. This year we returned with a new seismic deployment focused on observations of ultra-long period signals recorded near the flanks of the active dome.
We established three stations (two with tilt) in a triangular array northeast of
Caliente within 500 m of the erupting edifice. Explosion activity in 2012 is
noticeably different than 2009: the rate of explosive degassing has slowed considerably and coincides with elevated effusion of lava and apparent increase in degassing unassociated with explosions. Prior to explosions tilt signals are occasionally evident. Inflationary tilt signals typically start 10 minutes before explosion
onsets and rapid deflation follows the explosions. Tilt is not observed for every
seismic degassing signal, suggesting that there are variations in source dynamics
and explosion geometry. Infrasound at Santiaguito exhibits pressure fluctuations
that vary in periods from tens of seconds to high-frequency oscillations in the 1
Hz band.
Photogrammetry and Seismic Observations of Eruptive Activity at Santiaguito
Volcano, Guatemala 2007–2012
Nies, A. P., Geological Sciences, University Of North Carolina, Chapel Hill,
NC, [email protected]; LEES, J. M., University Of North Carolina, Chapel
Hill, NC, [email protected]; ANDREWS, B. J., Smithsonian Institution,
Washington, DC, [email protected]; JOHNSON, J. B., New Mexico Inst. Of
Mining & Technology, Soccoro, NM, [email protected]; LYONS,
J. J., Instituto Geofisico, Escuela Politecnica Nacional, Quito, Ecuador,
[email protected]; ANDERSON, J., New Mexico Inst. Of Mining &
Technology, Soccoro, NM, [email protected]
The Santiaguito Volcano complex in Guatemala has been continuously active
since 1922, with eruptive activity centered at the Caliente dome since 1967.
Multi-sensor studies carried out in 2007, 2009, and 2012 indicate that explosions have become less frequent and more intense during the past five years.
Seismic events recorded at Santiaguito include explosive degassing, block and
ash flows, and tremor. Source processes often occur simultaneously, producing
signals which can be difficult to interpret. Time lapse photography collected in
2012 allows discrimination of rockfalls and explosions within the seismic record.
Photogrammetry of the 2012 dome indicates lava flow velocities on the order of
10 m per hour and local inflation/deflation of ~1 m per minute. Seismic data from
2012 contain several distinct recurring waveforms, which in this study are characterized according to spectral content and other parameters. Source processes
for these waveforms are identified using a combination of methods with emphasis
on seismic and optical observations. We use data from the more comprehensive
2012 deployment to inform interpretation of previously collected seismic data.
Events over the 2007-2012 period are catalogued according to selected criteria.
Using statistical analyses, we identify variations in seismic activity between the
three deployments, and discuss implications for eruptive processes at Santiaguito.
4&5
Session Chair: Vera Schulte
An Integrated Geophysical-Geological Study of a Landslide in Paleogene
Volcanic Deposits along the Wasatch Front, Utah
Hoopes, J. C., Department of Geological Sciences, Brigham Young University,
Provo, UT, [email protected]; MCBRIDE, J. H., Department of
Geological Sciences, Brigham Young University, Provo, UT, john_mcbride@byu.
edu; CHRISTIANSEN, E. H., Department of Geological Sciences, Brigham
Young University, Provo, UT, [email protected]; KOWALLIS, B.
J., Department of Geological Sciences, Brigham Young University, Provo, UT,
[email protected]; THOMPSON, T. J., GeoStrata, LLC, Bluffdale, UT, timt@
geostrata-llc.com; TINGEY, D. G., Department of Geological Sciences, Brigham
Young University, Provo, UT, [email protected]; OKOJIE-AYORO, A.
O., Department of Geological Sciences, Brigham Young University, Provo, UT,
[email protected]
Construction in northern Utah has expanded from the traditional valley areas
up into the slopes and foothills of the Wasatch Mountains where there is a
higher risk of landslides. Landslides along the Wasatch Front are complex features, Pleistocene to historical in age, with dense vegetation and poor outcrop.
They thus require integration of geological and geophysical methods to understand their thicknesses, slopes, lateral extents, and emplacement styles. As part
of an evaluation of Traverse Mountain (just south of Salt Lake City) for potential development, we applied a suite of geophysical and geological techniques to
analyze the internal and boundary structure of a mapped landslide on the south
slope of the mountain. Our study incorporates trenching, boreholes, LiDAR, and
vibroseis surveys. The seismic survey consisted of a longitudinal profile plus transverse profiles. The seismic data, processed as common mid-point images and as a
tomographic P-wave velocity model, constrain cross-sections of the upper 500 m
of the landslide. A major reflector at 80-100 m depth is interpreted as a contact
between Eocene-Oligocene volcanic rocks and a Pennsylvanian carbonate-siliciclastic sequence and thus as a possible base to a landslide. This reflector defines an
asymmetric graben-like depression bounded by a NNW-trending normal fault
system. The geological and geophysical data were used to construct a cross-section
of the uppermost part of the landslide, while the LiDAR constrains the interpretation of landslide boundaries. This analysis reveals a faulted, chaotic body
of block-and-ash-flow tuffs, surrounded by andesite lavas. Kinematic indicators
include normal faults and south-verging thrusts, which imply a south-directed
flow for the landslide deposit with a post-Paleogene emplacement age. Our study
demonstrates how integration of LiDAR, trenching, boreholes, and seismology
can provide the range of data needed to assess the complex geology of Wasatch
Front landslides.
True versus Apparent Vertical Moho Offsets across Continental Strike-Slip
Faults from Azimuthally Dependent Joint Inversion of Surface Waves and
Receiver Functions
SCHULTE-PELKUM, V., University of Colorado Boulder, Boulder, CO, vera.
[email protected]; BEN-ZION, Y., University of Southern California, Los
Angeles, CA, [email protected]
The question of whether continental strike-slip faults extend through the Moho
has wide-ranging implications for crustal and mantle rheology and fault behavior. Since strike-slip faults juxtapose crustal blocks that were originally far apart,
cross-fault lithological contrasts are common. We show that standard imaging
techniques, ignoring the contrasts of upper crustal blocks, result in an apparent
offset in Moho depth. Such studies suggest continuation of the fault to the Moho
in cases where the actual Moho depth may be constant across the fault. In particular, the popular technique of receiver function common conversion point stacking suffers from a severe velocity-depth tradeoff. We demonstrate with synthetic
calculations that observed shallow lithology contrasts across the San Andreas and
San Jacinto faults lead to artificial Moho offsets of the order of 5 km (comparable
to offsets proposed based on this technique). Joint inversion of surface waves and
receiver functions offer much better depth and velocity constraints than each
technique by itself, particularly when additional constraints on the shallow structure are available, such as from local tomography including fault head waves. The
typical horizontal resolution for ambient noise surface wave tomography is too
coarse for subvertical fault zone imaging. We investigate exploiting azimuthal
dependence of dispersion curves and receiver functions to improve the horizontal
resolution. Tuned in this fashion, joint receiver function and surface wave analysis may resolve the shallow to deep structure tradeoff and allow more accurate
imaging of the structures around and below large faults.
Three-Dimensional Vp and Vp/Vs Structure Models, Earthquake Relocations
for the Coso, Southern California
Zhang, Q., Marine Geology and Geophysics, University of Miami, Miami,
FL, [email protected]; LIN, G. Q., Marine Geology and Geophysics,
University of Miami, Miami, FL, [email protected]
The Coso volcanic field lies at the west edge of the Basin and Range province
and is well known as a geothermal area. In this study, we present our comprehensive analysis of three-dimensional (3-D) velocity structure, high-precision earthquake relocation and in situ Vp/Vs estimates. Our data are first-arrival times and
waveform data of both P and S-waves for the 177, 000 events between 1984 and
2010 recorded by the Southern California Seismic Network (SCSN) stations. We
apply the VELEST algorithm to create a one dimensional (1-D) velocity model
as the initial model for the inversion of the crust and upper mantle structure.
We apply the tomoDD algorithm to the 1893 master events to invert for Vp and
Vp/Vs models. These events are chosen from the entire data set in our study area
based on the criteria: the numbers of P and S picks are more than 13 and 8 respectively; horizontal and vertical event-event distances are greater than 5 km and 2
km respectively. The horizontal grid spacing in our 3-D velocity model is 6 km
and the depth layers are at -1, 0, 3, 6, 9, 12, 15, 20, and 26 km. The resulting new
3-D velocity model is used to improve absolute event location accuracy. We then
apply a similar event cluster analysis, waveform cross-correlation, and differential
time relocation methods to improve relative event location accuracy and estimate
in situ near-source Vp/Vs ratio within each event cluster using differential times
from cross-correlation. The high-precision earthquake relocation and fine-scale
velocity structure will help to understand the regional and local tectonic settings
and also to track magma chambers beneath the geothermal field.
Moho-Depth Diking and Structural Controls on Microplate Rifting
Mechanisms along the Northern Sierra Nevada-Walker Lane Boundary
Smith, K. D., NSL-University of Nevada Reno, Reno, NV, ken@seismo.
unr.edu; VON SEGGERN, D., NSL-University of Nevada Reno, Reno, NV,
[email protected]; KENT, G. M., NSL-University of Nevada Reno, Reno,
NV, [email protected]; EISSES, A., NSL-University of Nevada Reno, Reno,
NV, [email protected]; DRISCOLL, N. W., SIO-UCSD, San Diego, CA,
[email protected]
An ongoing swarm of deep (28-35 km) low magnitude earthquakes began in
August 2011 near Sierraville (SV), California (to date. over 1600 events have been
located). The swarm has nearly all of the characteristics of a deep sequence under
N. Lake Tahoe in 2003, about 45 km to the SE. Both are interpreted as dike injection events. NSF-Earthscope will support 4 broadband instruments to supplement the local network. Both sequences align along, and define, a N45W striking
50-degree east dipping Moho-depth structure. To date, the top of the SV sequence
is about 5 km deeper than the 2003 N. Tahoe swarm, implying an ~10% gradient
in Moho depth between Tahoe and SV (assuming the depth extent defines the
base of the crust). In addition, the first Long-Period event identified at this latitude (9/27/2011) lies along the interpreted structure at depth, yet is not spatially
associated with either sequence. The structure is nearly parallel to the northern
San Andreas transform. Local GPS motions are also parallel to the strike of the
structure and models define relatively high extensional strain along the Sierran
front near SV. Consistent with the evolution of stress orientations with respect to
the northward propagation of the Mendocino Triple Junction (MJT), the extension direction rotates counterclockwise northward along the Sierran front and is
ultimately oriented toward the MTJ. We interpret the processes at depth in the
Tahoe-SV area to represent a northward propagating rift and rupture of the Sierra
Nevada microplate. As the rift progresses northward, decompression melting and
extension weaken, and ultimately rupture a strong upper Moho layer. Following
diking and Moho rupture, slip progresses along the structure under fault friction
laws. The structure imaged by near-Moho depth earthquakes provides insights
into fundamental questions regarding the uplift of the northern Sierra, and the
physiography and evolution of the northern Walker Lane.
New Insights into Geometric Attenuation for Eastern North America
Santa Barbara, Santa Barbara, CA.
In eastern North America Atkinson (2004) finds that the geometric attenuation
(GA) of Fourier amplitude spectrum is proportional to R^(-1.3), where R is the
hypocentral distance. She analyzed ~1700 digital seismograms from 186 earthquakes in southeastern Canada and northeastern United States. Based on the
residuals, she also concluded that the exponent is depth dependent, being higher/
lower for shallower/deeper source depths. Motivated by these results, we examine
GA of peak ground velocity (PGV) for hypocentral distances between 30-70 km.
We use a modified version of Bent’s (1996) 1D layered model in which a thin
surface layer with Vs = 2.8 m/s is added. This modified velocity structure agrees
with the assumptions of crustal properties in Atkinson (2004). Using the method
of Zhu and Rivera (2002) we computed velocity seismograms for point sources at
depths between 1 and 30 km, strike angle changing every 30 deg and dip angles
between 40 and 80 deg. For each source we computed a linear fit in the log-log
domain between PGV and R. Preliminary results show that the exponent for GA
varies between -1.8 and -1. To better understand the physics of these results, we
set up a ray-shooting model which includes the SH radiation pattern and reflectivity coefficients of SH rays. We calculated the theoretical decay in amplitude
of the rays that take off at different angles. We made a linear fit between relative
ray amplitude at the surface and hypocentral distances in the log–log domain.
From this model we see contributions to the exponent of the GA from depth of
the source, velocity structure and focal mechanism. From these calculations we
conclude that GA from double-couple point sources in complex velocity structures will be different from the classical result of 1/R for homogeneous media and
isotropically radiating sources.
Kappa Scaling for Western U.S. Ground Motion Prediction Equations
Alatik, L., San Francisco, CA, [email protected]; KOTTKE, A., PEER,
UC Berkeley, Berkeley, CA, [email protected]; ABRAHAMSON, N.,
PG&E, San Francisco, CA; RENAULT, P., Swissnuclear, Switzerland.
Current ground motion prediction equations (GMPEs) for the Western U.S.
(WUS) characterize the site condition using VS30 and some models also include
the depth to rock. For rock sites, another site term, kappa, can have a large effect
on the short-period ground motion; however, there are few hard-rock sites in the
WUS data sets to constrain the kappa scaling. We estimate the kappa scaling
using the following steps: (1) compute the rock (VS30=620 m/s) response spectral values for short distances, (2) use random vibration theory (RVT) to convert
the response spectrum to a the Fourier amplitude spectrum (FAS), (3) estimate
the reference kappa0 from the FAS based on the slope in the high frequency spectrum, (4) define a new FAS at high frequencies (about 20 Hz) based on the kappa0
value, (5) for a range of kappa values, apply scaling to the FAS based on a ratio
of kappa/kappa0, (6) convert the kappa scaled FAS to response spectral values
using RVT, and (7) compute the ratio of the spectral values for a given kappa to
the response spectral values for kappa0. This process has an advantage over the
traditional hybrid empirical approach (Campbell 2003, 2004) because it does not
need to assume that the response spectral shape of the GMPE is consistent with
the response spectral shape of the point source stochastic model. By applying the
kappa scaling to the FAS consistent with the GMPE and using RVT to estimate
the response spectral values, we require the scale factors to be consistent with the
response spectral shape of the GMPE. This leads to kappa scaling that properly
shifts the peak in the spectrum in a reliable and systematic way. The kappa scaling
is added to the GMPE by adding a period-dependent term based on the ratio of
kappa/kappa0 and which includes a taper to reduce the effect at large distances
and low VS30 values. The kappa scaling applicable to the Abrahamson and Silva
(2008) model is shown.
Earthquakes of 2011
4&5
Session Chairs: Stephen Horton and Robert Williams
Foreshock and Aftershock Sequences of the 2011 M 5.6 Oklahoma Earthquake
Keranen, K. M., University of Oklahoma, Norman, OK, [email protected];
HOLLAND, A., Oklahoma Geological Survey, Norman, OK, austin.holland@
ou.edu; SAVAGE, H., Lamont-Doherty Earth Observatory, Palisades, NY,
[email protected]; ATEKWANA, E., Oklahoma State University,
Stillwater, OK, [email protected]; COCHRAN, E., United States
Geological Survey, Pasadena, CA, [email protected]; SUMY, D., United States
Geological Survey, Pasadena, CA, [email protected]; RUBINSTEIN,
J., United States Geological Survey, Menlo Park, CA, [email protected];
Kaven, J., United States Geological Survey, Menlo Park, CA, okaven@usgs.
gov
The historic M5.6 Oklahoma earthquake on Nov. 6 2011 ruptured a N55Estriking zone near Prague, OK, near the Wilzetta Fault. A M4.7 foreshock preceded this event on Nov. 5 2011, and a M4.7 aftershock occurred on Nov. 8. A
dense network of portable seismometers, in part a PASSCAL RAMP deployment, recorded foreshocks and aftershocks of the M5.6 event. Three broadband
seismometers were installed following the M4.7 foreshock, surrounding the epicenter and aftershocks of the M4.7 event. These stations recorded ~700 events
in 12 hours leading up to the M5.6 event, ~200 of which have been located. An
additional 7 broadband sensors, 8 short-period sensors, and 5 strong-motion sensors were installed following the M5.6 event, in a dense array surrounding the
zone of aftershocks, along with 3 additional temporary stations installed by the
USGS. To date, over 500 aftershocks have been relocated. The aftershocks define
a narrow, linear, steeply-dipping fault plane that correlate to the zone of maximum structural damage, and are consistent with the Global CMT solution for
this event. The zone illuminated by the aftershocks deviates from the mapped
trend of the Wilzetta Fault, and may illuminate the appropriate subsurface location of the buried fault, or may have ruptured a splay of the main fault structure.
A subset of aftershocks delineates a nearly orthogonal zone corresponding to the
east-west strike of the fault plane in the M4.7 aftershock. The dense recording
of many hundreds of foreshocks and thousands of aftershocks of the M4.7, 5.6,
and 4.7 events presents a complex and rich dataset for the investigation of fault
mechanics and seismicity in the midcontinent.
Are Seismicity Rate Changes in the Midcontinent Natural or Manmade?
Ellsworth, W. L., US Geological Survey, Menlo Park, CA; HICKMAN,
S. H., US Geological Survey, Menlo Park, CA; LLENOS, A. L., US Geological
Survey, Menlo Park, CA; MCGARR, A., US Geological Survey, Menlo Park,
CA; MICHAEL, A. J., US Geological Survey, Menlo Park, CA; RUBINSTEIN,
J. L., US Geological Survey, Menlo Park, CA.
A remarkable increase in the rate of M 3 and greater earthquakes is currently in
progress in the US midcontinent. The average number of M ≥ 3 earthquakes/year
increased starting in 2001, culminating in a six-fold increase over 20th century
levels in 2001. Is this increase natural or manmade? To address this question,
we take a regional approach to explore changes in the rate of earthquake occurrence in the midcontinent (defined here as 85° to 108° West, 25° to 50° North)
using the USGS Preliminary Determination of Epicenters and National Seismic
Hazard Map catalogs. These catalogs appear to be complete for M ≥ 3 since 1970.
From 1970 through 2000, the rate of M ≥ 3 events averaged 21 ± 7.6/year in the
entire region. This rate increased to 29 ± 3.5 from 2001 through 2008. In 2009,
2010 and 2011, 50, 87 and 134 events occurred, respectively. The modest increase
that began in 2001 is due to increased seismicity in the coal bed methane field
of the Raton Basin along the Colorado-New Mexico border west of Trinidad,
CO. The acceleration in activity that began in 2009 appears to involve a combination of source regions of oil and gas production, including the Guy, Arkansas
region, and in central and southern Oklahoma. Horton, et al. (2012) provided
strong evidence linking the Guy, AK activity to deep waste water injection wells.
In Oklahoma, the rate of M ≥ 3 events abruptly increased in 2009 from 1.2/year
in the previous half-century to over 25/year. This rate increase is exclusive of the
November 2011 M 5.6 earthquake and its aftershocks. A naturally-occurring rate
change of this magnitude is unprecedented outside of volcanic settings or in the
absence of a main shock, of which there were neither in this region. While the
seismicity rate changes described here are almost certainly manmade, it remains
to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production.
The Rupture Process of the 23 August 2011 Louisa County, Virginia Earthquake
Chapman, M., Geosciences Department, Virginia Tech, Blacksburg, VA,
[email protected]
The 23 August 2011 Virginia earthquake was a complex rupture. Local and teleseismic recordings show three distinct slip events. A small initiation pulse was
followed by two larger events, visible on records at the six nearest stations, and at
several stations at teleseismic distances. Only 4 stations recorded the mainshock
P waves at epicentral distances inside 150 km: the mainshock hypocenter cannot
be usefully determined from the sparse mainshock arrival time data. However,
the aftershock sequence was recorded by dozens of portable instruments deployed
by several groups, and those hypocenters are well constrained. The early aftershocks define a plane striking N29E and dipping 51 degrees to the southeast. I
used the sparse local arrival time data from both the mainshock and the three
largest early aftershocks to locate the main shock initiation (hypocenter) relative
to the aftershock hypocenters, assuming a common fault plane. The time intervals
between the sub-events, observed both locally and teleseismically, were used to
solve for the location of the two larger sub-events relative to the initiation, again
assuming a common fault plane. The analysis is complicated by the shallow focal
depth which causes pP interference with the direct arrival from the 3rd sub-event.
Waveform modeling was used to try and sort out this difficulty and infer the relative moments.
The rupture initiated at a depth between 6.5 and 7.5 kilometers, near the
southwestern end of the aftershock zone. The second sub-event occurred 0.75
seconds later, approximately 1.0 km to the northeast along strike, and 1.0 km updip from the hypocenter. The third sub-event occurred 1.5 seconds after rupture
initiation, and is difficult to spatially locate: the mean estimate (relative to the
initiation) is between 1.3 and 1.8 km to the northeast along strike, and between
1.3 and 2.5 km up-dip. Preliminary estimates of the sub-event moments are 0.2,
2.1 and 1.7 × 10**17 N-m, respectively.
Aftershock Imaging with Dense Arrays (AIDA) after the 23 August 2011, Mw
5.8, Virginia Earthquake: Results from a Prototype Rapid Deployment of Large
Numbers of Seismometers for High Resolution Source Characterization,
Structural Imaging and 4D Monitoring
Brown, L. D., Cornell University, Ithaca, NY, [email protected]; HOLE,
J. A., Virginia Tech, Blacksburg, VA, [email protected]; QUIROS, D. A., Cornell
University, Ithaca, NY, [email protected]; DAVENPORT, K., Virginia Tech,
Blacksburg, VA, [email protected]; HAN, L., Virginia Tech, Blacksburg, VA,
[email protected]; CHEN, C., Cornell University, Ithaca, NY, cc669@cornell.
edu; MOONEY, W., U.S. Geological Survey, Menlo Park, CA, mooney@usgs.
gov; Chapman, M., Virginia Tech, Blacksburg, VA, [email protected]
Following the Mw 5.8 Virginia earthquake of 23 August 2011, an unusually
high density seismic array of instruments from the EarthScope Flexible Array
was deployed to assess the utility of unaliased wavefield recording of aftershock
sources. On 27 August 2011, four days after the main shock, 103 portable “Texan”
one component, short-period recorders were placed along two linear profiles near
the hypocentral zone in order a) to demonstrate the feasibility of rapidly deploying high density arrays, b) to evaluate the value of such arrays in providing more
accurate hypocentral locations derived from c) higher resolution velocity models, and d) to test the feasibility of imaging hypocentral structure with reflection
methods using aftershocks and ambient noise as virtual sources by applying interferometric techniques. An additional 105 “Texan” instruments were added six
days later to extend the array more directly over the then better defined aftershock
zone as well as along a regional NE-SW profile. The latter employed three component sensors to quantify regional attenuation characteristics. The seismic stations were deployed at 100m and 200m spacing in the aftershock zone, and 2 km
along the regional profile. The aftershocks we recorded have also been located by
independent temporary arrays of three-component seismographs. Here we report
results demonstrating the value of such arrays for detailing source characteristics, imaging relevant structure, and potentially monitoring temporal variations
in physical properties related to seismogenic stresses. This experience suggests
that deployment of arrays of 1000 or more seismographs are not only feasible but
could have a transformative impact on the study of seismicity.
Finite Source Modeling and Stress Drop of the 2011 M 5.8 Virginia Earthquake
Based on Seismic Waveforms
Shao, G., University of California, Santa Barbara, Santa Barbara, CA;
Santa Barbara, Santa Barbara, CA; JI, C., University of California, Santa
Barbara, Santa Barbara, CA.
On 23 August 2011, a M5.8 earthquake hit central Virginia. It has been reported
as the most widely felt earthquake in US history— reflecting, in part, the population density in the eastern US and the low attenuation of this region. Another
factor is that the source was particularly energetic. We first calculated earthquake source parameters by analyzing the S wave spectra of the accelerograms
recorded at the North Anna Nuclear Power Plant (Virginia; 18.7 km), CVVA
(Charlottesville, VA; 53.5 km), CBN (Fredericksburg Observatory, VA; 58 km)
and station 2555 (Reston Fire Station 55, Virginia; 121.5 km). From the corner
frequency in the spectrum we compute a Brune (1970, 1971) stress drop about
30 MPa. We also constrain the source rupture process by modeling teleseismic
P waves (up to 2Hz) at 43 stations and SH waves (up to 1Hz) at 22 stations, and
strong motion data at 3 stations (up to 2 Hz). Given the regional trend of the
geology and aftershock distribution, we prefer a fault plane that has a strike of
28° and dip of 55° based on the University of Saint Louis regional CMT solution.
Our preliminary slip model suggests that this earthquake initiated with a 0.6 s
nucleation phase and was followed by energetic moment release over the next 2
s. Most slip is confined to an area that is 6 km along strike and 3 km down dip,
in a depth range between 4 and 6 km, consistent with the seismic gap defined by
aftershocks. In the major slip region, the average rupture velocity is ~2.7 km/s. It
released a total seismic moment of 5.08x1017 Nm, consistent with the GCMT
solution. Using the slip on the fault and the software Coulomb 3.2, we compute
an average stress drop of 14 MPa in the averaged rake angle (115°) direction with
values that range between -17 to 41 MPa across the fault. The difference in stress
drop between the finite fault inversion and the source spectral analysis might be
explained by a complex rupture history.
Seismic Investigations of Mineral, VA Earthquake Impact to the North Anna
Nuclear Power Plant
Li, Y., US Nuclear Regulatory commission, Rockville, MD.
On 23 August 2011, a magnitude 5.8 (Mw) earthquake occurred near Mineral,
Virginia. The local community observed some damages such as collapsed chimneys, cracked walls and falling objects. The North Anna nuclear power plant is
located about 18 km from the epicenter and the power plant has two pressurized
water reactor units. The Safe Shutdown Earthquake ground motions (SSE) at the
plant site are 0.12 g for rock and 0.18 g for soil. Both reactors experienced strong
shaking and automatically shutdown. Immediately after the earthquake, the US
Nuclear Regulatory Commission dispatched an Augmented Investigation Team
to the site to inspect the earthquake impact to the nuclear power plant. The team
conducted walkdowns to the structures, systems and components (SSC) both
inside and outside the reactor containment buildings. The investigators checked
various seismic instruments located at different floor levels and reviewed corresponding seismic recordings. The investigators also interacted and interviewed a
large number of staff engineers working for the plant. Based on the investigations,
the team concluded that the earthquake ground motion exceeded the SSEs at the
plant site at the frequencies important to SSCs, but no significant damages to
safety related SSCs were observed because large seismic margins were embedded
in the original reactor design.
Earthquake Studies
Oral Session · Wednesday 8:30 am, 18 April · Pacific Salon
6&7
Session Chairs: Mian Liu, Randy Keller, Larry Brown, and
Yongshuan (John) Chen
New Opportunities of U.S.-China Collaborations in Seismological and
Earthquake Studies
Liu, M., University of Missouri, Columbia, MO, [email protected]; KELLER,
G. R., University of Oklahoma, Norman, OK, [email protected]; BROWN,
L., Cornell University, Ithaca, NY, [email protected]; CHEN, Y. J., Peking
University, Peking, China, [email protected]
China is an important natural laboratory for seismological and earthquake studies. From the rise of the Tibetan Plateau to extension and volcanism in North
China, China is one of the best places to study continental collision and intracontinental tectonics. With frequent large earthquakes and more than 2000
years of historic earthquake records, China is also a key test bed for earthquake
models and hypotheses. US and Chinese scientists have a long tradition of productive collaboration in seismological and earthquake studies, and the environment for U.S.-China collaboration has never been better. Driven by China’s
booming economy and need for mineral resources and mitigation of geohazards,
China has greatly increased funding for earth science research in recent years,
creating unprecedented opportunities for international collaboration. In this
presentation we will introduce some of the major initiatives in China for seismological and earthquake studies, including SinoProbe (www.sinoprobe.org)
and China Earthquake Administration’s new programs of seismic imaging, fault
mapping, and geodetic measurements. We will highlights some of our ongoing
collaborative studies of intraplate earthquakes and intra-continental tectonics,
and describe the opportunities for those who are interested to participate.
Opportunities and Challenges for Expanded U.S.-China Research in
Seismology
Simpson, D. W., IRIS Consortium, Washington, DC, simpson@iris.
edu; WILLEMANN, R. J., IRIS Consortium, Washington, DC, ray@iris.
edu; DONG, S., Chinese Academy of Geological Sciences, Beijing, China,
[email protected]; WU, Z., Institute of Geophysics, Chinese Earthquake
Administration, Beijing, China, [email protected]
The US and China have enjoyed a long collaboration in a variety of earthquake
monitoring and research programs. For more than thirty years, collaboration
in the operation and exchange of data from the China Digital Seismograph
Network of the China Earthquake Administration as part of the USGS/IRIS
Global Seismographic Network has provided data of significant value for regional
and global earthquake studies. The Chinese territory is rich in variety of geological, tectonic and seismic conditions and numerous field programs, many using
IRIS/PASSCAL instruments, have been carried out in collaborative studies
between Chinese and US scientists in most of the seismically active regions of
China. In recent years, both countries have made significant new investments in
observational systems for seismology and related fields, including portable instrumentation for USArray, ChinArray and SinoProbe and upgrades to permanent
national monitoring networks. Similar technological advances in observational
systems are underway in other national programs elsewhere in the world. These
developments, coupled with enhanced data management and improved conditions for open data exchange, can lay the framework for a new stage of enhanced
collaboration in international research programs on earthquakes, crustal structure, fault zone dynamics and regional tectonics.
A Review of the Deep Seismic Structure of the Crust of China
Mooney, W. D., USGS, Menlo Park, CA, [email protected]; WANG, C.
Y., Institute of Geophysics, China Earthquake Administration, Beijing, China,
[email protected]; ZHANG, Z. J., Institute of Geology and Geophysics,
Chinese Academy of Sciences, Beijing, Chna, [email protected]; ZHAO, J. M.,
Institute of Tibetan Plateau Research, Chinese Ac. of Sciences, Beijing, China,
[email protected]
The deep crustal structure of China has been investigated in the past several
decades with seismic surface waves and receiver functions, seismic reflection profiles, and seismic refraction/wide-angle reflection profiles. Here we review new
results obtained by these techniques and discuss the implications for the tectonic
evolution of China. More than 100 active- and passive-source deep seismic profiles have been recorded in China. A contour map of crustal thickness reveals
a north-south trending belt with a strong, east-west lateral gradient in crustal
thickness immediately to the east of the Tibetan plateau; crustal thickness is
30-45 km in the east and 45-75 km in the west. The seismic properties of the
lower crust are important for the modelling of crustal strength, as mafic rocks
are less viscous than quartz-rich felsic rocks. We find a 20-km thick high-velocity
(7.1-7.4 km/s) layer in the lower crust of the stable Tarim basin and Ordos plateau.
However, in young orogenic belts, such as the Tibetan plateau, this layer is either
thin (5-10 km thick) or absent, implying removal by lower crustal delamination.
Crustal composition can be inferred from Poisson’s ratio. Across the Tibetan
plateau Poisson’s ratio has a nearly constant value of 0.24-0.25 in the upper and
middle crust indicating a felsic bulk composition to an average depth of 40 km
(i.e., 20 km deeper than typical crust). We suggest that late Cenozoic convergence
is mainly accommodated by thick-skinned tectonic deformation with thickening
of the upper and middle crust. Batholithic intrusions into the upper crust may
also play a significant role locally.
Project INDEPTH: Origins and Evolution of a 20-Year International
Collaboration
Brown, L. D., Cornell University, Ithaca, NY, [email protected]; ZHAO, W.,
Chinese Academy of Geological Sciences, Beijing, China.
In 1991 a relatively small group of Chinese and U.S. scientists met to plan a modest set of geophysical surveys in the Himalaya of southern Tibet. The success of
those pilot experiments developed into Project INDEPTH (INternational DEep
Profiling of Tibet and the Himalaya), a major interdisciplinary, multinational
effort to traverse the entire Himalaya-Tibet collision zone. With the recent completion of Phase IV, a series of geophysical and geological investigations across the
boundary between the Tibet Plateau and the Qaidam Basin, Project INDEPTH
has now largely fulfilled its initial vision. U.S. interest in deep reflection profiling of the Himalaya was stimulated in the late 70’s by COCORP’s success in
mapping crustal scale, low-angle thrust faulting in the Appalachians of the SE
U.S., and participation by COCORP scientists in several conferences in China
that addressed Tibet in the early 80’s. An informal meeting of Chinese, U.S.,
British and German scientists at the 1987 IUGG meeting in Vancouver, Canada
resulted in a formal invitation from the Chinese Academy of Geological Sciences
for an international scouting party to visit Tibet in 1991 to assess the feasibility of
crustal reflection profiling there. The report of that scouting party led to proposals to the U.S. National Science Foundation (Continental Dynamics Program),
the Chinese National Natural Science Foundation and the Ministry of Geology
and Mineral Resources to carry out a test survey of multichannel reflection profiling in the Himalayas, an experiment that came to be known as Phase I. The politically sensitive nature of the study area, coupled with the relative unfamiliarity of
the participants with each other, were factors which sometimes exacerbated the
already challenging logistics of the experiment. The dramatic success of Phase I
owes as much to the perseverance and good will of the individuals involved in
dealing with these irritants as it does to the scientific results, most prominent of
The Seismic Structure at the Edge of the Tibetan Plateau
SANDVOL, E., University of Missouri, Columbia, MO, sandvole@missouri.
edu; CEYLAN, S., University of Missouri, Columbia, MO, savas.ceylan@mail.
missouri.edu; LIANG, X., University of Missouri, Columbia, MO, liangxiao@
missouri.edu; NI, J., New Mexico State University, Las Cruces, NM, jni@nmsu.
edu; HEARN, T., New Mexico State Univerisity, Las Cruces, NM, thearn@
nmsu.edu; CHEN, Y., Peking University, Beijing, China, [email protected];
LIU, M., Univeristy of Missouri, Columbia, MO, [email protected]
Data from large aperture two dimensional seismic arrays throughout eastern
portion of the Tibetan plateau and the western edge of the Ordos plateau have
resulted in some of the first high resolution images of lithospheric structure and
seismic anisotropy in these regions. These studies have confirmed that low-velocity Tibetan crust ends abruptly at approximately 105 degrees longitude. These
low velocity structures are consistent with measurements of low Lg and Pg Q values indicating that these anomalies are a result of high temperatures and not just
composition. The low velocities show a strong correlation with the strain rates
computed from GPS and Quaternary fault data suggesting that strain heating
plays some role in the generation of these anomalies.
The mantle flow pattern, inferred from a large number of new shear wave
splitting in eastern Tibet and around the Ordos plateau, shows a clockwise rotation around the eastern Himalayan Syntaxis. Azimuthal anisotropy from surface
waves indicates significant anisotropy present throughout the lithosphere and
asthenosphere with fast directions only weakly depending upon frequency. This
is consistent with the presence of vertically coherent deformation extending into
the asthenosphere. Furthermore seismic anisotropy fabric appear to follow the
boundaries of the lithospheric roots under the Ordos plateau and Sichuan basin,
indicating the control of lithospheric structure on the sub-lithospheric mantle
flow.
Large two dimensional arrays in eastern Tibet have yielded a number of
important results and the proliferation of large numbers of seismic instrument
pools in china offer a tremendous opportunity to further improve the resolution
of three dimensional models within china. In particular large aperture, close
spaced arrays of broadband stations across the margins of the Tibetan plateau
should help to address fundamental questions about the different modes of deformation within the plateau.
Sino-US Cooperation on Deep Seismic Studies and Education Focused on
Continental Tectonics: Initial Results of Cooperation on SinoProbe02 Projects
Gao, R., Institute of Geology, CAGS, Beijing, China, [email protected];
KELLER, G. R., the University of Oklahoma, Norman, OK, [email protected];
LIU, M., University of Missouri, Columbia, MO, [email protected]; LI, Q. S.,
Institute of Geology, CAGS, Beijing, China, [email protected]; ZHANG,
S. H., China University of Geosciences (Beijing), Beijing, China, shzhang@
cugb.edu.cn; LI, Y. K., Geological Cores and Samples Center, Beijing, China,
[email protected]; HUANG, D. D., No 6 Geophysical Prospecting Company,
SINOPEC, Nanjing, Jiangsu, China.
In the framework of the cooperative agreement between the NSF PIRE project and SinoProbe02, the University of Oklahoma and Institute of Geology,
CAGS are working jointly using integrated seismic techniques to explore the
deep structures beneath the Chinese continent. So far, three seismic lines have
been completed (funded by NSF PIRE (0730154), SinoProbe02 & China NSF
(40830316)).
The North China line extends from the Huailai Basin of northwestern
Beijing, crossing through the Solonker suture zone to the China-Mongolia
boundary. Reflection in this profile is characterized with north-dipping features
in the lower crust and transparent features in the granite bodies of the upper
crust. The north-dipping reflection structures are interpreted as accreted wedges
formed along the north margin of the North China craton. These observations
challenge the south-dipping subduction events as proposed by previous geological models.
The Northeast China profile starts from the NW of Harbin and extends
westwards from the Greater Khingan Range to the Chinese border. This profile reveals strong and stacked reflections in the lower crust. We interpret these
features as multiple imbricate thrusts that result from plate convergence. Also,
several near-vertical strike-slip faults appear to cut the whole crust. Arc-shape
stacked reflections in the upper crust may indicate crustal extension and magmatism.
The Longmenshan lines starts from the Sichuan basin, crossing through
the Longmenshan fault zone to the NE Tibet Plateau. A broadside WAR/R line
is deployed to the north of the main profile. Initial interpretation results indicate a deep structural relationship between the Sichuan basin and Longmenshan
fold-thrust belt. Crust of the Sichuan basin does not appear to subduct under the
Longmenshan as previously suggested but instead subducted eastwards underneath the Huaying Mountain. The Longmenshan fault zone itself is apparently
characterized by strike-slip shearing of the lithosphere.
Joint Active and Passive Arrays for Study of Active Orogens
Wu, F. T., SUNY Binghamton, Binghamton, NY, [email protected]
Studies of subsurface geological processes have made important advances as
the portable field seismological instruments adopted digital technology, wider
dynamic range, large data storage and low power consumption—since the early
1990’s. The currently used instruments will probably be updated soon as technology advanced and our needs change. An interesting subclass of the problems
that benefit from this advance is the study of active orogens. Using TAIGER
experiments as an illustration of current technology and a base to project future
development. Throughout the project the following principles were used: set the
instruments in continuous recording mode as much as possible in order to catch
local and distant earthquakes as well as the active sources on the dense active
source arrays, just like the broadband stations. The 3-year deployment plans collected over 3 TB (not counting marine seismics). Recent work has already produced results that provoke new thinking about the Taiwan orogeny. Examples:
Vp tomography defines the crustal thickening, discovers a significant high velocity rise under eastern Taiwan, mapping of the high velocity anomaly (associated
with active and inactive subduction) in the upper mantle and use Vp/Vs tomography to constrain petrology and temperature under the Central Range. Similar
studies can be carried out in other active orogens, including many in China, especially at a time when Sinoprobe is planning a series of active and passive deployments across the active structures such as western Tianshan, certainly most of
Tibet, Qilianshan, Longmenshan, Yunnan mountains etc. The lower seismicity
in these area can be partially compensated by using more dense arrays. Future
instruments can probably benefit from technology currently developed for smart
phones. With dual- or quadcore cpu, 64 or more GB of memory and lithium battery much of the core elements are already here.
Constraints on Regional Stresses Prior to the 2008 Mw 7.9 Wenchuan, China,
Earthquake from Coseismic Slip Models and Aftershock Mechanisms
Hetland, E. A., University of Michigan, Ann Arbor, MI, ehetland@umich.
edu; MEDINA LUNA, L., University of Michigan, Ann Arbor, MI, lmedina@
umich.edu; FENG, G., King Abdullah University of Science and Technology,
Thuwal, Kingdom of Saudi Arabia, [email protected]
The 2008 Mw 7.9 Wenchuan earthquake occurred along the middle segment of
the Longmen Shan fault zone, marking the eastern margin of the Tibetan plateau
and the Sichuan basin. Models of coseismic slip indicate that the Beichuan fault
slipped primarily as thrust on moderately dipping fault segments in the southwest, and as dominantly dextral strike-slip on more steeply dipping segments in
the northeast. The shallowly dipping Pengguan fault, located to the east of the
Beichuan fault, also slipped mostly in thrust motion during the Wenchuan earthquake. Additionally, focal mechanisms of the aftershocks were mainly thrust in
the southwest and strike-slip in the northeast. We test whether coseismic slip
models and the aftershock focal mechanisms are consistent with a homogeneous
pre-mainshock regional stress, or if a heterogeneous stress field is required. We
assume that coseismic slip is parallel to the direction of the maximum shear stress
on the faults, and that aftershocks result from both the pre-mainshock stress and
the coseismic stress changes. We find that coseismic slip models of the Wenchuan
earthquake are statistically consistent with a constant orientation of principal
stresses along the fault prior to the mainshock. The inferred most compressive
stress direction is near horizontal and east-west trending while the intermediary
compressive stress is also near horizontal, but trending north-south, consistent
with inferences of fault loading. In contrast, the aftershocks by themselves indicate a heterogeneous stress field, which may reflect the heterogeneous coseismic
stress changes in the Wenchuan earthquake. Our initial analysis does not rely on
models of static frictional stability, although we explore such models in order to
further constrain the stresses responsible for the Wenchuan earthquake.
Seismic Hazard Assessment and Mitigation Policy for Tianshui, Gansu
Province, China
Wang, Z., University of Kentucky, Lexington, KY, [email protected];
WOOLERY, E., University of Kentucky, Lexington, KY, [email protected];
WANG, L., Lanzhou Institute of Seismology, China Earthquake Administration,
Lanzhou, Gansu, China, [email protected]
Recent earthquakes, particularly the 2008 Wenchuan, China earthquake,
the 2010 Haiti and Chile earthquakes, and the 2011 New Zealand and Japan
earthquakes, demonstrate that mitigation, in particular better seismic design for
buildings, bridges, and other infrastructure, is the most effective way to reduce
seismic risk.
The city of Tianshui in the southeastern part of the Gansu Province is
home to approximately 3.5 million citizens. It sits along the northeastern edge
of the Qinghai-Tibetan Plateau, where the interaction between the Eurasian and
Indian Plates has been the driving mechanism for the high level of seismicity on
the Qinghai-Tibetan Plateau and its foreland including the Tianshui area. Thus,
the city of Tianshiui is in a highly active tectonic area and has experienced many
strong earthquakes in the past 2, 000 years.
Through a collaboration between the University of Kentucky and the
Lanzhou Institute of Seismology, a seismic hazard assessment was conducted
for the Tianshui area by utilizing China’s rich historical records and geological
studies on earthquakes. Our study shows that the earthquakes along the West
Qinling North Boundary Fault Zone, particularly the Gangu-Wushan fault segment, will have the most significant impact on the city of Tianshui. As a result,
we recommend the following parameters for engineering design and other mitigation consideration in the Tianshui area: 1) PGA of 0.20g (Chinese intensity
VIII) with 10 percent probability of exceedance (PE) in 50 years; 2) PGA of 0.30g
(Chinese intensity VIII) with 5 percent PE in 50 years; and 3) PGA ≥ 0.40g
(Chinese intensity IX) with 2 percent PE in 50 years.
Extent of Sedimentary Fill beneath Tangshan, China as Modeled by 3D
Seismic Survey
Chang, J. C., University of Oklahoma, Norman, OK, jeffersonchang@
ou.edu; KELLER, G. R., University of Oklahoma, Norman, OK; QU, G.,
NERSS, China Earthquake Administration, Beijing, China; HARDER, S. H.,
University of Texas at El Paso, El Paso, TX.
Excessive destruction from the 1976 Tangshan earthquake (M 7.5) in northern
China was likely due to the amplification of ground motion by thick underlying sediments; yet the extent of sedimentary fill and underlying geologic structures, beneath Tangshan and surrounding areas are poorly constrained. These
parameters should be elucidated to better assess seismic hazards and hazard
mitigation in the area. We developed a new geometry for a cost-effective threedimensional (3D) seismic survey, comprising 9 seismic transects, centered on the
city of Tangshan. In January of 2010, we deployed 500 REFTEK 125A (“Texan”)
recorders at 500 m spacing in an area approximately 40 km × 60 km and fired
10 shots. The preliminary modeling was done with 3D tomographic inversion
using first arrivals, and further refined by 2D raypath modeling of the later
seismic phases. Our analyses suggest that, with respect to the city of Tangshan,
poorly consolidated sedimentary fill (seismic velocity of about 1.8 km/s) has an
average thickness of 1km, thins to the north (bedrock outcrops just north of the
study area), and thickens to the south (up to 4 km in some areas). Upper crustal
velocities are 5.2 to 6.6 km/s, and increase to 7.0 km/s at mid-crustal depths.
Our results also showed that the basin structure complex die to both NNE and
WNW trending faults.
EARTHSCOPE and SINOPROBE Magnetotelluric Arrays: Contrasts and
Collaborations across Interdisciplinary Continental Scale Programs
Schultz, A., Oregon State University, Corvallis, OR, adam@coas.
oregonstate.edu; HU, X., China University of Geosciences, Wuhan, China.
The USArray magnetotelluric (MT) program includes a 70 km grid Transportable
Array (MT TA), a 7 station permanent MT Backbone network, and investigatorled MT FlexArray studies. Approximately 350 long-period MT TA stations
have been operated thus far in the northwestern US and the Mid-Continent
Rift region. MT data are made available soon after acquisition through the IRIS
DMC. The SinoProbe program is completing an MT array on a 444 km (4° × 4°)
grid covering China. A multi-site, facet-element MT measurement is employed
to reduce the effect of inhomogeneous local resistivity and noise. A standard grid
node placed every four latitude and longitude crossing points consists of a central
measurement site with long-period and broadband MT instruments, and four
north-south and four east-west auxiliary sites with broadband measurements
only. The grid in North China and Qinghai-Tibetan Plateau is refined to 1° × 1°,
and every node consists of two additional north-south auxiliary sites. EarthScope
and SinoProbe use seismic and MT methods to develop advanced integration of
geophysica1 techniques for detailed deep detection. Several typical areas with
both complex geological settings and different level of artificial noise such as the
Tibet plateau, the western orogen, and mountain areas with crystalline rocks in
south China are selected as target areas for such efforts, while areas including
Cascadia and the Snake River Plain-Yellowstone region have been targeted for
integrated studies in the US.
We report on results of inversions of EarthScope and SinoProbe MT data
carried out by a number of groups, using data available from IRIS and SinoProbe
Data Centers. A number of these features correspond to seismically delineated
crust and upper mantle anomalies, including indications of crustal melt accumulations, and plume-like mantle melt sources. Common experiences in both programs are leading to opportunities for US-Chinese collaboration in integrated
MT and seismic investigations.
Crustal Structure of the Solonker Collision Zone: Preliminary Interpretation
of a Deep Seismic Reflection Profile in North China
Zhang, S., China Univ Geosciences Beijing, Beijing, China, shzhang@cugb.
edu.cn; GAO, R., Institute of Geology, CAGS, Beijing, China, ruigao126@126.
com; HOU, H., Institute of Geology, CAGS, Beijing, China, hesheng.hou@126.
com; LI, H., China Univ Geosciences Beijing, Beijing, China, hai2216@cugb.
edu.cn; LI, Q., Institute of Geology, CAGS, Beijing, China, liqiusheng@
cags.ac.cn; LI, C., China University of Geosciences Beijing, Beijing, China,
[email protected]; RANDY, K. G., University of Oklahoma, Norman,
OK, [email protected]; Liu, M., University of Missouri, Columbia, MO, liuM@
missouri.edu
The Solonker collision zone is part of the Central Asian Orogenic Belt. It may
contain the final collision suture representing the amalgamation of the North
China Craton (NCC) and the Mongolian composite terrane in the late Paleozoic.
We have recently completed a ca. 630 km deep seismic reflection profile as part of
the SinoProbe-02 Project. The profile crosses the Solonker collision zone, providing new insights into the Paleozoic accretion and collision of the juvenile crustal
blocks along the north margin of the NCC.
The most striking observation is the low angle reflector stacks in the lower
crust. In some areas reflectors extend upward into the shallow crust, connecting to the outcropped deep metamorphic Precambrian basement rocks. But in
most cases, the reflectors are truncated by floor and roof decollements. Numerous
transparent bodies in the upper part of the crust are related to granites outcrops.
These interpreted granitic bodies truncate the thrust systems. The Moho is easy
to be identified, because the lower crust is full of strong reflection fabric, but the
mantle is transparent.
Based on the interpretation of the whole profile, we suggested that (1) a
continent-continent collision, not arc-arc collision, dominated the crustal structures of this region, (2) most granites are likely post-collisional, (3) significant
uplift occurred and the Moho was modified.
and their Relationship to Ground Motion Parameters
Oral Session · Wednesday 1:30 pm, April 18, · Pacific Salon
6&7
Session Chairs: Klaus-G. Hinzen, Luigi Cucci, Mariano
Garcia-Fernandez, and Andrea Tertulliani
Using Chimney Damage to Quantify Ground Motions of Historic Earthquakes
in Eastern North America
Ebel, J. E., Weston Observatory/Boston College, Weston, MA, [email protected]
For eastern North America, quantifying the amount of chimney damage at
a locality can provide a measure of the strength of the ground shaking at that
locality. As the strength of ground shaking increases, the number of chimneys
on houses in a town that are damaged increases, and so does the severity of the
damage to the chimneys. Because typical wood-frame or brick houses in eastern
North America are relatively short structures, their chimneys tend to be damaged
by the higher frequency ground shaking ranging from pga to a period of about
0.3 sec. Fragility curves for low-rise unreinforced masonry (URM) structures
like chimneys can be used to quantify the relationship between the number and
severity of damaged chimneys and the ground motion that was experienced at the
locality where the chimneys were damaged. For modern earthquakes, the fragility
curves for URM structures in MHAZUS can be used with counts of chimneys
that experienced minor, moderate and severe damage at a locality to make a quantitative estimate of the ground motion at that locality. For historic earthquakes,
the fragility curves may need to be adjusted for the strength of the mortar that
was used in the chimneys at the time of the earthquake. As an example, in Boston
in the 1755 Cape Ann earthquake, about 3% of the chimneys suffered extensive
damage, about 33% suffered moderate damage, and about 64% sustained either
slight damage or no damage at all. This pattern of damage is consistent with a pga
in Boston of somewhere between 0.08g to 0.11g. The existence and amount of
chimney damage can be used to constrain the level of ground shaking at a locality
in a more quantitative way than is possible from a simple macroseismic intensity
estimate.
ShakeMap Best Practices: Historic and Modern Events
Johnson, K. L., U.S. Geological Survey, Golden, CO, [email protected];
GARCÍA, D., U.S. Geological Survey, Golden, CO, [email protected];
WORDEN, C. B., U.S. Geological Survey, Pasadena, CA, cbworden@gmail.
com; LIN, K., U.S. Geological Survey, Golden, CO; MAH, R., U.S. Geological
Survey, Golden, CO, [email protected]; MARANO, K. D., U.S. Geological
Survey, Golden, CO, [email protected]; HEARNE, M., U.S. Geological
Survey, Golden, CO, [email protected]; Wald, D. J., U.S. Geological Survey,
The ShakeMap system is a widely used tool for assessing the ground motion during an earthquake in near-real time applications, as well as for past events and
future earthquake scenarios. The original ShakeMap Atlas (Allen et al., 2008)
is a compilation of nearly 5, 000 ShakeMaps of macroseismic intensity (MI) and
ground motion parameters of damaging and potentially damaging global earthquakes between 1973 and 2007. The Atlas is an invaluable resource for examining strong ground motions near the source, and is used to calibrate the Prompt
Assessment of Global Earthquakes for Response (PAGER) as well as other loss
systems. We present the best practices developed during the compilation of the
next Atlas version, which extends to events thru 2010. Best practices include the
use of: (1) a new version of ShakeMap (V3.5; Worden et al., 2010); (2) refined prediction equations selection; and (3) numerous additional intensity and ground
motion data. ShakeMap V3.5 treats native and converted data separately when
producing each map layer (MI, PGA, PGV, and PSA). This is especially important for intensity observations, which are the main data source in most countries.
ShakeMap V3.5 also allows for inclusion of direct intensity prediction equations
(IPEs) and uses improved mapping techniques and uncertainty estimations. We
focus on best practices for choosing GMPEs, IPEs, and conversion equations
between intensity and ground motion. We use a new global scheme to distinguish
between types of earthquakes (García et al., 2012) and select the most appropriate
prediction equations for ShakeMap to estimate intensities and ground motions
when data are limited. We present the suite of equations deemed most appropriate for various regions around the globe. Finally, we have added thousands
of newly available observations from national and regional networks. All these
practices make the new ShakeMap Atlas an enhanced resource for global hazard
analyses and earthquake loss calibration.
Spatial Correlation of Modified Mercalli Intensity Derived from High-Density
Internet-Based Reports
Worden, C. B., Synergetics, Inc., Ft. Collins, CO USA, cbworden@usgs.
gov; WALD, D. J., USGS, Golden, CO USA, [email protected]; JOHNSON, K.
L., USGS, Golden, CO USA, [email protected]; QUITORIANO, V., USGS,
Golden, CO USA, [email protected]
The intraevent spatial correlation of peak ground motions has become an increasingly important topic in seismic engineering, loss modeling, and ground motion
interpolation. Little work, however, has been done on the spatial correlation of
macroseismic intensity. Like ground-motion, intensity has important applications in loss modeling, and is often the only data available for global and historic
earthquakes. We use a database of high-density felt reports from the USGS’s
“Did You Feel It?” (DYFI) system for a number of moderate- to large-magnitude
earthquakes to determine the spatial correlation structure of Modified Mercalli
Intensity (MMI). The high density of observations in the DYFI data allows thousands of comparisons at even sub-100 meter resolution, which is better than that
achieved by most studies of peak ground motions.
Following the approach other authors have used for peak ground motions,
we apply semivariogram analysis to pairs of intensity residuals at varying separations in order to model the intraevent correlation of MMI. Because MMI is a
spatially averaged parameter, we accommodate the zero-distance uncertainty in
our model by combining an exponential function with a “nugget effect”.
The correlation structure is well behaved, exhibits high correlation at relatively close distances, and is quite consistent among events. The high-density of
our data also allows us to explore anisotropic effects, zonal variability, and the
effects of soil amplification. We compare the results obtained from California
earthquakes to those of earthquakes in the central and eastern United States to
assess the effects of differing tectonic regimes. Finally, we use a database of traditionally-assigned MMIs to determine the applicability of our models to historic
earthquakes.
Computer-aided Assessment of Macroseismic Intensity by the Fuzzy Sets
Method
Tripone, D., Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy,
[email protected]; VANNUCCI, G., Istituto Nazionale di Geofisica e
Vulcanologia, Bologna, Italy, [email protected]; GASPERINI, P.,
Universitá di Bologna, Dipartimento di Fisica, Bologna, Italy, paolo.gasperini@
unibo.it; FERRARI, G., Istituto Nazionale di Geofisica e Vulcanologia, Bologna,
Italy, [email protected]
Seismic intensity assessment usually consists in the subjective judgment, made
by a macroseismic investigator (“expert”), of which degree of the scale better
corresponds to the macroseismic effects observed at a site. In previous work, in
order to make this decisional process more objective, we developed a computational procedure, based on the Fuzzy Set Theory, that formalizes the main steps
of the process of intensity assessment that consists of i) the identification of significant macroseismic effects and their collection in a database, ii) the association
between the effects and the degrees of the intensity scale, iii) the assessment of the
intensity degree using multi-attribute decision-making algorithms. We applied
this procedure to 8 Italian earthquakes. All the results showed a good statistical
agreement among fuzzy intensities and expert ones. In this work we tested the
fuzzy procedure with the U.S. macroseismic data for the Hector Mine (1999),
Napa (2000) and Nisqually (2001) earthquakes, derived from the Did You Feel
It? (DYFI) database. Those data are very different from Italian ones, because the
DYFI information derives from standardized online macroseismic questionnaires. The different type of data has required some methodological changes. We
are now able to analyze the DYFI data in almost real time. The new intensity
values were compared with MMI estimated by the expert from data collected via
postal questionnaires, media reports, and engineering reports. The fuzzy method
well reproduces the expert intensity (MMI). The agreement is very similar to the
one obtained comparing DYFI and MMI values. Our approach may be useful
to providing an objective and reproducible intensity assessment. The database of
effects we have built could also be employed to testing the long-term temporal
and geographical consistency of U.S. macroseismic intensity values.
Peak Ground Acceleration in Port-au-Prince, Haiti, during the M7.0 12
January 2010 Haiti Earthquake Estimated from Horizontal Rigid Body
Displacement
Hough, S. E., US Geological Survey, Pasadena, CA, [email protected];
TANIGUCHI, T., Tottori University, Tottori, Japan, [email protected].
ac.jp
No strong motion records are available for the 12 January 2010 M7.0 Haiti earthquake. We use aftershock recordings as well as detailed considerations of damage
to estimate the severity and distribution of mainshock shaking in Port-au-Prince.
Relative to ground motions at a hard-rock reference site, peak accelerations are
amplified by a factor of approximately 2 at sites on low-lying deposits in central
Port-au-Prince and by a factor of 2.5-3.5 on a steep foothill ridge in the southern
Port-au-Prince metropolitan region. The observed amplification along the ridge
cannot be explained by sediment-induced amplification, but is consistent with
predicted topographic amplification by a steep, narrow ridge. Although damage was largely a consequence of poor construction, the damage pattern inferred
from analysis of remote sensing imagery provides evidence for a correspondence
between small-scale (0.1-1.0 km) topographic relief and high damage. Mainshock
intensities can be estimated crudely from a consideration of macroseismic effects.
To explore mainshock severity further we present detailed, quantitative analysis
of the marks left on a tile floor by an industrial battery rack displaced during the
mainshock, at the location where we observe the highest weak motion amplifications. Results of this analysis indicate that mainshock shaking was significantly
higher at this location (approximately 0.5g, MMI VIII) relative to the shaking
in parts of Port-au-Prince that experienced relatively light damage. Our results
further illustrate how observations of rigid body horizontal displacement during
earthquakes can be used to estimate peak ground accelerations in the absense of
instrumental data.
The Earthquake Rotated Obelisk in Lorca, Spain
Hinzen, K.-G., Cologne University, Cologne, Germany, hinzen@uni-koeln.
de; FERNANDEZ, M. G., Institute of Geosciences (CSIC-UCM), Madrid,
Spain, [email protected]
During the 5 May 2011 M W 5.1 Lorca earthquake in southern Spain, heavy macroseismic effects were observed in large parts of the town, reaching a maximum
intensity of VII (EMS). Among the damaged structures is an obelisk-shaped
monument in the city center of Lorca composed of 11 frustrum with a height of
5.66 m resting on a 1 m high foundation. Three of the top blocks of the obelisk
show rotations from 0.2° to 4°. We use a discrete element model of the monument to study its dynamic behavior. Besides analytic ground motion signals, the
3D acceleration time history of ground motion during a magnitude 4.5 foreshock
and the main shock measured at a strong motion station 360 m north of the monument and 3.4 km epicentral distance were used as boundary conditions for the
model calculations. The measured ground motions did not reveal the observed
rotations in the model calculations, and even increasing the simulated ground
motions to double the peak ground acceleration did not cause rotations as large as
the observed ones. By increasing the signal duration und using a harmonic 3 Hz
motion in form of a Morlet wavelet, we were able to initiate vertical rotations in
the range of the observed values. The first assumption of differences in site effects
is not supported by H/V measurements at the station location and next to the
obelisk; both do not show significant peaks. Further studies will include topographic effects and near-fault pulses.
Triggering
6&7
Session Chair: Michel Campillo
Relations Between Velocity Changes, Strain Rate and Non-Volcanic Tremors
during the 2009–2010 Slow Slip Event in Guerrero, Mexico
Rivet, D., ISTERRE, Université Joseph Fourier, Grenoble, France, diane.
[email protected]; CAMPILLO, M., ISTERRE, Université Joseph
Fourier, Grenoble, France, [email protected]; ZIGONE, D.,
ISTERRE, Université Joseph Fourier, Grenoble, France, [email protected]; RADIGUET, M., ISTERRE, Université Joseph Fourier, Grenoble,
France, [email protected]; CRUZ-ATIENZA, V., Ins.
Geofisica, UNAM, Mexico D.F., Mexico, [email protected]; SHAPIRO,
N. M., IPGP, Paris, France, [email protected]; G-GAP team
We use ambient noise cross correlations to monitor slight changes in seismic
velocities during the slow slip event (SSE) of 2009-2010 in Guerrero. This is a test
of the sensitivity of the seismic velocity to variations of deformation, in absence
of strong motions. The 2009-2010 event presents a complex slip sequence with
two subevents occurring in two distinctive slipping patches (Walpersdorf et al.,
2011). From a seismic array of 59 seismometers, consisting mostly of short-period
sensors, we detect a velocity drop with a maximum of amplitude at the time of
the first subevent. We analyze the velocity change at different period band and we
observe that the perturbation associated to the SSE maximizes for periods longer
than 12s. To determine the depth of the portion of the crust affected by this perturbation, we performed a linearized inversion of the velocity change measured at
different period band. We detect no perturbation in the upper crust (first 10km),
while the velocity perturbation increases with depth, affecting the middle and
lower crust. Besides, we compute the deformation produced by the SSE in an
elastic model using the slip evolution recovered from the inversion of continuous
GPS. The comparison of the velocity changes and the deformation suggests that
the velocity change is related with the strain rate. This result is similar to what was
observed during a SSE in 2006 (Rivet et al., 2011).
The velocity changes can be interpreted together with other observables
such as non-volcanic tremors. During the 2009-2010 SSE we measured nonvolcanic tremors activity using continuous seismic record filtered between 2
and 8 Hz. We observed a correlation between velocity changes (measured at
long period) and tremors activity whereas no correlation exists between velocity
changes and seismic noise at long periods. This suggests that the over-riding plate
exhibits a nonlinear mechanical behavior in response to the slight deformation
produced by the SSE.
Episodic Tremor as Slow-Slip Events (SSE) at Parkfield, CA
Guilhem, A., Lawrence Berkeley National Laboratroy, Berkeley, CA,
[email protected]; NADEAU, R. M., U. C. Berkeley Seismological
Laboratory, Berkeley, CA, [email protected]
Recurring episodes of nonvolcanic tremor (NVT) in the Parkfield, California
area are reminiscent of seismic events associated with episodic tremor and slip
(ETS) and slow-slip events (SSEs) observed in subduction zones. To explore possible relationships between the Parkfield episodes and subduction zone ETS/
SSEs, we propose a simple SSE model for 52 Parkfield episodes and estimate
model parameters using the locations and timing of NVT and LFEs episodes,
the duration of NVT activity during the episodes, and the correlated response
between episodes and repeating earthquake activity along the San Andreas Fault
during an ~ 9.7 yr. period.
Our findings suggest that: 1) slow-slip occurs on a SAF parallel patch that
is ~ 25 km long and 15 km wide centered at ~ 25 km depth, 2) slip on the SSE
patch is on average ~ 7.8 mm for each SSE, implying a stress drop of ~ 10 kPa,
3) SSE source time functions have durations of ~ 10 days with a distinct peak
after ~ the first 3 days, 4) SSE moment magnitudes range between 5.0 and 5.4 are
remarkably consistent with those predicted by Aguiar et al., 2009, 5) recurrence
time-moment scaling is consistent with subduction zone SSEs, 6) seismicity patterns above the SSE zone show correspondence with the SSE timing, and 7) NVT
episodes can provide in-situ measurements of inferred fault slip transients below
the seismogenic zone.
Modeling of 3D Complex Tremor Migration Patterns
Luo, Y., Seismological Laboratory, Caltech, Pasadena, CA, [email protected];
AMPUERO, J. P., Seismological Laboratory, Caltech, Pasadena, CA, ampuero@
gps.caltech.edu
The discovery of slow-slip events (SSE) and non-volcanic tremors has broadened
the spectrum of earthquake behavior. Observations of these phenomena offer
a unique window into the mechanics of the deeper portions of the seismogenic
zone of active faults, a region of great importance in the nucleation of large earthquakes. In the Cascadia subduction zone, tremors show a hierarchy of migration
patterns: large-scale along-strike tremor propagation at about 10 km/day, rare
swarms that propagate 10 times faster in the opposite direction (“rapid tremor
reversals” or RTR) and even 10 times faster swarms that propagate along-dip.
Moreover, during the initial phase of ETS (Episodic tremor and Slip) the tremor
source amplitude shows a linear growth and up-dip propagation. Here we propose a model to reproduce these observations based on interaction of brittle
asperities (frictionally unstable, velocity-weakening patches) embedded in a
relatively stable fault, mediated by creep transients. We performed a quantitative
study of this model through numerical simulations of heterogeneous rate-andstate faults under quasi-dynamic approximation. In our previous 2D simulations,
we successfully reproduced the slow forward migration and RTR. In the current
work we extend our simulations to 3D. We successfully simulated all the three
major tremor migration patterns. The slow forward migration is obviously due to
tremor triggering near the leading front of the propagating SSE pulse. Less trivially, our model also produces RTRs and along-dip swarms with similar characteristics as in Cascadia: sparsely distributed scattered RTR swarms back-propagating at fast speed about 100 km/day, and faster along-dip swarms about 1000 km/
day. Our model also produces the observed features of the initial growth phase of
ETS, in particular a semi-circular initial front, and predicts radial and azimuthal
tremor migration patterns that are a potential target for future high-resolution
observations.
Observations of Tectonic Tremor on the Alpine Fault, New Zealand
Fry, B., GNS Science, Lower Hutt, New Zealand, [email protected]; CHAO, K.,
Georgia Institute of Technology, Atlanta, GA, [email protected]; PENG,
Z., Georgia Institute of Technology, Atlanta, GA, [email protected]
dip migration obtained with the USArray can be explained by this artifact. Thus,
low frequency back-projection needs to be further tested and validated in order
to contribute to the characterization of frequency-dependent rupture properties.
Deep non-volcanic tremor has been observed at major subduction zones around
the Pacific Rim, including the Hikurangi subduction zone in the North Island,
New Zealand, and the San Andreas Fault system in California. These observations provide new information on variable fault slip behaviors below the seismogenic zone. Here we present evidence for triggered and ambient non-volcanic
tremor at depth along the Alpine Fault, a transpressional feature that facilitates
the majority of plate convergence between the Pacific and Australian plates in
New Zealand. We identify triggered tremor as high-frequency non-impulsive
signals that are in phase with the large-amplitude teleseismic waves. By using a
non-linear envelope-based algorithm, we roughly locate the events and provide a
context for their occurrence. High heat-flow and a lack of deep earthquakes suggest the brittle-ductile transition is remarkably shallow below the Alpine Fault.
However, paleoseismic studies suggest that shallow seismic strain is accommodated by large crustal earthquakes which pose a seismic hazard. Understanding
the relation of tremor to the brittle-ductile transition and the seismic spectrum
will inform our understanding of stress-accommodation and ultimately seismic
hazard.
Global Observations of Triggered Tectonic Tremor
Peng, Z., Georgia Institute of Technology, Atlanta, GA, [email protected];
CHAO, K., Georgia Institute of Technology, Atlanta, GA, kevinchao@gatech.
edu; WU, C., Georgia Institute of Technology, Atlanta, GA, chunquanwu@
gatech.edu; FRY, B., GNS Science, Lower Hutt, New Zealand, [email protected].
nz; ENESCU, B., NIED, Tsukuba, Japan, [email protected]; AIKEN, C.,
Georgia Institute of Technology, Atlanta, GA, [email protected]
Investigating Interactions of Creeping Segments with Adjacent Earthquake
Rupture Zones in the Mendocino Triple Junction Region
Taira, T., Berkeley Seismological Laboratory, Berkeley, CA, taira@seismo.
berkeley.edu
We investigate the spatially and temporally varying crustal deformation and
seismicity in the Mendocino Triple Junction (MTJ) region, California with a
focus on resolving where and when slip is accommodated seismically and aseismically, by making use of repeating earthquake and non-volcanic tremor activities.
Using M > 3 MTJ earthquakes (~1000 events during 1992-current) with broadband seismic data, we identify a number of repeating earthquake sequences (~30
sequences). These sequences appear to be localized along the Mendocino fracture
zone that has experienced a number of M > 5 offshore earthquakes. Our preliminary result suggests that this fracture zone exhibits some degree of aseismic
creep. We additionally find a non-volcanic tremor activity (~2 hour durations)
associated with the 2008 Mw 5.3 normal-fault earthquake. Using data from
Grafenberg Broadband Array in southeast Germany, we identify pP and sP depth
phases and measure pP-P and sP-P differential times. With the ak135 velocity
model, the obtained differential times yield that the focal depth of this event
is 39.5 km, suggesting that the event occurred within or below the subducting
plate. The identified tremor activity was observed ~6 hours after the 2008 Mw 5.3
earthquake. This temporal correlation may suggest that the occurrence of the Mw
5.3 event is related to aseismic slip, assuming the detected tremor as a slow slip
indicator. These observations will provide an additional constraint on the interactions between seismic and aseismic deformation processes in the MTJ region.
We will examine smaller earthquakes to detect additional repeating earthquake
sequences and will evaluate aseismic slip rates from the identified repeating earthquake sequences. Additionally, we will search for other non-volcanic tremor episodes related to the Mendocino earthquakes.
Can We Do Back-Projection at Low Frequency?
Meng, L., Caltech, Pasadena, CA, [email protected]; AMPUERO, J. P.,
Caltech, Pasadena, CA, [email protected]; LUO, Y., Caltech, Pasadena,
CA, [email protected]; WU, W., University of Science and Technology of
China, Hefei, Anhui, China, [email protected]; NI, S., Institute of Geodesy
and Geophysics, Wuhan, Hubei, China, [email protected]
Comparing teleseismic array back-projection source images of the 2011 Tohoku
earthquake to results from static and kinematic source inversions reveal little
overlap between the high and low frequency slip regions. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies,
down to about 0.1Hz, propose that the progressive transition of frequency-dependent rupture properties is observable. Here, by adapting the concept of array
response function to non-stationary signals, we demonstrate that the “swimming
effect”, a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We also show that
the multitaper-MUSIC back-projection technique suffers less from this artifact.
We perform extensive synthetic tests that include a 3D regional velocity model
for Japan. We analyze the recordings of the Tohoku earthquake at the USArray
and at the European array at periods from 1 s to 16 s. The resulting migration as
a function of increasing period has characteristics that are consistent with the
expected “swimming” effect. In particular, the apparent frequency dependent up-
Deep tectonic tremor has been observed at major plate-boundary faults around
the Pacific Rim. While regular or ambient tremor occurs spontaneously or
accompanies slow-slip events, sometimes tremor could be triggered by large distant earthquakes. Because triggered tremor occurs on the same fault patches as
ambient tremor and is relatively easy to identify, a systematic global search of
triggered tremor could help to identify the physical mechanisms and necessary
conditions for tremor generation. We follow our previous studies and conduct
a global search of tremor triggered by large teleseismic earthquakes. We mainly
focus on major subduction zones around the Pacific Rim. These include the
southwest and northeast Japan subduction zones, the Hikurangi subduction
zone in New Zealand, the Cascadia subduction zone, and the major subduction
zones in Central and South America. In addition, we examine major strike-slip
faults around the Caribbean plate, the Alpine fault in the South Island of New
Zealand, the Queen Charlotte fault in northern Pacific Northwest Coast, and the
San Andreas fault system in California. In each place, we first identify triggered
tremor as a high-frequency non-impulsive signal that is in phase with the largeamplitude teleseismic waves. When possible, we locate triggered tremor using a
standard envelope cross-correlation technique. We also calculate the dynamic
stress and check the triggering relationship with the Love and Rayleigh waves.
Finally, we calculate the triggering potential with the local fault orientation and
surface-wave incident angles. Our current results suggest that tremor could be
triggered at many plate-boundary faults in different tectonic environments. Their
triggering behavior could be best explained under the Coulomb-Griffith failure
criteria. The apparent triggering threshold is on the order of 1-10 KPa, although
this value could be partially influenced by the background noise level or quality
and quantity of seismic data.
Joyner Lecture
Wednesday 5:15 pm, 18 April • Town and Country Room
Building Near Faults
BRAY, J. D., University of California, Berkeley, Berkeley, CA, [email protected].
edu
Designing facilities very near active faults presents unique challenges that require
an interdisciplinary approach. Sound engineering and earth science principles
can be employed to address the hazards associated with surface fault rupture
and near-fault ground shaking. Robust procedures exist for evaluating the consequences of permanent and transient ground movements. Whereas their use in
designing systems to accommodate ground movements due to a variety of phenomena is widely accepted, their use in areas containing surface traces of active
faults is often questioned, even when the anticipated ground movements are minimal. Active faults cannot always be avoided, nor should they be avoided when
their hazard is far less than other hazards. We can live with the earth’s faults.
What’s Next?
Poster Session · Wednesday am, 18 April · Golden Ballroom
Stress Rotations and Stress Ratio Changes due to Great Earthquakes:
Implications for Subduction Zone Coupling
Hardebeck, J. L., U.S. Geological Survey, Menlo Park, CA, jhardebeck@
usgs.gov
One surprising observation following the 2011 M9.0 Tohoku, Japan, earthquake
was the large number of normal faulting aftershocks. These events imply that the
stress drop of the mainshock was large enough, relative to the background stress,
to reverse the style of faulting. The stress rotation due to the Tohoku earthquake,
constrained by inversion of earthquake moment tensors, was used to estimate the
ratio of the stress drop to the pre-mainshock shear stress on the subduction zone
interface. The results imply that the Tohoku earthquake completely relieved the
shear stress. The 2011 Tohoku event released less than the expected total moment
accumulation since the 869 Jogan earthquake. Therefore, if the Tohoku earthquake was indeed a complete stress drop event, this implies that the plate interface is not fully coupled.
I perform a systematic search for stress rotations due to other great subduction zone earthquakes, in order to study coupling in other subduction zones. I
use the Global CMT catalog, and invert the pre-mainshock events and 6 months
of aftershocks for the stress tensor orientation and the relative magnitudes of the
principal stresses. I invert the pre-shocks and aftershocks together in a damped
inversion to minimize the chance of apparent rotations due to random errors.
Stress rotations are observed for a few great earthquakes, including the 2010
M8.8 Maule, Chile, earthquake, where the stress rotation implies that the earthquake relieved at least half of the shear stress on the plate interface. A number
of great earthquakes are found to alter the relative magnitudes of the principal
stresses. The change in the principal stress ratio can also be used to estimate the
fraction of the pre-mainshock shear stress released by the earthquake. Stress ratio
changes due to the 2004 M9.2 Sumatra earthquake and its 2005 M8.6 aftershock
imply that these events relieved about one third of the shear stress on the plate
interface.
Historical Seismograms: An Endangered Species?
Okal, E. A., Northwestern University, Evasnton, IL, emile@earth.
northwestern.edu; Kirby, S. H., USGS, Menlo Park, CA; Lee, W. H. K.,
USGS, Menlo Park, CA.
Modern techniques for the analysis of large earthquakes have been routinely
applied to broadband digital data for less than 40 years, a time scale much shorter
than typical seismic cycles at subduction zones, hence the exceptional value of historical seismograms, and the need for their permanent preservation. We review a
number of methodologies for the application of modern seismological methods
to analog datasets, in particular the PDFM mantle wave algorithm, which allows
the inversion of moment tensors from scant surface wave datasets, and discuss
a number of significant results obtained from its application. We then examine
the state of preservation of collections of historical seismograms worldwide,
and reveal a number of alarming trends towards the outright disposal of these
priceless datasets, including at institutions with a long reputation as a cradle of
Seismology. Even the WWSSN collections are now threatened, as there exist no
more than two or three readily accessible complete sets. Regarding pre-WWSSN
data, collections maintained by various observatories worldwide feature an
extremely diverse state of physical conservation, completeness and accessibility;
their conversion to permanent archival and documentation on digital supports
represents a necessary but phenomenal task. We give examples of superbly managed projects in this repsect, and call on the scientific community to keep fighting
tooth-and-nail to keep these fundamental records from destruction before it is
too late and they meet an irreversible fate at the hands of administrators often
lacking any scientific vision.
Seismicity Associated with a Stranded Plate Fragment Above the Juan de
Fuca Slab in the Vicinity of the Mendocino Triple Junction
MCCRORY, P. A., US Geological Survey, Menlo Park, CA, pmccrory@usgs.
gov; WALDHAUSER, F., Lamont-Doherty Earth Observatory, Palisades, NY,
[email protected]; OPPENHEIMER, D. H., US Geological Survey,
Menlo Park, CA, [email protected]; BLAIR, J. L., US Geological Survey, Menlo
Park, CA, [email protected]
Our new model of the subducted Juan de Fuca (JdF) plate beneath western
North America, combined with the spatial resolution of double-differenced
earthquake relocations, offers new insights regarding seismic sources in the complex tectonic setting near the Mendocino triple junction. Relocated seismicity
resolves a double seismic zone within the slab that strongly constrains the location of the plate interface and delineates a cluster of seismicity ~10 km above
the interface that includes the 1992 M7.1 Cape Mendocino earthquake near its
eastern edge. This cluster does not just represent aftershocks to the M7.1 event,
but has persisted through time. About half of the earthquakes within the cluster
occurred within the year following the April 1992 event. However, the remaining
earthquakes either occurred within the 17 years preceding April 1992 or the 17
years following April 1993. The seismogenic structure forms a triangular shape
approximately 80-km long in a N-S direction and up to 50-km long in a W-E
direction. The structure is up to 8-km thick, and its surface dips gently landward
from depths of ~6 to 14 km. Interpretation of the M7.1 event as occurring above
the subduction interface requires a more complex slab geometry than previously
envisioned. Specifically, the slab just east of the trench dips about 15° and then
flattens to a dip of just a few degrees from ~15–25 km before it steepens again to
about 25° from ~25–45 km, which is the maximum depth it can be imaged by
hypocenters. The seismicity cluster is situated above the slab where it flexes concave upward in the transition from its initial moderate dip to a flat dip. These data
provide compelling evidence that a significant fault with no surface expression
exists in the forearc above the plate interface. We speculate that the seismicity
cluster represents a detached fragment of oceanic plate that did not subduct and
has been stranded within the accretionary prism, similar perhaps to the fragment
of Farallon plate found in the King Range to the south. Similar subsurface tectonic elements within the Cascadia forearc, such as remnants of the Resurrection
plate, may also have the potential to generate damaging earthquakes—complicating our efforts to characterize earthquake hazards within the Cascadia subduction system.
Our model of the subducted Juan de Fuca plate beneath North America,
combined with the spatial resolution of double-differenced earthquake relocations, offers new insights regarding seismic sources near the Mendocino triple
junction. Relocated seismicity resolves a double seismic zone within the slab
that strongly constrains the location of the plate interface and delineates a cluster of seismicity ~10 km above the interface that includes the 1992 M7.1 Cape
Mendocino earthquake. Half the earthquakes within this cluster occurred within
the year following the April 1992 event. The remaining earthquakes occurred
within the years preceding or following this interval. The seismogenic structure
forms a triangular shape ~80-km long in a N-S direction and up to 50-km wide
in a W-E direction. The structure is up to 8-km thick, and dips gently landward
from depths of ~6 to 14 km. Interpretation of the M7.1 event as occurring above
the subduction interface requires a more complex slab geometry than previously
envisioned. Specifically, the slab just east of the trench dips about 15° and then
flattens to a dip of just a few degrees from ~15–25 km before it steepens again to
about 25° from ~25–45 km. The seismicity cluster is situated above the slab where
it flexes concave upward in the transition from its initial moderate dip to a flat dip.
These data provide compelling evidence that a significant fault with no
surface expression exists in the forearc above the plate interface. We speculate
that the seismicity cluster represents a detached fragment of oceanic plate that has
been stranded within the accretionary prism, similar perhaps to the fragment of
Farallon plate found in the King Range to the south. Similar subsurface tectonic
elements within the Cascadia forearc, such as remnants of the Resurrection plate,
may also have the potential to generate damaging earthquakes—complicating
our efforts to characterize earthquake hazards within the Cascadia subduction
system.
A Multiscale Slip Inversion Study Focused on the Initial Rupture of the 2011
Tohoku Earthquake
Uchide, T., DPRI, Kyoto University, Uji, Kyoto, Japan, [email protected].
kyoto-u.ac.jp
The 2011 Tohoku earthquake (M 9.0) is characterized by a shallow huge slip more
than 40 m, which produced the devastating tsunami. For modeling this earthquake, the stress accumulation which caused it and the resultant kinematic rupture process should be understood. Here I focus on the kinematics of this earthquake in the early stage. A couple of studies already came out. Chu et al. (2011)
found that the first 4 s of the rupture is equivalent to an Mw 4.9 thrust event.
Uchide et al. (AGU, 2011) reported the source process in the first 20 s in detail by
the multiscale slip inversion analysis (Uchide and Ide, 2007). Their result implies
that rupture propagated eastward until 8 s, and after that the rupture propagated
westward. The peak slip rate is around 1 m/s, which implies the dynamic rupture.
Hi-net data in Tohoku area shows that the velocity amplitude increases
stepwise. Hi-net data are eventually clipped but they work at least in the first 20 s.
The steps are found around 4 s and 16 s. In the first 1 s, the velocity amplitude of
the M9 event is comparable to that of nearby M4 events (Mw 4.3–4.9). A deconvolution analysis using an M4 event (Mw 4.6 on 19 Dec. 2004 at 10:16 (UTC))
indicates a small event in the first 0.5 s.
Using Hi-net, KiK-net (borehole strong-motion network), and F-net
(broadband and velocity strong-motion network) data, I perform a multiscale
slip inversion analysis to investigate the first 4.5 s and 20 s of the rupture process
together with the entire process.
Giant Eruptions Did Not Frequently Occur in the Periods When Giant
Earthquakes Frequently Occurred and Vice Versa after 1900
Fujii, Y., Hokkaido University, Sapporo, Japan.
It was found that, at least after 1900, giant eruptions (VEI4+) had not frequently
occurred in the periods when giant earthquakes (MW 8+) had frequently
occurred, namely, 1950-1970 and 2000 to the present, and vice versa. A reduced
major axis for the logarithms of the annual seismic and eruption energies which
were calculated by accumulating them for each decade was drawn with a correla-
tion coefficient of -0.39. The coefficient value implies a weak but negative correlation between the giant earthquakes and eruptions. It was also confirmed
that MW 8+ earthquakes did not occur just after and in the vicinity of the three
VEI6+ eruptions after 1900, namely, Santa Maria in 1902, Novarupta in 1912
and Pinatubo in 1991. It is well known that the VEI5 eruption of St. Helens in
1980 was just after the MW 5.1 earthquake, however, VEI6+ eruptions did not
occur just after and in the vicinity of the MW 8+ earthquakes.
MW 8.8+ earthquakes are of course located on the subduction zones
around the Pacific Ocean. It seems that the location of the epicenters is basically
exchanged between Peru-Chile Trench and such trenches as Aleutian, KurilKamchatka and Japan. It irregularly flies to Java Trench. The epicenters seem to
be too sparse to consider that they are mechanically related with each other. It was
found, however, that the epicenters of the five MW 8.8+ giant earthquakes and
the three VEI6+ eruptions between 1900-2011 and five of the six VEI7+ eruptions since 6440BC (except for Santrini in 1610BC±14) as well as the major subduction zones were located along a great circle. Stress change can not be released
by expansion or shrinkage on a great circle and it can affect to seismicity and
vocalic activities on the whole great circle. Further considerations are required,
however, the great circle would be the key to understanding the mechanism of the
global scale interaction between giant earthquakes and eruptions on the subduction zones.
Geologic Controls on the Rupture of the Semidi and Fox Islands Sections of
the Alaska-Aleutian Megathrust with Implications for the Generation of a
Trans-Pacific Tsunami
Ryan, H. F., U. S. Geological Survey, Menlo Park, CA, [email protected]; VON
HUENE, R., U. S. Geological Survey, Menlo Park, CA, rhuene@mindspring.
com; SCHOLL, D. W., U. S. Geological Survey, Menlo Park, CA, dscholl@usgs.
gov; KIRBY, S. H., Menlo Park, CA, [email protected]
In the aftermath of the 2004 Sumatra and 2011 Tohoku earthquakes, we reexamined the forearc structure along the Alaska-Aleutian subduction zone (AASZ) to
ascertain whether structures are present that would support the generation of a
giant earthquake and attendant trans-Pacific tsunami. Of particular concern are
the Semidi Islands (SIS) and Fox Islands (FIS) sections of the subduction zone.
The coast of California is vulnerable to a trans-Pacific tsunami spawned along the
SIS and Hawaii is vulnerable to one from the FIS.
The SIS ruptured in 1938 producing a M=8.2 event. However, during this
earthquake, most of the moment was released at the down-dip end of the megathrust. Currently the SIS is almost fully coupled and enough time has passed for
strain to accumulate for a repeat of a 1938-sized event. A remaining question is
whether the next event could also rupture the up-dip section similar to the tsunamigenic earthquake that occurred along the Tohoku margin. Both margins are
structured similarly indicating similar tectonic processes, including the presence
of a steep seafloor scarp composed of bedrock above the up-dip end of the megathrust. This raises concerns that a Tohoku-like event is possible along the SIS.
The FIS is one of the least studied sections of the AASZ and little is known
about current subduction zone strain. It was assumed that the FIS ruptured during the 1957 Andreanof Mw= 8.6 event. However, reexamination of the aftershocks has shown little moment was released along the FIS in 1957 (E. Okal, pers.
comm.). A lack of M > 5 earthquakes indicate that the FIS is either aseismic or
fully coupled. Based on similarities in forearc structure to the Adak Island asperity that ruptured in 1957, we suggest that the FIS may indeed be coupled. In addition, non-volcanic tremor has recently been discovered along the FIS (Peterson
et al., 2011) and evidence for multiple tsunami events has been noted in the Fox
Islands (G. Carver, pers. comm.).
Role of Thermal-Pressurization on Megathrust Ruptures
Cubas, N., CalTech, Pasadena, CA, [email protected]; AVOUAC, J. P.,
CalTech, Pasadena, CA, [email protected]; LAPUSTA, N., CalTech,
The Tohoku-Oki earthquake has challenged our classical view of earthquake
dynamics. Although modeling of geodetical strain had revealed a deep locked
patch, the maximum of slip didn’t occur in the locked patch, as for the Maule
earthquake for instance, but in the shallower portion of the megathrust where
the stress build-up was very low. Recent studies (Noda and Lapusta, in prep.)
have shown that thermal-pressurization could reconcile all the seemingly contradictory observations for the Tohoku-Oki earthquake. The shallow portion of
the megathrust could have a rate-strengthening behavior and creep aseismically
but on rare occasions have a rate-weakening behavior and thus slip seismically.
In order to better understand the differences between the Tohoku-Oki and the
Maule earthquakes, we propose to study their spatial variations of frictional properties from mechanical analysis and dynamic earthquake cycle simulation. Two
different mechanical approaches are applied to determine static and dynamic
frictions. The first one relies on the critical taper theory and allows to constrain
the effective basal friction as well as the internal pore fluid pressure. The second
one is based on limit analysis and allows to determine the dynamic friction from
positions of active faults. Aseismic areas appear to be at mechanical critical state
with high effective basal friction, whereas seismogenic zones are characterized
by a low basal friction. A high pore fluid pressure anomaly is also observed where
the maximum of slip occurred for the Tohoku-Oki earthquake. These frictional
properties are then integrated in a 3D earthquake sequence model to investigate
whether the low friction in the seismogenic zone is due to an intrinsically lower
static friction or the result of a dynamic weakening process induced by thermalpressurization. Mechanical conditions allowing or impeding the propagation
of the rupture as well as afterslip in the up-dip rate-strengthening area are then
investigated.
Exploring Relationships Between Three-Dimensional Subduction Zone
Geometry and Coupling in Subduction Zones
Hayes, G. P., U.S. Geological Survey, National Earthquake Information
Center, Golden, CO, [email protected]; WALD, D. J., U.S. Geological Survey,
National Earthquake Information Center, Golden, CO, [email protected];
BRIGGS, R. W., U.S. Geological Survey, Geological Hazards Science Center,
With the recent increases in the quality and availability of high-resolution data
sets of subduction zone seismicity, and of active source seismic surveys across the
shallow region of the megathrust, our knowledge of the detailed three-dimensional geometry of subduction zones—particularly seismically active ones—has
significantly improved. Similarly, improvements in the temporal and spatial
extent of geodetic networks above subduction zones, and in the quality of the
data collected, have facilitated the modeling of ‘coupling ratio’, and the spatial
variability of this parameter, in many of the same regions. To date, however, little
has been done to explore the relationship between the detailed aspects of these
two observations.
Here we utilize Slab1.0, a new USGS compilation of the three-dimensional
geometries of global subduction zones, and compare them to published models
of geodetically inferred seismic coupling. We examine both what the geometry
models alone can tell us about properties of the seismogenic zone (e.g., down-dip
width, along-strike segmentation), and also whether relationships exist between
three-dimensional geometry and the spatial variability of seismic coupling, and
what such relationships might tell us about the potential for future megathrust
earthquakes in these regions.
Aftershocks of the 2011 Tohoku-Oki Earthquake and Their Relation to Stresses
in the Japan Trench Megathrust Seismic Cycle
MEDINA LUNA, L., University of Michigan, Ann Arbor, MI, lmedina@
umich.edu; WEST, S. E., University of Michigan, Ann Arbor, MI, westsue@
umich.edu; BAI, L., University of Michigan, Ann Arbor, MI, [email protected];
HETLAND, E. A., University of Michigan, Ann Arbor, MI, ehetland@umich.
edu; RITSEMA, J., University of Michigan, Ann Arbor, MI, jritsema@umich.
edu; KANDA, R. V. S., National Taiwan University, Taipei, Taiwan, rkanda@
alumni.caltech.edu
Focal mechanisms of the aftershocks larger than magnitude 5.5 following the
great Tohoku-Oki earthquake vary drastically. We investigate whether the
aftershocks are consistent with typical stresses in a subduction seismic cycle, or
whether they indicate unexpected processes such as normal slip on the megathrust or dynamic overshoot during the Tohoku-Oki earthquake. Specifically we
test if the aftershocks are consistent with stresses due to inferred coseismic slip
in the mainshock. As coseismic stresses are highly variable in space, accurate
hypocentral locations of the aftershocks are paramount. We consider epicentral
locations based on both the JMA and USGS catalogs, focal mechanisms from the
CMT catalog, and constrain focal depths by modeling teleseismic P waveforms.
We consider that either of the best double-couple nodal planes may be the slip
surface, and compare the direction of shear stress change due to the mainshock
with the slip direction of the aftershocks. Allowing for possible uncertainty in
the hypocentral locations, the majority of all of the aftershocks are consistent
with slip in the direction that the mainshock loaded one of the nodal planes. This
suggests that either mainshock stress changes were roughly in the same direction
as the accumulated stresses on the aftershock faults prior to the mainshock, or
that coseismic shear stress changes were larger than the accumulated stresses. To
further test this preliminary finding, we consider additional constraints on both
the focal mechanisms and the hypocentral locations of the aftershocks. Ongoing
analysis is also including Coulomb stability, models of stress accumulation
prior to the mainshock, and different distributions of coseismic slip during the
Tohoku-Oki earthquake. In the latter, we primarily explore models in which the
maximum slip is near the trench or further down-dip.
Weakening of the near Surface in Japan after the 2011 Tohoku-Oki Earthquake
Detected by Deconvolution Interferometry
Nakata, N., Colorado School of Mines, Golden, CO, [email protected];
SNIEDER, R., Colorado School of Mines, Golden, CO, [email protected]
The Mw 9.0 Tohoku-Oki earthquake on 11 March 2011 was one of the largest earthquakes in recent history. A strong-motion network in Japan, KiK-net,
recorded ground motion caused by the seismicity around the time of the main
shock. Each KiK-net station has two receivers; one receiver on the surface and
the other in a borehole. By applying deconvolution interferometry to KiK-net
data, in which we deconvolve waveforms recorded at a surface receiver by those
recorded at a borehole one, we extract the shear wave that propagates between
these two receivers. Picking the arrival time of the shear wave, we estimate the
shear velocity in the near surface while using the depth of the borehole. When we
deconvolve one station data in the Fukushima prefecture (200 km far from the
epicenter of the main shock), we detect a reduction of shear velocity in the upper
100 m of about 10%, and a subsequent healing that varies logarithmically with
time. By applying short-time moving-window seismic interferometry (deconvolving each 20-s time window as moving the window with 10-s interval) to the
main-shock records, we find the shear-velocity reduction occurs at 30-40 s after
the origin time of the main shock and increases while the shaking increases. After
the strongest shaking at 130 s, the shear velocity starts healing. Using all available earthquake records (more than 300 earthquakes) that occurred between 1
January 2011 and 26 May 2011, we detect a shear-velocity reduction of about 5%
in the upper few hundred meters after the Tohoku-Oki earthquake throughout
northeastern Japan. The area of the velocity reduction is about 1, 200 km wide,
which is much wider than earlier studies reporting velocity reduction following
other larger earthquakes. The reduction of the shear-wave velocity is an indication
that the shear modulus, and hence the shear strength, is reduced over a large part
of north Japan.
Poster Session · Wednesday am, April 18· Golden Ballroom
Systematic Analysis of Spatial Symmetry Properties of Aftershocks in
California with Respect to Epicentral Locations of Mainshocks
Ross, Z. E., University of Southern California, Los Angeles, CA, zross@usc.
edu; ZALIAPIN, I., University of Nevada, Reno, Reno, NV, [email protected]; BENZION, Y., University of Southern California, Los Angeles, CA, benzion@usc.
edu
We examine short term aftershock sequences for spatial asymmetry with respect
to the mainshock using analysis that assumes no prior information about local
fault structure or orientation. The goal is to provide a generalized robust method
for inferring on the possibility of preferred rupture propagation direction of
earthquakes on given faults. Earthquake catalogs for northern and southern
California are separated into individual clusters by exploiting a bimodal property
of seismicity in space-time, with one mode corresponding to background seismicity and the other to clustered events. Next, we examine clusters that are highly
localized in space and time that correspond to aftershock sequences. For each
cluster we use the quantile associated with the mainshock location with respect
to the 2-D spatial distribution of the aftershocks, normalized by the mainshock
magnitude, as a measure of spatial asymmetry. The quantiles are combined with
vectors from mainshock to the aftershock centroid in places with an asymmetry
index above a given threshold to characterize the orientations of aftershock asymmetry without including information about local fault structure. The technique
is calibrated using data from the sections of the San Andreas fault near Parkfield
and south of Hollister, where previous studies suggest a material contrast and
preferred direction may exist. We use the calibrated procedure to examine the
symmetry properties of seismicity in California, with particular focus on the
behavior associated with San Jacinto, San Andreas and other large faults.
Using Cross Correlation to Indicate Induced Seismicity
Oprsal, I., Seismik s.r.o., Prague, Czech Republic, [email protected]; EISNER,
L., Seismik s.r.o., Prague, Czech Republic, [email protected]
Determining the relationship between injection volumes and seismicity in an
area where injection is occurring through cross correlation, could have the potential to be an important tool for investigating the possibility of induced seismicity.
However, we show that a direct cross correlation between the daily (or weekly)
injection volumes and seismicity would result in high cross correlation values
even for random functions. The injection volumes, as well as the seismicity (event
count), are both positive functions, and direct cross correlation of these does not
indicate relationship between two phenomena. Instead, the cross correlation of
their “Useful Functions” (original functions with their running measure of the
mean subtracted) should be used.
We show several examples on the Greenbrier area seismic activity, where,
after removing the mean, the re-computed cross correlation values are peaking at
around 0.45 (with a lag of around 18 weeks) using weekly binning of combined
injection volumes and CERI seismicity catalogue for the area. We show that: 1.
Cross correlation is very sensitive to the completeness of the catalogue, 2. Crosscorrelations of event count for events within or outside epicentral distance of 5
km show similar peaks, although further than 5km distant events are unlikely
to be triggered by injection. We will show through theory and several numerical examples that a set of random functions exhibit high autocorrelation values
(>0.75) for non-zero lag, if these functions have values in the interval [0, 1] with
mean=0.5, and also for functions with variable mean and standard deviation
values of sigma<0.3. Still the autocorrelation of their “Useful Functions” is as
expected very small (less than 0.05), even for functions with as few as 100 samples. For smaller standard deviation (similar to the case of using weekly injection
volumes, instead of using daily volumes), the autocorrelation is even closer to 1 for
(non-zero mean) purely random functions.
Correlation of Peak Dynamic and Static Coulomb Failure Stress with
Seismicity Rate Change after the M 7.2 El Mayor-Cucapah Earthquake
Withers, K. B., SDSU, San Diego, CA, [email protected]; OLSEN, K. B.,
SDSU, San Diego, CA, [email protected]
We have investigated the relation between the April 4 Mw7.2 El Mayor-Cucapah
earthquake and seismicity rate changes in southern California and northern
Baja California in the months following the mainshock. Specifically, we use a
dynamic rupture model with observational constraints for the event simulated in
the SCEC 3D CVM4.0 (Roten and Olsen, 2009) to calculate the changes in the
resulting static (dCFS) and dynamic Coulomb failure stress, parameterized by its
largest positive amplitude (peak dCFS(t)). We employ a modified cross correlation between the seismicity rate change (for both undeclustered and declustered
catalogs) and both dCFS and peak dCFS(t) in time and space (as used by Kilb
et al., 2002). We find that the correlation parameter is greater for peak dCFS(t)
compared to dCFS and highest for periods after the mainshock of longer than
1 week for dCFS, and a maximum at 1 month for peak dCFS(t). We perform
this analysis using both CVM-4 and CVM-H, investigating, in particular,
which model better describes the increased seismicity NW of the rupture. The
stress changes are rotated onto the focal mechanism of the 15 June 2010 Mw5.7
aftershock as well as onto optimum oriented planes (King, 1994). For regionally rotated stresses we find that while the dCFS values are very similar for the
two CVMs, the corresponding peak dCFS(t) values are noticeably different. In
particular, CVM-H generates a lobe of (directivity-induced) large peak dCFS(t)
between the Elsinore and San Jacinto Faults toward the Los Angeles basin not
present in the results from CVM-4. However, both CVMs produce similar peak
dCFS(t) lobes near San Diego. Finally, we searched for threshold levels of dCFS
and peak dCFS(t) that may be required to trigger earthquakes/aftershocks of different magnitude that might provide clues to earthquake prediction; we found
a possible peak dCFS(t) threshold value of 0.7 bars for aftershocks (>4000) in
regions of positive static stress.
The Impact of Fault Segmentation, Slip Variability and Coupling on
Probabilistic Tsunami Hazard Analysis
Thio, H., URS Corporation, Los Angeles, CA.
The results of a probabilistic tsunami hazard analysis (PTHA) are very sensitive
to the details of the rupture model, such as maximum magnitude, slip variability
and coupling. Because tsunami amplitudes scale directly with slip, this sensitivity
is significantly greater for tsunami hazard than for ground shaking, which tends
to saturate at large magnitudes. For PTHA it is therefore important to address
the possibility and effects of multi-segment ruptures and integrate over a range
of average and maximum slips. We have carried out a comprehensive PTHA for
the coast of California, which includes sources from all the major circum-Pacific
subduction zones as well as local sources. We will illustrate the effect of different
choices of segmentation models and slip variability using events on the Alaska
subduction zone, for distant tsunamis, as well as the Cascadia subduction zone,
to show the effect for near-field tsunamis, and also show how they affect the final
tsunami hazard maps.
Even for distant tsunami, there is still considerable sensitivity to details
of the slip, and in particular the maximum slip. This was also demonstrated by
the impact of the Tohoku earthquake on the California coast. For local tsunami
impact, these details are even more important, and we will discuss how we have
quantified the variability in segmentation and slip in our models, and how an
event like the Tohoku earthquake fits in the range of models that we consider in
our analysis.
The uncertainty in seismic coupling also has a direct impact of the PTHA
results, not only by causing a systematic increase or decrease in the hazard rates,
but also since spatial variability in coupling will affect the details of slip distribution, and therefore tsunami waveheights. These issues wills be demonstrated with
examples from the Alaska subduction zone.
Coseismic and Postseismic Deformation of the 2010 El Mayor-Cucapah
Earthquake from ALOS PALSAR and GPS Data
Funning, G. J., University of California, Riverside, CA, [email protected];
RYDER, I., University of Liverpool, Liverpool, UK, [email protected];
FLOYD, M. A., MIT, Boston, MA, [email protected]
The 4 April 2010 M7.2 El Mayor-Cucapah earthquake ruptured approximately
110 km of the plate boundary zone in northern Baja California and southern
California, including a previously unmapped section through the Colorado
River delta. The event was unusual in that it had a longer rupture length than
recent events of a similar magnitude elsewhere, perhaps a manifestation of crustal
thinning in the region, in the transition between transform motion on the San
Andreas-Imperial fault system to the northwest and seafloor spreading in the
Gulf of California to the southeast.
Here we examine the deformation associated with the event, using a combination of InSAR and GPS time series. In order to identify the spatial pattern
of deformation, we process the full archive of ALOS PALSAR data spanning
the earthquake and the nine months following the event. We supplement these
data with campaign GPS measurements made on a series of campaigns in Baja
California by researchers from UCR, Scripps Institiute of Oceanography and
CICESE, starting one day after the event, and archival campaign data from the
past two decades, which we use to estimate pre-earthquake positions. We produce
a coseismic slip model, and use this as the basis for forward models of Maxwell
viscoelastic relaxation using a range of viscosities.
We find that the first year of postseismic deformation was marked by i)
a narrow zone of ~10 cm of subsidence bounded to the north by the Colorado
delta segment of the main fault rupture; ii) a secondary area of initial subsidence
located a few kilometers to the northeast, that is recovered within ~6 months
of the earthquake; iii) near-field right-lateral shear of ~5 cm across the Sierra
Cucapah. The first two of these deformation signals are consistent with a combination of transient poroelastic deformation and the third with shallow afterslip.
Our models of Maxwell viscoelastic relaxation do not explain this early, rapid
deformation.
El Mayor Cucapah Earthquake: Postseismic Deformation from InSAR and
GPS Observations
GONZALEZ ORTEGA, A., CICESE, Earth Sciences Division, Ensenada,
Baja California, Mexico, [email protected]; SANDWELL, D., IGPPSIO, San Diego, CA, [email protected]; FIALKO, Y., IGPP-SIO, San
Diego, CA, [email protected]; GONZALEZ GARCIA, J., CICESE, Earth
Sciences Division, Ensenada, Baja California, Mexico, [email protected];
NAVA PICHARDO, A., CICESE, Earth Sciences Division, Ensenada, Baja
California, Mexico, [email protected]; FLETCHER, J., CICESE, Earth Sciences
Division, Ensenada, Baja California, Mexico, [email protected]; LIPOVSKY,
B., Standford, Departament of Geophysics, Stanford, CA; Floyd, M., MIT,
Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA.
El Mayor Cucapah earthquake ocurred on 4 April 2010, rupturing several previously mapped as well as unidentified faults, including the Pescadores, Borrego
and Paso Superior faults in Cucapah Mountains, and Indiviso fault in the
Mexicali valley.
We conducted several campaign GPS surveys of pre-existing and newly
established benchmarks within 30 km of the earthquake rupture. Most of the
benchmarks were occupied within days after the earthquake, allowing us to capture the entire postseismic transient. GPS timeseries indicate a gradual decay in
postseismic velocities having the same sense as the coseismic displacements.
We also analyzed available Synthetic Aperture Radar (SAR) data from
ENVISAT and ALOS satellites. The main deformation features seen in the line
of sight displacement maps indicate subsidence in the southern and northern part
of the Indiviso and Paso Superior faults, respectively. We investigate to which
extent GPS and InSAR observations can be explained by commonly assumed
mechanisms of postsesimic deformation. In particular, we present a best-fitting
afterslip model for the time period of 6 months after the earthquake.
Slip on Faults and Destruction of Irrigation Canals Triggered in the Mexicali
Valley, Baja California, Mexico, by the 4 April 2010 Mw 7.2 El Mayor-Cucapah
Earthquake
Glowacka, E., CICESE, Ensenada, BC, Mexico, [email protected];
ROBLES, B., IMTA, México, [email protected]; SARYCHIKHINA,
O., CICESE, Ensenada, México, [email protected]; SUAREZ, F., CICESE,
Ensenada, México, [email protected]; RAMIREZ, J., UABC, Mexicali,
Mexico, [email protected]; NAVA, F. A., CICESE, Ensenada, México, fnava@
cicese.mx; GONZALEZ, J., CICESE, Ensenada, México, [email protected];
Gonzalez, A., CICESE, Ensenada, México, [email protected]; Mellors,
R., LLNL, Livermore, CA, [email protected]; VILLELA Y MENDOZA,
A., CICESE/Mexico, [email protected]; Farfan, F., CICESE/Mexico,
[email protected]; DIAZ DE COSSIO, B. G., CICESE/Mexico, gbatani@
cicese.mx; Garcia, M. A., CICESE/Mexico, [email protected] .
The Mw 7.2 El Mayor earthquake destroyed many roads, irrigation canals, houses
and other structures in the Mexicali Valley.
The irrigation system of the Mexicali Valley has been built over more
than 100 years, since the beginning of the XXth century. The system is maintained, at present, by the National Water Council (Comisión Nacional de Agua).
It features about 1500 km of canals and aqueducts, and brings water from the
Colorado River to the two large cities of Mexicali and Tijuana, many small towns
around the Mexicali Valley, and is the source of water for field irrigation. About
700 kilometers of canals were affected when the El Mayor–Cucapah earthquake
struck, causing water shortage for irrigation purposes and large economic losses.
During interseismic periods the canals are affected by three problems
related to the geographical situation and antropogenic activity in the Mexicali
Valley: subsidence (up to 20cm/year caused by geothermal fluid extraction), canal
ruptures and water leakage in the zones where active tectonic faults with aseismic
slip cross the canal network.
We use published and new data from field mapping, precise leveling,
InSAR, and geotechnical instruments observations to compare effects of subsidence, triggered slip on faults, and liquefaction caused by seismic waves, with the
damage pattern reported along the irrigation canals.
The aim of this presentation is to show the importance of fault mapping in
the area of Mexicali Valley. We suggest that destruction could have been minimized if the traces of the faults had been taken into account when building the
infrastructure. Since the subsidence process cannot be stopped, because of the
importance of electricity production, at least the slipping faults can be mapped
and studied for the purpose of creating hazard maps which can be used to define
rules and codes to minimize the damage caused by both the slow continuous process of subsidence and violent fault reactivation during earthquake.
Analysis of Site Effects Observed at the NEES@UCSB Wildlife Station from
the 2010 Ocotillo Swarm
Huthsing, D. A., Earth Research Institute, UCSB, Santa Barbara, CA,
[email protected]; SEALE, S. W. H., Earth Research Institute, UCSB, Santa
Barbara, CA, [email protected]; STEIDL, J. H., Earth Research Institute,
UCSB, Santa Barbara, CA, [email protected]
The largest aftershock of the 4 April 2010 M7.2 El Mayor-Cucapah earthquake
was a M5.7 event that occurred near Ocotillo, CA, on 15 June 2010. The NEES@
UCSB Wildlife Station is a permanently-instrumented borehole array located
57km northeast of Ocotillo. Over a period of three months, 60 aftershocks with
M > 3.0 were recorded at Wildlife with good signal-to-noise ratio. This data
set presented a unique opportunity to study site effects, as the events were colocated with respect to the site and they all have similar focal mechanisms. We
present spectral ratios for downhole-to-surface signals on all three components.
The recorded accelerations have been rotated into radial and transverse components, relative to the M5.7 event. The spectral ratios show clear amplification
of the signal at frequencies of engineering interest (< 40 Hz). We also present
spectral ratios of signals recorded in two adjacent boreholes of 5.5m depth, where
one borehole has a standard casing and the other has a flexible PVC casing. Our
analysis shows that within two standard deviations, the influence of the casing
material on the horizontal components of motion is not significant. The vertical
component of motion is influenced by the casing material, probably due to the
effect of tube waves.
Detecting and Locating Earthquakes in the Northern Gulf of California Using
Surface Wave Back-Projection
Butcher, A. J., California State Polytechnic University, Pomona, Pomona,
CA, [email protected]; POLET, J., California State Polytechnic
University, Pomona, Pomona, CA, [email protected]; THIO, H. K., URS
Corporation, Los Angeles, CA.
The tectonic environment of the Northern Gulf of California is characterized by
a transition from oceanic to continental crust and lithosphere. While the land
area north of the Gulf is relatively well covered by seismic networks, the seismicity of the northern portion of the Gulf, and thus the tectonics that govern the
earthquake occurrence, are relatively poorly constrained. Since this area lies just
south of the 4 April 2010 Mw7.2 El Mayor-Cucapah earthquake rupture, a better
understanding of the seismicity and tectonics of this region may provide insight
into its seismic hazard and into the rupture process of the 2010 earthquake. We
applied a short-period (12-30 sec) Rayleigh wave back-projection algorithm to the
broadband waveform data from the 2002-2007 temporary Baja seismic network,
to detect and locate earthquakes in the Northern Gulf. Since transform fault
earthquakes in the area are known to be more robust in low frequency energy
than high frequency energy; this surface wave back-projection method may be
more effective for event detection than the typical body wave based methods. We
will show that this method can detect and locate earthquakes in the Northern
Gulf of California down to a magnitude 3.2, even without implementing any
tomography-based travel time corrections yet. We will present our results of a
calibration analysis that maps the stacked amplitude generated by the back-projection algorithm into magnitude, using magnitudes from an earthquake catalog
that we compiled from existing databases. We will compare our back-projection
magnitudes with those from the existing catalogs to investigate whether we can
detect any systematic variations in long period versus short period magnitude
with tectonic environment.
Observations of Multiple Body Wave Phases of the 2010 El Mayor-Cucapah
Earthquake Using a High-Density Seismic Array
Lester, A., US Army Corps of Engineers ERDC, Vicksburg, MS USA,
[email protected] ; TAYLOR, O. D. S., US Army Corps of
Engineers ERDC, Vicksburg, MS USA, [email protected];
MCKENNA, M., US Army Corps of Engineers ERDC, Vicksburg, MS USA,
[email protected]
A Southern California passive urban infrastructure monitoring array recorded
the 2010 El Mayor Cucapah Earthquake. The array was not specifically designed
to record earthquakes; however, it recorded over 41-s of seismic activity. The
array’s 10hz vertical geophones are typically used in refraction-reflection surveys
and are directly coupled to the earth. The sensitivity of these instruments in conjunction with the 2-kHz sampling rate provide detailed recordings of the various
P and S-wave arrivals within a local to regional site-to-source distance (>1.5°). The
coupled geologic media yields a unique propagation environment by filtering out
the incoming surface waves and shear movement and allowing for identification
of distinct phase arrivals.
An initial P-wave arrival uniformly propagates across the array and is identified as a directly propagating compression wave, as the 3.6-km/s average group
velocity is too slow to be considered as a deeper waveform. In practice direct
P-waves are not typically expected at distances exceeding tens of kilometers, yet
the combination a low group velocity, geological overburden, and site-to-source
distance make the possibility of a deeper waveform unlikely. The Pg is identified
approximately 0.5 seconds prior to the direct P-wave arrival, with similar frequency content, and a average group velocity of 4.1-km/s. This velocity is lower
than typically expected, however due to the geological conditions the array’s location in respect to the cross-over distance, and on identified S-waves within the P-S
interval (direct S, Sg, and S*) this P-wave is most likely the Pg. The identification
of specific P and S-waves provide insight into the complexities of wave propagation within this region of Southern California.
Permission to publish was granted by the Director, Geotechnical and
Structures Laboratory and is approved for public release; distribution is unlimited.
Linear and Nonlinear Soil Response at the Mexicali Valley, Baja California,
México During the El Mayor-Cucapah Earthquake of 4 April 2010 (Mw 7.2) and
other Past Earthquakes of the Region
Munguia, L., CICESE, Ensenada, Baja California, Mexico, lmunguia@
cicese.mx; Gonzalez, M., CICESE, Ensenada, Baja California, Mexico,
[email protected]
In this study we investigated how the deep soils of the Mexicali Valley behave during weak and strong earthquake ground shaking. For this, we used acceleration
recordings produced by earthquakes occurred and recorded mostly in the valley,
with particular attention given to data from the recent El Mayor-Cucapah earthquake. With such dataset, the site response at several locations in the Mexicali
Valley was estimated and compared with the response of the same sites to the
stronger motions of the El Mayor-Cucapah and other large earthquakes of the
area. The weak-motion site response was determined using the single-station
H/V spectral-ratio method and acceleration time histories that had peak ground
accelerations between 20 and 80 gals. This PGA interval was chosen to ensure
good signal-to-noise ratios of the records and to consider only amplitude motions
in a range at which a linear response of soils might be expected. Stable site amplification functions were obtained by averaging all the H/V ratios calculated from
the weak motion recordings of each individual station. The maximum amplifications on these functions were observed in the 0.5- to 3.0-Hz frequency band,
with amplification factors in the 3-10 range. We then compared the above transfer functions with the response of soils calculated from recordings of the stronger
events. Those comparisons showed strong-motion amplifications that are lower
than the reference weak-motion amplifications at frequencies higher than about
2-3 Hz. Such amplification reductions, interpreted here as evidences of nonlinear
soil response during intense ground shaking, occurred only for favorable combinations of distance and PGA. Our preliminary results show nonlinearity effects
for epicenter distances shorter than 10 km and PGA larger than about 150 gals.
In such cases, the strong-motion amplifications were reduced by factors of up to
4, respect to the weak-motion soil amplifications.
Structural Characteristics of the Southeast Mexicali, Baja California,
México, Region before the El Mayor-Cucapah, M 7.2 Earthquake of 4 April
2010, from Seismic Reflection
GONZALEZ-ESCOBAR, M., CICESE, Ensenada, Baja California, Mexico.,
[email protected]; CHANES-MARTINEZ, J. J., CICESE, Ensenada,
Baja California, Mexico, [email protected]; SUAREZ-VIDAL, F., CICESE,
Ensenada, Baja California, Mexico, [email protected]; ARREGUI-OJEDA, S.,
CICESE, Ensenada, Baja California, Mexico, [email protected]
The study area is located within the Colorado River Delta region, southeast of
the April 4th 2010, El Mayor-Cucapah earthquake epicenter. This region is dissected by the San Andreas-Gulf of California fault system. Therefore, the geological evolution record (since 5-6 m.a) of this system is register in more than 6000
mts in the sedimentary column. The delta includes an area of ~8600 km2 located
along the border between the Pacific-North America plates. After the occurrence
of the el Mayor-Cucapah Earthquake we initiate a geological-geophysical study
processing and interpreted the existed PEMEX 2D seismic reflection lines and
data from exploratory well, to identified and define the structural features that
controlled the sedimentation and geologic evolution of the southeast part of the
Mexicali Valley, within the Colorado River Delta region. Thanks to an agreement
of cooperation between Petróleos Mexicanos (PEMEX) and CICESE we have
access to the information of seismic reflection take during the 1970 decade and
the beginning of the 80’s. The seismic parameters of acquisition were an arrangement of 48 channels with central shot, dynamite as energy source. The recording time was 6 seconds with an interval of sampling 2 ms. The distances between
recipients was 50 m. and distances between sources 100 m.
Until the occurrence of the El Mayor-Cucapah Earthquake the only active
fault recognized in the region of the modern Colorado River Delta was the Cerro
Prieto fault. Immediately after the quake of 4 April 2010, Mw=7.2, whose epicenter was located 50 km south-west of the city of Mexicali, a unknown structure
broke up and became visible at the surface and hereafter named as the “Indiviso
Fault” (By the Indiviso farm village). Preliminary results of the seismic reflection
interpretation, show the existence of some structures with dimensions at depth of
more than 5 km, although they are not visible in surface since they are buried by
recent sediments. In the seismic reflection lines we observe a structure that can be
related to Indiviso Fault, but the fault trace is located more towards the southeast
of the area where the aftershocks are located. Same happen with the rollover fault
which is located more to the west of Indiviso Fault in a zone that at present time
there in not seismic activity.
An attempt is make to correlate the identified structures between seismic
lines and construct a structural map of the region that helps to locate those active
structures that represents a hazard to the Mexicali-Imperial Valley population,
as well as to establish the structural and tectonics interrelation with some of the
known active structures such as the Laguna Salada, Borrego, Cucapah faults
located in the Sierra Cucapah and El Mayor and responsible of the 4 April 2010,
El Mayor-Cucapah earthquake of Mw=7.2.
A Crustal Velocity Model for Southern Mexicali Valley, Baja California,
México
RAMIREZ-RAMOS, E. E., Department of Seismology, Earth Sciences Division,
CICESE, Ensenada, Baja California, México, [email protected]; VIDAL-
VILLEGAS, J. A., Department of Seismology, Earth Sciences Division, CICESE,
Ensenada, Baja California, México, [email protected]
We installed 16 three-component short-period stations and one broad band station (separated around 6 km) along a refraction profile to record an explosion
done in southern California, near the border between Arizona and Sonora,
Mexico. Data from this profile are used to determine a crustal velocity model
for the southern Mexicali Valley. This 117 km long profile goes from San Luis
Rio Colorado, Sonora to the central part of Sierra Juárez, Baja California. For
a long 45 km section of the profile (between San Luis Rio Colorado and Sierra
El Mayor) we used, as the reverse shot, an aftershock (M3.2) of the El MayorCucapah earthquake (M7.2) Seismograms show impulsive P-arrivals for closer
stations, significant superficial waves, and long-tailed codas. Phases observed in
the vertical-component record section are interpreted in terms of arrival times
and relative amplitudes to do a forward modeling. As initial model, we started
with a modified version (7 horizontal layers and the Moho at 20 km) of the model
proposed in 1980 by McMechan and Mooney for the Imperial Valley. This modified model is used to locate earthquakes of Mexicali Valley. At present we are still
processing our data. We will present details of our results at the meeting.
and their Relationship to Ground Motion Parameters
Rotational Effects Produced by the Mw 6.3 2009 L’Aquila Earthquake: A Review
on How the Seimological, Geological, Topographical and Geomorphological
Factors Can Influence the Occurrence of Earthquake-Induced Rotations
Cucci, L., Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy,
[email protected]; Tertulliani, A., Istituto Nazionale di Geofisica e
Vulcanologia, Rome, Italy, [email protected]; Pietrantonio, G.,
Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, grazia.pietrantonio@
ingv.it; CASTELLANO, C., Istituto Nazionale di Geofisica e Vulcanologia,
Rome, Italy, [email protected]
The Mw6.3 2009 L’Aquila earthquake produced an impressive number of rotational effects on vertically organized objects such as chimneys, pillars, capitals
and gravestones. The dataset of such effects consists of 121 observations at 38
different sites and represents a compendium of earthquake-induced istances of
rotational effects that is unprecedented in recent times. In this work we focus
on the 37 objects that can be more reliably considered as representative of pure
rotational ground motion, and find a relation between the distribution of the
observed rotations, the epicentral distance, the macroseismic intensities and the
directivity effects that characterize the L’Aquila event. We also clearly put in
evidence that scarce geophysical and/or geotechnical characteristics or unfavourable geomorphological conditions at the site deeply influence the occurrence of
earthquake-induced rotations. A purpose of this work is also to verify if the same
kind of investigations carried out at the scale of the mesoseismic area (~500 km 2)
provide similar results when applied at the local scale as in the case of downtown
L’Aquila (~2 km 2). In downtown L’Aquila we find 1) a remarkable convergence
between distribution of the rotations and of the damage; 2) 100% of the rotations
occurred at sites characterized by high factors of amplification and poor geological setting; 3) the ground rotations are not strongly dependent on topographic
effects. Finally, from quantitative analyses of GPS data we find that the effect of
the seismic arrival on an individual vertical object retrieved rotated is an overall
rotation with a substantially unpredictable direction.
Rotation of Objects during the 2009 L’Aquila Earthquake Analyzed with 3D
Laserscans and Discrete Element Models
Hinzen, K.-G., Cologne University, Cologne, Germany, hinzen@uni-koeln.
de; CUCCI, L., INGV, Roma, Italy, [email protected]; TERTULLIANI, A.,
INGV, Roma, Italy, [email protected]
In addition to heavy destruction in the mesoseismal zone, the 2009 M W 6.3
L’Aquila earthquake produced a large amount of earthquake-rotated objects
(EROs). Previous studies have shown a clear correlation between the distribution
of EROs and the local site conditions as well as source mechanism. In a field campaign in 2011 selected EROs, still in the original rotated position, were surveyed
by 3D laserscanning resulting in a set of virtual models. These models provided
detailed measures of displacements and rotations and served as a basis for the construction of discrete element models (DEMs). Included are several gravestones
and monuments in L’Aquila and a war memorial in the village of Paganica. This
memorial is located less than 350 m from the surface rupture of the causative
fault. It is of special interest because the 15° counterclockwise-rotated monument
is a simple block with a height to width ratio of 1.5; however, it is surrounded
by four columns holding a baldachin-like top structure. Numerical tests with
the DEMs show that locally measured three-component translational acceleration time histories are sufficient to explain the rotation and toppling of objects
in the L’Aquila cemetery. However, pure translational ground motions could not
reproduce rotation of the Paganica monument. Further calculations also involving rotational ground motion components are currently planned in order to find
an explanation for the observations.
Visualizing Structural Response and Site Amplification Using Earthquake
Data Recorded at the NEES@UCSB Field Sites
SEALE, S. W. H., Earth Research Institute, UCSB, Santa Barbara, CA, sandy@
eri.ucsb.edu; STEIDL, J. H., Earth Research Institute, UCSB, Santa Barbara,
CA, [email protected]; SEALE, L. B., Earth Research Institute, UCSB, Santa
Barbara, CA, [email protected]; CHOURASIA, A., San Diego
Supercomputer Center, San Diego, CA, [email protected]
We present animation created with data recorded at the Garner Valley Downhole
Array field site (GVDA) from two events. The two events were both located
directly below GVDA. The M3.1 event occurred on 3 June 2011 and the M3.6
event occurred on 14 June 2011. Both of these events were recorded by all channels in the boreholes at GVDA and on the Soil-Foundation-Structure-Interaction
(SFSI) and the Mini-SFSI structures. Animation of the displacement response of
the SFSI structures was created with Blender (http://www.blender.org/), an opensource 3D content creation suite. The animation shows distinct arrivals of P-, S-,
and surface waves and also illustrates characteristics of the braced (Mini) and
unbraced SFSI structures. Resonance of the unbraced roof of the structure after
the arrival of the S-wave is quite pronounced. The greatest displacements occur
in the horizontal plane compared to the vertical component. Rocking modes
excited by the earthquake are also clearly visible. Visualization Services group at
the San Diego Supercomputer Center created animation of the ground excitation
response to a M4.1 event. Using data recorded in the boreholes at GVDA, the
animation clearly shows the amplification of the signal in the near-surface materials. These visualizations created from actual earthquake data provide new insight
into ground and structural response to strong motion. The animations will be
used as teaching tools for college-level engineering courses.
Triggering
Array Analysis for Cascadia Tremor Spectra and Physical Properties of NonVolcanic Tremor Sources
Yao, H., Scripps Institution of Oceanography, UCSD, La Jolla, CA, huyao@
ucsd.edu; GERSTOFT, P., Scripps Institution of Oceanography, UCSD, La Jolla,
CA, [email protected]; SHEARER, P., Scripps Institution of Oceanography,
UCSD, La Jolla, CA, [email protected]; ZHANG, J., Los Alamos National
Laboratory, Los Alamos, NM, [email protected]; VIDALE, J. E., University of
Washington, Seattle, WA, [email protected]
During the last decade, the discovery and analysis of non-volcanic tremor have
greatly broadened the research spectrum of earthquake seismologists in understanding plate boundary dynamics. However, due to very weak amplitudes and
the non-impulsive nature of tremor signals (which may be generated from thousands of low frequency earthquakes), most previous tremor analyses focused on
frequencies of 1 to 10 Hz, which limits the understanding of tremor source properties at higher frequencies. The use of array analysis techniques, such as beamforming, can substantially enhance the signal-to-noise ratio of tremor signals in a
much broader frequency band (e.g., 1 to 20 Hz) and provide better constraints on
the physical properties of the tremor source (e.g., Zhang et al., 2011, G3). In this
study, we apply an array beamforming technique to a week of continuous tremor
data from the Big Skidder array deployed in Cascadia in 2008 to analyze the spatio-temporal migration of tremor events as well as the tremor source spectra. We
systematically analyze over 10, 000 3-second-long tremor windows using beamforming analysis to determine their spectral characteristics (corner frequency
and high-frequency falloff rates). The statistics of the spectra show that tremor
corner frequencies lie mostly within 2 to 5 Hz, which is much lower than that
of small earthquakes that radiate seismic energy of comparable amplitude. This
implies that tremor sources may have abnormally low stress drops (on order of
KPa) or abnormally slow rupture speeds. The high-frequency falloff rates mainly
fall in the range of f-2 to f-3, similar to earthquakes, but different from previous
tremor spectral analyses that suggested shallower falloff rates. Our results imply
that tremor sources may be formed by swarms of microearthquakes with unusual
physical properties. We will present additional details on the spatial distribution
of tremor corner frequencies and falloff rates.
Event Detection in 2009 Socorro, NM Earthquake Swarm and Costa Rican
Non-Volcanic Tremor Using the Subspace Detector Method
Morton, E. A., New Mexico Tech, Socorro, NM, [email protected]; BILEK,
S. L., New Mexico Tech, Socorro, NM, [email protected]; ROWE, C. A., Los
Alamos National Laboratory, Los Alamos, NM, [email protected]
Development of waveform scanning techniques has significant value in a range of
scientific studies, including detecting volcanic events and characterizing earthquake swarms. Because seismic events from the same source area have similar
waveforms, we can use previously detected events to detect new events. This has
been done with the waveform cross-correlation based scanner, which implements
a cross-correlation between a past event (template) and the signal being scanned.
While this technique has been modestly successful in previous applications,
including repeating earthquakes in the Socorro Magma Body region of New
Mexico (e.g. Stankova et al., 2008), there are difficulties in using the cross-correlation method when there are slight variations between the template and target
events. Other methods exist to deal with these variations, such as the subspace
detector method, which uses multiple template waveforms. This method creates
a subspace spanned by the basis vectors of the templates and determines whether
the scanned signal is in this subspace. Here we examine differences in results
between the 2 methods, focusing on a 2009 Socorro, NM earthquake swarm
previously examined with the cross-correlation scanner. Using the first day of
data, we applied the subspace detector to different frequency bands, finding use
of high-passed (at 5 Hz) data the most successful detection method. This filtering
is necessary when searching for microseisms in broadband station traces. Both the
high-passed method and the separate frequency bands method out-performed the
cross-correlation based scanner. Combining several different methods (correlation scanner and subspace detector, various filtering) together detected 10 out
of 12 previously detected events, and found 33 new events, detecting 43 events
total. Additional work includes applying the detector to the remaining days of
the Socorro earthquake swarm and new application to data recorded in the Costa
Rica subduction zone.
Dual-Frequency Coherence, Repeated Events, and Non-Volcanic Tremor
Dorman, L. M., Scripps Institution of Oceanography, Univ of Calif, San
Diego, La Jolla, CA, [email protected]; SCHWARTZ, S. Y., Dept or Earth Sci,
Univ of Calif, Santa Cruz, Santa Cruz, CA, [email protected]
We demonstrate how dual-frequency coherence (DFC) can be used to detect
non-Gaussianity and, in particular, repeated events. The motivation for this is
the recent realization that non-volcanic tremor (NVT) consists of swarms of low
frequency earthquakes (LFE). DFC analysis may help to reveal LFE periodicity or
intervals. A pair of identical events produces a banded pattern in the frequencyfrequency space in which DFC is displayed. This is similar to the scalloping in
the power spectra of a signal containing repeated events. The use of coherence,
instead of the power spectrum has two beneficial effects. First: that coherence
is generally flatter than the power spectrum, so scalloping is not superimposed
on a sloping power spectrum and is more easily recognizable. Second: the averaging in the coherence calculation suppresses the parts of the frequency range
dominated by the more random parts of the time series. We show simple synthetic
examples how banded DFC patterns can be generated by repeated events (two or
more) with a repeat time equal to the reciprocal of the offset frequency between
bands. Slip occurring at plate boundaries creates seismic tremor as well as ”normal” earthquakes. This non-volcanic tremor appears to consist of swarms of lowfrequency earthquakes which lack impulsive P and S arrivals. We report dualfrequency coherence (DFC) calculations on tremor and normal microseismic
background noise observed on Ocean-Bottom Seismographs and land seismic
stations around the Nicoya Peninsula, Costa Rica, and in Japan. Both the OBS
and land tremor signals show a banded pattern in DFC that is absent in normal
noise. The similarity in the DFC patterns between OBS and land tremor signals
suggests a common source, eliminating the possibility that DFC is a property of
the OBS or seafloor environment.
Asperities in the Transition Zone Control Spatiotemporal Evolution of Slow
Earthquakes
Ghosh, A., University of Washington, Seattle, WA (*now at UC Santa Cruz),
[email protected]; VIDALE, J. E., University of Washington, Seattle,
WA, [email protected]; CREAGER, K. C., University of Washington, Seattle,
WA, [email protected]
Slow earthquakes, characterized by slow slip and associated seismic radiation
called non-volcanic tremor, has been observed in major subduction zones world-
wide. The factors governing tremor generation and rupture propagation during
slow earthquakes, however, remain enigmatic. We develop a novel multi beambackprojection (MBBP) method to detect and locate tremor using multiple seismic arrays. This technique detects more duration of tremor activity and provides
higher resolution in tremor location compared to a conventional envelope crosscorrelation method. We apply the MBBP technique to image tremor activity
during two large episodic tremor and slip (ETS) events, and an entire inter-ETS
time period in Cascadia. Our results suggest that the majority of the tremor is
occurring near the plate interface. We observe strongly heterogeneous tremor distribution with several spatially stable patches in the transition zone that experience repeated tremor episodes and produce majority of the tremor. Two large ETS
events in 2010 and 2011 appear to break the same patches up-dip in the tremor
zone. Smaller inter-ETS episodes also repeatedly rupture same patches, but are
located down-dip in the tremor zone. During the large ETS event, alongstrike
rupture propagation velocity varies by a factor of five, and seems to be modulated
by the tremor patches. The patches behave like asperities, and appear to control
tremor generation and rupture propagation during slow quakes. In addition, we
find a range of tremor propagation velocities over shorter time scales indicating
complexity in slip propagation. For example, we observe tremor streaks [Ghosh
et al., 2010, G-cubed] propagating rapidly at a velocity of ~100 km/hour, and
slower up-dip propagation at 1 km/hour in the same ETS event. These observations support a model in which transition zone is heterogeneous and consists of
patches of asperities with surrounding regions slipping mainly aseismically.
Constructing a Comprehensive Low-Frequency Earthquake Catalog from a
Dense Temporary Deployment of Seismometers along the Parkfield-Cholame
Segment of the San Andreas Fault
Sumy, D. F., United States Geological Survey, Pasadena, CA, danielle.sumy@
gmail.com; COCHRAN, E. S., United States Geological Survey, Pasadena,
CA, [email protected]; HARRINGTON, R. M., Karlsruhe Institute of
Technology, Karlsruhe, Germany, [email protected]
The Parkfield Experiment to Record MIcroseismicity and Tremor (PERMIT) is a
thirteen-station broadband array installed between May 2010 and July 2011 near
Cholame, California, to improve seismic network coverage south of the High
Resolution Seismic Network (HRSN). The array is located along a portion of the
San Andreas fault that transitions from locked to creeping northward along fault
strike. The overarching goal of the project is to explore the spatiotemporal relationships between low frequency earthquakes (LFEs) and local earthquake activity reported in the Northern California Seismic Network (NCSN) catalog and
identified in the temporary array data. We identify LFEs from a catalog of tremor
episodes automatically detected using a neural network approach. We apply
cross-correlation techniques to isolate template events from eight strong tremor
episodes that occurred during the first three weeks of the temporary deployment.
The templates are then used to detect and locate LFEs during the entire thirteenmonth deployment. Previous studies have shown that tremor activity increased
along this section of the San Andreas before and after the 2004 Parkfield earthquake, suggesting that stress interactions exist between earthquakes in the shallow, seismogenic zone and the deeper transition zone. Understanding the range of
fault slip behaviors, including how tremor and earthquakes interact, will provide
critical information for assessing seismic hazard.
Triggered Activity on an Adjacent Fault Deduced from Relocated Aftershocks
of the 2010 Haiti Earthquake
Douilly, R., Purdue University, West Lafayette, IN, [email protected];
SYMITHE, S., Purdue University, West Lafayette, IN, ssymithe@purdue.
edu; HAASE, J. S., Purdue University, West Lafayette, IN, jhaase@purdue.
edu; ELLSWORTH, W. L., United States Geological Survey, Menlo Park,
CA, [email protected]; BOUIN, M. P., Observatoire Volcanologique et
Sismologique de Guadeloupe, Guadeloupe, [email protected]; CALAIS, E., Purdue
University, West Lafayette, IN, [email protected]; ARMBRUSTER, J. G.,
Lamont Doherty Earth Observatory, Palisades, NY, [email protected];
Mercier de Lepinay, B. F., Geoazur–Universite de Nice, Sophia Antipolis,
France, [email protected]; Deschamps, A., Geoazur—Universite de
Nice Sophia Antipolis, France, [email protected]; Mildor, S.-L.,
Bureau des Mines et de l’Energie, Port-au-Prince, Haiti, Saintmildor1953@
yahoo.fr; Meremonte, M., United States Geological Survey, Golden,
CO, [email protected]; Hough, S. E., United States Geological Survey,
Pasadena, CA, [email protected].
Haiti has several active faults that are capable of producing large earthquakes
such as the 2010, Mw 7.0, event. This earthquake and its magnitude were not
unexpected, given the rate of strain accumulation on the Enriquillo Plantain
Garden Fault Zone, the major fault system in southern Haiti, and the timing of
large historical earthquakes (Manaker et al. 2008). GPS and INSAR data (Calais
et al., 2010) show, however, that the 2010 rupture occurred on the previously
unmapped Léogâne fault, a 60° north dipping oblique blind thrust located immediately north of the Enriquillo Fault. We use the complete set of broadband, short
period, strong motion and ocean bottom seismometers (OBS) that were deployed
following the earthquake to relocate all of the aftershocks from March 17 to June
24. We also determine the regional one-dimensional crustal structure and focal
mechanisms. The aftershock locations from the combined data set clearly delineate the Léogâne fault, with a geometry close to that inferred from geodetic data.
The strike and dip closely agree with that of the centroid moment tensor solution,
but the fault appears to be more steeply dipping than the finite fault inversions.
OBS observations provide significant improvement in the aftershock locations
west of the rupture zone, which now show a south-dipping structure coincident
with the Trois Baies fault. An independent calculation of coulomb failure stress
(CFS) provides evidence that these aftershocks were triggered by the main shock.
There is no clear evidence for aftershocks on the eastern rupture segment inferred
in the Hayes et al. (2010) mainshock rupture model, or on the Enriquillo fault
itself. The orientations of the focal mechanisms for aftershocks in the hanging
wall of the Leogane fault are not parallel to the deeper fault geometry. This could
be indicating that the shallow events are responding to stress changes within the
volume rather than indicating the orientation of the fault for this cluster.
plate. It has a nearly pure normal faulting focal mechanism, initiating at 94 s after
the origin time of the first subevent. It has a moment magnitude of 7.2-7.4 and
most of seismic moment occurred in 10 s. Though the causative fault plane is not
able to be resolved, the strikes of nodal planes are consistent with the local trench
geometry and focal mechanisms of nearby aftershocks. Further finite fault study
reveals that the slip distribution of the first strike-slip subevent highly correlates
with the inland portion of the Weitin Fault. We notice that the static Coulomb
stress drop induced by this subevent is negative in the source region of the second
normal fault rupture. The rupture of this event is then an evidence of dynamic
triggering.
Triggered Microearthquakes on the Parkfield section of the San Andreas
Fault By the 2003 Mw 6.5 San Simeon Earthquake
Meng, X., EAS, Georgia Tech, Atlanta, GA, [email protected]; PENG, Z.,
EAS, Georgia Tech, Atlanta, GA, [email protected]; HARDEBECK, J. L.,
USGS, Menlo Park, CA, [email protected]
Three-dimensional velocity models serve as an essential platform for the production of realistic ground motion analyses for earthquake hazard assessments. In
preparation for ground motion modeling in the Pacific Northwest, we developed
a new three-dimensional structural model, Casc 1.5, integrating P- and S-wave
velocities of the Cascadia region including the Cascadia subduction zone. Built
with EarthVision® software, Casc 1.5 is an updated model from a previous version that incorporates new parameters and velocity data acquired from recent
Earthscope seismological studies and regional network ambient noise investigations. The model covers an area from about 40.20 N to 500 N latitude, and
-1220 W to -1290 W longitude with a depth range of 0 to 60 km. The basic structural model was developed from published data interpretations in geological and
geophysical literature. Seven geologic structural blocks constitute the model: 1)
Oceanic Mantle, 2) Continental Mantle, 3) Oceanic Crust (subducting slab), 4)
Continental Crust, 5) Oceanic Sediments (accretionary wedge), 6) Continental
Tertiary Sediments, and 7) Continental Quaternary Sediments. Each structural
block is attributed with available Vs and Vp parameters and density derived
through empirical relationships. We intend to use this model as a platform for
earthquake simulations up to M 9 on the Cascadia megathrust. Future development of this model will include topography as well as bathymetry data.
Whether aftershocks are triggered by static or dynamic stress changes is still
in debate. Previous studies on aftershock triggering mostly utilize earthquakes
listed in catalogs, which could be incomplete immediately after moderate to large
earthquakes. In this study, we apply a recently developed matched filter technique
to detect missing earthquakes along the Parkfield section of the SAF around the
occurrence time of the 2003 Mw6.5 San Simeon earthquake. Previous studies
have found the mainshock induced ~10 kPa positive Coulomb stress changes on
the SAF, which is inconsistent with the observation of a decrease of seismicity
rate around Parkfield after the mainshock according to NCSN catalog. Here we
use waveforms of ~3000 earthquakes recorded by 12 HRSN stations around
Parkfield as templates, and scan through the continuous data 8 days before and
10 days after the San Simeon mainshock. We band-pass filter waveforms of 2-8
Hz to depress the effects of large aftershocks from the San Simeon rupture. A
total of 749 events are detected, of which only 18 are listed in the NCSN catalog.
The seismicity rate from the newly detected events shows a clear increase around
Parkfield about 4 days after the mainshock. In comparison, swarm-like activity
at south of Gold Hill started about 8 days before and turned off immediately
before the mainshock, which resulted in an apparent decrease of seismicity rate.
No detections are found further north in the creeping section of the SAF after the
mainshock, despite many templates in this region. We also compared the detections with 2-8 Hz and 10-25 Hz band-pass filters and find that the results are
comparable. Our observations suggest that the SAF near Parkfield was positively
loaded by the mainshock. This is consistent with the Coulomb stress calculation,
triggered right-lateral creep, and a clear increase of deep tectonic tremor after the
mainshock, although we cannot rule out the possibility of dynamic triggering at
this stage.
A Revisit of the 2000 Mw 8.0 New Ireland Earthquake: Evidence of Dynamic
Trigger
Li, X., University of California, Santa Barbara, Goleta, CA, xiangyuli@umail.
ucsb.edu; SHAO, G., University of California, Santa Barbara, Goleta, CA,
[email protected]; JI, C., University of California, Santa Barbara, Goleta,
The 16 November 2000 Mw 8 New Ireland earthquake is one of the largest strikeslip earthquakes ever recorded. It was followed by one abnormally strong aftershock sequence including one Mw 7.8 thrust earthquake three hours later and
another Mw 7.8 event one day after. This earthquake excited large local tsunami
at Bougainville and Buka islands that locate at about 300 km southeast of the
epicenter, in contrast with the nature that the strike-slip motion is generally not
efficient in exciting tsunami. Previous finite fault source study (Yagi and Kikuchi,
2000) suspected the existence of a secondary thrust subevent occurred about 2
mins after the mainshock but was not able to constrain its location. Here this
complex earthquake is revisited by joint investigating the broadband body waves
and long period surface waves. Both back-projection analysis of teleseismic body
waves and multiple double couple (MDC) analysis using long period surface
waves capture the second subevent. It occurred about 300 km southeast of the
relocated ISC epicenter and on the outer-rise region of subducted Solomon sea
A New 3-D Structural Model of the Cascadia Subduction Zone Incorporating
P and S Wave Velocities
ANGSTER, S. J., Geologic Hazards Science Center, U.S. Geological Survey,
Golden, CO, [email protected]; STEPHENSON, W. J., Geologic Hazards
Science Center, U.S. Geological Survey, Golden, CO, [email protected]
Global Correlations of Tomographic Models with Tectonic Regions
Paulson, E. M., University of Southern California, Los Angeles, CA,
[email protected]; JORDAN, T. H., University of Southern California, Los
We project the three-dimensional aspherical variations of shear-wave velocities
from 21 published whole-mantle tomographic models onto various global tectonic regionalizations. For each model, we obtain the radial shear-velocity profiles of oceanic regions (divided according to crustal age) and continental regions
(divided according to Phanerozoic tectonic stability). We evaluate the statistical
significance of the inter-regional differences from intra-regional variances that
account for the spectral content of the models. The regionalized shear-velocity
profiles for all models show strong variations in the uppermost mantle consistent
with plate-tectonic expectations, and the profiles for most converge to zero in
the lower mantle, consistent with lower-mantle heterogeneity that is uncorrelated
with surface tectonics. A model with these two basic properties can be characterized by a set of convergence depths, which we define to be the minimum depths
where the regional averages become statistically indistinguishable from one
another. We have used the inter-regional differences and intra-regional variance
analysis of the tomographic model ensemble to estimate two types of convergence
depths: ZO, where oceanic profiles of crustal magmatic age t converge to a common average for oceanic upper mantle, and ZC, where the stable-continent profiles converge with those for the mature oceanic lithosphere. Vertical smearing of
the aspherical anomalies by the tomographic inversion filters explains most of the
variation in these depth bounds across the model ensemble. Accounting for vertical smearing yields ZO > 170 km and ZC > 350 km. The first is consistent with
regional structural studies in the Pacific Ocean, though not with standard platecooling models. The second is inferred to be an approximate bound on the average
thickness of the kinematically coherent tectosphere beneath stable continents.
High Resolution Interseismic Crustal Velocity Model of the San Andreas Fault
from GPS and InSAR
Tong, X., UCSD/SIO, La Jolla, CA, [email protected]; SANDWELL, D. T.,
UCSD/SIO, La Jolla, CA, [email protected]; KONTER, B., University of
Texas at El Paso, El Paso, TX, [email protected]
We recovered interseismic deformation along the entire San Andreas Fault
System (SAFS) at a spatial resolution of 200 meters by combining GPS and
InSAR observations using a dislocation model. Previous efforts to compare 17
different GPS-derived strain rate models of the SAFS shows that GPS data alone
cannot uniquely resolve the rapid velocity gradients near faults, which are critical for understanding the along-strike variations in stress accumulation rate and
associated earthquake hazard.
To improve the near-fault velocity resolution, we integrated new GPS observations with InSAR observations, initially from ALOS ascending data (spanning
2006.5-2010), using a remove/restore approach. More than 1100 interferograms
were processed with GMTSAR. The integration uses a dislocation-based velocity
model to interpolate the Line-Of-Sight (LOS) velocity at the full resolution of
the InSAR data in radar coordinates. The residual between the model and InSAR
LOS velocity were stacked and high-pass filtered, then added back to the model.
Our initial result show previous unknown details in the along-strike variations of surface fault creep. We estimated the creep rate and creep depth for 37
fault segments along the SAFS considering two types of fault zone structure: a
dislocation in a homogeneous medium and a dislocation within a compliant fault
zone.
A key question is whether the Creeping section in Central California is partially locked at intermediate depth. InSAR observations revealed that the portion
of the Creeping sections from latitude 36.2° to 36.4° is creeping at a rate of 20-25
mm/yr, significantly lower than the geologic fault slip rate of 35 mm/yr. Since
ascending ALOS data are mainly sensitive to vertical motions, a more complete
analysis of both the GPS data and the descending tracks from other SAR satellites
(e.g. ERS and Envisat) is needed to provide accurate estimates of the depth and
locations of the locations of the asperities.
Gravity Profiles across the San Jose Fault on the Cal Poly Pomona Campus
Potter, H., Cal Poly Pomona, Pomona, CA, [email protected];
PAZOS, C., Cal Poly Pomona, Pomona, CA; POLET, J., Cal Poly Pomona,
Pomona, CA.
The campus of California State Polytechnic University, Pomona is located on the
southeastern edge of the San Jose Hills, a NE-SW trending range separating the
San Gabriel and Pomona Valleys. To the southeast, these hills are bounded by
the San Jose fault, traces of which are known to run through campus. Several
geotechnical investigations have been conducted to attempt to locate and classify these traces, but results have been inconsistent. In 2010, the California State
University (CSU) Seismic Review Board categorized several buildings on campus
as having top priority for seismic retrofitting. The CSU board of trustees voted,
last year, to raze the iconic Classroom, Laboratory, and Administration building, located on one of the postulated fault traces, due to poor construction and
seismic concerns.
Using a LaCoste and Romberg gravimeter, several gravity profiles were
measured across Cal Poly Pomona campus. The goal of these surveys was to ascertain whether any gravity anomalies could be detected that would correspond to
the proposed locations of the San Jose fault. The profiles were chosen to run perpendicular to traces of the fault postulated by GeoCon geotechnical investigation and range from 75 to 100 meters in length. The gravity surveys also included
a total station surveying instrument, ensuring accurate elevation measurements
for the corrections. The Bouguer anomaly profiles show lateral variations of subsurface density that would be consistent with the presence of the San Jose fault in
the area of the Main Quad, with a relative change of about one milligal between
the highest and lowest measurements. A second profile measured on the east side
of campus across another proposed strand does not show the pattern expected for
a reverse fault, suggesting this strand may taper out to the northeast. We will present profiles of elevation and Bouguer gravity anomalies and compare our results
with those from geotechnical trenching and geological mappings studies.
The Obsidian Creep Project: Active and Passive Source Imaging of Faults in
the Brawley Seismic Zone and Salton Sea Geothermal Field, Imperial County,
California
MCGUIRE, J. J., WHOI, Woods Hole, MA, [email protected];
CATCHINGS, R. S., USGS, Menlo Park, CA, [email protected]; LOHMAN,
R. B., Cornell Univ, Ithaca, NY, [email protected]; RYMER, M. J., USGS,
Menlo Park, CA, [email protected]; GOLDMAN, M. R., USGS, Menlo Park,
The portion of the Brawley Seismic Zone (BSZ) just south of the Salton Sea
accommodates the transfer of plate motion between the San Andreas and
Imperial Faults, encompasses the Salton Sea Geothermal field and is one of the
most seismically active regions in California. However, because this region is predominately agricultural, the faults that accommodate this strain have remained
undetected until recently. We present the results of a combining active source
imaging of shallow fault structures, with precise earthquake locations utilizing
the local borehole network and inversions of geodetic data utilizing realistic fault
geometries.
We are relocating a dataset of over 1000 M>1 earthquakes since 2005 that
are well recorded on the local borehole seismic network, including a large swarm
in 2005 that produced both a surface rupture and a large geodetically observable
displacement field [Lohman and McGuire, 2007]. This swarm caused a surface
rupture of the Kalin fault [Rymer et al., 2009], had primarily strike-slip focal
mechanisms, and produced surface displacements compatible with normalfaulting motion on an NNE-SSW-striking fault with a steep dip to the WNW
[Lohman and McGuire, 2007].
In March 2010, we acquired medium- and high-resolution reflection and
refraction data across both a 6.4-km-long north-south profile and a 3.4-km-long
east-west profile in this region. Preliminary interpretation of shot gathers from
blasts in the north-south profile suggests that the BSZ and SSGF are structurally
complex, with abundant faults extending to or near the ground surface. Also, we
infer relatively high-velocity material that shallows beneath the SSGF. This may
be due to high temperatures and resultant metamorphism of buried materials in
the SSGF. In the shallow subsurface along the east-west profile we interpret from
reflection images that a prominent fault extends to the ground surface on projection of the Kalin fault.
Crustal Reflectors In Nevada from Ambient Seismic Noise Autocorrelations,
at Scales of Meters to Tens of Kilometers
Tibuleac, I. M., Nevada Seismological Laboratory, Reno, NV; VON
SEGGERN, D. H., Nevada Seismological Laboratory, Reno, NV
The depth of reflecting layers in the Earth’s crust is usually estimated using controlled sources or earthquake signals. Ambient seismic noise, however, can also
be used for this purpose. We have developed and applied a new method, based on
continuous waveform analysis, to estimate the two-way P-wave reflection component of the Green’s Function beneath each seismic station. We demonstrate
application of the method at two scales. First, at a scale of tens of km, the Green’s
Functions are retrieved from continuous record autocorrelation stacks at broadband sensor locations within the USArray EarthScope Transportable Array in
the Western Great Basin and the Sierra Nevada, in a region with complex crustal
and upper mantle structure. We show evidence of a reflector at the crust-mantle
boundary (Moho discontinuity) derived for the first time from ambient-noise
autocorrelations using short-period (~ 1 sec) data. Our results compare well with
earthquake and controlled source investigations, and with tomography findings
in the region. Moho depth is difficult to resolve seismically because of the lack
of favorable spatial distribution of source and receiver geometries. In contrast,
our method can be applied at any desired sensor spacing to estimate Earth reflector depth beneath surface-located sensors, providing unprecedented resolution.
Second, at a scale of tens of meters to km, characteristic to exploration geophysics
experiments, we investigate the feasibility of this new method using waveforms
collected by two co-located surveys, one active (by Optim, Inc.) and one passive
(deployed by the University of Nevada, Reno) at a potential geothermal exploration site near Reno, NV. Preliminary results are encouraging; however, we find
that further investigations are necessary for the ambient noise method to be used
as a stand-alone exploration technique.
Using an Active Source to Analyze Coherence vs Distance and Estimate Q at
the Garner Valley and Wildlife NEES@UCSB Field Sites
Steidl, J. H., University of California Santa Barbara—Earth Research
Institute, Santa Barbara, CA, [email protected]; CIVILINI, F., University
of California Santa Barbara—Earth Research Institute, Santa Barbara, CA,
[email protected]
Mobile shakers provide an active way to excite waves at various frequencies
through the top layers of a site for characterization purposes. A temporary linear surface array of eight accelerometers at 10 meter spacing was deployed for a
mobile shaker experiment at the Garner Valley Downhole Array (GVDA) and
Wildlife Liquefaction Array (WLA) seismic stations, which are part of the
George E. Brown Jr., Network for Earthquake Engineering Simulation (NEES)
program. The mobile shaker “T-Rex”, also part of the NEES program, was posi-
tioned at three locations around the linear array and produced both Ricker and
steady pulses at frequencies ranging between 3 Hz to 16 Hz in the vertical, lateral,
and transverse directions. In addition to the site instrumentation and temporary
accelerometer array, data channels on the mobile shaker provided the input drive
signal, plate acceleration, and calculated output force acceleration for each shake.
The observed attenuation of waves across the arrays suggests that energy across
the sites has a directional dependence. Spectral energy and coherence analysis of
the observed waveforms from the linear arrays at both sites provides information
on the coupling efficiency of the shaker truck at each site. The analysis of spectral energy across the array for each input frequency shaker force suggest that the
mobile shaker couples well at 12 Hz and above at GVDA and at 8Hz and above at
WLA. These results suggest that site effects directly affect the ability of a mobile
shaker to couple with the site. We will include data from another “T-Rex” experiment at GVDA scheduled for February of 2012, incorporating new procedure
to further test our current hypotheses. Additionally, we plan to use these data to
estimate a Q value for each of the sites.
A Regional High-frequency Attenuation (Kappa) Model for Northwestern
Turkey
Sisman, F. N., Middle East Technical University, Ankara, Turkey,
[email protected]; PEKCAN, O., Middle East Technical University,
Ankara, Turkey, [email protected]; ASKAN, A., Middle East Technical
University, Ankara, Turkey, [email protected]
The high-frequency attenuation of spectral amplitudes of S-waves is modeled as
an exponential decay in terms of Kappa factor (Anderson and Hough, 1984). It is
thus an important parameter of soils identifying the high-frequency attenuation
behavior of ground motion as well as one of the key parameters for stochastic
strong ground motion simulation method. In particular, for regions with sparse
seismic networks, it is crucial to use simulated ground motions which require
well-defined regional seismic parameters. Several stochastic simulations have been
made for recent earthquakes occurred in Turkey; however there is not yet a systematic investigation of the Kappa parameter from the recently recorded Turkish
ground motions. In this study, we examine a strong ground motion dataset from
Northwestern Turkey with varying source properties, site classes and epicentral
distances. We manually define Kappa from the S-wave portion of each record.
We use both traditional regression techniques and data mining approaches to
describe the (potential) relationships between Kappa values and independent
variables such as the site class, distance from the source or magnitude of the event.
Unlike the classical methods, data mining techniques provide a deeper insight to
the problem through data analytics, in which a better understanding of existing
patterns of data results in higher prediction performances. We then compare the
outcomes of data mining techniques with those of traditional methods to better
highlight the important characteristics of the ground motion dataset. We express
the initial findings of a regional Kappa model for Northwestern Turkey with
focus on magnitude, site class and distance dependencies.
The Long Beach Seismic Experiment: A Novel High-Density Array to Examine
Seismic Scattering
Dominguez, L. A., UCLA, Los Angeles, CA; DAVIS, P. M., UCLA, Los
Angeles, CA; HOLLIS, D., Nodal Seismic, Los Angeles, CA,
The Long Beach (LB) seismic experiment is a novel array of 5000 seismic stations deployed in a highly populated area. Seismic studies are usually limited by
the number and spacing of seismic stations and uncertainties in the location,
time and magnitude of the event. In particular, analysis of propagation of seismic waves near the surface is complex due the highly heterogeneous nature of
the crust. The LB array offers an extraordinary opportunity to examine scattered
wavefields in great detail. We present waveform and entropy analysis for two
events in the vicinity of the array that show the enormous potential of this kind
of experiment in urban areas.
Our analysis includes two events: 1) the Mw=2.5 Carson event and 2) the
Mw=3.4 Compton event. The first event occurred ~9km W of the array, while
the Compton event happened ~16km NW. For both events, we compute the
frequency-wavenumber analysis at different frequency bands (1-2Hz, 2-4Hz,
4-8Hz, 6-12Hz, 8-16Hz and 10-20Hz) in a sliding time window to estimate the
temporal behavior of the field. In addition, we designed an entropy analysis to
determine the coherency of the scattered field. Our results show that isotropic
scattering of body waves is the major contributor to the late arriving coda wavefield as shown by the FK analysis. On the other hand, the entropy-energy analysis
demonstrates the transition point in the early coda between direct coherent body
waves and incoherent coda waves. The events show different features. Whereas
the Compton event shows two distinctive arrivals at the time of the arrival of the
S- wave, the Carson event denotes the self-similarity of the entropy compared
with the Compton event.
A Model-Based Approach to the Geophysical Estimation of the Thickness of
Lateritic Weathering Profiles
Nelson, S. T., Dept. of Geological Sciences, S-, Provo, UT, oxygen.isotope@
gmail.com; MCBRIDE, J. H., Dept. of Geological Sciences, S-, Provo, UT, john_
[email protected]; JUNE, N., Dept. of Geological Sciences, S-389 ESC, Brigham
Young Univ., Provo, UT; TINGEY, D. G., Dept. of Geological Sciences, S-389
ESC, Brigham Young Univ., Provo, UT; ANDERSON, J., Dept. of Biochem.
and Physical Sci., Brigham Young Univ. HI, Laie, HI; TURNBULL, S. J., DPW
Environmental, Schofield Barracks, HI,
Igneous rocks in the tropics can develop thick weathering profiles such that many
ocean islands and heavily populated volcanic arcs are susceptible to weather and
seismically induced ground failures. However, conventional exploration seismology may provide insufficient engineering information to characterize laterites if
velocity inversions are present and if discrete breaks in material properties are
absent.
Standard walk-through CDP reflection surveys and model-based shear
wave velocity (MASW) profiles were obtained to examine ground where material
property gradients and velocity inversions are expected. Experiments were run
at the Schofield Barracks, Oahu, Hawaii where laterite thickness is constrained
from nearby wells or gullies. A baseline profile was obtained near Fillmore, Utah
where local aridity should produce little weathering of buried basalt, and the
boundary with overlying valley fill should be sharp.
In Oahu, reflections within laterites likely show relict differences in volcanic textures. MASW profiles produced shear wave models that correlate with
both reflection profiles and well logs. The base of laterite can be recognized, as
well as basalt horizons intercalated within thick laterite, where the latter can also
be observed in well logs and the walls of nearby gullies.
The baseline Fillmore section validates interpretations from Oahu. A
nearby driller’s log correlates to an abrupt rise from low Vs (valley fill) to high
Vs (basalt) material at the expected 4-5 m depth. Significant velocity variations
within basalt must reflect primary volcanic textures, including vesicularity, cooling joints, etc. Comparison of the Fillmore to Oahu profiles indicate that the
MASW method is an excellent approach for characterizing the acoustic properties of thick laterites, including gradients in material properties and velocity
inversions. Application of this approach may lead to improved site-specific characterization of seismic hazards in tropical region.
Earthquakes of 2011
Relocation and Comparison of the 2010 M 4.3 and 2011 M 5.6 Earthquake
Sequences in Lincoln County, Oklahoma
Toth, C. R., University of Oklahoma, Norman, OK; HOLLAND, A. A.,
Oklahoma Geological Survey, Norman, OK; KERANEN, K., University of
Oklahoma, Norman, OK; GIBSON, A., Oklahoma Geological Survey, Norman,
OK,
On 27 February 2010 a M4.3 earthquake occurred in southeastern Lincoln
County. 111 aftershocks of this earthquake were recorded through August 2011.
At the start of the sequence, the seismic network consisted of six Oklahoma
Geological Survey seismic monitoring sites distributed across the state, IRIS
Transportable Array coverage on the western half of the state, and NetQuake
instruments ~40 km to the west. Over the remainder of 2010, the coverage of the
Transportable Array gradually expanded to include the whole state of Oklahoma.
Consequently, part of the 2010 M4.3 aftershock sequence had poor station coverage, particularly at the beginning of the sequence, and events could not be precisely
located. On 6 Nov. 2011, a M5.6 occurred in the same region. Aftershocks of this
event have been well-recorded with a dense network of temporary local, OGS,
and TA stations. Using VELEST, we inverted for a 1-D velocity profile using
the P and S-phase picks for 212 earthquakes from the well-resolved 2011 M5.6
earthquake sequence. Sonic logs from nearby wells were used as a priori information to constrain velocity inversion. The well-located M5.6 2011 sequence and
the M4.3 2010 sequence were located together using HypoDD. The earthquake
locations and associated uncertainties for the 2010 M4.3 earthquake sequence
improved dramatically through joint location. The relocated earthquakes for the
M4.3 2010 sequence occurred in approximately the same location and delineate
a zone with the same orientation as the larger Nov. 2011 earthquake sequence.
Statistical Modeling of Seismicity Rate Changes in Oklahoma
Llenos, A. L., US Geological Survey, Menlo Park, CA, [email protected];
MICHAEL, A. J., US Geological Survey, Menlo Park, CA, [email protected]
The rate of M≥3 earthquakes in Oklahoma substantially increased beginning
in 2009 and continued through 2011 prior to the November M5.6 earthquake.
We use standard statistical models and tests to investigate the significance and
cause of this seismicity rate increase. Rate changes are often studied by declustering a catalog in an attempt to remove aftershocks and produce a set of event
origin times that can be compared to a Poisson distribution. Instead, we use the
Epidemic-Type Aftershock Sequence (ETAS) model, a stochastic model based
on empirical aftershock scaling laws such as Omori’s Law and the GutenbergRichter magnitude distribution, to detect whether this rate increase is due to an
increase in the background seismicity rate, a change in the aftershock productivity, or some combination of these effects, given the past history of earthquake
occurrence. We apply the ETAS model to the USGS PDE catalog of M≥3 earthquakes in Oklahoma occurring from 1973-2011 and find that a single set of
parameters cannot fit the entire time period, suggesting that a significant change
in the underlying process occurred in 2009. We find this by converting the origin
times to transformed times and testing the null hypothesis that the transformed
times are drawn from a Poisson distribution with constant rate, as one would
expect where no external processes trigger earthquakes besides the tectonic loading rate. The null hypothesis can be rejected with p<0.001 based on an autocorrelation test and a Runs test which both show that successive interevent times
are related to each other, which would not be true for a Poisson model. Next, we
estimate ETAS parameters from the 1973-2008 data to determine which parameters must vary to fit the later data. Preliminary results suggest possible changes
in both the background rate of independent events and the triggering properties.
These tests may shed some light on whether these earthquake rate changes are
natural or manmade.
Deep Fluid Injection near the M 5.6 Oklahoma Earthquake of November, 2011
Horton, S. P., CERI, University of Memphis, Memphis, TN, shorton@
memphis.edu
For about 2 years preceding the M5.6 earthquake, small earthquakes are reported
by the Oklahoma Geological Survey to have occurred within the epicentral area
defined by the current seismic activity. This suggests a build-up of seismic activity
characteristic of earthquake sequences triggered by fluid injection into the subsurface in Colorado in the 1960s and 1990s and recently (2010-2011) in Central
Arkansas that led to larger earthquakes (M5.3, M4.3, and M4.7 respectively).
One active waste disposal well (API 081-23499) injects fluid into a deep underground aquifer (the Arkbuckle Formation) within 4km of the reported location
of the M5.6 earthquake. Fluids are injected under low pressure (gravity flow),
but with a high volume (average volume ~ 83, 239, 800 gallons/year) at ~1.3
km depth. Two enhanced recovery wells (API 081-3909 and 3910) also operate
within 4km of the M5.6 location injecting smaller volumes (average combined
volume ~ 3, 500, 000 gallons/year) with an average well head pressure of 500psi
at ~1.3km depth in the Hunton Formation. The Wilzetta fault zone provides
a potential conduit for fluid transport from the injection depth at each well to
earthquake source depths between 3 and 6 km. Monthly injection rate reports for
2011 are not currently available. Based on the previous injection history, proximity of the wells to the earthquakes and the previous seismic activity in the source
area, the M5.6 earthquake was possibly triggered by fluid injection at these wells.
The 2011 M 5.7 Mineral, VA and M 5.6 Sparks, OK Earthquake Ground Motions
and Stress Drops: An Important Contribution to the NGA East Ground Motion
Database
Cramer, C. H., CERI, University of Memphis, Memphis, TN, ccramer@
memphis.edu; KUTLIROFF, J. R., CERI, University of Memphis, Memphis,
TN, [email protected]; DANGKUA, D. T., CERI, University of Memphis,
The M5.7 Mineral, VA earthquake of 23 August 2011 is the largest instrumentally recorded earthquake in eastern North America since the 1988 M5.9
Saguenay, Canada earthquake. The M5.6 Sparks, OK earthquake occurred on
6 November 2011 in a different tectonic environment. The Next Generation
Attenuation (NGA) East project to develop new ground motion prediction equations for stable continental regions (SCRs), including eastern North America
(ENA), is ongoing at the Pacific Earthquake Engineering Research Center. The
available recordings from the M5.7 VA and M5.6 OK earthquakes have been
added to the NGA East ground motion database. Close in (less than 100 km)
strong motion recordings are particularly interesting for both ground motion
and stress drop estimates as most close-in broadband seismometers clipped on the
mainshock, particularly for the VA event. A preliminary estimate for earthquake
corner frequency of ~0.7 Hz for the M5.7 VA earthquake and ~0.6 Hz for the
M5.6 OK earthquake have been obtained from strong motion recordings ~50 km
from the mainshock epicenters. This suggests a Brune stress drop of ~250 bars
for the VA event and ~100 bars for the OK event. The direct observations of corner frequency for these events are complicated by site and shallow source effects.
Comparisons suggest the ground motions from the M5.7 VA earthquake agree
well with current ENA ground motion prediction equations (GMPEs) at short
periods (PGA, 0.2 s) and are below the GMPEs at longer periods (1.0 s), which
is the same relationship seen from other recent M5 ENA earthquakes. Ground
motions from the M5.6 OK earthquake tend to fall below the predictions of current GMPEs, in keeping with the lower stress drop. Beyond 200 km, source radiation, directivity, and possibly propagation parallel to geologic structure may be
the cause of a two fold increase in ground motions in the azimuth 30-60 degrees
from the epicenter for the VA event.
Bayesian Extreme Maximum Magnitude (Mmax) Distributions
Tavakoli, B., Bechtel Corporation, Frederick, MD USA, btavakol@bechtel.
com; GREGOR, N., Bechtel Corporation, San Francisco, CA USA, njgregor@
bechtel.com
Maximum magnitude (Mmax) is defined as the largest possible earthquake
within a given seismogenic zone in the current tectonic setting, and is a significant seismicity parameter in probabilistic seismic hazard analyses (PSHA). The
resulting ground motions can be sensitive to small changes in Mmax within the
seismic source zones, especially when the annual frequencies of interest (≤104) is small, as an example for nuclear facilities sites. Professional judgments are
often applied to the largest observed magnitude to estimate a range in expected
Mmax values. However, for limited-earthquake catalogs, one cannot in general
add any single constant (e.g., 0.5 magnitude unit) to the magnitude of the largest observed earthquake to obtain an expected statistical best estimate of Mmax.
This study provides a formal probability-based procedure for the estimation
of Mmax, which is generic and can produce results that depend mainly on the
assumptions about the probabilistic model and/or the prior information available
about past seismicity. To achieve this goal, the most often-used procedure, which
is based on the classical double-truncated frequency-magnitude relationship and
Bayesian extreme value distribution is investigated. According to this Bayesian
extreme Mmax procedure, a posterior Mmax, which incorporates uncertainties
in the PSHA, is developed based on convolving a prior distribution of Mmax
with a bias-adjusted Mmax likelihood function obtained in the area of interest.
As an example case, the Bayesian extreme Mmax procedure is used to assess the
probability distribution of Mmax for the central Virginia seismic zone where
the M5.8 Virginia earthquake of 2011 August 23 occurred in association with
reverse faulting on a north or northeast-striking plane within the seismic zone.
The resulting Mmax distribution is then compared with the previous studies of
Mmax in this area based on judgment, consideration of the overall tectonic, geologic, and observed seismicity.
Fault Zone
Poster Session · Wednesday pm, 18 April · Golden Ballroom
What Tales Does San Jacinto’s Microseismicity Tell?
Tormann, T., ETH Zurich, Switzerland, [email protected].
ch; WIEMER, S., ETH Zurich, Switzerland, [email protected];
HARDEBECK, J. L., U.S. Geological Survey, Menlo Park, CA, jhardebeck@
usgs.gov
The frequency magnitude scaling of earthquakes, described by the b-value in the
Gutenberg-Richter law, has been found in laboratory experiments and nature to
be sensitive to the local stressing regime. In highly stressed regions earthquakes
tend to reach larger magnitudes more often, resulting in lower b-values. Mapped
with high resolution along fault traces, b-values calculated from micro-seismicity
(M1-4) can therefore indicate the location and extent of asperities and barriers
capable of moderate to large earthquakes, aiding realistic estimates of the local
hazard potential.
In 2000, Wyss and others published a study that analyzes two decades of
earthquake data along the San Jacinto-Elsinore fault system and identifies via
local a and b-values five anomalous regions of estimated short recurrence times
for M6+ earthquakes. Four of them coincide with the locations of five historical
mainshocks. We revisit those fault segments and apply an improved b-value imaging technique to re-evaluate those earlier findings. Since the productivity of the
region is high, we also investigate, in selected places, the temporal evolution of the
b-values, to help reconstruct the loading state and evolution along the San Jacinto
fault over the last three decades. Building on findings from the Parkfield segment
in Central California, we attempt to correlate spatial and temporal variability in
b with independent physical observational data along the fault, e.g. surface creep
rates.
Modeling Spatio-Temporal Varaitons of Seismicity in the San Jacinto Fault
Zone
Zöller, G., University of Potsdam, Potsdam, Germany, zoeller@uni-potsdam.
de; BEN-ZION, Y., University of Southern California, Los Angeles, CA,
Assessing Strain Accumulation Rates across the San Andreas and San
Jacinto Faults in the Vicinity of San Bernardino, California
Upton, E., Occidental College, Los Angeles, CA, [email protected]; MCGILL,
S. F., California State University, San Bernardino, CA, [email protected];
SPINLER, J., University of Arizona, Tucson, AZ, [email protected];
BENNETT, R. A., University of Arizona, Tucson, AZ, [email protected]
We investigate spatio-temporal properties of earthquake patterns in the San
Jacinto fault zone (SJFZ), California, between Cajon Pass and the Superstition
Hill Fault, using long records of simulated seismicity constrained by available
data. The model provides an effective realization (e.g. Ben-Zion 1996; Zöller et
al. 2007) of a large segmented strike-slip fault zone in 3D elastic half space, with
heterogeneous distributions of static/kinetic friction and creep properties, and
boundary conditions consisting of constant velocity motion around the fault. The
computational section of the fault contains small brittle slip patches which fail
during earthquakes and may undergo some creep deformation between events.
The creep rates increase to the end points of the computational section and with
depth. Two significant offsets of the SJFZ at San Jacinto Valley and Coyote Ridge
are modeled by strength heterogeneities. The simulated catalogs are compared to
the seismicity recorded at the SJFZ since 1932 and to recently reported results
on paleoearthquakes at sites along the SJFZ at Hog Lake (HL) and Mystic Lake
(ML) in the last 1500 years (e.g. Onderdonk et al., 2012; Rockwell et al., 2012).
We address several questions including the following intriguing issue raised by
the available paleoseismological data: are large earthquakes with signatures in
ML and HL typically correlated? In particular: is a typical paleoevent in HL an
incomplete rupture that is continued later in ML, and vice versa? The simulation
results provide insights on the statistical significance of these and other patterns,
and the ability of the SJFZ to produce large earthquakes which have not been
observed in recent decades.
Since 2002, numerous students have collected survey-mode GPS data from 31
benchmarks in and around the San Bernardino Mountains, California. We
use the velocity data from these sites, along with velocities from the Southern
California Earthquake Center’s Crustal Motion Model 4 as input for onedimensional elastic modeling of fault slip rates. Using a spreadsheet macro, we
tested about 3.2 million unique combinations of possible slip-rates for 15 faults
within a transect across the Pacific-North America plate boundary in the vicinity
of San Bernardino. The results show that, for models that fit the data well, the San
Jacinto fault (SJF) and San Andreas fault (SAF) have a total combined slip rate of
between 18-28 mm/yr (with a most reasonable fit of 20-24 mm/yr), thus accounting for about 50% of the movement along the plate boundary. Additionally, the
results show that the best-fitting slip-rate of the SJF lies between 12-14 mm/
yr, while the best-fitting slip-rate of the SAF is between 8-10 mm/yr. These
results, which are based on a much more robust dataset from the San Bernardino
Mountains than has previously been available, are consistent with previously
published geodetic studies that suggest the San Bernardino section of the SAF
slips more slowly than other sections of the SAF as a result of slip transfer from
the Coachella Valley SAF northward into the Eastern California shear zone,
and slip transfer from the Mojave section of the SAF southward onto the SJF.
Our best-fitting slip rate for the SAF near San Bernardino is slightly lower than
but overlaps with the uncertainties of some recently reported latest Pleistocene
slip-rate estimates for the San Bernardino section of the San Andreas fault. Our
best-fitting rate for the northern San Jacinto fault is also consistent with many
published late Pleistocene and Holocene slip rate estimates for that fault, and suggests that the northern SJF slips slightly faster than the San Bernardino section
of the SAF.
Time-Varying Deformation Adjacent to the San Jacinto Fault, 1985–2011:
Results from Pinon Flat Observatory
Agnew, D. C., IGPP/Scripps/UCSD, La Jolla, CA, [email protected];
WYATT, F. K., IGPP/Scripps/UCSD, La Jolla, CA, [email protected]
Pinon Flat Observatory (PFO) is located 14 km from the Anza section of the San
Jacinto fault, a location chosen in part because of the identification of this as a
possible seismic gap. Precise and stable measurements of strain, using longbase
laser strainmeters, have been a primary monitor of possible fault activity; these
became most useful following the anchoring of these instruments (in 1985 for
one component, 1988 for a second, and 2004 for the third). These records provide
a temporal depth and noise level superior to either borehole strain or GPS.
The best-anchored instrument (NWSE extension) showed long-term accumulation from 1985 through 2001, interrupted by a large postseismic signal from
the 1992 Landers earthquake and much smaller ones from the 1999 Hector Mine
and 2010 El-Mayor/Cucapah shocks. In 2001 the strain rate reversed, only to
go to nearly zero after the 2005 Anza earthquake (magnitude 5.2). After the
El-Mayor/Cucupah earthquake, rapid but decaying strain changes were evident
on all instruments, though within a few hours these were replaced by strain
changes similar to ones observed after the 2005 Anza event; modeling suggests
that aseismic slip at 10-15 km depth and about 10 km NW of the 2005 epicenter
could explain the signals seen, which were not observed at other locations. In late
2010 the strain rates changed from their previous behavior: the NWSE strainmeter went into rapid compression and the EW one changed from slower extension to slow compression, both by amounts of 0.25 microstrain/yr. This behavior
lasted until October 2011, and is consistent with slip with a moment magnitude
equivalent to a 5.8 earthquake, on the San Jacinto fault in a region close to the
hypocenter of the 2005 Anza earthquake: probably too small to detect with the
existing GPS network.
[email protected]
Wave Propagation
Signatures of Ocean-Bottom Topography and Seawater Layer Effects on
Waveforms Recorded at the Ocean-Bottom Floor and Teleseismic Distances
from Offshore Earthquakes
Pitarka, A., Lawrence Livermore National Laboratory, Livermore, CA,
[email protected]; GRAVES, R. W., US Geological Survey, Pasadena, CA;
HELMBERGER, D. V., Caltech, Pasadena, CA.
The analysis and modeling of ground motion waveforms recorded at the oceanbottom floor and teleseismic distances from offshore earthquakes requires a good
understanding of seawater layer and ocean-bottom topography effects. Recent
subduction zone earthquakes have provided excellent ground motion data that
can be used to guide the analysis.
We study the effects of seawater and a solid-fluid boundary with complex
geometry by simulating ground motions from shallow double-couple point
sources using a 3D subduction zone seismic velocity structure. We calculate three
component synthetic seismograms along linear arrays located on the ocean-bottom floor and beneath the source. By progressively including geological features
and a water layer into the 3D model we are able to analyze separately their effects
on wave propagation as well as contributions to down-going waves recorded at
teleseismic distances.
We use a 3D staggered grid finite-difference method (Graves, 1996; Pitarka,
1999) to simulate wave propagation in heterogeneous structures with solid-liquid
boundaries based on the scheme proposed by Okamoto and Takenaka (2005). In
this scheme the continuity of normal stress and discontinuity of the shear stress
across the solid-air and solid-fluid boundaries is implicitly satisfied using finite
difference operators of second order accuracy.
Our preliminary simulation results suggest that coupling between oceanbottom topography and seawater has a significant effect on both P and S coda
waves. Water-layer reverberations of P waves are visible in the simulated oceanbottom seismograms. Additionally, reverberations of the water phase pwP
(reflected from the air-water interface), the depth phase pP (reflected from the
water-crust interface), and P-S converted waves generated at the water-crust
interface form a ringing pattern in the coda of the down-going P wave, which is
observed at teleseismic distances.
Dynamic Ruptures with Off-Fault Visco-Elastic Brittle Damage
Xu, S., University of Southern California, Los Angeles, CA, [email protected];
BEN-ZION, Y., University of Southern California, Los Angeles, CA, benzion@
usc.edu; AMPUERO, J. P., California Institute of Technology, Pasadena, CA,
[email protected]; LYAKHOVSKY, V., Geological Survey of Israel,
Jerusalem, Israel, [email protected]
egmdpri01.dpri.kyoto-u.ac.jp; Iwaki, A., NIED, Tsukuba, Japan, iwaki@bosai.
go.jp; Mariotti, C., CEA, Bruyères-Le-Chatel, France, [email protected].
The high stress concentration at the front of a dynamic rupture in the brittle
seismogenic zone is expected to produce brittle rock damage (reduction of elastic
moduli) in the material surrounding the main fault plane. Off-fault yielding and
energy absorption in the damage process is expected to reduce the amplitude of
the ground motion. However, the reduced elastic moduli in the damaged zone
(observed around fault) can amplify locally the motion and create a waveguide
that may allow the motion to propagate with little geometric attenuation. In
addition, asymmetric damage across the fault generated by in-plane rupture may
produce dynamically bimaterial interfaces that can influence the frictional dissipation, the radiation efficiency, and the rupture mode.
A number of previous studies incorporated plastic yielding in simulations
of dynamic rupture (e.g., Andrews, 2005; Ben-Zion and Shi, 2005; Templeton
and Rice, 2008; Ma and Andrews 2010; Xu et al., 2012) while keeping the elastic moduli unchanged. In this work we examine the dynamics of earthquake
ruptures on a frictional fault in a model that includes a continuum visco-elastic
brittle damage rheology for the evolution of elastic moduli above a yielding level
(e.g., Lyakhovsky et al., JMPS, 2011). We perform 2D numerical simulations of
in-plane ruptures using the Spectral Element Method (SEM2DPACK-2.3.6,
http://sourceforge.net/projects/sem2d/) to study how the functional form and
parameters of the friction law, damage rheology, background stress and possible
pre-existing elasticity contrast across the fault control various properties of the
off-fault damage zone, rupture mode and velocity, slip rate on the fault, components of the energy balance, and properties of the generated ground motion. The
results are compared to analogous simulations using a visco-plastic rheology.
The capability of numerical methods to predict earthquake ground motion
is investigated through the ongoing Euroseistest Verification and Validation
Project. The project focuses on the Mygdonian basin (Greece) which has been
a subject of extensive geophysical and geotechnical investigations for more than
two decades.
A detailed 3D model of the basin (5 km wide, 15 km long, with maximum
sediment thickness 400 m and minimum S-wave velocity 200 m/s) as well as
recordings of local earthquakes by the Euroseistest array provide a reasonable
basis for the verification and validation of the numerical methods.
Here, we present the results of the verification phase of the project for 3D
numerical methods.
Numerical-modeling teams from Europe, Japan and USA employ the
finite-difference, finite-element, global pseudospectral, spectral-element, discrete-element and discontinuous Galerkin methods.
The problem configurations include elastic and viscoelastic rheologies,
basin models built from smooth velocity gradients or composed of three homogeneous layers with varying thicknesses, one hypothetical event and six local events
with magnitude between 3 and 5.
Numerical predictions for frequencies up to 4 Hz are compared using quantitative time-frequency envelope and phase goodness-of-fit criteria computed at
288 receivers.
The agreement between numerical predictions is shown to depend on the
ability of each method to implement the free-surface and absorbing boundary
conditions, large Vp/Vs ratios (up to 7.5 in shallow layers), strong contrasts at the
sediment-bedrock interface, in particular at basin edges with non-vertical slopes,
and material interfaces in sediments.
Numerical simulations for a set of five additional 3D canonical configurations have been also performed in order to better understand the accuracy of the
applied methods and their capability to account for the particular ingredients in
3D numerical simulations of earthquake ground motion in sedimentary basins.
PyLith: A Finite-Element Code for Modeling Quasi-Static and Dynamic Crustal
Deformation
AAGAARD, B. T., U.S. Geological Survey, Menlo Park, CA; WILLIAMS, C.
A., GNS Science, Lower Hutt, New Zealand; KNEPLEY, M. G., University of
Chicago, Chicago, IL.
We have developed open-source finite-element software for 2-D and 3-D dynamic
and quasi-static modeling of crustal deformation. This software, PyLith (current
release is version 1.6) can be used for quasi-static viscoelastic modeling, dynamic
spontaneous rupture and/or ground-motion modeling. Unstructured and structured finite-element discretizations allow for spatial scales ranging from tens
of meters to hundreds of kilometers with temporal scales in dynamic problems
ranging from milliseconds to minutes and temporal scales in quasi-static problems ranging from minutes to thousands of years. PyLith development is part of
the NSF funded Computational Infrastructure for Geodynamics (CIG) and the
software runs on a wide variety of platforms (laptops, workstations, and Beowulf
clusters). Binaries (Linux, Darwin, and Windows systems) and source code are
available from geodynamics.org. PyLith uses a suite of general, parallel, graph data
structures called Sieve for storing and manipulating finite-element meshes. This
permits use of a variety of 2-D and 3-D cell types including triangles, quadrilaterals, hexahedra, and tetrahedra.
Current PyLith features include prescribed fault ruptures with multiple
earthquakes and aseismic creep, spontaneous fault ruptures with a variety of fault
constitutive models, time-dependent Dirichlet and Neumann boundary conditions, absorbing boundary conditions, time-dependent point forces, and gravitational body forces. PyLith supports infinitesimal and small strain formulations
for linear elastic rheologies, linear and generalized Maxwell viscoelastic rheologies, power-law viscoelastic rheologies, and Drucker-Prager elastoplastic rheologies. Current software development focuses on coupling quasi-static and dynamic
simulations to resolve multi-scale deformation across the entire seismic cycle and
the coupling of elasticity to heat and/or fluid flow.
Verification of 3D Numerical Modeling of Earthquake Ground Motion in the
Mygdonian Basin, Greece
Chaljub, E., ISTerre, Grenoble, France, [email protected];
MAUFROY, E., ISTerre, Grenoble, France, [email protected];
HOLLENDER, F., CEA, Cadarache, France, [email protected]; BARD,
P. Y., ISTerre, Grenoble, France, [email protected]; KRISTEK,
J., Comenius University, Bratislava, Slovakia, [email protected]; MOCZO,
P., Comenius University, Bratislava, Slovakia, [email protected]; KLIN, P.,
OGS, Trieste, Italy, [email protected]; Priolo, E., OGS, Trieste, Italy, epriolo@
inogs.it; Etienne, V., Geoazur, Nice, France, [email protected].
fr; Bielak, J., CMU, Pittsburgh, USA, [email protected]; Aoi, S., NIED,
Tsukuba, Japan, [email protected]; Iwata, T., DPRI, Kyoto, Japan, iwata@
3D Finite-Difference Modeling of Tremor along the San Andreas Fault near
Cholame, California
Gottschaemmer, E., Karlsruhe Institute of Technology, Karlsruhe,
Germany, [email protected]; HARRINGTON, R. M., Karlsruhe
Institute of Technology, Karlsruhe, Germany, [email protected];
COCHRAN, E. S., U.S. Geological Survey, Pasadena, CA, escochran@gmail.
com
We use a kinematic model to simulate tremor on a vertical, strike-slip fault.
Models are constrained by tremor observations from a temporary 13-station
broadband array deployed along the San Andreas fault near Cholame, California.
Recent observations of both triggered and ambient tremor suggest that tremor
results from simple shear-failure events. Tremor episodes on the San Andreas
fault near Parkfield are thought to comprise clusters of individual events with
frequencies between 2-8 Hz. Such low frequency earthquakes (LFEs) are thought
to occur at depths where the frictional properties of the fault surface are primarily slip-strengthening with embedded patches of slip weakening material that
slip seismically when the surrounding fault creeps in a slow-slip event. We model
80 seconds of tremor signals kinematically for frequencies up to 8 Hz using a
staggered-grid finite-difference scheme with a grid spacing of 50 m. We solve the
elastic equations of motion using the 3D P-wave-velocity model from Thurber
et al. (2006), assuming a Poisson solid. During the simulated time-interval of
80 seconds, different source regions on the San Andreas Fault are assumed to
be active. Each source region (patch cloud) comprises small individual patches
(50m by 50 m each) breaking with 0.15–0.25 seconds delay between neighboring patches. Simultaneous breaking of different patch clouds and re-rupturing
of patches is possible. The patches are located at a depth of ~ 25 km, and radiate
energy with center frequencies around 4 Hz. Our simulations indicate that multiple seismically slipping patches in an aseismic region recreate tremor characteristics. This kinematic model is the first step to simulating the size, distribution,
and behavior of tremor along strike-slip faults. To further understand the tremor
source process, future work will use a dynamic model that incorporates rate-state
friction and include a mosaic of slip-weakening and slip-strengthening patches
across the fault.
Initialization of Spontaneous Rupture Propagation in a Dynamic Model with
Linear Slip-Weakening Friction—A Parametric Study
Galis, M., Comenius University Bratislava, Bratislava, Slovakia, martin.galis@
fmph.uniba.sk; PELTIES, C., LMU Munich, Munich, Germany, pelties@
geophysik.uni-muenchen.de; KRISTEK, J., Comenius University Bratislava,
Bratislava, Slovakia, [email protected]; MOCZO, P., Comenius University
Bratislava, Bratislava, Slovakia, [email protected]
Artificial procedures are used to initiate spontaneous rupture on faults with the
linear slip-weakening (LSW) friction law. Probably the most frequent technique
is the stress asperity. It is important to minimize effects of the artificial initialization on the phase of the spontaneous rupture propagation. The effects may
strongly depend on the geometry and size of the asperity, spatial distribution of
the stress in and around the asperity, and a maximum stress-overshoot value.
A square initialization zone with the stress discontinuously falling down
at the asperity border to the level of the initial stress has been frequently applied
(e.g., in the SCEC verification exercise). Galis et al. (2010) and Bizzarri (2010)
independently introduced the elliptical asperity with a smooth spatial stress distribution in and around the asperity. In both papers the width of smoothing/
tapering zone was only ad-hoc defined.
Numerical simulations indicate that the ADER-DG method can account
for a discontinuous-stress initialization more accurately than a FE method.
Considering the ADER-DG solution as a reference we performed numerical
simulations in order to define the width of the smoothing/tapering zone to be
used in the FE and FD-FE hybrid methods for spontaneous rupture propagation.
We considered different sizes of initialization zone, different shapes of the
initialization zone (square, circle, ellipse), different spatial distributions of stress
(smooth, discontinuous), and different stress-overshoot values to investigate conditions of the spontaneous rupture propagation.
We compared our numerical results with the 2D and 3D estimates by
Andrews (1976a, b), Day (1982), Campillo & Ionescu (1997), Favreau at al.
(1999) and Uenishi & Rice (2003, 2004).
Results of our study may help modelers to better setup the initialization
zone in order to avoid, e.g., a too large initialization zone and reduce numerical
artifacts.
Dynamic Rupture Process and Deformation of Sea Floor Associated with the
Mw 9.0 Tohoku Oki Earthquake
Tamura, S., University of Tokyo, Tokyo, Japan, [email protected];
IDE, S., University of Tokyo, Tokyo, Japan, [email protected]; MA, S.,
San Diego State University, San Diego, CA, [email protected]
The Mw 9.0 Tohoku-Oki earthquake hit the northeast Japan on 11 March
2011 generating huge strong motion and tsunami and the area with the largest
slip amount was located near the Japan Trench. Exploring the dynamics of the
Tohoku-Oki earthquake is important for understanding physics of mega-thrust
earthquakes and estimating the probability of rupture extensions or tsunami
geneses to prevent future disasters. We model a shallow dipping mega-thrust
earthquake on a bi-material interface with a free surface by using a 3D finite element method to solve elastodynamic equations and a slip-weakening friction law
on the fault plane. As a preliminary study, we simulate in the relatively simple
situations with a planar fault and a homogeneous prestress. Reflected body waves
from the free surface strongly affect the normal and shear stress on the fault, and
both the normal and the shear stress decrease just after the rupture reaches the
trench. The slip on the fault reflects at the trench and rapidly propagates downward at the P-wave velocity. This downward reflected slip is consistent with the
west-northwest directivity of the Tohoku-Oki earthquake. Final slip distribution
with largest slip at the trench is also consistent with some kinematic slip models.
Deformation style of the free surface changes depending on the dip angle and
material contrast. The amount of vertical motion of the hanging wall is larger
for the case of more compliant hanging wall and much larger than that of the
footwall. Our simulations suggest that the huge tsunami is generated due to large
amount of the surface deformation which is enhanced in the wedge part of the
compliant hanging wall.
Inclusion of Topographic Effects in Large Scale Ground Motion Simulations
Using an Octree/Quadtree Mesh Based Finite Element Approach
RAMIREZ-GUZMAN, L., Instituto de Ingenieria UNAM, Mexico City,
Mexico, [email protected]
An approach to include topographic effects in large scale computations is presented and analyzed. The use of octree/quadtree based semi-structured meshes
and finite elements formulations (e.g. Tu et al., 2006; Burstedde et al., 2011) is a
proven alternative to more traditional approaches, such as the Finite Difference
method, in the solution of wave propagation problems. Nevertheless, the computations are typically performed without considering topographic effects. In this
research, the topography is first approximated by the stair-case method (Pitarka
and Irikura, 1996; Koketsu et al., 2004) by removing elements from a rectangular
prism domain. The mesh generation and removal is constrained by the Digital
Elevation Model of the true topography and its gradient. In order to improve
the accuracy and honor the free traction boundary condition on the surface,
corrective forces are applied to the elements at each time step with satisfactory
results. Four examples are compared with semi-analytical and Indirect Boundary
Element method solutions in 2D and 3D configurations.
Dynamic Response and Ground-Motion Effects of Building Clusters During
Large Magnitude Earthquakes
Isbiliroglu, Y. D., Carnegie Mellon University, Pittsburgh, PA, yisbilir@
andrew.cmu.edu; TABORDA, R., Carnegie Mellon University, Pittsburgh, PA,
[email protected]; BIELAK, J., Carnegie Mellon University, Pittsburgh, PA,
[email protected]
The objective of this this study is to analyze the response of building clusters
during earthquakes, the effect that they have on the ground motion, and how
individual buildings interact with the surrounding soil and with each other.
We conduct a series of large-scale, physics-based simulations that synthesize the
earthquake source and the response of entire building inventories. The configuration of the clusters, defined by the total number of buildings, their number of
stories, dynamic properties, and spatial distribution and separation, is varied for
each simulation. In order to perform these simulations efficiently while recurrently modifying these characteristics without redoing the entire simulation
every time, we use the Domain Reduction Method (DRM). The DRM is a modular two-step finite-element methodology for modeling wave propagation problems in regions with localized features. It allows one to store and reuse the background motion excitation of sub-domains without loss of information. Buildings
are included in the second step of the DRM. Each building is represented by
a block model composed of additional finite-elements in full contact with the
ground. These models are adjusted to emulate the general geometric and dynamic
properties of real buildings. We conduct our study in the greater Los Angeles
basin, using the main shock of the 1994 Northridge earthquake for frequencies
up to 2Hz. In the first step of the DRM we use a domain of 85km × 85km ×
42.5km. Then, for the second step, we use a smaller sub-domain of 12 km × 6
km × 1.125 km, with the buildings. The results suggest that site-city interaction
effects are more prominent for building clusters in soft-soil areas. These effects
are manifested in changes in the amplitude of the ground motion and dynamic
response of the buildings. The simulations are done using Hercules, the parallel
octree-based finite-element earthquake simulator developed by the Quake Group
at Carnegie Mellon University.
Dynamic Rupture along the San Gorgonio Pass Section of the San Andreas
Fault
Shi, Z., San Diego State University, San Diego, CA, [email protected];
MA, S., San Diego State University, San Diego, CA, [email protected];
DAY, S. M., San Diego State University, San Diego, CA, [email protected];
ELY, G. P., Argonne National Laboratory, Argonne, IL, [email protected]
We perform 3D numerical simulations of dynamic rupture along the San
Gorgonio Pass section of the San Andreas Fault (SAF). As revealed by geological
and geophysical studies, the fault geometry along this section of SAF is rather
complicated with considerable variations of strike direction and dip angle. Recent
3D simulations of dynamic rupture along rough faults (e.g., Shi and Day [2012])
showed that fault geometry has fundamental impacts on properties of dynamic
rupture and patterns of resultant ground motion. Nevertheless, the role of fault
geometry on earthquake propagation was not physically accounted for in the previous ShakeOut simulations of the Southern California region. In this study, we
investigate the effect of complex fault geometry of the San Gorgonio Pass section of SAF on earthquake rupture propagation and associated wave propagation.
For our 3D numerical simulation, the employed fault geometry for this section
of SAF is based on the most recent SCEC Community Fault Model (CFM version 4.0) and the employed velocity structure is based on the most recent SCEC
Community Velocity Model (CVM-H version 11.9.0). A major issue we attempt
to address is under what kind of conditions the earthquake rupture can break
through the geometrically complicated San Gorgonio Pass section. To that end,
we will focus on the effects of rupture propagation direction, stress configuration,
plasticity, fault friction and etc. The current study will contribute to the better
understanding of physically plausible earthquake scenarios and more importantly the potential seismic hazard in the greater Los Angeles area.
Improving Resolution of Finite Fault Modeling, Tohoku-Oki Earthquake
Wei, S. J., Caltech, Pasadena, CA, [email protected]; GRAVES, R., USGS,
Pasadena, CA, [email protected]; LI, D. Z., Caltech, Pasadena, CA, dli@
caltech.edu; HELMBERGER, D., Caltech, Pasadena, CA, [email protected].
edu
Since most of the finite fault inversions use 1D velocity models, the effect produced by 2D and 3D structure has not been widely investigated. The recent well
recorded Mw9.0 Tohoku-Oki earthquake provides a unique opportunity to test
such effects at various frequency bands. Based on our previous work [Wei et al.,
2012], we have generated 3D synthetics at strong motion stations using JIVSM
(Japan Integrated Velocity Structure Model) and a velocity model from NIED. A
revised source time function has been used to enhance the high frequency radiation. These synthetic data is then inverted with a 1D layered velocity model. The
inversions indicate that when the soft rock stations are used, the inversion results
will be easily biased as demonstrated with checkerboard testing. However, the
1D velocity model does a pretty good job of recovering the test models at the hard
rock stations. Thus, it is essential to identify those sweet paths in finite fault inversion. Based on these sweet path stations, a source time function with enhanced
high frequency energy is used for inverting the real data, which improves the fitting to the higher frequency waveforms compared with the traditional source
time functions, and resolves the deeper asperities associated with the TohokuOki Earthquake.
High Resolution Identification of Shear and Torsional Wave Velocity Profiles
of Buildings—Methodology and Application to Millikan Library
Rahmani, M. T., U. So. California, Los Angeles, CA, [email protected];
TODOROVSKA, M. I., U. So. California, Los Angeles, CA, [email protected]
Two new algorithms for structural system identification of buildings from
recorded seismic response are presented, for use in structural health monitoring
(SHM) systems, and their application to identification of NS, EW and torsional
responses of Millikan Library in Pasadena [1]. Both are based on a wave propagation model of a building (layered shear beam or torsional shaft), and identify its
velocity profile in a frequency band. One performs nonlinear LSQ fit of pulses in
the impulse response functions, and the other one iterative time shift matching.
These algorithms reduce markedly the identification error of the direct algorithm
[2], especially for high spatial resolution models (such that resolve the individual
floors). Good accuracy of identification of high resolution models, which is most
challenging, is necessary to be able to detect efficiently local damage and smaller
damage. The main advantages of the wave travel time methods for SHM over the
modal methods are their insensitivity to the effects of soil-structure interaction
and local nature. The results for Millikan library show that the NS response is
predominantly in shear and nondispersive for frequencies up to about 15 Hz. For
the EW response, this is true for frequencies up to about 7.5 Hz, and dispersive
behavior was detected for higher frequencies. The torsional response is nondispersive, for frequencies up to about 15-20 Hz. The structural fixed base frequencies
are also identified from the transfer function of the fitted model.
[1] Rahmani MT, Todorovska MI (2011) High resolution 1D system identification of buildings using impulse responses: methodology and application to
Millikan Library, Soil Dynamics and Earthquake Engrg, Jose Roësset Special
Issue, submitted.
[2] Todorovska MI, Rahmani MT (2011) System identification of buildings using wave travel time analysis and layered shear beam models—spatial resolution and accuracy, Struct. Control Health Monit., accepted.
Generating of Rotational and Shear Seismic Waves by Anthropogenic
Sources
Malek, J., Institute of Rock Structure and Mechanics ASCR, Prague, Czech
Republic, [email protected]; BROKESOVA, J., Charles University, Prague,
Czech Republic, [email protected]
Rotational seismic motions can be generated together with S waves by anthropogenic sources. However, traditional sources of seismic energy as shots or vibrators
radiate mainly P waves. Examples of rotational records near quarry blasts are presented and rotation to translation ratio (RTR) is calculated. Even if conversion
P to S near the source is strong, these sources are not convenient for rotational
seismic prospection, and therefore a new prototype of mechanical generator of
pure transverse S-wave and seismic rotational motions has been developed. The
generator is composed from a fixed part anchored to the ground, and the mobile
(rotary) part. After being activated, rotary part is stopped instantaneously by
the braking mechanism. This instantaneous stopping radiates high-frequency S
waves into the rock massif. This source is represented by equivalent forces known
as center of rotation. The generator has relatively small dimensions and weight,
which makes it easy to move it in the field. It is designed to be used for sequentially repeated experiments, so that essentially the same pulse of rotational seismic waves is generated. The signals from repeated measurements are combined
during data processing in order to achieve high sensitivity by suppressing noise
via stacking. Non-linear combination of signals (so called GAS method) can
be applied for this purpose. The generator is intended for use in a measuring set
together with rotational sensor system Rotaphone. The example of application
of the device demonstrates rotation rate components produced by the generator
pulses and their propagation through shallow geological structure beneath the
generator. The results agree with theoretical radiation pattern for a center of rotation. The RTR is much higher than for traditional anthropogenic sources.
Forensic Analysis of the Effects of the 1918 Puerto Rico Earthquake
Laforge, R., Fugro Consultants, Inc., Lakewood, CO, [email protected];
MCCANN, W., Earth Scientific Consultants, Westminster, CO.
The last major earthquake to affect Puerto Rico, Ms 7.2, occurred in 1918 and was
accompanied by a destructive tsunami. The most severe damage was sustained
in the towns of Mayaguez, Aguadilla, Aguada, and Anasco. Fatalities numbered
116 and there was substantial infrastructure damage. The 1918 Congressional
Report by Reid and Taber, as well as the Special Earthquake Commission reports
housed in the San Juan Archives, provide an unparalleled examination of building performance, and earthquake and tsunami related damage for Puerto Rico.
The detailed building damage reports, other document and photographic images
were identified, copied digitally, complied, and analyzed. These documents had
lain unexamined in the Archive since the early 1920’s. The records included official correspondence, damage reports and monetary repair estimates of publically
owned buildings and other infrastructure, and records of repair transactions. Of
particular interest was a program whereby citizens could petition the government
for the cost of repairing or replacing damaged or destroyed homes. This resulted
in damage reports at specific addresses, most of which are locatable today. These
provided detailed descriptions of structural damage and tsunami runup heights.
This information will help calibrate tsunami generation and ground shaking
(ShakeMap) models for a repeat of such an event. By cross-referencing petitions with the summary program records, it was determined that all 339 of the
Mayaguez, 89 of the 275 Aguadilla, and 139 of the 171 Anasco, and none of the
86 Aguada petitions were found in the Archive. These were carefully read, translated into English, and entered into spreadsheets. An analysis of the Aguadilla
petitions, in conjunction with Lidar elevation data, permits a mapping of the
maximum tsunami runup in that town.
Report on Progress at the Center for Engineering Strong Motion Data
Haddadi, H. R., California Geological Survey, Sacramento, CA, hhaddadi@
consrv.ca.gov; STEPHENS, C. D., U.S. Geological Survey, Menlo Park,
CA, [email protected]; SHAKAL, A. F., California Geological Survey,
Sacramento, CA, [email protected]; SAVAGE, W., U.S. Geological Survey,
Menlo Park, CA, [email protected]; HUANG, M., California Geological
Survey, Sacramento, CA, [email protected]; LEITH, W., U.S. Geological
Survey, Reston, VA, [email protected]; PARRISH, J. G., California Geological
Survey, Sacramento, CA, [email protected]
Strong motion data from the United States and other seismically active countries are served to seismologists, engineers, and public safety authorities through
the Center for Engineering Strong Motion Data (CESMD) at www.strongmotioncenter.org. In 2011, the CESMD staff at the US Geological Survey and the
California Geological Survey, in cooperation with colleagues at international
strong motion seismic networks, has disseminated strong motion data from
major earthquakes in Japan, New Zealand, Turkey, and the U.S.
The CESMD now automatically posts strong motion data from an increasing number of seismic stations in California within minutes following an earthquake as an Internet Quick Report, The next phase will be to extend this to the
rest of the US. These reports have been used by public safety authorities and engineers for rapid response to earthquakes.
Transfer and upgrade of the COSMOS Virtual Data Center (VDC) to
the CESMD is nearing completion. The operational and maintenance responsibilities for the VDC, developed at the UC Santa Barbara, are being assumed by
the CESMD. The VDC Tagged Format (VTF) has been adopted as an internal
standard for converting strong motion data to facilitate uploading data into the
VDC database. The revised uploading process makes it possible to upload groups
of records automatically without detailed human interaction, a major improvement of the VDC upload operation.
In response to requests from seismologists and engineers, the CESMD now
provides strong motion records from lower magnitude and smaller amplitude
records in California for use in developing ground motion prediction equations
in areas with less frequent earthquakes, such as the Central and Eastern US. The
CESMD benefits from cooperation with COSMOS, which assists in gaining
access to strong motion data from other countries, and also provides input on the
development of user applications.
Excitation of Seismic Signals in Basaltic Fissure Eruptions
Dunham, E. M., Stanford University, Stanford, CA, [email protected];
LIPOVSKY, B. P., Stanford University, Stanford, CA, [email protected];
SOTO, E. S., Stanford University, Stanford, CA, [email protected]
We have developed a code that couples flow of a viscous, compressible magma
through a deformable volcanic conduit with plane strain elastodynamic response
of the surrounding wall rock. Magma is described by a nonlinear equation of state
that accounts for compressibility changes caused by gas exsolution. We apply this
code to basaltic fissure eruptions, first finding a steady state solution featuring a
depth-dependent dike width determined self-consistently with the distribution
of excess pressure. Self-excited oscillations from flow instabilities do not arise in
our model, leading us to investigate the role of external forcing as a mechanism
for volcanic tremor. We therefore study the ability of various types of perturbations, in either the fluid or solid part of the system, to excite seismic and acoustic
waves. Fluid-solid coupling is most pronounced below the exsolution depth, so
perturbations within the conduit (e.g., bursting of gas bubbles) efficiently excite
crack waves along the conduit walls that convert to seismic waves at both the
exsolution surface and the edge of the dike. In contrast, fluid perturbations in
the upper part of the conduit primarily excite acoustic waves within the highly
compressible magma, with minimal coupling to the solid. We also investigate the
system response to moment tensor sources (e.g., earthquakes) in the conduit wall
rock. Our aim is to quantify the amplitude and type of sustained perturbations
required to explain observed levels of continuous volcanic tremor in these systems.
Insight into Eruptive Cyclic Behavior of Mount Etna during 2011: Geophysical
and Geochemical Constraints
Coltelli, M., INGV, Catania, Italy, [email protected]; PATANE, D., INGV,
Catania, Italy, [email protected]; AIUPPA, A., CFTA, Università di Palermo,
Palermo, Italy; ALIOTTA, M., INGV, Catania, Italy; ALOISI, M., INGV,
Catania, Italy; BEHNCKE, B., INGV, Catania, Italy; CANNATA, A., INGV,
Catania, Italy, [email protected]; Cannavò, F., INGV, Catania, Italy; Di
Grazia, G., INGV, Catania; Gambino, S., INGV, Catania; Gurrieri,
S., INGV, Catania; Mattia, M., INGV, Catania; Montalto, P., INGV,
Catania; Prestifilippo, M., INGV, Catania; Puglisi, G., INGV, Catania;
Salerno, G., INGV, Catania; Scandurra, D., INGV, Catania.
The period 2009–2011 at Mt. Etna was characterized by a gradual intensification of volcanic activity. In particular, after the end of the 2008-2009 eruption a
resting phase took place and lasted up to the first months of 2010. In 2010 several
episodes of minor explosions, taking place at the summit craters and accompanied by mild ash emissions, testified the ongoing recharging phase started at the
end of 2009 suggested by ground deformation GPS data. During 2011 volcanic
activity culminated with a series of 18 lava fountains, occurring at the new SouthEast crater. A multiparametric approach, consisting in collecting and comparing
volcanological, geophysical and geochemical data, was applied to investigate the
volcano dynamics during 2009-2011. In particular, temporal and/or spatial variations of volcanic tremor, long period events, very long period events, soil deformation (GPS and tiltmeter data), SO2 flux, SO2/CO2 ratio were studied. Further,
on the basis of such data FEM models were developed to follow the evolution of
intrusive and eruptive processes. In conclusion, new insights into the geometry of
the magma plumbing system feeding the fountaining activities, as well as into the
processes of magma discharge and recharge, were obtained.
Multi-Year Spatiotemporal Evolution of Seismicity in Hawaii from HighPrecision Relocations
Matoza, R. S., UC San Diego, La Jolla, CA, [email protected]; SHEARER,
P. M., UC San Diego, La Jolla, CA, [email protected]; LIN, G., University
of Miami, Miami, FL, [email protected]; WOLFE, C. J., University of
Hawaii at Manoa, Honolulu, HI, [email protected]; OKUBO, P. G.,
Hawaiian Volcano Observatory, US Geological Survey, Hawaii National Park,
HI, [email protected]
The Island of Hawaii is one of the most active volcanic regions in the world, and a
natural laboratory for studying seismicity and deformation associated with volcanic and tectonic processes. We present preliminary results from a comprehensive
re-analysis of waveforms recorded by the USGS Hawaiian Volcano Observatory
(HVO) seismic network from 1992 to 2009. The data represent more than 130,
000 seismic events at a range of depths, including crustal seismicity at Kilauea
volcano and its rift zones, seismicity along crustal detachment faults separating volcanic pile and old oceanic crust at ~9 km below Hawaii’s south and west
flanks, events along inferred magma conduits beneath active volcanoes, events
along a mantle fault zone near 30 km depth beneath Kilauea, and swarms of deep
long-period mantle earthquakes near 40 km depth beneath Mauna Loa.
Our goal is to produce a comprehensive and systematically processed
multi-year catalog of relocated seismicity for all of Hawaii Island using waveform
cross correlation and cluster analysis. We have converted all waveform data to
a standard format to facilitate fast and systematic analysis, and have performed
high-precision relative relocation, using methods similar to those developed for
Southern California seismicity [Lin et al., 2007]. The 17 years of relocated seismicity exhibits a dramatic sharpening of earthquake clustering along faults and
magmatic features, consistent with previous studies that have focused on specific
regions of Hawaii. We present the results of our relocation to date, together with
preliminary interpretations.
Lin, G., P. Shearer and E. Hauksson (2007), Applying a three-dimensional
velocity model, waveform cross correlation, and cluster analysis to locate southern California seismicity from 1981 to 2005, J. Geophys. Res., 112, B12309,
doi:10.1029/2007JB004986
Measurements of Volcanic Tremor at Kilauea from a Temporary Seismic
Deployment
Greenwood, R. N., Cal Poly Pomona, Pomona, CA, rngreenwood@
csupomona.edu; POLET, J., Cal Poly Pomona, Pomona, CA, jpolet@csupomona.
edu; THELEN, W. A., Hawaiian Volcano Observatory USGS, Hawaii National
Park, HI, [email protected]
In June 2011, we deployed three broadband seismometers on and near Kilauea
volcano on the Big Island of Hawaii as a pilot project in geophysical undergraduate education at Cal Poly Pomona. During the deployment period of one week,
the seismometers recorded numerous seismic events such as volcanic tremors, a
landslide (crater wall collapse), and earthquakes. The seismic data provides information about all these volcanic and tectonic processes at Kilauea volcano and
their interrelationships. A more complete picture and interpretation of these
seismic processes in a framework of overall volcanic behavior and activity may
be achieved through the correlation with additional data sets, such as lava lake
height and tilt, from the Hawaiian Volcano Observatory (HVO) of the United
States Geological Survey (USGS).
Analysis of the seismic data shows numerous earthquakes that are included
in the HVO earthquake catalog, as well as some that are not, along with several
episodes of strong volcanic tremor. The Uwekakahuna station, located closest to
Kilauea crater and the lava lake believed to be the source of this signal, shows the
best evidence for tremor, displaying greater amplitude ground motion than the
other two stations. The horizontal components of the seismogram show higher
amplitude values for the tremor than the vertical component. The tremor tends to
be active for long periods of each day with short pauses. Most tilt events appear to
be accompanied by an increase in summit tremor during the deflation phase. The
three major episodes of tremor displayed similar sustained amplitudes of ground
motion. The frequency range of the tremor ground motion was consistent at 6-11
Hz. We will present the results of a temporal correlation of the seismic tremor
signal with the tilt data from Kilauea, as well as measurements of lava lake height.
The August and October 2008 Earthquake Swarms on the Explorer/Pacific
Plate Boundary
Czoski, P. A., New Mexico Institute of Mining and Technology, Socorro,
NM, [email protected]; TREHU, A. M., Oregon State University,
Corvallis, OR, [email protected]; WILLIAMS, M. C., Oregon State
University, Corvallis, OR, [email protected]; DZIAK, R. P.,
NOAA, Newport, OR, [email protected]; EMBLEY, R. W., NOAA,
Newport, OR, [email protected]
In August and October of 2008, earthquake swarms occurred on the Explorer/
Pacific plate boundary. The August swarm lasted for ~4 days. 75 earthquakes
up to magnitude 5.9 were reported by the Canadian National Seismograph
Nework (CNSN). The U.S. Navy’s Sound Surveillance System (SOSUS) hydrophones reported 148 events. T-phases from over 250 events were recorded on the
Central Oregon Locked Zone Array (COLZA), a temporary array of 15 ocean
bottom seismometers (OBS) and hydrophones. The October swarm lasted about
2 days with only one reported CNSN M4.4 earthquake and 119 events reported
by SOSUS. Many T-phases from this swarm were also observed by COLZA.
T-phases are generated by earthquakes and converted to acoustic energy at the
seafloor. We used the CNSN magnitudes to calibrate an empirical magnitude
scale for maximum amplitudes handpicked from the COLZA T-phase observations. This enabled us to lower the magnitude threshold to 2.8. A b-value of
0.78 was obtained for the August swarm, suggesting that it may be driven by tectonic event rather then magmatic processes. Focal mechanisms reported by the
Harvard CMT catalog for 3 of the largest events show strike-slip motion, supporting a tectonic origin. The reported SOSUS hypocenter locations indicate a
linear NE/SW trend west of and parallel to the Explorer Ridge while the CNSN
locations are offset to the NE by up to 30 km and suggest a northwest/southeast trend in line with the Dellwood-Revere transform fault. We plan to relocate the events using the COLZA T-phase data and cross-correlation techniques
developed to locate seismic tremor to determine whether activity was primarily
focused along the Explorer Ridge axis, along the Dellwood-Revere transform, or
within the plate. This investigation could provide new insight into the evolution
and possible fragmentation of the Explorer plate.
A Comparison of Deformation and Seismicity at the Yellowstone Caldera
during the 2004–2010 Uplift Episode
Puskas, C. M., UNAVCO, Boulder, CO, [email protected]; FARRELL,
J., University of Utah, Salt Lake City, UT, [email protected];
HODGKINSON, K., UNAVCO, Santa Fe, NM, [email protected];
CHANG, W. L., National Central University, Jhongli, Taiwan, wuchang@ncu.
edu.tw; MASSIN, F., University of Utah, Salt Lake City, UT; SMITH, R. B.,
University of Utah, Salt Lake City, UT, [email protected]
The Yellowstone caldera in Yellowstone National Park, WY, experienced a
rapid uplift episode starting in 2004 that culminated in two large earthquake
swarms: the December 2008–January, 2009 Yellowstone Lake swarm and the
January-February 2010 Madison Plateau swarm. Maximum uplift rates of 7
cm/yr were reached in 2005 in the northeast caldera before rates declined and
shifted to subsidence by 2010. We calculate the average annual horizontal strain
rate field across the caldera based on the deformation rates from the permanent
GPS network and from annual GPS campaign measurements conducted from
2007 to 2011. The strain rate fields are then compared with earthquake locations
to determine whether background seismicity correlates with ongoing deformation. Although earthquakes are expected to occur in areas of high strain rates, the
magma reservoir heats the surrounding crust and effectively restricts earthquakes
to depths less than ~5 km, and historically the majority of recorded earthquakes
are located northwest of the caldera. The horizontal strain rate tensors are also
compared with available focal mechanisms to determine how well strain rates
match the stress orientations as deformation changes over time. The strain rates
are converted to moment rates, allowing the parts of the caldera with the greatest
loading rates to be mapped. We also analyze the borehole strainmeter records and
the consistency of the short-term strains (over periods of seconds to days) from
the strainmeters and longer-term strains (periods of months to years) from GPS.
Particular attention is paid to the strain history at the time of the two earthquake
swarms in 2008-2009 and 2010. These were two of the largest swarms recorded in
Yellowstone, and may be associated with the onset of subsidence.
Temporal Variations in Shear-Wave Splitting Associated with Kilauea’s
Summit Eruptive Vent
Johnson, J. H., University of Hawaii at Hilo, Hilo, HI, jessjohnson@usgs.
gov; POLAND, M. P., Hawaiian Volcano Observatory, USGS, Hawaii National
Park, HI, [email protected]; OKUBO, P. G., Hawaiian Volcano Observatory,
USGS, Hawaii National Park, HI, [email protected]
Using shear wave splitting analysis, we have examined seismic anisotropy at
Kilauea Volcano, Hawai’i. We use an automatic shear wave splitting algorithm
to reduce observer bias and to enable the analysis of large volumes of data. The
polarization of the fast shear wave, phi, is thought to be parallel to the maximum
horizontal stress or orientation of strong structures.
Thus far we have analyzed local volcano-tectonic earthquakes from around
Kilauea recorded since August 2008. Our observations of phi at stations more
than 5 km from Kilauea’s summit eruptive vent are strongly aligned NE-SW. This
is consistent with previous studies and suggests that regional stress is stable over
timescales of years. We also observe anisotropy aligned with prominent faults
trending obliquely to the regional direction of NE-SW when the stations are close
( < 1 km) to the fault, indicating highly fractured zones around the faults that
overprint the anisotropy from regionally stress-aligned micro-cracks. Stations
close to the summit eruptive vent display significant temporal variations over timescales of months to years, suggesting that we might be able to measure changes
in the local stress associated with volcanic activity. We observe phi radial to the
summit vent prior to December 2008 and tangential to the summit vent after this
time. These changes occurred during a period of deflation and relatively steady
tremor, and so are not obviously associated with variations in magma movement,
although there was a major collapse of the vent wall and a pause in the eruption
for about a month at this time. The anisotropy variations may therefore reflect
a relaxation of stresses associated with the summit eruptive vent, which formed
in March 2008. Additional comparison with local travel-time tomography and
numerical models will help to elucidate the mechanism of temporal changes in
seismic anisotropy at Kilauea.
Errors or Biases in Event mb: Influence on Stress-Parameters Estimated by
mb vs Mw for Continental Crust Earthquakes
Dewey, J. W., U.S. Geological Survey, Denver, CO, [email protected]; BOORE,
D. M., U.S. Geological Survey, Menlo Park, CA, [email protected]
For shallow-focus, continental crust earthquakes occurring from 1976 to 2010,
with moment-magnitudes Mw(GCMT) of 6 and larger, short-period magnitudes
mb(PDE) are approximately normally distributed with a standard-deviation of
about 0.2 magnitude-units for a given value of Mw. We estimate stress-parameters for these earthquakes on the basis of their (mb, Mw) values, assuming a
stochastic source model whose displacement spectrum has a single corner-frequency and a decrease with amplitude at high-frequency that is proportional
to the square of frequency. If event-to-event dispersion in mb were due entirely
to variation of the true stress-parameter, and taking account of the fact that the
stress-parameter does not scale exactly linearly with (mb, Mw), our theory implies
that the earthquake-to-earthquake variation of the true stress-parameter for the
sample is approximately log-normally distributed and that 95% of the true stressparameters are distributed within a factor of six of the mean stress-parameter
at a given Mw. If, however, the dispersion in (mb, Mw) is partly due to errors/
biases in event mb and Mw, and if these errors/biases are statistically independent
of the true stress-parameter, the estimated event-to-event variation of log(true
stress-parameter) is correspondingly reduced. The important question is the size
of the reduction. For earthquakes of Mw 6 and larger, our procedure for estimating stress-parameter is much more sensitive to errors in event mb than errors in
Mw, and this poster focuses on estimating variances of event mb and developing
formal strategies for identifying situations in which mb is likely to be substantially in error.
The Quantification of Consistent Logic Tree Branch Weights for PSHA
Runge, A., University of Potsdam, Potsdam, Germany, antonia.runge@geo.
uni-potsdam.de; SCHERBAUM, F., University of Potsdam, Potsdam, Germany.
Epistemic uncertainties in PSHA are commonly treated within a logic tree framework in which the branch weights express the degree-of-belief values of an expert
in the corresponding set of models. For the calculation of the distribution of hazard curves, these branch weights are subsequently used as subjective probabilities.
A major challenge for experts in this context is to provide weight estimates which
are logically consistent (in the sense of Kolmogorov’s axioms) and to be aware
of and to deal with the multitude of heuristics and biases which affect human
judgment under uncertainty. For example, people tend to give smaller weights to
each branch of a logic tree the more branches it has, mentally starting with equal
weights for all branches and then adjusting this uniform distribution based on
his/her beliefs about how the branches differ. This effect is known as pruning
bias. A similar unwanted effect, which may even wrongly suggest robustness of
the corresponding hazard estimates, will appear if models are first judged according to a numerical quality measure and the resulting weights are subsequently
normalized to sum up to one.
To address these problems, we have developed interactive graphical tools
for the determination of logic tree branch weights in form of logically consistent subjective probabilities. Instead of determining the set of weights for all the
models in a single step, the computer driven elicitation process is performed as
a sequence of evaluations of relative weights for small subsets of models. From
these, the logic tree weights for the whole model set are determined as a solution
of an optimization problem. The model subset presented to the analyst in each
step is designed to maximize the expected information. The result of this process is a set of logically consistent weights together with a measure of confidence
determined from the amount of conflicting information which is provided by the
expert during the relative weighting process.
Using Averaging-Based Factorization to Compare Seismic Hazard Models
Derived from 3D Earthquake Simulations with NGA Ground Motion Prediction
Equations
Wang, F., Univ. Of Southern California, Los Angeles, CA, [email protected];
JORDAN, T., Univ. of Southern California, Los Angeles, CA, [email protected]
Seismic hazard models based on empirical ground motion prediction equations
(GMPEs) employ a model-based factorization to account for source, propagation,
and path effects. An alternative is to simulate these effects directly using earthquake source models combined with three-dimensional (3D) models of Earth
structure. We have developed an averaging-based factorization (ABF) scheme
that facilitates the comparison of these two types of seismic hazard models. For
any fault source k with epicentral position x, we calculate the excitation functions
Ek(x, s) for sites s in a geographical region R, such as 5% damped spectral acceleration at a particular period. Through a sequence of averaging and normalization
operations over x, k, and s, we uniquely factorize Ek(x, s) into four components:
A, B(s), Ck(s), and Dk(x, s). Factors for a target model can be divided by those of
a reference model to obtain four corresponding factor ratios, or residual factors:
a, b(s), ck(s), and d k(x, s). We show that these residual factors characterize differences in basin effects primarily through b(s), magnitude and distance scaling primarily through ck(s), and source directivity primarily through d k(x, s). We illustrate the ABF scheme by comparing CyberShake Hazard Model (CSHM) for the
Los Angeles region (Graves et. al. 2010) with the Next Generation Attenuation
(NGA) GMPEs modified according to the directivity relations of Spudich and
Chiou (2008). Relative to CSHM, all NGA models underestimate the directivity and basin effects. In particular, the NGA models do not account for the coupling between source directivity and basin excitation that substantially enhance
the low-frequency seismic hazards in the sedimentary basins of the Los Angeles
region. Assuming CyberShake simulations are representative of earthquake excitation in this region, we show the degree to which regionally modified versions of
the NGA models can reduce epistemic uncertainties.
Significance of the Site Classification Map in Earthquake Loss Estimation by
HAZUS Based on a Case Study of the Gyeongju Area, Korea
Kang, S., Korea Ocean Res. & Dvlp. Inst., Ansan, Gyeonggi-do, Republic of
Korea, [email protected]; KIM, K. H., Korea Ocean Res. & Dvlp. Inst., Ansan,
Gyeonggi-do, Republic of Korea, [email protected]
Regionally varying seismic hazards can be estimated using an earthquake loss
estimation system(e.g. HAZUS). The resulting estimates for actual earthquakes
help federal and local authorities develop rapid, effective recovery measures.
Estimates for scenario earthquakes help in designing a comprehensive earthquake hazard mitigation plan. Local site characteristics influence the ground
motions ensuing from earthquakes. Realistic loss estimates can be obtained using
a site classification map, which faithfully portrays the characteristics of the shallow subsurface. We estimated the losses due to a magnitude 6.7 scenario earthquake in Gyeongju, with and without a site classification map. Significant differences in loss estimates were observed. The loss without the site classification
map decreased without variation with increasing epicentral distance, while the
loss with the site classification map varied from region to region, due to both the
epicentral distance and local site effects. The major cause of the large loss expected
in Gyeongju is the short epicentral distance. Pohang Nam-Gu is located farther
from the earthquake source region. Nonetheless, the loss estimates in the remote
city are as large as those in Gyeongju and are attributed to the site effect of soft
soil found widely in the area.
Testing of Ground-Motion Prediction Equations via Mixture Models
Kuehn, N. M., University of Potsdam, Potsdam, Germany, [email protected]; SCHERBAUM, F., University of Potsdam, Potsdam, Germany.
The quantification of ground motions via empirical ground-motion prediction
equations (GMPEs) is a key step in any probabilistic seismic hazard analysis. It is
commonly accepted that no single model is able to capture the whole range of possible ground motion characteristics at a site under study. Thus, a set of models is
used, which results in epistemic uncertainty that can dominate the hazard at low
exceedance frequencies. This uncertainty is usually captured within a logic tree
framework. A number of practical problems arise in this context concerning the
selection of GMPEs and defining the corresponding logic tree branch weights.
These problems are exacerbated in regions where the sparsity of instrumental
ground motion recordings prohibit the generation of region specific GMPEs. In
the present work, we show how it is still possible to provide quantitative information about the relative importance of different GMPEs in such a case. Therefore,
we adhere to an alternative view to the logic tree framework in which we assume
that the candidate models are components of a standard mixture model each of
which may capture a particular aspect of the data generation process. Based on
data such as macroseismic intensities or strong-motion recordings, it is possible
to estimate the mixture weights given a set of models. The idea of a GMPE mixture model to the testing is applied to Switzerland, for which there is no generic
GMPE but a large number of macroseismic intensities is available. A set of empirical GMPEs is selected, for which mixture weights are calculated for different
magnitude/distance ranges and different oscillator periods. Overall, the mixture
models fit the data better than the individual models. Using a Bayesian approach
to learning the weights allows to incorporate prior/subjective information about
the models. The mixture weights give an impression of how the models perform
as an ensemble and can thus provide valuable information for the hazard analyst.
Constraints on the 1811–1812 New Madrid Earthquake Magnitudes from a
Direct Comparison of Intensity Observations with Known M7 Earthquakes
memphis.edu; BOYD, O. S., U.S. Geological Survey, Memphis, TN, olboyd@
usgs.gov
Uncertainty in the magnitudes of the 1811–1812 New Madrid mainshocks
contributes significantly to the uncertainty in the seismic hazard in the central
United States. A direct comparison of intensity observations between these historic and more recent M7 stable continental region earthquakes provides new
constraints on the magnitudes of the 1811–1812 New Madrid mainshocks.
Evernden (1975) suggested proximal large-intensity values are influenced by magnitude, source depth, and other factors; however, distant lower-intensity values
are influenced mostly by the magnitude of the earthquake. We confirm this by
fitting intensity observations for each of the four largest 1811–1812 New Madrid
earthquakes, the 1929 M7.2 Grand Banks earthquake, and the 2001 M7.6 Bhuj,
India earthquake. We compare the mean Modified Mercalli Intensity (MMI)
curve vs. distance and its 95% confidence interval for each New Madrid event
from several interpretations of the intensities with those of the Grand Banks and
Bhuj, India, earthquakes at distances greater than 1000 km. Factors affecting the
direct comparisons are (1) the method of assigning intensities to observations,
(2) sampling limitations due to few observations and incomplete demarcation of
felt area, (3) source effects on intensity such as radiation pattern, stress drop, and
directivity, (4) propagation effects such as regional attenuation differences and
structural focusing of radiated energy, and (5) site effects such as soil thickness
and nonlinearity. At large distances these factors have small effects on MMI suggesting our direct comparisons can reduce uncertainty. Our direct comparison of
mean intensity curves beyond 1000 km suggests M~7.6, M7.2–7.6, and M>7.6
for the three 1811–1812 New Madrid mainshocks, and M~7.0 for the December
16, 1811 New Madrid “dawn” aftershock. Our estimates are consistent with those
of Bakun and Hopper (2004) and higher than those of Hough and Page (2011),
even using their MMI interpretations.
The Hard Shock Revisited: New and Revised Felt Reports for the February 7,
1812 New Madrid Earthquake
Moran, N. K., CERI/University of Memphis, Memphis, TN, nkmoran@
memphis.edu
The 1811-1812 New Madrid earthquakes were seismic events experienced across
a wide swath of the eastern and southern United States and adjacent regions of
Canada. They have been studied using the historic record accorded by newspaper accounts to find felt reports in the far field. This research effort left much
information undiscovered. One ongoing project is exemplified by the New
Madrid Compendium newspaper research project, which discovers, examines,
and catalogs new felt reports for all three major New Madrid earthquakes and
their aftershocks. In previous presentations new and revised felt reports have been
documented for the December 16, 1811 and January 23, 1812 earthquakes. This
poster is a representation of new and revised felt reports for the February 7, 1812
earthquake with corrections to felt reports from previous research efforts.
The use of historic data to help map the effect of the New Madrid earthquakes
in the far field was pioneered by Street and Nuttli in 1984. However, a review of
the data and additional research has shown more felt report locations and better
defined the locations uncovered in the previous study. These new reports help
in reducing the uncertainty about felt report information in many of these locations. The true locations of some felt reports are also clarified and revised. The
largest of the earthquakes (February 7, 1812) generated a large amount of written
data that, when accessed, can provide a clearer view of its far field effects, and will
contribute to better defining the magnitude of the quake using modern methods
of data analysis. Also CERI is developing an organized and easily accessible website for the 1811-1812 earthquake observations.
3-D Rocking Response of Precariously Balanced Rocks
Veeraraghavan, S., California Institute of Technology, Pasadena, CA,
[email protected]; KRISHNAN, S., California Institute of Technology,
Dynamic Rupture Modeling of the 2008 Wenchuan Earthquake
Liu, Q., University of California, Santa Barbara, CA; JI, C., University of
California, Santa Barbara, CA; ARCHULETA, R. J., University of California,
Santa Barbara, CA.
There are several precariously balanced rocks (PBRs) in western US. Analyzing
the toppling behavior of these rocks can provide limits on the largest ground
motions (of the type that the rocks are sensitive to) that could have occurred at
the rock sites in the time that they have been precarious. We are creating detailed
3-D models of some of the PBRs that have been imaged using Terrestrial Laser
Scanning(TLS) techniques in order to analyze the toppling behavior accurately.
To establish the proof of concept, we are modeling the Echo Cliff PBR which is
located in the Western Santa Monica Mountains. We first obtain equally spaced
nodes throughout the rock using Matlab. Then, under the assumption that the
rock and the pedestal behave like rigid bodies, we use rigid body dynamics to
solve for the response of the rock to different ground motions. The state of the
rigid body at any instant in time can be fully described by the position vector
of the center of mass (CM), velocity of CM, a rotation matrix (which is a transformation mapping between the local body fixed configuration and the global
configuration) and the angular momentum of the rigid body about CM. At each
time step, these state variables are updated using force and moment balance equations. Forces and moments arise out of the inertia of motion as well as the normal
contact and tangential friction between the rock and pedestal. The impact from
the collision is forced to be perfectly inelastic (i.e., no bouncing) by applying an
impulse at each contact point to reduce the relative normal velocity between the
rock and the pedestal to zero at that point. Two linear complementarity problems
are solved, one for the impulse force to be applied, and the other for the contact normal and frictional forces simultaneously. Using this algorithm, toppling
analysis will be performed on several precariously balanced rocks in southern
California to help characterize seismic hazard in the region.
Both finite fault kinematic inversions based on different datasets (seismogram,
GPS, InSAR) and field studies (surface rupture observations) suggested a complicated rupture process of the 2008 Mw 7.9 Wenchuan earthquake, particularly its
initial stage. The rupture started and unilaterally propagated northeast on the low
angle Pengguan fault, which only released 27% of total seismic moment. Rupture
on the high angle Beichuan fault initiated as late as 17 s and 40 km northeast
of the epicenter. Rupture on the Beichuan fault propagated bilaterally— to the
northeast and also southwest back towards the epicenter. While fault geometry,
including the varying dip angles of the segments is likely to influence the rupture, stress heterogeneity, both in magnitude and direction over the two faults, is
almost certain to exert a significant importance in controlling the rupture. Here
we use a 3-D finite element code to forward model such an complicated dynamic
rupture interaction. We simplify the fault geometry as two planar rectangular
faults, with dipping angles of 50 degree (upper one, representing Beichuan fault)
and 30 degree (lower one, representing Pengguan fault), intersecting at 12 km
depth. Inferred from the kinematic slip model, we use a simple initial stress distributions to test various combinations of stress amplitude and material properties
capable of reproducing the kinematic inversion results for the source description.
The dynamic rupture simulation could shed some light on the background tectonic movement between the Tibet plateau and the Sichuan Basin as well as lower
and upper crust interaction.
Earthquake Studies
Late Pleistocene Paleoseismology on the Maoergai Fault, Eastern Tibet:
Implications for Seismic Hazard and Selection of Trench Site on a Purely
Strike-Slip Fault
Ren, J. J., Institute of Crustal Dynamics, China Earthquake Administration,
Beijing, China, [email protected]; DING, R., Institute of Crustal Dynamics,
China Earthquake Administration, Beijing, China; XU, X. W., Institute of
Geology, China Earthquake Administration; ZHANG, S. S., Institute of
Crustal Dynamics, China Earthquake Administration, Beijing, China; GONG,
Z., Institute of Crustal Dynamics, China Earthquake Administration, Beijing,
China; YEATS, R. S., Dept. of Geosciences, Oregon State University, Corvallis,
OR.
The Maoergai fault, ~ 200 km northwest of the Longmenshan thrust on the
eastern margin of the Tibetan Plateau, is the eastern branch of the Longriba
fault zone that separates the Bayan Har block into the Ahba and Longmenshan
sub-blocks. Re-measured GPS data shows there is strong shear zone with a strain
rate of up to 4-6 mm/yr on the Longriba fault zone. Primary field investigation
indicates that the Maoergai fault is purely right-lateral strike-slip fault with the
typical characteristics, for example, shutter ridges, offset river terraces, and linear
fault valleys, which demonstrate the fault underwent a strong tectonic activity in
late Quaternary. However, there is no surface-rupturing earthquake on this fault
in the ~400-year-long literature. In addition, due to sparse seismic stations in this
area, only a few of small earthquakes were recorded since 1970. While numerous
infrastructures are building and several famous scenic spots such as Jiuzhaigou
Valley, are located in this area. Hence, it is urgent to explore the history of large
earthquakes on the Maoergai fault. In this paper, we combined the interpretation of the high-resolution Satellite imagery, detailed fieldwork to choose the
sits to excavate trenches. Two trenches were excavated at Caoyuan and Maoergai
villages, respectively. Analysis of trench logs and radiocarbon dating reveal that
since 12 ka, there were three paleo-events on this fault, which occurred at ~ 8510
a, ~ 7100 a and ~ 5170 a. The Maoergai fault may adapt to a cluster mole of large
earthquakes and there is no surface-rutpured event occurred on it since ~5170 a,
which probably suggests the fault has a high seismic hazard in the future. RTK
GPS survey of offset terraces reveals that on a purely strike-slip fault, there will be
a high scarp on the offset terrace when the terrace has a relative large slop angle.
This might provide a clue for the selection of trench site for paleoseismological
study on a purely strike-slip fault.
Slip History of the 2008 Mw 7.9 Wenchuan Earthquake Constrained by Jointly
Inverting Seismic and Geodetic Observations
Shao, G., University of California, Santa Barbara, CA, [email protected];
JI, C., University of California, Santa Barbara, CA, [email protected]; LU, Z.,
United States Geological Survey, Vancouver, WA; HUDNUT, K., United States
Geological Survey, Pasadena, CA; LIU, J., Chinese Academy of Sciences, Beijing,
China; ZHANG, W., Graduate University of Chinese Academy of Sciences,
Beijing, China; WANG, Q., Institute of Seismology, China Seismological
Bureau, Wuhan, China.
We investigate the kinematic rupture process of the 2008 Mw 7.9 Wenchuan
earthquake with all the available geophysical and geological datasets. Teleseismic
broadband body waves, long period surface waves, local strong motions, GPS vectors and interferometic radar (InSAR) images have been combined to constrain
the spatial and temporal slip distribution using a nonlinear finite fault inversion method. We derive the fault geometry from the geological surface breaks
and relocated aftershocks. We calculate the earth response using two 1D velocity
models: one for the Tibetan Plateau and the other for the Sichuan Basin, inferred
from local tomographic studies. In doing inversions, both the fault geometry and
the velocity structure have been further perturbed to reconcile different datasets.
Our preferred model shows the Wenchuan earthquake has a very complex rupture process. The rupture initiates southwest of the town of Yingxiu at a depth
of 12.0 km, where the low-angle Pengguan Fault and the high-angle Beichuan
Fault intersect. Rupture first propagates only on the lower potion of Pengguan
Fault in the first 17 s and then triggers rupture of Beichuan Fault at about 40 km
northeast of the hypocenter, where the Xiaoyudong Fault intersects those two
faults on the surface. Both faults are simultaneously slipping for about 40 seconds
before the faulting is confined only to the Beichuan Fault. The rupture propagates
unilaterally northeastward on the Pengguan Fault for about 100 km and on the
Beichuan Fault for about 270 km with an apparent rupture velocity of 3.0 km/s.
Except for the region near the hypocenter, the majority of slip occurs at depths
less than 12 km. The total seismic moment released by the Wenchuan earthquake
is 1.1 × 1021 Nm, with ~27% on the Pengguan Fault. The entire rupture duration is nearly 116 seconds; about 95% of the total seismic moment is released in
the first 90 seconds.
New Constraints on Crustal Structure and Moho Topography in Central Tibet
Revealed by Deep Seismic Reflection Profiling by SINOPROBE
Lu, Z., Institute of Geology, Chinese Academy of Geological Sciences, Beijing,
China, [email protected]; CHEN, C., Cornell University, Ithaca, NY,
[email protected]; GAO, R., Institute of Geology, Chinese Academy of
Geological Sciences, Beijing, China, [email protected]; BROWN, L. D., Cornell
University, Ithaca, NY, [email protected]; XIONG, X., Institute of Geology,
Chinese Academy of Geological Sciences, Beijing, China; LI, W., Institute of
Geology, Chinese Academy of Geological Sciences, Beijing, China; DENG, G.,
Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China.
From October 2009 to May 2010, Project SinoProbe collected a series of deep
seismic reflection profiles which extend from the northern Lhasa Terrane across
the Bangong-Nujiang suture and well into the southern Qiangtang block in order
to image deep crustal structure of central Tibet. The resulting seismic sections
show several prominent features: a distinct Moho reflector that lies at a depth
of about 70km~80km beneath the Qiangtang Block which deepens, but without offset, to about 80km beneath the Lhasa block. The boundary of the middle
and upper crust and the boundary of the middle and lower crust interpreted by
INDEPTH velocity model correspond to strong reflection horizons at 18km
and 30km depth respectively beneath south Qiangtang block. A north-dipping
series of reflection packages in the mid- to lower crust may mark subduction of
the Lhasa block beneath the Qiantang, i.e. the Bangong-Nujiang suture at depth.
There are several strongly reflective, albeit discontinuous, reflection sequences
that we suggest may represent ophiolitic fragments entrained during Triassic
collision, a tectonically dismembered Mesozoic sill or perhaps even partial
melting of underthrust sediments taken deeper by crustal thickening related to
Himalayan collision. The central portion of the reflection profile exhibits an antiformal structure in the upper crust which interpret as the subsurface eastward
extension of the Qiangtang anticlinorium at depth.
Tectonic Interactions Between the Yangtze Block and Songpan-Ganze
Terrane: New Constraints from Deep Seismic Reflection and Refraction
Profiles, as Well as Magnetic and Gravity Evidence
Guo, X., Institute of Geology, CAGS, Beijing, China, guomichele@gmail.
com; GAO, R., Institute of Geology, CAGS, Beijing, China, gaorui@cags.
net.cn; KELLER, G. R., School of Geology and Geophysics, the University of
Oklahoma, Norman, OK, [email protected]; XU, X., School of Geology and
Geophysics, the University of Oklahoma, Norman, OK, [email protected]
The Songpan-Ganze terrane (SGT) and Yangtze block (YB) are separated by
the Longmen Shan fault zone. They bound the northern and eastern sides of the
Tibetan Plateau, respectively. The SGT features a set of thick Triassic flysch sediments that were shortened during the Early Mesozoic. NW-SE trending faults
were produced. As the boundary between them, the NE-SW trending Longmen
Shan tectonic zone is characterized by a distinctive morphology and consists of
three major faults. Tectonic interactions between the SGT and YB along the
Longmen Shan have played an important role in the formation of the tectonic
collage of China. However, the amalgamation process between the SGT and
YB is still a matter of debate, and advanced research is needed. Our research is
focused on the information derived from the deep seismic reflection and refraction profiles of the SinoProbe-2 project, and new satellite magnetic and gravity
data. The seismic lines cross the Longmen Shan fault zone as they extend northwestwards from the Sichuan Basin to the SGT. The seismic data were collected by
a variety of instruments. More details of the Moho depth and crustal velocities
will be determined by analyzing the PmP, Pn and Pg phases. Additionally, the
satellite potential field data cover the entire area. The bottom of flysch sediments
can be estimated from the magnetic data and the suture zone between SGT and
YB is clearly shown by gravity anomalies. Integrated with the seismic velocity
model, the NW-SE trending structural profile crossing the Longmen Shan fault
zone will be well defined. Our approach is to consider other geological data and
the tectonic evolution of adjacent areas in order to advance our understanding of
the lithospheric structure and evolution of the SGT and YB. Tectonic interactions between the SGT and YB in terms of the amalgamation of China will be
modeled.
Preliminary Results of a Deep Seismic Reflection Profile Across the Great
Xing’an Mountain Range, NE China
Hou, H. S., Institute of Geology, CAGS, Beijing, China, hesheng.hou@126.
com; GAO, R., Institute of Geology, CAGS, Beijing, China, [email protected];
LI, Q. S., Institute of Geology, CAGS, Beijing, China, [email protected];
KELLER, R., The University of Oklahoma, Norman, OK, [email protected];
XIONG, X. S., Institute of Geology, CAGS, Beijing, China, [email protected];
LI, W. H., Institute of Geology, CAGS, Beijing, China, [email protected];
LI, H. Q., Institute of Geology, CAGS, Beijing, China, [email protected];
Zhu, X. S., Institute of Geology, CAGS, Beijing, China, zhuxiaosan129@
gmail.com; Kuang, C. Y., No.6 Geophysical Prospecting Team, SINOPEC;
Huang, D. D., No.6 Geophysical Prospecting Team, SINOPEC.
Deep seismic reflection profiles have provided images of detailed crustal structure that document crustal growth by both lateral and vertical accretion in many
locales around the world. In 2011, our group recorded a 400km long deep seismic
reflection profile that crossed the Mesozoic and Cenozoic circum-Pacific oro-
gens and the Great Xingàn mountain range in NE China. We were still able to
acquire high quality data although there were many logistic difficulties encountered during the field work, such as variation of surface lithology, poor conditions for geophone emplacement, large areas of farmland, and the Great Xingàn
mountain range. This profile lies between two areas (the Songliao basin to the SE
and the Hailar basin to the NW that extends into Mongolia) in which existing
oil prospecting reflection profiles and drilling data provide constraints on upper
crustal structure. This fact, along with other existing deep seismic reflection profiles in the region, will provide a 1500 km long seismic section across northeastern
China. The detailed structural information provided by this long profile should
be very useful to tectonic studies as well as provide important information for
hydrocarbon potential and mineral exploration. Preliminary processing results
image the contact relationship of the Great Xing’an mountain range and adjacent basins. We can identify many curved reflection phases from volcanic bodies
and complex Moho reflection events. It is notable that a strong Moho reflection
appears to be spatially associated with ancient collision or subduction zones. This
scenario may suggest multiple tectonic events that are spatially correlated. On the
time section, there is no obvious root beneath the Great Xingàn mountain range.
This research is supported by SinoProbe-02, China NSF (No.40830316,
No.41104060), China Geological Survey (No.1212011120975), US NSF PIRE
grant (0730154).
Crustal Structure of the Northern Margin of the North China Craton and
Adjacent Region from the Sinoprobe02 North China Seismic War/R
Experiment
Li, W. H., Institute of Geology, CAGS, Beijing, China, [email protected];
KELLER, G. R., The University of Oklahoma, Norman, OK, [email protected];
GAO, R., Institute of Geology, CAGS, Beijing, China, [email protected]; LI, Q.
S., Institute of Geology, CAGS, Beijing, China, [email protected]; COX,
C. M., The University of Oklahoma, Norman, OK, [email protected]; HOU, H. S.,
Institute of Geology, CAGS, Beijing, China, [email protected]
A 450 km long seismic WAR/R profile was recorded jointly by the CAGS and
the University of Oklahoma. Simultaneously, deep seismic reflection data were
recorded along the same profile. The profile extended from northwest of Beijing,
across the north margin of the North China craton and Central Asian orogenic
belt (CAOB) to the Solonker suture zone. The recording of seismic waves from 8
explosions was conducted in 4 deployments of 300 Texan recorders with station
spacings of 1-1.5 km. The P wave field on the sections provided good quality data
for most of the profile. Arrivals from of refracted and reflected waves from sediments and basement (Pg), intracrustal phases (PcP, PlP), and the Moho (PmP, Pn)
were typically observed. Travel time modeling was done layer by layer using the
top to bottom approach. The velocity model was altered by trial and error, and the
forward model was updated by damped least-squares inversion. In our modeling,
calculated travel times fit observed arrivals for all 1402 traces with average RMS
of 0.121.
The P wave velocity model shows: 1) A concave Moho to a depth of 47.5 km
beneath the Yanshan Mountains. It confirmed that the Yanshan orogen is dominated by thick-skinned tectonics as is typical in other intracrustal orogens around
the world. 2) The upper crust of the CAOB is associated with a broad domal feature with relatively high velocities. 3). More local structures in the CAOB appear
be related to outcropping ophiolites and the Bainaimiao arc appears be related to
low velocities in the lower crust.
Funded by NSF PIRE (0730154), SinoProbe02 and China NSF(40830316)
What’s Next?
Oral Session · Thursday 8:30 am, 19 April · Pacific Salon 1
Session Chairs: Margarita Segkou and William Ellsworth
Variation of Seismic Radiation Spectrum With Source Depth Along
Megathrust Faults in the Japan, Chile, and Sumatra Subduction Zones
Lay, T., Univ. California Santa Cruz, Santa Cruz, CA, [email protected]; YE, L.,
Univ. California Santa Cruz, Santa Cruz, CA, [email protected]; KANAMORI,
H., California Institute of Technology, Pasadena, CA, [email protected]
Seismic wave radiation from megathrust faults provides an important probe of
fault zone properties and rupture characteristics. Seismic waveform complexity
reveals heterogeneity of slip during large earthquakes, and this provides insight
into earthquake recurrence, the nature of aftershock sequences, and stress heterogeneity. In a recent study, we proposed that the main seismogenic zone on
plate boundary megathrusts can be usefully characterized as having 3 domains of
seismic radiation behavior. The shallowest domain (A), extends from the trench
to about 15 km depth, and involves tsunami earthquakes and/or aseismic slip.
Little short-period radiation is emitted when this part of the fault fails. Domain
B extends from 15 to 35 km deep, and large slip events occur in this region, with
moderate levels of short-period seismic radiation. Further along the megathrust,
from 35-50 km deep, is domain C, which has moderate slip events with relatively
enhanced levels of short-period radiation. This conceptual framework has largely
been derived from consideration of teleseismic radiation, with back-projection
methods providing constraints on locations of coherent short-period radiation
during large ruptures that may extend over more than one domain. We test this
concept using new spectral methods for both teleseismic and regional seismic
data for megathrusts in the vincinity of recent large tsunami earthquakes and
great ruptures like the 2011 Tohoku earthquake. The best data set is from combined Japanese networks (Hi-net, F-net, K-net, KiK-net), which provided dense
sampling of wavefields from local and teleseismic earthquakes. Comparisons of
network estimated source spectra, including empirical Green function methods,
allow us to isolate source spectrum variations as a function of depth along the
megathrust with very different path geometries than for earlier teleseismic analyses. Strong motions for the Tohoku earthquake appear to have originated from
domain C.
Is the Mariana Subduction Zone “Decoupled”
Emry, E. L., Washington University in St. Louis, St. Louis, MO, ericae@
seismo.wustl.edu; WIENS, D. A., Washington University in St. Louis, St. Louis,
MO, [email protected]
The Mariana Subduction Zone is widely accepted to be the aseismic endmember
of global subduction zones. The northern and central Mariana have no recorded
earthquakes larger than Ms 7.4, whereas the southern region experienced a Mw
7.7 underthrusting event in 1993. We have studied the northern Mariana plate
interface using an array of ocean bottom seismographs deployed from 2003-2004.
We merged phase arrival times from locally-recorded earthquakes with globallyrecorded GCMT earthquakes and relocated events relative to each other using
a hypocentroidal decomposition algorithm. Focal mechanisms for a few locallyrecorded earthquakes were determined by fitting synthetic waveforms computed
by reflectivity. Results indicate that the seismogenic plate interface of Northern
Mariana extends from 20-60 km in depth, causing the seismogenic width in
this region to be ~100 km. This shows that apparent aseismicity is not due to an
anomalously thin seismogenic zone, as suggested by previous studies. Seismicity
patterns suggest depth-dependent and along-strike differences in the seismogenic
plate interface which indicate heterogeneous coupling that may be related to the
deficit of large earthquakes. In addition, we explored intraplate earthquakes in
the outer rise and trench as indicators of variable coupling. GCMT earthquakes
along the entire margin were relocated, and best-fitting depths were modeled by
fitting P- and SH-waveforms computed by seismic ray theory. Results show that
the brittle part of the incoming Pacific plate is entirely under extension in the
northern and central Mariana, whereas some deeper compressional intraplate
earthquakes occur in the southern region. We interpret this as indicating greater
seismic coupling in the southern region where the 1993 event occurred. Taken
altogether, we build a comprehensive picture of the Mariana plate interface and
discuss factors that may impact the occurrence of great earthquakes there.
Seismic Potential of the Lesser Antilles Subduction Zone: Insights from a
Reinterpretation of the 8 February 1843 Earthquake
Hough, S. E., US Geological Survey, Pasadena, CA, [email protected]
The seismic potential of the Lesser Antilles subduction zone and the adjacent
Puerto Rico trench remains a matter of debate. The central arc of the Lesser
Antilles subduction zone is currently accumulating elastic strain at a rate slower
than the plate motion (Manaker et al., 2008), and a recent study concludes that
no major subduction zone earthquake has occurred along the Puerto Rico trench
during the 500-year historical record (tenBrink et al., 2012). The 8 February 1843
earthquake is the largest historical event on the Lesser Antilles arc. A recent study
estimated a preferred magnitude of 8.5 based on near-field macroseismic effects
(Feuillet et al., 2011), but the generally accepted value has been 7.5-8. A consideration of the regional and far-field macroseismic effects reveals a felt distribution
comparable to those of recent great (Mw ≥ 9.0) earthquakes. Credible archival
accounts provide compelling evidence that the earthquake was felt throughout a
wide region of the eastern United States. A modest tsunami was described by two
witnesses; another account describes uplift of a stone wharf in Antigua. These
observations support the inference of a high (M≥8.5) magnitude, a relatively deep
rupture, and significant moment release towards or possibly around the northern
corner of the Lesser Antilles Arc.
Further re-examination of the global catalog of earthquakes during the
historical era suggests that the magnitudes of some great historical earthquakes
have been underestimated, with approximately half of all Mw≥8.5 earthquakes
missing or underestimated in the 19th century. Since very large magnitudes are
generally inferred for historical earthquakes based on tsunami wave heights, magnitudes would tend to be underestimated for deeper subduction earthquakes that
generated small tsunamis and/or earthquakes that produced tsunamis that were
not documented. The 1843 Lesser Antilles earthquake emerges as a prime candidate for a “missing” great earthquake.
Questioning the Elastic Source Models for Shallow Subduction Zone
Earthquakes
Ma, S., San Diego State University, San Diego, CA USA, [email protected].
edu
Elastic dislocation theory has been widely used to infer earthquake rupture process and coseismic slip distribution in shallow subduction zones by inverting seismic, geodetic and tsunami data. However, the assumption that materials deform
elastically during the shallow subduction zone earthquakes is questionable, as
demonstrated in recent dynamic rupture simulations (Ma, 2011). Due to the low
strength and permeability of sediments in the accretionary wedge an updip-propagating rupture on a shallow-dipping plate interface can induce large pore pressure increase, reducing the wedge strength and leading to widespread Coulomb
failures in the wedge. The widespread failures in the wedge give rise to not only
slow rupture velocity but also large seafloor uplift (in the case of a small fault dip).
For large initial pore pressure approaching the lithostatic overburden rupture can
stop naturally far from the trench without resorting to the velocity-strengthening friction. This poroplastic model, reminiscent of the critical taper theory of
fold-and-thrust belts and accretionary wedges (Davis et al., 1983; Dahlen, 1990)
requiring Coulomb failures everywhere in the wedge, thus provides a rigorous
physical interpretation to many anomalous features of tsunami earthquakes. The
slip near the trench is likely small. The large inelastic off-fault deformation in the
wedge represents a significant portion of seismic moment release, compared to
the contribution from the slip on the fault. A possible bias in the elastic source
models is that the large inferred slip near the trench might be manifestations of
large inelastic deformation in the wedge combined with small slip on the fault. I
will discuss possible biases in elastic source models using examples from recent
large subduction zone earthquakes.
Maximum Earthquake Size for Subduction Zones
Kagan, Y. Y., UCLA/ESS, Los Angeles, CA, [email protected];
JACKSON, D. D., UCLA/ESS, Los Angeles, CA, [email protected]
We analyze seismicity in the Flinn-Engdahl seismic zones to infer the maximum
earthquake size (Mmax) for major subduction zones. The maximum size is usually guessed from the earthquake history or estimated segment size. These methods often under-estimate Mmax. Two quantitative methods include (1) a statistical analysis of the available earthquake record, and (2) the moment conservation
principle. The latter technique allows us to study how much of the tectonic deformation rate in any region is released by earthquakes. We demonstrate that for
subduction zones no earthquake catalog suffices to provide a reliable statistical
measure of Mmax. However, the moment conservation principle produces consistent estimates: for all the major subduction zones the maximum moment magnitude suggested by various measurements is of the order 9.0 to 9.7. Moreover,
differences in Mmax between subduction zones are not statistically significant.
Since mega-earthquakes have occurred in several subduction zones, other zones
would eventually be expected to have shocks of similar magnitude. The 2004
Sumatra and the 2011 Tohoku earthquakes demonstrated the validity of this
prediction. We also consider another moment conservation method— comparing the site-specific deformation rate and its release by earthquakes rupturing the
site. This technique depends on less reliable assumptions, but it also suggests that
Mmax is approximately 9 in the Tohoku area. If the maximum earthquake size is
known, the magnitude-frequency relation yields a reliable estimate of the recurrence time of mega-events.
Seismology Cannot Address Global Clustering of M9 Earthquakes
Goldfinger, C., Oregon State University, Corvallis, OR, [email protected].
edu
Two recent papers suggest that analysis of instrumental earthquakes informs us
about clustering of M~9 earthquakes. Several flaws are apparent: 1) Recurrence
of M~9 earthquakes can be hundreds of years. Cascadia recurrence varies from
170-1200 years, with two superquakes in 10ka, and long term cycling and clustering. NE Japan likely had its penultimate M~9 event in 869, with two likely predecessors at ~ 1000 year intervals. During the intervening ~1000 years, numer-
ous smaller earthquakes in the 8.2-8.4 range used only a small fraction of the
accumulated strain, requiring the eventual superquake of March 2011 (forecast
by Ikeda, 2005). The Sumatran subduction zone, Cascadia, and NE Japan apparently each have long term energy cycling, with groups of smaller events punctuated by larger events and long time gaps in their histories. These regions are the
only ones with paleoseismic records long enough to address this issue. 2) Absent
enough M~9 events, smaller earthquakes from other fault systems with higher
frequencies are used. This answers an entirely different question, whether global
rates of M> 7 earthquakes have clustered in the 20th century. A direct connection between these two questions is not apparent. One need look no further than
Cascadia, with a b value of near zero, to see the fallacy of this assumption. 3) The
observation that M9 events have clustered twice in the last 100 years is questioned
because no mechanism is known. Both static and dynamic triggering seem to fail,
though these tests also rest on smaller earthquakes. Geology has a rather sordid
history of throwing out observations for lack of a good mechanisms, i.e. Plate
Tectonics and the Missoula Floods. Observations virtually always exist before
explanations are found. Absence of evidence for a mechanism is not evidence of
absence of global clustering. The test will when we have long records from enough
subduction zones to examine whether this phenomenon exists or not.
From Stable to Destructive: How Creeping Fault Segments Can Join
Earthquakes and Implications for Seismic Hazard
Lapusta, N., California Institute of Technology, Pasadena, CA, lapusta@
caltech.edu; NODA, H., Japan Agency for Marine-Earth Science and
Technology, Yokohama, Japan, [email protected]
Seismic and aseismic fault slip is often assumed to be separated in space and to
occur on two different types of fault segments: one with stable friction properties and the other with potentially unstable, weakening, friction that leads to
stick-slip. The Mw 9 2011 Tohoku-Oki earthquake shook such assumptions by
accumulating its largest seismic slip in the area that was assumed to be creeping.
We propose a model in which stable, rate-strengthening behavior at low, aseismic slip rates is combined with co-seismic weakening due to rapid shear heating, allowing unstable slip to occur in segments which can also creep between
events. The model parameters are constrained by lab measurements on samples
from the fault of 1999 Mw 7.6 Chi-Chi earthquake in Taiwan. The long-term
slip behavior of the model is examined using a numerical approach that simulates both earthquake sequences and stable slip while including all wave effects.
The model explains how the largest slip in Tohoku-Oki earthquake could occur
in a creeping segment as well as reproduces the overall pattern of large events in
the area. The model also reproduces one of the most puzzling observations from
both Chi-Chi and Tohoku-Oki earthquakes, that areas of lower slip radiate more
high-frequency energy than areas of higher slip. The implication that seismic slip
may break through large portions of creeping segments—currently perceived as
barriers—requires re-evaluation of seismic hazard in many areas.
Rupture to the Trench in Dynamic Rupture Simulations of Megathrust
Subduction Zone Earthquakes
Kozdon, J. E., Stanford, Stanford, CA, [email protected]; DUNHAM,
E. M., Stanford, Stanford, CA, [email protected]
There is strong evidence from GPS, seismic, and differential bathymetry data that
the 11 March 2011 Tohoku-Oki earthquake rupture reached the seafloor. This is
surprising since it is believed that the top segment of the fault is frictionally stable
(based on an absence of background seismicity), thus preventing strain accumulation in the surrounding material. It was therefore thought that coseismic rupture of this part of the fault was not possible, and that megathrust earthquakes
would stop well before the trench axis. Recently, several mechanisms have been
proposed in the literature for explaining this seeming inconsistency, including
the presence of subducted seamounts that enhance plate coupling and/or the activation of extreme dynamic weakening mechanisms like thermal pressurization.
We present two-dimensional dynamic rupture simulations that suggest a
simple alternative explanation for the rupture reaching the trench. Our models
feature rate-and-state friction laws with depth-dependent properties. We find
that rupture to the trench is possible even if the upper section of the fault is velocity strengthening. Slip near the trench is driven by stress waves released by slip
on the deeper velocity-weakening part of the fault. Furthermore, because of the
small dip angle, rupture near the trench is strongly enhanced by seismic waves
reflected off the seafloor that transmit an additional shearing to the fault. In
addition to a set of Tohoku-specific simulations employing the detailed geometry
and material properties determined from seismic surveys of the Japan Trench, we
explore the robustness of our result and determine important controlling parameters (dip angle, background stress, depth-dependence of frictional parameters,
etc.) through a large ensemble of simulations of a simplified geometry.
Frequency-Depth Dependent Rupture Modes of Subduction Zone Megathrust
Earthquakes: Insights from Seismic Array Analysis
Yao, H., Scripps Institution of Oceanography, UCSD, La Jolla, CA, huyao@
ucsd.edu; SHEARER, P., Scripps Institution of Oceanography, UCSD, La Jolla,
CA, [email protected]; GERSTOFT, P., Scripps Institution of Oceanography,
UCSD, La Jolla, CA, [email protected]
In the past ten years, a number of giant megathrust earthquakes have occurred in
subduction zones, including the 2004 Mw 9.2 Sumatra earthquake in Indonesia
and its Mw 8.6 aftershock in 2005, the 2010 Mw 8.8 Maule earthquake in
Chile, and the most recent 2011 Mw 9.0 Tohoku earthquake in Japan. Various
seismological methods have been used to investigate the rupture details of these
earthquakes, aiming to understand the physics of megathrust earthquakes and
the associated properties of subduction zone systems and plate interfaces. Our
study focuses on the frequency-dependent spatiotemporal energy release during
earthquake rupture using newly developed seismic array methods: frequencydomain compressive sensing (Yao et al., 2011, GRL) and time-domain iterative
back-projection methods (Yao et al., 2012, submitted to GJI). For the Tohoku
earthquake, our results using dense array data in the United States reveal apparent frequency-depth dependent rupture modes in which low frequency (e.g.,
0.05-0.1 Hz) radiation dominated in the up-dip region (close to trench) while
the high-frequency (e.g., 0.2-1 Hz) radiation mainly occurred in the down-dip
region (close to Japan coast). Together with historical seismicity and aftershock
data, as well as the dominant slip region from slip inversion methods, we can infer
the frictional properties of the plate interfaces, the relative size of asperities, and
possibly information about seismic coupling along the subduction zones. In this
presentation, we will compare results of a few megathrust subduction zone earthquakes and generalize their similarities and differences.
Frequency-Dependent Energy Radiation and Fault Coupling for the 2010 Mw
8.8 Maule, Chile, and 2011 Mw 9.0 Tohoku, Japan, Earthquake
Wang, D., Kyoto University, Uji, Kyoto, Japan, [email protected].
ac.jp; MORI, J., Kyoto University, Uji, Kyoto, Japan, [email protected].
ac.jp
We carried out back-projections of teleseismic data filtered in different frequency
bands for the 2010 Maule, Chile and the 2011 Tohoku, Japan earthquakes. For
the Maule earthquake, there were differences along strike of the fault, with the
high-frequency energy mainly originating from an area 200 km northeast of the
epicenter, whereas low-frequency energy came from a location closer to the epicenter. The Tohoku earthquake shows strong frequency dependence in the dip
direction. High-frequency sources were located about 100 km west of the epicenter, while low-frequency sources were around epicenter, near the Japan Trench.
We compare the spatial distributions of energy with estimates of seismic coupling
before the earthquakes. Areas of high-frequency radiation seem correlated with
regions that were strongly coupled before the earthquakes. Areas of high coupling, may be associated with fault properties that are more heterogeneous and/
or have overall higher stress, producing higher frequency seismic waves.
Rupture Characterizations of the 2011 Mw 9.1 off the Pacific Coast of Tohoku
Earthquake and Its March 9th Mw 7.4 Foreshock
Shao, G., University of California, Santa Barbara, CA, [email protected].
edu; JI, C., University of California, Santa Barbara, CA, [email protected];
ARCHULETA, R. J., University of California, Santa Barbara, CA; ZHAO, D.,
Tohoku University, Sendai, Japan.
Recent studies reveal that giant (M 9) earthquakes, such as 1960 Mw 9.5 Chile
earthquake, often occur after multiple cycles of M 8 earthquakes in the same fault
area [e.g., Cisternas, et al., 2005]. However, the physical cause of such a seismic
recurrent cycle is not yet clear. The rupture history of the 2011 Mw 9.1 TohokuOki earthquake and its Mw 7.4 foreshock shed a light to address this question.
We investigate the kinematic rupture processes of the Tohoku-Oki mainshock
and its foreshock by jointly inverting teleseismic waveforms, local strong motion
data and GPS vectors. Our results show that the closely located foreshock and
mainshock have experienced very different rupture histories. For the foreshock,
the rupture initiated at a depth of 14 km and then broke an elliptical shape asperity in the downdip. The inferred average static stress drop is 0.9 MPa, consistent
with the median value of subduction M 7 earthquakes. The foreshock is characterized with an average slip of 1.2 m, rise time of 5.7 s, and slip rate of 0.2 m/s.
Meanwhile, the rupture of the Tohoku-Oki earthquake, occurring 51 hours later,
first propagated in down-dip direction for about 40 s and then broke a big near
trench asperity in the up-dip. It produced an unexpected large average slip of 30.3
m and a high average stress drop of 9 MPa. The mainshock re-ruptured the slip
zone of the foreshock with a much larger slip (25 m), rise time (22 s), and slip
rate (1.3 m/s). Our further analyses by comparing the fault slip distributions with
background seismicity and velocity anomaly along the plate interface suggest
that the foreshock and its frequent predecessors might have ruptured a relatively
weaker patch inside a large strongly coupled asperity, and the giant Tohoku-Oki
event broke the largest strong asperity and released the deficit slip in the foreshock region. The correlation between the slip rate and stress drop is consistent
with the high-velocity weakening mechanism observed in laboratory.
Lateral Stress Drop Variations and the Tohoku Aftershocks in the Context of
Earthquake Source Characteristics in Japan
Oth, A., European Center for Geodynamics and Seismology, Walferdange,
Luxembourg, [email protected]
A fundamental controversy still exists upon the scaling characteristics of seismic source parameters such as stress drop and radiated energy. Over the past
two decades, a significant number of studies provided persuasive evidence for an
increase of the latter with seismic moment respectively magnitude, while other
researchers casted doubt on these findings, arguing for constancy of stress drop
and seismic energy-to-moment ratio and thus similarity of the rupture process
between small and large earthquakes.
Recently, a countrywide study in Japan carried out by Oth et al. (2010)
showed no evidence of any clear scaling break between small and large magnitude
earthquakes. On the other hand, the continuation of this countrywide study,
analyzing individual earthquake sequences as well as separating the catalogue
of used events into different mechanisms, provided indications that these individual sequences can show significant deviations from self-similarity, and that
these deviations are closely related to the dominant faulting mechanism of the
sequence.
In this study, as a continuation of the work presented by Oth et al. (2010),
I first significantly extended the K-NET and KiK-net dataset used to derive the
scaling characteristics throughout Japan and also included aftershocks from the
giant Tohoku earthquake in order to study the scaling characteristics of these
events. Besides the scaling properties of the sequences already investigated previously, the lateral variations of stress drop throughout Japan will be discussed, and
the question where the source parameters of the Tohoku aftershocks fit into this
context will be investigated.
Interlocking of Heterogeneous Plate Coupling for the 2011 Tohoku-Oki
Megathrust Earthquake: An Integral Account of Asperity Model with Effective
Plate Coupling
TAJIMA, F., LMU, Munich, Germany, [email protected]; GRANT LUDWIG,
Lisa, Univ. California, Irvine, Irvine, CA.
The asperity model [Ruff and Kanamori, 1980, 1983; Lay and Kanamori, 1981]
characterized the ruptures of large shallow subduction zone earthquakes in context of plate coupling strength that has correlation with plate age and convergence rate. The 2011 Tohoku-Oki earthquake (Mw9) ruptured a large portion
of the boundary between the subducting Pacific and the overriding Okhotsk
plates where the coupling was considered weak and represented by sparsely distributed small asperities [e.g., Tajima and Kanamori, 1985 a, b] so that such a
great earthquake had not been anticipated. Off the coast of northeast Japan a
typical asperity break was expected to produce an event of about Mw7.5 to lower
8 with a recurrence interval of 30-40 years. The sequence of a large earthquake
was subsequently accompanied by a significant expansion of aftershock activity
that represents stress migration into the weakly coupled areas beyond the main
rupture zone. This pattern is in contrast to a fault zone that is characterized by a
uniform, large asperity, the rupture of which could produce a megathrust event,
e.g., the 1964 Alaska earthquake (Mw9.2) with little expansion of the aftershock
area. Unlike previous large earthquakes, however, the Mw9 Tohoku-Oki earthquake sequence does not show much expansion of the aftershock area, but the
areas of slip deficit in the main rupture zone are progressively filled in by aftershocks. When the rupture of the 2011 Tohoku-Oki earthquake was initiated, the
tectonic stress levels should have been close to the maximum shear strength in
the source areas of the past distinct earthquakes. We call this condition as the
effective (or super-critical) plate coupling that could promote interlocking rupture propagation through a broad region. Here note that the asperity model also
pointed out temporal variations of large earthquake ruptures along the same subduction zones such as those in South America. The 2011 Tohoku-Oki earthquake
is an extreme case.
Triggering of Tremors and Slow Slip event in Guerrero (Mexico) by the 2010
Mw 8.8 Maule, Chile, Earthquake
Zigone, D., Institut des Sciences de la Terre, Grenoble, France, dimitri.
[email protected]; RIVET, D., Institut des Sciences de la Terre,
Grenoble, France, [email protected]; RADIGUET, M., Institut
des Sciences de la Terre, Grenoble, France, [email protected].
fr; CAMPILLO, M., Institut des Sciences de la Terre, Grenoble, France,
[email protected]; VOISIN, C., Institut des Sciences de la
Terre, Grenoble, France, [email protected]; COTTE, N., Institut
des Sciences de la Terre, Grenoble, France, [email protected].
fr; WALPERSDORF, A., Institut des Sciences de la Terre, Grenoble, France,
[email protected]; Shapiro, N. M., Institut de Physique
du Globe de Paris, Paris, France., [email protected]; Cougoulat, G., Institut
des Sciences de la Terre, Grenoble, France. [email protected];
Roux, P., Institut des Sciences de la Terre, Grenoble, France, philippe.roux@
obs.ujf-grenoble.fr; Kostoglodov, V., Instituto de Geofísica, Universidad
Nacional Autónoma de México, Mexico City, Mexico, [email protected].
mx; Husker, A., Instituto de Geofísica, Universidad Nacional Autónoma de
México, Mexico City, Mexico, [email protected]; Payero, J. S., Instituto
de Geofísica, Universidad Nacional Autónoma de México, Mexico City, Mexico,
[email protected].
We investigate the triggering of seismic tremor and slow slip event in Guerrero
(Mexico) by the 27 February 2010 Maule earthquake (Mw 8.8). Triggered tremors start with the arrival of S wave generated by the Maule earthquake, and keep
occurring during the passing of ScS, SS, Love and Rayleigh waves. The Rayleigh
wave dispersion curve footprints the high frequency energy envelope of the triggered tremor, indicating a strong modulation of the source of tremors by the passing surface wave. This correlation and modulation by the passing waves is progressively lost with time over a few hours. The tremor activity continues during
the weeks/months after the earthquake. GPS time series suggest that the second
sub-event of the 2009-2010 SSE in Guerrero is actually triggered by the Maule
earthquake. The southward displacement of the GPS stations starts coincidently
with the earthquake and tremors. The long duration of tremors indicate a continuing deformation process at depth, which we propose to be the second subevent of the 2009-2010 SSE. We show a quasi-systematic correlation between
surface displacement rate measured by GPS and tremor activity, suggesting that
the NVT are controlled by the variations in the slip history of the SSE. This study
shows that two types of tremors emerge: (1) Those directly triggered by the passing waves and (2) those triggered by the stress variations associated with slow slip.
This indicates the prominent role of aseismic creep in the Mexican subduction
zone response to a large teleseimic earthquake, possibly leading to large-scale
stress redistribution.
A 5600-Year Historic and Paleoseismic Record of 10 Great Subduction
Earthquakes and the Seismic Cycle at the Copper River Delta, Alaska
Plafker, G., U.S. Geological Survey, Menlo Park, CA, [email protected];
LIENKAEMPER, J. J., U.S. Geological Survey, Menlo Park, CA, Lienkaemper
The Copper River Delta (CRD) on the Gulf of Alaska coast in the eastern
Aleutian arc is 135 km north of the PAC/NA plate boundary at the Aleutian
Trench and ~15 km above the gently north-dipping Aleutian megathrust. The
Mw 9.2 1964 Alaska earthquake was generated by >25 m slip displacement on
the megathrust and 2.2±0.2 m coseismic uplift in the Alaganic Slough estuary of
the CRD. The uplift abruptly brought a 12 km wide zone of intertidal mud flats
above the highest tide level resulting in rapid conversion to subaerial peat marsh,
ponds, and patchy forest.
Slough bank exposures and drill cores to 12.3 m below the marsh surface
show 9 pre-1964 layers of dominantly fresh-water peat 8–45 cm thick. Peat layers
commonly have sharp basal contacts and are overlain gradationally by beds of
intertidal mud 0.2–2.3 m thick. Each peat/mud “couplet”, represents an earthquake cycle of coseismic uplift and peat formation followed by gradual resubmergence into the intertidal zone and burial of the peat by intertidal sediments. The
base of the peat approximates the age of the “event horizon”. Median 14C calendar ages of the paleoearthquakes range from ~850 to 5600 calendar years ago.
The 1964 Alaska earthquake, with Mw 9.2 and coseismic uplift of 2.2 m,
followed a recurrence interval (RI) of ~850 years. Assuming that magnitude and
uplift scale roughly with RI, magnitudes of the 8 events for which RI’s are known
range from ~Mw 8.7 to 9.2+ and uplift per event is ~0.8–2.3 m (average ~1.5
m). We find no evidence of earthquake uplift events in the CRD strata less than
Mw 8.7.
Our data suggest that (1) Energy release in this segment of the Aleutian
megathrust is primarily during very large seismic events with minimum median
RI’s that exceed 300 yrs; (2) the 1964 event was the largest in 4600 yrs; (3) The
largest event, at 4600 yrs, was Mw 9.2–9.25, and (4) Coefficient of variation for
the sequence is ~0.36, which suggests more regular recurrence than most earthquake sequences.
Observation of a “Locking Event”: A Newly Observed Transient variation in
the Pattern of Slip Deficit at the Alaska Subduction Zone
Freymueller, J. T., Geophysical Institute, University of Alaska Fairbanks,
Fairbanks, AK, [email protected]
Over the last decade we have observed a variety of transient slow slip events.
Recently, I have detected what appears to be a “locking event”, in which a section
of a fault that had been creeping stopped for a few years, and then began creeping again. Two abrupt changes in site motion observed in the Lower Cook Inlet
region appear to be due to the cessation and resumption 5 years later of creep of
a large patch on the subduction plate interface. The first change in velocities is
consistent with an expansion of the downdip width of the locked zone by ~40
km in late 2004. The second change in early 2010 was opposite in sign to the first,
returning velocities to very close to their pre-2004 values. The change appears to
be synchronous across most or all sites, position changes are linear on each side of
the change, and the change occurred within over less than a few months.
The occurrence of this event shows that the behavior of the subduction
plate interface is more dynamic than we thought, and may vary over a variety
of timescales. One interpretation of this discovery is that geodetic data can’t tell
us much about long-term seismic hazards at subduction zones—if the locked
zone can widen or narrow for reasons we don’t understand, then perhaps a region
observed to be creeping now might lock up later on. I think this interpretation
can’t be ruled out, but is unlikely. First, there is a good correlation (along strike)
between present-day geodetic locked zones and great earthquake ruptures at
several subduction zones, which would be unlikely if the present distribution of
locked and creeping behavior was unrelated to the long-term slip deficit that must
be released in earthquakes. Second, the fact that the velocity field has reverted
to the pre-2004 velocity field, or very close to it, suggests that there may be preferred states or a range of variation that is limited enough to preserve the observed
along-strike correlations.
Panel Discussion on Challenging the Idea of Seismic Coupling along
Subduction Zones: Sumatra Chile, Tohoku… What’s Next?
Segou, M., USGS, Menlo Park, CA, [email protected]; ELLSWORTH, W.,
USGS, Menlo Park, CA, [email protected]; THATCHER, W., USGS, Menlo
Park, CA, [email protected]
The Special Session held in the 2012 Annual Meeting of the Seismological Society
of America aims to promote the discussion between seismologists, geodesists and
geophysicists about earthquake occurrence along subduction zones. Extreme
events like the M9.2 Sumatra and M9.0 Tohoku earthquakes in the last decade
challenged our scientific knowledge in many ways. Can we determine the maximum expected magnitude for any subduction zone around the world? Is there any
evidence where future epicenters might be? Our answers rely on the existing data
but since these extreme events have return periods of a few thousand years our
system remains underdetermined. Can modern cutting edge technologies, such
as sea floor GPS, make amends for an incomplete and sometimes biased historical
catalog? Sumatra, Cascadia and Japan are a few cases where paleoseismic records
are extensive enough to support the calculation of long reccurrence intervals, but
what about other subduction zones? In many cases paleoseismic records rely on
tsunami deposits, but are there any other interesting features related to tsunamigenic extreme events? After the Tohoku earthquake is it scientifically justified to
consider that interplate seismic coupling is time-invariant? We expect that hosting a panel discussion will encourage the attendees to participate in exploring
the aforementioned main questions but also bring other important issues to the
attention of the scientific community.
and Simulations
Session Chairs: Ivan Wong
Site-Specific Probabilistic Seismic Hazard Analyses for Ground Shaking and
Fault Displacement in Downtown San Diego, California
Wong, I., URS Corporation, Oakland, CA, [email protected];
THOMAS, P., URS Corporation, Oakland, CA, [email protected];
ZACHARIASEN, J., URS Corporation, Oakland, CA, judy.zachariasen@
urs.com; SCHUG, D., URS Corporation, La Jolla, CA; STROOP, R., URS
Corporation, La Jolla, CA.
The Rose Canyon fault system traverses the city of San Diego and is the seismic
source that dominates the ground shaking hazard in the region. It also represents
a surface faulting hazard where it manifests itself at the ground surface. The slip
rate for the main Rose Canyon fault is not well constrained, but north of downtown it is estimated to be about 1 to 2 mm/yr. The fault zone comprises numerous
fault traces, including the Spanish Bight, Coronado, and Silver Strand-Descanso
faults, and extends across San Diego Bay and downtown San Diego, making it difficult to assess the proportion of slip occurring on each fault. We have performed
site-specific probabilistic seismic hazard analyses for both ground shaking and
fault displacement at a site in downtown San Diego. The site is located on the
San Diego fault, a minor active fault within the Rose Canyon fault system. We
have considered three possible rupture scenarios for strands of the Rose Canyon
fault system in downtown San Diego: (1) the San Diego fault is the link between
the Rose Canyon fault to the north and the Silver Strand-Descanso fault to the
south and ruptures coseismically with these faults; (2) the San Diego fault ruptures within a broad step over zone with other strands of the Rose Canyon fault
system; and (3) the San Diego fault branches from the Coronado fault and only
ruptures coseismically with the Coronado fault. We assigned the greatest weight
to scenario 2 where the San Diego fault is not an independent seismic source but
ruptures coseismically with other strands of the Rose Canyon fault system. At a
building code return period of 2, 475 years, the peak horizontal acceleration for
a soil site condition (VS30 275 m/sec) at our site is 0.75 g. For the same return
period, the probabilistic fault displacement for both primary and secondary
faulting is zero and hence was not considered a hazard at the site.
Dynamic Probabilistic Seismic Hazard Maps
Holliday, J. R., University of California, Davis, Davis, CA, jrholliday@
ucdavis.edu; RUNDLE, J. B., University of California, Davis, Davis, CA,
[email protected]
One of the loftier goals in seismic hazard analysis is the creation of an end-to-end
earthquake prediction system: a “rupture to rafters” work flow that takes a prediction of fault rupture, propagates it with a ground shaking model, and outputs
a damage or loss profile at a given location. So far, the initial prediction of an
earthquake rupture (either as a point source or a fault system) has proven to be the
most difficult and least solved step in this chain. However, this may soon change.
The Collaboratory for the Study of Earthquake Predictability (CSEP) has
amassed a suite of earthquake source models for assorted testing regions worldwide. These models are capable of providing rate-based forecasts for earthquake
(point) sources over a range of time horizons. Furthermore, these rate forecasts
can be easily refined into probabilistic source forecasts. While it’s still difficult
to fully assess the “goodness” of each of these models, progress is being made:
new evaluation procedures are being devised and earthquake statistics continue
to accumulate. The scientific community appears to be heading towards a better
understanding of rupture predictability. It is perhaps time to start addressing the
second step in the earthquake prediction system.
A Survey of Uses and Users of the USGS ShakeCast System
Lin, K., U.S. Geological Survey, Lakewood, CO, [email protected]; WALD, D. J.,
U.S. Geological Survey, Lakewood, CO, [email protected]
USGS ShakeCast, a post-earthquake application that automatically retrieves
earthquake data from ShakeMap, estimates shaking at users’ specific facilities,
and within minutes generates a potential damage assessment notification, facility
damage maps, and other Web-based products for emergency management and
response. With ShakeCast, users can automatically estimate the shaking levels at
their critical facilities, set thresholds for notification of damage for each facility,
and automatically notify responsible parties about the damaged facility so they
can set inspection and other priorities for response. Though available for the past
several years, recent ShakeCast system improvements and outreach have led to
a rather significant increase in users in 2010 and 2011, with representation over
a wide range of uses and user sectors. Primary users now represent government,
business, transportation, critical lifeline, utility, emergency management, and
international community sectors.
Many of the recommended improvements to the ShakeCast system, and in
fact much of the publicity, outreach, and financial support for ShakeCast, come
from several prominent users, including Caltrans, the U. S. Nuclear Regulatory
Commission (NRC) and the International Atomic Energy Agency (IAEA).
Domestically, key users include Caltrans, NRC, Bay Area Rapid Transit, East
Bay Metropolitan Utility District, Los Angeles Unified School District, Red
Cross, and Wal-Mart. Internationally, the IAEA takes advantage of the global
ShakeMap system for rapid and automatic estimates of shaking levels at nuclear
infrastructure around the world. To further inform and facilitate the use of
ShakeCast, three ShakeCast User Workshops were held in Pasadena, Oakland,
and Seattle over the past year. Further outreach has been made via web pages,
scientific, technical, and engineering meetings, and from users. Results of a recent
ShakeCast user/use survey following the recent workshops will be presented.
A Time-dependent Update of the New Zealand National Seismic Hazard
Model for the Canterbury Earthquake Sequence
Gerstenberger, M. C., GNS Science, Lower Hutt, New Zealand,
[email protected]; RHOADES, D., GNS Science, Lower
Hutt, New Zealand; MCVERRY, G., GNS Science, Lower Hutt, New
Zealand; BERRYMAN, K., GNS Science, Lower Hutt, New Zealand;
CHRISTOPHERSEN, A., GNS Science, Lower Hutt, New Zealand; FRY, B.,
GNS Science, Lower Hutt, New Zealand; NICOL, A., GNS Science, Lower Hutt,
New Zealand; Pettinga, J. R., University of Canterbury, Christchurch, New
Zealand; Steacy, S., University of Ulster, Coleraine, Ireland; Stirling, M.,
GNS Science, Lower Hutt, New Zealand; Reyners, M., GNS Science, Lower
Hutt, New Zealand; Williams, C., GNS Science, Lower Hutt, New Zealand.
In November 2011, a three day expert panel workshop was held to consider a
time-dependent update of the New Zealand National Seismic Hazard Model
(NSHM) for the Canterbury earthquake sequence. The sequence began in
September 2010 with the Mw 7.1 Darfield earthquake. It has continued with a
damaging sequence of events including the Mw 6.3 earthquake in February; the
June Mw 6.0 earthquake; and the December Mw 6.0 earthquake. These major
aftershocks have occurred in very close proximity to Christchurch. The sequence
is in what is a moderate hazard area in the NSHM. With significant rebuilding
effort required, a re-investigation of the NSHM was requested in terms of the
NZ building code and other needs. Initially a time frame on the order of weeks
was given for the update. On this schedule, modifications were made to both the
ground motion prediction equation and to the source models. To re-investigate
some of these decisions, a later expert panel workshop was convened.
The panel, made up of international and NZ-based scientists, was presented
with 50 questions for which they were expected to provide weights. The questions were divided into five categories: 1) Time-dependent seismicity models, 1
and 50 year forecast; 2) Long-term seismicity models, 50 year forecasts; 3) Min
and max magnitude of forecast models; 4) Depth distribution of forecast models; and 5) Variability in predicted ground motions. The experts were presented
existing work done in response to the Canterbury sequence; the goal of the workshop was not to develop new ideas for immediate consideration in the NSHM.
Understanding the uncertainty in the hazard was a primary goal of the workshop. To this end, the expert panel followed the methodology of Cooke where
the responses of each expert were weighted based on answers to questions which
targeted how well experts estimate the uncertainties in their own knowledge.
Here we will present the model and forecasts that resulted from the workshop.
Geomechanical Modeling of Induced Seismicity for Hazard Prediction
GOERTZ-ALLMANN, B. P., Swiss Seismological Service, ETH Zurich,
Zurich, Switzerland, [email protected]; BACHMANN, C., Swiss
Seismological Service, ETH Zurich, Zurich, Switzerland, [email protected];
GISCHIG, V., Swiss Seismological Service, ETH Zurich, Zurich, Switzerland,
[email protected]; WIEMER, S., Swiss Seismological Service, ETH Zurich,
Zurich, Switzerland, [email protected]
The analysis of seismicity induced by fluid injection in a geothermal reservoir
revealed a radial dependence of earthquake stress drop and Gutenberg’s b-value.
A linear correlation of stress drop with pore pressure, forward modeled using linear diffusion, suggests a causal link between low stress drop and high pore pressure perturbation near the injection well. To further investigate this observation,
we forward-model the seismicity cloud, including a semi-stochastic element to
obtain event magnitudes. We randomly distribute potential failure points (seeds)
in a 3D volume around the injection well and assign values for the principal
stresses to each seed using a Gaussian distribution around a regional background
stress. A seed will produce an event if the Mohr circle, defined by the effective
stress, crosses the assumed failure criterion. The effective stress is time-dependent
by forward modeling the pore pressure. Defining a linear relation between differential stress and b-value on the one hand and differential stress and stress drop
on the other allows us to assign stress drop and magnitude values to each event.
We assign magnitudes by randomly drawing from the underlying GutenbergRichter distribution of each seed. The result is a seismicity cloud evolving in space
and time. The same seed can fail consecutively with increasing pore pressure,
thus modeling repeating events. We can explain the radial dependence of stress
drop and b-value by simply introducing a dependence with differential stress.
Furthermore, we can estimate the probability of exceeding a certain magnitude
with time and distance from the injection point, which can be used for risk assessment. We can calibrate the synthetic seismicity to the real data. Performing such
a calibration repeatedly using an evolving measured seismicity cloud allows for a
real-time hazard prediction of an ongoing stimulation. This could be of use for
geothermal reservoir stimulations as well as for shale gas fracing.
Probabilistic Seismic Hazard Assessment of Eastern Marmara Region
Gulerce, Z., METU, Ankara, Turkey, [email protected]; Ocak, S.,
METU, Ankara, Turkey, [email protected]
The objective of this study is to evaluate the seismic hazard in Eastern Marmara
Region using an improved PSHA methodology. Two significant improvements
over the previous seismic hazard assessment practices are accomplished in this
study; advanced seismic source models in terms of source geometry and recurrence relations are developed and improved global ground motion models (NGA
models) are employed to represent the ground motion variability. Linear fault segments are defined and composite magnitude distribution model was used for all
seismic sources in the region to properly represent the characteristic behavior of
North Anatolian Fault without an additional background zone. Multi-segment
ruptures were considered using the rupture model proposed by Working Group
on California Earthquake Probabilities (WG-2003). Events in the earthquake
catalogue are matched with the seismic sources and scenario weights are determined by balancing the accumulated seismic energy. The uniform hazard spectra
at 10% probability of exceedance in 50 years hazard level for different soil conditions (soil and rock) are provided for specific locations in the region (Adapazarı,
Düzce, Gemlik, Izmit, Iznik and Sapanca) and compared to Turkish Earthquake
Code (TEC-2007) requirements. Hazard maps of the region for rock site conditions at the accepted levels of risk by TEC-2007 are provided to allow the readers
perform site-specific hazard assessment for local site conditions and develop sitespecific design spectrum for any site conditions.
Fault Zone
Session Chairs: Yehuda Ben-Zion, Tom Rockwell, and Frank
Vernon
Space Geodetic Investigation of Interseismic Deformation along the San
Jacinto Fault: Effects of Heterogeneous Elastic Structure and Fault Geometry
Lindsey, E. O., UCSD, La Jolla, CA, [email protected]; SAHAKIAN,
V. J., UCSD, La Jolla, CA, [email protected]; FIALKO, Y., UCSD, La Jolla,
CA, [email protected]; BOCK, Y., UCSD, La Jolla, CA, [email protected];
ROCKWELL, T. K., SDSU, San Diego, CA, [email protected]
The geodetic slip rate inferred across the San Jacinto Fault zone (SJFZ) is highly
variable, but recent estimates suggest a higher rate compared to geologically
inferred values. We investigate to what extent the geodetic rate is sensitive to
assumptions about the fault geometry and spatial variations in crustal rigidity, in particular compliant fault zones. To address this issue, we use a forward
model that incorporates heterogeneous elastic moduli computed from the SCEC
CVM-H seismic tomography model of Southern California, as well as other
higher-resolution tomographic models. The models are compared to surface
velocities derived from a combination of all available continuous and campaign
GPS sites in the region, processed in a consistent North American fixed frame
(NAFD), and InSAR data spanning 1992-2006. The parameter space is examined using an efficient Monte Carlo algorithm which evaluates the joint probability distribution for the model parameters and allows for a formal evaluation
of uncertainties and trade-offs. The inversion indicates that geodetic slip rates are
sensitive to even minor changes in the the assumed fault geometry, while heterogeneous elastic structure has only a small effect. Our results indicate that more
deformation is occurring across the Southern SJF zone than can be accounted for
by geologic slip rates on the Coyote Creek and Clark faults, suggesting a substantial amount of off-fault deformation. Further to the North near Anza, CA our
results are in better agreement with geologic measurements, consistent with the
more competent rock type and a more localized, single fault trace in that region.
We also investigated the presence of shallow creep on the fault near Anza, CA,
using a 400-m alignment array established across the fault in 1990. These data
appear to rule out shallow creep at a rate greater than 0.5 mm/yr.
Seismic Velocity Structure in the Trifurcation Area of the San Jacinto Fault
Zone and Surrounding Region from Double-Difference Tomography
Allam, A. A., University of Southern California, Los Angeles, CA, aallam@
usc.edu; BEN-ZION, Y., University of Southern California, Los Angeles, CA,
[email protected]
We present tomographic images of crustal structures in the southern California
plate boundary area, with a focus on the trifurcation area of the San Jacinto Fault
Zone (SJFZ), based on double-difference inversions of earthquake arrival times.
Large-scale regional structure of both Vp and Vs is established using travel times
of 359, 410 P- and S- wave phase picks for 5493 earthquakes (Mw>2.0) recorded
at 139 stations in Southern California. The examined 270km by 180km by 35km
volume stretches from Cajon Pass to the northernmost Imperial Fault Zone and
displays clear velocity contrasts across the central portion of the SJFZ and southern San Andreas faults, as well as low velocity zones along sections of the SJFZ,
most notably the trifurcation area, and in the Salton Trough, San Bernardino and
San Jacinto basins. In order to resolve additional details of the complex trifurcation area, we invert for Vp and Vs in a smaller 50km by 50km by 20km region. We
begin by using a uniformly spaced 500m grid, with 4280 earthquakes recorded at
20 stations, and intend to use a smaller grid spacing and additional data recorded
on densely-spaced near-fault instruments. Though ray coverage is limited at shallow depths, we obtain high-resolution images of seismic velocities from 2 to 12
km. We verify the resolution of our model results by calculating the derivative
weight sum (DWS) and by applying checkerboard tests. The current results indicate that the velocity of the trifurcation area as a whole is lower than adjacent
unfaulted material. In addition, there are clear velocity contrasts across the Buck
Ridge and Clark segments of the SJFZ, but not the Coyote Creek segment. The
Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong
(up to 20%) contrast at all resolvable depths. We will present updated results
based on finer grids and additional near-fault data at the meeting.
Comparison of Tectonic Tremor in California
Peng, Z., Georgia Institute of Technology, Atlanta, GA, [email protected];
CHAO, K., Georgia Institute of Technology, Atlanta, GA, kevinchao@gatech.
edu; AIKEN, C., Georgia Institute of Technology, Atlanta, GA, chastity.aiken@
gatech.edu
Recent studies have shown that deep tectonic tremor could be instantaneously
triggered by passing surface waves of regional and teleseismic earthquakes. So
far many distant large earthquakes have triggered tremors along the ParkfieldCholame section of the SAF in central California, and the ambient tremors (i.e.,
spontaneously occurred with triggering by distant earthquakes) are very active
in that region. By comparison, only the 2002 Mw7.9 Denali Fault earthquake
has triggered clear tremor along the Anza section of the San Jacinto Fault (SJF)
in southern California, and the central segment of the Calaveras fault in northern California (Chao et al., BSSA, 2012). In addition, ambient tremor has not
been detected with current instrumentation in both regions. It is not clear what
is the primary cause of such different behavior. Here we conduct a systematic
comparison of triggered and ambient tremor in California. We first search for
evidence of tremor in California triggered by the 2011 Mw9.1 Tohoku-Oki
earthquake. As was found before, while clear tremor has been triggered in central
California, only subtle tremor signals were observed during the large-amplitude
surface waves around the SJF in southern California. The surface wave amplitudes and pre-event back noises in these two regions are similar, yet the triggered
tremor amplitudes differ by nearly an order of magnitude. We suggest that such
difference could be related to different ambient tremor rate or tremor triggering
threshold in these regions. We are conducting a similar search of triggered tremor
associated with regional earthquakes in these regions. In addition, we have
detected low-frequency earthquakes (LFEs) during triggered tremor in northern
and southern California associated with the 2002 Denali Fault earthquake. We
plan to use those LFEs as template to scan the continuous data at other times for
evidence of ambient tremor at these regions.
Heterogeneity, Rotations of Source Tensors, and Volumetric Strain near
Faults from Focal Mechanism Data
Ross, Z. E., University of Southern California, Los Angeles, CA, zross@
usc.edu; BEN-ZION, Y., University of Southern California, Los Angeles, CA,
[email protected]; BAILEY, I. W., University of Southern California, Los
We examine spatio-temporal strain and displacement patterns using focal mechanisms of aftershocks in close proximity to southern California faults that sample
the entire range of seismogenic depths. This is done with the intent of quantifying large-scale heterogeneities, rotations, and volumetric changes of strain around
large rupture zones and near the brittle-ductile transition depth. Summations of
potency tensors are derived from earthquake focal mechanisms in space-time
regions with high densities of aftershocks. Rotation angles are computed between
local tensor sums and a regional reference mechanism tensor to quantify the spatio-temporal variations of mechanism heterogeneities. These angles are combined
with horizontal P and T axis projections for a simple visualization of source tensor properties. We observe statistically significant rotation of focal mechanisms
within a short spatio-temporal window after a mainshock, which evolves over
time to approach the orientation distribution of background seismicity. The focal
mechanisms are also used in conjunction with the elasto-static representation
theorem to obtain the evolving elastic displacement and strain fields produced by
the occurrence of earthquakes in different regions. Volumetric components and
other features of the calculated fields are compared with statistical characteristics
associated with the long-term seismicity.
Ground Motion Prediction Equations for Data Recorded in the Immediate
Vicinity of the San Jacinto Fault Zone
Kurzon, I., University of California San Diego, La Jolla, CA, ikurzon@
ucsd.edu; VERNON, F. L., University of California San Diego, La Jolla, CA,
[email protected]; BEN-ZION, Y., University of Southern California, Los
Angeles, CA, [email protected]; ATKINSON, G. M., University of Western
Ontario, London, ON, Canada, [email protected]
We present a new set of Ground Motion Prediction Equations (GMPEs) for horizontal Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and 5%
damped pseudo-acceleration spectra (PSA), developed for the immediate vicinity of the San Jacinto Fault Zone (SJFZ). The idea of developing a local GMPE
for a specific fault source is to provide clearer physical insight to the parameters
controlling ground motions, and potentially reduce the variability in their prediction. The analyzed dataset includes ~6000 PGA and ~8000 PGV observations from ~350 events related to the MW 5.2 Anza-Clark (AC) earthquake in
June 2005 and to the MW 5.4 Coyote Creek (CC) earthquake in July 2010. The
events span the magnitude range 1.5 ≤ M ≤ 5.5 and are recorded by up to 70 stations at distances ranging from the fault zone itself up to 100km away. In the
first stage, we examined the data against several previous GMPEs, such as the
Next Generation Attenuation models (e.g., Boore & Atkinson 2008, 2011) and
Cua & Heaton (2008). All of these models appear to underestimate the PGA
and PGV values of the motions in the higher magnitude range (4.5 ≤ M ≤ 5.5),
and to underestimate the response spectra for the complete magnitude range
(1.5 ≤ M ≤ 5.5) of the SJFZ events. These initial results reinforce the potential of
local GMPEs to increase our understanding.
We present several versions of the GMPE, including different schemes for
characterizing the site effects, and discuss their advantages and disadvantages.
Our San Jacinto Fault Zone GMPE may allow for better representation of path
and site effects, including within the near vicinity of the sources, and may aid
in mapping upper crustal heterogeneity within the San Jacinto Fault Zone area.
Using Spectral Ratios of Pore Pressure and Strain Observations Recorded at
EarthScope PBO Borehole Strainmeter Sites to Analyze Tectonic Deformation
and Changes in Well Parameters due to Nearby Earthquakes
Civilini, F., University of California Santa Barbara—Earth Research
Institute, Santa Barbara, CA, [email protected]; STEIDL, J. H.,
University of California Santa Barbara—Earth Research Institute, Santa
Barbara, CA, [email protected]
Water level fluctuations in response to earthquakes and tidal strains have been
observed in wells for many decades. The ratio of the increase or decrease in the
water level of an aquifer to the induced strain of Earth tidal forces is a well documented relationship, and can be used to calibrate various constitutive equations
of a poroelastic medium to obtain Skempton’s coefficient, a variable describing
the effect of induced strain on pore pressure. The pore pressure response of the
October 1999 Hector Mine earthquake (Mw 7.1) at the Garner Valley Downhole
Array (GVDA) is compared to pore pressure and strain observations from two
stations of the Earthscope Plate Boundary Observatory (PBO) for three magnitude 4.9 and above earthquakes in 2010: an El Mayor-Cucapah aftershock Mw
5.7 and two events of Mw 4.9 and Mw 5.4. Sudden pore pressure steps, both
positive and negative, ranging from 500 Pa to 10 KPa are observed in all but one
of the records, with the last being a more gradual decrease. The strain records
for the same earthquakes reveal sharp and sustained changes of strain matching
the pore pressure behavior. This suggests that in at least some of the cases, the
observed pore pressure responses correspond to tectonic deformation caused by
the strain field associated with the earthquakes. We will present spectral ratio
comparisons before and after these earthquakes for three observed strain components: areal strain, differential extension strain, and engineering shear strain.
The similarity of the pore pressure step during the 1999 Hector Mine event to
those of the 2010 earthquakes suggests that this response was also related to the
co-seismic tectonic strain field. A strainmeter recording at Garner Valley is not
available for the Hector Mine earthquake; therefore the ratio between the water
level and induced strain will be calculated using the BAYTAP-G code to generate
a synthetic tidal signal.
Summary of Paleoseismic Observations along the San Jacinto Fault
Rockwell, T. K., San Diego State University, San Diego, CA, trockwell@
geology.sdsu.edu; ONDERDONK, N., Cal State University Long Beach, Long
Beach, CA, [email protected]; MCGILL, S. F., Cal State University, San
Bernardino, CA, [email protected]; BUGA, M., San Diego State University, San
Diego, CA, [email protected]; SALISBURY, J. B., Arizona State University,
Tempe, AZ, [email protected]; PANDEY, A., San Diego State University, San
Diego, CA, [email protected]
Paleoseismic studies along the length of the San Jacinto fault zone demonstrate
that earthquake production over the past 1-4 millennia are consistent with new
slip rate estimates of 12-15 mm/yr. Paleoseismic data have now been acquired for
most major segments of the SJF, with sufficient resolution to start building a millennial-scale rupture history. Ages of past large earthquakes at Mystic Lake and
Hog Lake suggest that some events may rupture both the Clark and Claremont
segments together, and some Hog Lake events are recognized at Clark Lake in
the southern third of this segment. These possible correlations are consistent
with geomorphic observations along the Clark strand that indicate rupture of
the entire segment in Mw7.3 earthquakes, as likely occurred on Nov. 22, 1800.
Smaller Mw6.9 earthquakes, as in 1918, rupture only part of the northern Clark
segment. The surface rupture for 1918 has now been identified by geomorphology
and trenching, with an average of 1.25 m of displacement over at least 20 km. The
northern Coyote Creek fault last failed with up to 1.5m of displacement in the
past few hundred years, with the 1968 earthquake apparently filling in a section
of fault that experienced lower slip south of Borrego Mountain. Observations at
most sites show some degree of clustering of past events, although some of the
events in a cluster may represent rupture overlap. All of these observations support the idea that perceived segment boundaries are soft, even for a segmented
fault such as the SJF. Our data also suggest that slip during ruptures along the
SJF may behave in a bimodal fashion, with large earthquakes (M7+) that involve
entire segments, or multiple segments, and smaller events (M6.2-6.9) that fill in
areas of lower displacement.
Temporally Steady but Spatially Variable Middle Pleistocene to Holocene
Slip Rates across the San Jacinto Fault Zone, California
Blisniuk, K., BGC/UC Berkeley, Berkeley, CA, [email protected]; OSKIN,
M. E., UC Davis, Davis, CA, [email protected]; ROCKWELL, T., SDSU,
San Diego, CA, [email protected]; SHARP, W., BGC, Berkeley, Ca,
[email protected]; FLETCHER, K., BGC, Berkeley, CA, kathryn.elise.fletcher@
gmail.com
To understand how deformation is distributed across the Pacific-North America
plate boundary, we established a comprehensive slip rate history for the San
Jacinto fault zone (SJFZ) at multiple locations and for multiple time-intervals. At
six sites, we dated displaced landforms falling into three age brackets: the middle
Pleistocene, the late Pleistocene and the Holocene. Offsets are constrained from
field mapping and high-resolution LiDAR topography data, and displaced landforms were dated with 10Be and 26Al in buried sediments, U-series on pedogenic
carbonate clast-coatings, and/or in situ cosmogenic 10Be on surface clasts. Our
results show that (1) the slip rate across the bedrock portion of the southern SJFZ
has remained relatively uniform since the mid-Quaternary; (2) the slip rate of the
Clark fault strand of the SJFZ diminishes as slip is transferred to the adjacent
Coyote Creek fault strand; (3) pronounced southward-decreasing slip-rate gradients exist along both the Clark and Coyote Creek strands as fault-slip transitions
to folding of thick sediments of the Salton Trough; and (4) the summed slip rates
of ~12 to 16 mm/yr across the bedrock portion of the southern SJFZ, together
with similar observations by others on the southern San Andreas fault, suggest
that since the mid-Quaternary, deformation across the Pacific-North America
plate boundary at this latitude has been partitioned fairly evenly between the San
Andreas and SJFZ. This leaves about 40% of the plate motion to be accommodated on other structures across the region.
Late Holocene Slip Rate and Slip per Event of the Northern San Jacinto Fault
Zone
Onderdonk, N., CSU Long Beach, Long Beach, CA, nate.onderdonk@
csulb.edu; MCGILL, S., CSU San Bernardino, San Bernardino, CA, smcgill@
csusb.edu; ROCKWELL, T., San Diego State University, San Diego, CA,
[email protected]
Laterally displaced streams and paleochannels were used to calculate slip rate and
slip per event along the Claremont segment of the San Jacinto fault zone in the
Moreno Valley area. Trenches excavated across deflected paleochannels exposed
deposits that were used to date the time of abandonment and the corresponding
initiation of the active channels that have since been deflected by fault movement.
At one site, the active channel has been deflected 20 to 26 m since it was initiated
between 48AD and 371AD. The calculated slip rate is 10.2 to 15.9 mm/yr. If
we assume that the earthquake history recorded at the Mystic Lake paleoseismic
site, about 7 km to the southeast along the fault, is also valid for this site, the
measured offset occurred in eight or nine events. This results in 2.2 to 3.2 m of
slip per event. In the same area, 3D trenching was used to evaluate a buried chan-
nel offset across the fault. The channel was offset 5.4 to 5.9 m in two earthquakes
(which overlap in age with the last two events at Mystic Lake) giving a slip per
event of 2.7 to 3 m. A second paleochannel in the area was also trenched and
dating of deposits within the paleochannel indicates that the active channel was
initiated between 1426 and 1494 AD. This channel has since been deflected 8 to
12m across the fault. Comparison of the age of channel initiation with the Mystic
Lake event history suggests the displacement of the active channel has occurred
during the past three earthquakes, resulting in an average slip per event of 2.7 to
4 m. These slip per event data suggest the Claremont fault has experienced offset
amounts of at least 3 m in one or more of the last several earthquakes, and may
have ruptured in a similar manner in many of the past eight or nine earthquakes.
This corresponds to earthquake magnitudes of about M7, suggesting that the
northern San Jacinto fault zone may fail in large events that rupture the entire
length of the Claremont fault.
Slip Rate of the Northern San Jacinto Fault from Offset Landslides in the San
Timoteo Badlands
MCGILL, S. F., Dept of Geological Sciences, Calif State Univ, San Bernardino,
San Bernardino, CA, [email protected]; OWEN, L. A., Department of
Geology, University of Cincinnati, Cincinnati, OH, [email protected];
KENT, E., University of Plymouth, Plymouth, United Kingdom, emiko.kent@
plymouth.ac.uk; ROCKWELL, T. K., Dept of Geological Sciences, San Diego
State University, San Diego, CA, [email protected]; KENDRICK,
K. J., U.S. Geological Survey, Pasadena, CA, [email protected];
ONDERDONK, N., Dept of Geological Sciences, Calif State Univ, Long Beach,
Long Beach, CA, [email protected]; RHODES, E., Dept. of Earth and
Space Sciences, Univ of Calif Los Angeles, Los Angeles, CA, [email protected].
edu
Along the Claremont fault (northern San Jacinto fault zone) in the northern San
Timoteo badlands, boulder-size debris has been shed from exposed basement
northeastward across the fault, through landslide and/or debris flow processes
and form what we refer to as the Quincy Ridge debris fan. Our preliminary estimate of right-lateral offset of the fan is between 1.0 to 1.6 km. Be-10 dates from
9 boulders on the debris fan range from 16 to 68 ka, using the Lal (1991)/Stone
(2000) time-dependent model. However, two soil pits next to the 68 ka boulder
exposed a very well developed, 50-cm thick, argillic B horizon, exhibiting common, thick clay films and pedogenic reddening (7.5YR colors). Within this semiarid region of southern California, such well-developed Bt horizons are generally
associated with surfaces that are >100 ky old. This suggests that all nine of the
dated boulders may underestimate the age of the surface as a result of exhumation
and/or surface weathering, and that the slip rate is < 10-16 mm/yr since the late
Pleistocene. Analysis of a Be-10 depth profile near the 68 ka boulder is pending.
A younger landslide, the Ebenezer Canyon slide, is sourced from older
landslide or debris-flow deposits and has been right-laterally offset 270 ± 100 m.
Three boulders from the head scarp have Be-10 ages of 9 ka, 10 ka and 21 ka. The
headscarp was suddenly exposed by the landslide event but may have continued
to erode over time. Thus, 21 ka is considered a minimum age for this slide. Ten
boulders from the slide deposit itself have Be-10 ages of 8, 14, 17, 19, 27, 30, 34,
37, 74 and 93 ka. We interpret the 74 and 93 ka ages as inherited from the older
deposits that are the source of this slide. The four youngest boulders are younger
than the headscarp, and at least two of these are in locations where exhumeation
may have occurred. Using an age range of 21-37 ka we infer a slip rate of 5-18 mm/
yr since the latest Pleistocene.
Preliminary Paleoseismic Results from Southern Clark Fault, San Jacinto
Fault Zone, Southern California; Comparison to the Hog Lake Paleoseismic
Record
Buga, M. T., San Diego State University, San Diego, CA, [email protected];
ROCKWELL, T. K., San Diego State University, San Diego, CA; SALISBURY,
J. B., San Diego State University, San Diego, CA, [email protected]
We present preliminary results from a new paleoseismic site on the Clark strand
of the San Jacinto Fault Zone in Clark (Dry) Lake, western Salton Trough, southern California. We excavated trenches across a prominent lineament and surface
scarp, exposing a major fault with clear evidence of recurrent activity. The main
strand of the fault juxtaposes mid-Holocene lake deposits against late Holocene,
inter-bedded lake and alluvial deposits. We identified past surface ruptures by
the presence of filled fissures, upward fault terminations, folding and angular
unconformities, and presence of growth strata, from which we identify evidence
for eight surface ruptures that have occurred in the past 1900-2400 years. The
earliest two events are poorly dated with weak age control, but the past six events
suggest an average recurrence interval of 200 ± 114 years and a lapse time of over
210 years. The two most recent events are likely the November 22, 1800 and ca
1550 earthquakes, and correlate to events 1 and 2 at Hog Lake, ~50 km to the
NW, based on geomorphic offset mapping along the Clark fault. Three earlier
events (3, 4 and 5 at Clark Lake) are constrained to have ruptured between about
1209 and 915 AD and likely correlate to events 5, 6 and 7 at Hog Lake, suggesting
that even some of the dates used in this chronologic model contain some inheritance. Only one of these events at Clark Lake likely corresponds to one of the
three surface ruptures that occurred as a cluster at Hog Lake between about AD
1250 and 1450, suggesting that some of the ruptures in the Hog Lake cluster may
correspond to rupture of the northern part of the zone, similar to what occurred
in the 1918 M6.9 earthquake. These observations along with geomorphic offset
observations suggest that the entire Clark fault, and possibly the Casa Loma fault,
fail together in some large earthquakes (Mw7.3) whereas the northern Clark fault
may fail more frequently in M6.5-6.9 earthquakes, as occurred in 1899 and 1918.
The Fault Zone Architecture of the San Jacinto Fault, Southern California
Morton, N., San Diego State University, San Diego, CA, nissamorton@
gmail.com; GIRTY, G. H., San Diego State University, San Diego, CA, ggirty@
geology.sdsu.edu; ROCKWELL, T. K., San Diego State University, San Diego,
At Horse Canyon, the Clark segment of the San Jacinto fault juxtaposes
Cretaceous tonalites of the Horse Canyon (NE block) and Cahuilla Valley (SW
block) plutons. The fault zone architecture of the SW block consists of an ~9 m
thick damage zone characterized by the presence of mm-thick seams of microbreccia, and an ~19 cm thick transition zone that becomes progressively enriched
in gouge toward the ~3-18 cm thick secondary fault core. In contrast, within the
NE block, an ~1.25 m thick damage zone characterized by seams of gouge gives
way inward to an ~40 cm thick transition zone. Moving inward and toward the
mapped trace of the fault, the NE transition zone becomes progressively enriched
in gouge, and terminates against the 25 cm thick main fault core, a tabular mass
of black to gray aphanitic cataclasite. As these architectural elements are traced
to the SE, a lense of high grade schist separates the main from the secondary fault
core. Chemical, clay mineralogy, point-count, and volumetric strain data suggest that: (1) plagioclase was dissolved and quartz concentrated within the main
and secondary fault cores, (2) that the boundary of the main fault core marks
the illite/smectite to illite transition, (3) that Al, Ca, and Na mass were removed
from the fault core, while Mg, Mn, and Fe mass was introduced, (4) that following periods of healing, the fault core developed through multiple fragmentation
events, and (5) that relatively high dilational strains (~23–~27%) and porosities
occur within the fault cores and transition zones. We interpret these observations to imply that during and shortly after rupture fluid was focused through the
fault core dissolving plagioclase and driving reactions that resulted in the formation of illite. Given temperatures commonly cited for the illite/smectite to illite
transition, temperatures within the main fault core during such events may have
reached ~120o C.
Permeability Structure of the San Jacinto Fault Zone, Horse Canyon,
California
Mitchell, T. M., Instituto Nazionale di Geofiica e Vulcanolgia, Rome, Italy,
[email protected]; GIRTY, G. H., San Diego State University,
San Diego, CA, [email protected]; MORTON, N., San Diego State
University, San Diego, CA, [email protected]; ROCKWELL, T. K., San
Diego State University, San Diego, CA, [email protected]; RENNER,
J., Ruhr-University Bochum, Bochum, Germany, [email protected]
We report measurements of the permeability and porosity structure of the San
Jacinto fault zone at Horse Canyon. Here, the fault zone has been exhumed from
a depth of ~0.4 km, and consists of a narrow main fault core where the majority of fault displacement was accommodated, surrounded by an inner and outer
damage zone with a total fault zone width of ~45 m. The inner damage zone is
defined on the basis of the presence of observable macroscale gouge or microbreccia seams. Such structures were not observed in the outer damage zone where
mode I crack microscale damage is evident. The damage zone on the SW side
is significantly wider than that on the NE side of the main fault core. On the
SW side in the Cahuila Valley tonalite, permeability in the outer damage zone
increases from background levels of around 4 × 10 -19 up to 2 × 10 -15 m2 (10 MPa
effective pressure, ~400 m depth) while porosity increases from 1% to ~7%. The
peak in permeability and porosity correlates with the outer edge of the inner
damage zone. Permeability then decreases below that measured from the outer
damage zone and reaches a low of 2 × 10 -20 m2 and a porosity of 1.5% within
the main fault core. On the NW side of the fault in the Horse Canyon tonalite, porosity shows similar increases and decreases in the outer and inner damage
zone, but permeability in the outer damage zone increases more modestly from
background values of 9 × 10 -19 m2 to 7 × 10 -18 m2 towards the main fault core.
The above observations suggest microfracture connectivity and a strongly asymmetric permeability structure around the fault core, with the greatest increase in
permeability occurring on the SW side of the fault core. The nearly 5 orders of
magnitude increase in permeability toward the inner damage zone is likely due
to a connected and pervasive network of high density microfractures that may be
the result of damage from passing earthquake ruptures.
Speculations On the Role of Ground Shaking In the Production of High
Dilational Volumetric Strains In Saprock Adjacent to the Elsinore Fault,
Southern California
Maroun, M., San Diego State University, San Diego, CA, marckmaroun@
mac.com; REPLOGLE, C. T., San Diego State University, San Diego, CA;
CARRASCO, T. L., San Diego State University, San Diego, CA, taylorcarrasco@
gmail.com; COLBY, T. A., San Diego State University, San Diego, CA, tcolby12@
gmail.com; GIRTY, G. H., San Diego State University, San Diego, CA, ggirty@
geology.sdsu.edu; ROCKWELL, T. K., San Diego State University, San Diego,
Though saprolitization is commonly viewed as an isovolumetric process, data
obtained during this investigation, support the idea that significant volume
change has occurred during the conversion of corestone to saprock at 10 sites scattered about the trace of the Elsinore fault. Specifically, data presented here reveal
that at proximal sites, i.e., those that lie between 0 and 4 km of a major strand of
the Elsinore fault, dilational strains range from 25% ± 7% to 37% ± 7%. In contrast, at distal sites, i.e., those lying between 13 and 20 km to major strands of the
Elsinore fault, volumetric strains range from 6% ± 3% to 12% ± 5%. A positive
correlation between the orthogonal distance to the nearest strand of the Elsinore
and volumetric strain yields an R2 value of 0.80. Porosity values in proximal
samples range from 17% ± 9% to 26% ± 7%, and in distal samples from 10% ±
2% to 17% ± 3%. Preliminary results from a study of crack morphology suggests
that most of the porosity in studied saprock samples was primarily produced by
Mode I cracking, while chemical data and a linear regression model of porosity
versus volumetric strain indicates that as much as ~8% of the porosity was likely
produced by partial dissolution of plagioclase and biotite. This latter process produced statistically significant but relatively small losses of Ca, Na, Sr, and Ba mass
from plagioclase, and K, Fe, Mg, Mn, and Rb mass from biotite. Moreover, the
intensity of chemical weathering as reflected by the Chemical Index of Alteration
(CIA) at all distal sites is minor to moderate and ranges from ~52 to ~58. In
contrast, the CIA values at proximal sites are either like those at distal sites or
ranges from ~55 to ~72. Based on the above observations and data we speculate
that radiated seismic energy generated by ruptures along the Elsinore fault was
sufficiently strong enough to crack saprock, and thus produced the relatively high
dilational strains that decrease away from the fault trace.
Reconciling Precariously Balanced Rocks with Large Earthquakes on the
San Andreas Fault System
GRANT LUDWIG, L., University of California, Irvine, Irvine, CA, lgrant@
uci.edu; BRUNE, J. N., University of Nevada, Reno, Reno, NV, brune@seismo.
unr.edu; ANOOSHEHPOOR, R., US Nuclear Regulatory Commission,
Washington, DC, [email protected]; PURVANCE, M. D.,
University of Nevada, Reno, Reno, NV, [email protected]; BRUNE, R. J.,
Advanced Door, Costa Mesa, CA, [email protected]
Precariously balanced rocks (PBRs) are fragile landforms susceptible to toppling
by earthquakes.
Two major faults of the Pacific-North American plate boundary, the San
Andreas fault (SAF) and San Jacinto fault (SJF), merge to form one of the highest
seismic hazard zones in the USA, yet groups of fragile precariously balanced rocks
(PBRs) exist 7-10 km from the SAF-SJF junction where repeated shaking from
large earthquakes should have toppled them. We address this apparent contradiction by measuring fragilities of PBRs and examining the pre-instrumental and
paleoseismic record of earthquakes on the SAF and SJF. We show that observations of surviving PBRs, together with paleoseismic data, can be used to infer the
pattern of fault rupture over many seismic cycles. We infer that the large A.D.
1812 earthquake jointly ruptured the SAF and SJF, helping to explain PBR survival, damage to historic California Missions, and absence of rupture on the SAF
near San Bernardino. We find a pattern of complex rupture at the intersection
of the SAF and SJF, a complex trans-tensional step-over where ruptures initiate,
terminate, or propagate with persistent low ground motions that enable survival
of PBRs.
The July 7th 2010 M 5.4 Borrego Springs Earthquake as Recorded by PBO
Geodetic and Seismic Instruments
HODGKINSON, K. M. H., UNAVCO, Boulder, CO, hodgkinson@unavco.
org; BORSA, A., UNAVCO, Boulder, CO; MENCIN, D., UNAVCO, Boulder,
CO; WALLS, C., UNAVCO, Boulder, CO; FOX, O., UNAVCO, Boulder, CO;
Van Boskirk, E. UNAVCO, Boulder, CO.
On July 7th 2010 a M5.4 earthquake occurred on the Coyote Creek segment of
the San Jacinto fault about 13 miles north-north west of Borrego Springs. The
event was preceded by a M4.9 earthquake in the same area 4 weeks earlier and,
there have been four earthquakes of M5 and greater within a 20 km radius of the
epicenter in the past 50 years. UNAVCO has installed an array of geodetic and
seismic instruments around the San Jacinto fault as part of the Plate Boundary
Observatory (PBO). Along the length of the fault and its associated segments
PBO operates 25 GPS stations within 20 km of the surface trace; ten of these span
the two splays which produced the M6.5 1968 Borrego Mountain and M6.7 1987
Superstition Hills earthquakes. There are eight GPS stations and nine boreholes
sites in the Anza area. Most of the borehole sites contain a GTSM21 4-component strainmeter, a Sonde-2 seismometer, a MEMS accelerometer and a pore pressure sensor. Thus, the array has the capability to capture plate boundary deformation processes with periods of milliseconds (seismic) to decades (GPS). In this
study we will present the signals recorded by the different instrument types for
the 7 July 2010 event and will compare the coseismic displacements recorded by
the GPS and strainmeters with the displacement field predicted by Okada [1992].
All data recorded as part of the PBO observatory are publically available from the
UNAVCO, the IRIS DMC and the NCEDC.
Geomorphic Evidence for Structural Evolution of the Northern San Jacinto
Fault Zone in the San Timoteo Badlands
Kendrick, K. J., U. S. Geological Survey, Pasadena, CA, [email protected];
MORTON, D. M., U.S. Geological Survey, Riverside, CA, douglasmmorton@
Using a distance- and azimuth- dependent cluster analysis, we divide the
seismicity to several clusters. For each cluster we fit a plane, corresponding to the
dominant alignment of the cluster and reflecting a possible main fault surface at
this location. In order to validate the orientation of the fault plane we examine
the focal mechanisms of the events in the cluster. Our initial results show good
agreement, for several segments of the SJFZ, between the dominant focal mechanism and the plane fitting for each cluster. In addition to the re-construction of
local fault structures, the method can be used through the generated fault structures to improve constraints and reduce errors of the focal mechanisms.
Observations and Implications
Session Chairs: Gareth Funning and Mike Floyd
Seismotectonics of the Lake Van Region and the 23 October 2011 Van
Earthquake (Mw = 7.1)
Gülen, L., Sakarya University, Serdivan, Sakarya, Turkey, lgulen@sakarya.
edu.tr; UTKUCU, M., Sakarya University, Serdivan, Sakarya, Turkey,
[email protected]; BUDAKOGLU, E., Sakarya University, Serdivan,
Sakarya, Turkey, [email protected]; YALCIN, H. D., Sakarya
University, Serdivan, Sakarya, Turkey, [email protected]; Güneş, Y.,
KOERI, Bogazici Unıversity, Cengelkoy, Istanbul, Turkey, [email protected].
tr; KALAFAT, D., KOERI, Bogazici Unıversity, Cengelkoy, Istanbul, Turkey,
gmail.com
[email protected]
The northern San Jacinto Fault (SJF) exhibits the complexity of a youthful fault
system. A restraining left bend in the Claremont fault strand has deformed
the late Cenozoic formations of the San Timoteo badlands (STB) into a major
anticline on the NE side of the fault. Patterns of deformation, uplift, and erosion clarify the mechanism of evolution of the restraining bend. The region of
active folding and uplift corresponds to modeled uplift determined from fault
configuration. Uplift rates range from 0.35 to 1.0 m/ka. Once these folded and
uplifted sediments are displaced laterally from the region of uplift they are progressively eroded. Maximum denudation is located just to the SE of the restraining bend. A progression of drainages has developed in these uplifted sediments,
with the largest and oldest farthest from the region of uplift. Erosion rates range
from 0.07 to 0.14 mm/yr. The San Timoteo anticline, formed in the region surrounding the restraining bend, has been conveyed laterally out of this region and
with no further folding. The length of the fold corresponds approximately with
offsets reported for the SJF. We infer that this restraining bend has remained
fixed relative to the SW side of the fault, and dates from the initiation of fault
displacement. SE of the restraining bend is a releasing step-over between the Casa
Loma and the Claremont fault strands of the SJF. This step-over has lengthened
through time, and the spatial overlap of the fault strands is approximately equivalent to the total fault offset. Evidence of this lengthening of the step-over and
structural basin is preserved in the pattern of drainage development, the rearrangement of streams, and the migration of knickpoints in the STB. The stepover is lengthening towards the restraining bend from the SE. The Crafton Hills
fault complex has been laterally displaced towards the restraining bend from the
NW; continued encroachment through time will add to the complexity of this
landscape.
The tectonics of the Lake Van region is dominated by the active convergence of
the Arabian and Eurasian plates. These plates act as converging jaws of a huge
wise and the eastern Anatolia represents a crush zone which consists of numerous
blocks forming a crustal mosaic in between. The effects of continental collision
and the continuing plate convergence extends all the way north towards Caucasus
as evidenced by seismic activity and GPS measurements.
Fault plane solutions obtained from many earthquakes occurred in the
region indicate that the active convergence is taken up primarily as folding and
thrusting along the Bitlis-Zagros belt and along the Caucaus, but as mostly
oblique-slip faulting through a network of conjugate set of faults within eastern
Anatolia.
The 23 October 2011 Van Earthquake (Mw=7.2) occurred on Van thrust
fault that extends for 27 km on land in E-W direction between Lake Van and
Lake Erçek. The surface fault rupture of the Van thrust has been mapped by Emre
et al.(2011) and maximum 10 cm vertical displacements have been documented
along a northward dipping fault plane. Most of these observed displacements
developed several days after the occurence of the main shock suggesting that the
Van thrust fault is a blind thrust.
We have carried out a rupture process analysis using teleseismic body-wave
records obtained from IRIS-DMC. We inverted the teleseismic body waves
recorded by 35 stations to model the source process of the 23 October 2011 Van
Earthquake using the method of Kikuchi and Kanamori (1991). The rupture process can be satisfactorily modeled with two subevents that have seismic moments
of 3.47x1019 Nm and 2.34x1019 Nm, respectively corresponding to a total seismic moment of 4.59x 1019 Nm.
There are also a number of normal faults forming half graben structures
within the Lake Van basin (Wang and Finckh, 1978). The tectonic relationship
between these half grabens and the Van thrust fault needs to be investigated.
Local Fault Structures of the San Jacinto Fault Zone Based on Earthquake
Locations and Focal Mechanisms
Kurzon, I., University of California San Diego, La Jolla, CA, ikurzon@
ucsd.edu; VERNON, F. L., University of California San Diego, La Jolla, CA,
[email protected]
We present initial results on re-construction of fault-structures integrating surface fault traces, locations of seismic events, and focal mechanism heterogeneity. The method is developed for the San Jacinto Fault Zone (SJFZ), due to its
complexity in comparison to other large strike-slip fault zones (i.e., San Andreas
Fault). Unlike the San Andreas Fault, characterized by relatively straight fault
traces, coalescence of seismicity around the traces, and relatively homogeneous
strike-slip focal mechanisms, the SJFZ shows far more diverse features. Along its
~150km, segmentation is more complex with many sub-parallel traces, the seismicity clusters in numerous clouds shifted from the traces by several km, and the
focal mechanisms are very heterogeneous showing also significant normal and
reverse components, and in some cases solutions that are perpendicular to the
local fault traces.
Geologic and Engineering Observations from the Van Earthquake of 2011
Scharer, K., USGS, Pasadena, CA, [email protected]; KUTERDEM,
K., AFAD, Ankara, Turkey, [email protected]; ERKMEN, C., AFAD,
Ankara, Turkey, [email protected]; TEKIN, B., AFAD, Ankara, Turkey,
[email protected]; Çolakoğlu, Z., AFAD, Van, Turkey, zahide.
[email protected]; ÇELEBI, M., USGS, Menlo Park, CA, [email protected];
HOLZER, T., USGS, Menlo Park, CA, [email protected]
We report on observations from an USGS-AFAD collaboration of the surface
deformation produced during the Van earthquake. Snow cover limited observation of geomorphic features such as fractures and fault scarps, but our field observations combined with reports from AFAD, ITU, and MTU (http://supersites.
earthobservations.org/van.php) show that the Van event can be added to a number of large earthquakes with reverse slip for which there is limited to no surface
slip, such as 2010 Haiti, 1994 Northridge, CA, and 1989 Loma Prieta, CA. In
Turkey, surface offsets with a mix of reverse and dextral motion were small (<10
cm) and identifiable largely where cement irrigation structures and roads crossed
a line oriented ~N75E for just under 12 km eastward from the shoreline of Lake
Van. The trend of the breaks is coincident with (1) an exposure of fault gouge
cutting through Quaternary lacustrine deposits exposed in a road cut and (2) the
southwestern margin of an uplift bullseye predicted in some InSAR results. Due
to significant differences in the hypocentral location, it is unclear if the breaks are
located at the up-dip projection of the co-seismic fault rupture, or if the offsets
represent triggered slip along a nearby, older fault. Old scarps and uplifted surfaces
at the base of the mountains are characterized by short reaches and complicated
morphologies, suggesting a north-dipping master fault that breaks into multiple
splays at the surface. The western edge of Lake Ercek is close to the epicenter
declared by several institutes (USGS, AFAD, KOERI) but showed no evidence
of 2011 uplift. The shaking caused significant damage to the built environment in
the largest towns and in nearby villages. In both Ercis and Van, dozens of mid-rise
reinforced concrete frame buildings with infill walls collapsed causing fatalities.
In the future, similar failures could be avoided in seismic regions by using shear
wall dominant lateral load carrying systems rather than frame systems.
Geotechnical Field Observations from 23 October 2011 Van Earthquake (Mw =
7.1)
Gulerce, Z., METU, Ankara, Turkey, [email protected]; ÇETİN, K. Ö.,
METU, Ankara, Turkey; Yilmaz, M. T., METU, Ankara, Turkey; Huvaj,
N., METU, Ankara, Turkey; Ünsever, Y. S., METU, Ankara, Turkey;
Ünsal, S., METU, Ankara, Turkey; Sağlam, S., METU, Ankara, Turkey;
Sandikkaya, M. A., METU, Ankara, Turkey.
On 23rd October 2011 a magnitude 7.1 (Mw=7.1) earthquake hit the cities of
Van and Erciş located in Eastern Turkey. A reconnaissance team from Middle
East Technical University Geotechnical Engineering Division visited Van, Erciş
and many other small towns where most of the damage due to this devastating
earthquake occurred, immediately after the mainshock. The most attention was
given to the compilation of geotechnical and earthquake engineering related data
such as field case histories of landslides at natural slopes or highway embankments, rock falls, seismic soil liquefaction-induced lateral spreading and settlement, and sand boils. Most of the liquefaction-related failures were observed in
the near vicinity of the Lake Van. During the site surveys in-situ samples were
taken and laboratory experiments were performed later on these samples to verify
the basic properties of the soil. Grain size distribution of the samples were analyzed and compared to grain size distribution curves of the potentially liquefiable
soils. Failure of a highway embankment (N38.83478, E43.42336) on Van-Erciş
Highway interrupted the traffic for some time after the earthquake. A preliminary analysis of the stability of the embankment was performed with the help soil
parameters determined in the laboratory by Atterberg limit test, sieve analysis
and triaxial test results. The observations on the scars of the rupture zone on the
surface were documented. Preliminary analysis results of the collected data, documented geotechnical field observations and ongoing site response studies on the
available 2-D soil profiles of ground motion recording stations will be presented.
Preliminary Investigation of Co-Seismic and Immediate Post-Seismic
Deformation Due to the 23 October 2011, Mw 7.2 Van-Ercis, Turkey, Earthquake
Using Space-Based Geodesy
Floyd, M. A., Massachusetts Institute of Technology, Cambridge, MA,
[email protected]; ERGINTAV, S., TÜBİTAK Marmara Research Center, GebzeKocaeli, Turkey, [email protected]; ÇAKIR, Z., Istanbul Technical
University, Maslak-Istanbul, Turkey, [email protected]; Doğan, U.,
Yildiz Technical University, Esenler-Istanbul, Turkey, [email protected];
ÖZENER, H., Boğaziçi University, Çengelköy-Istanbul, Turkey, ozener@boun.
edu.tr; ÇAKMAK, R., TÜBİTAK Marmara Research Center, Gebze-Kocaeli,
Turkey, [email protected]; AKOGLU, A. M., KAUST, Thuwal, Saudi
Arabia, [email protected]; Mccaffrey, R., Portland State University,
Portland, OR, [email protected]; King, R. W., Massachusetts Insitute of
Technology, Cambridge, MA, [email protected]; Reilinger, R. E.,
Massachusetts Insitute of Technology, Cambridge, MA, [email protected].
We present GPS and InSAR data for the co-seismic and immediate post-seismic
deformation (two months) associated with the 2011 Van-Ercis, Turkey, earthquake. 20 continuous GPS sites are located within 300 km of the epicenter, of
which 12 show displacements significant at a 2σ level (> ~ 5 mm). Additionally,
survey GPS sites from SE Turkey and Armenia densify the network available for
co- and post-seismic analysis. For survey sites with poorly constrained pre-earthquake velocities, we improve velocity estimates using a block model approach,
allowing further expansion of the network useable for the co-seismic solution.
Additionally, 8 new survey sites within the epicentral region were established
within 2 weeks of the earthquake for future, near-field post-seismic observations.
Fault location, geometry and slip parameters are solved by inverting the GPS data,
providing a preliminary co-seismic fault displacement estimate of 2.50±0.28 m
for a north-dipping plane with uniform slip. This is in good agreement with tele-
seismic waveform models that show (non-uniform) displacements of up to 2.6
m, as well as with our initial analysis of available co-seismic InSAR observations.
cGPS sites show post-seismic motion of a third to a half of the magnitude of their
co-seismic motion within the first two months after the earthquake, consistent
also with initial results of post-earthquake InSAR analyses that indicate rapid
after-slip in the immediate epicentral area. This earthquake demonstrates that
shallow thrust events occur in an area of otherwise broad right-lateral shear
between the Arabian continent and the Turkish-Iranian plateau, helping to
constrain the mode of tectonic accommodation displayed within the southern
part of this collision zone, and therefore the nature of seismic hazards. On-going
co-seismic analysis and post-seismic observations will also aid assessment of the
changing strain and Coulomb stress field with respect to other potentially seismogenic structures.
Finite Fault Slip Evolution Model for the 23 October 2011 Mw 7.1 Van, Turkey
Earthquake from Geodetic and Seismic Waveform Analysis
Fielding, E. J., Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA, [email protected]; POLET, J., Seismological
Laboratory, California Institute of Technology, Pasadena, CA, jaschapolet@
gmail.com; LUNDGREN, P. R., Jet Propulsion Laboratory, California Institute
of Technology, Pasadena, CA, [email protected]; YUN, S. H., Jet
Propulsion Laboratory, California Institute of Technology, Pasadena, CA,
[email protected]; MOTAGH, M., Helmholtz Center Potsdam, GFZ
German Research Center for Geosci, Potsdam, Germany, motagh@gfz-potsdam.
de; OWEN, S. E., Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA, [email protected]; SIMONS, M., Seismological
Laboratory, California Institute of Technology, Pasadena, CA, simons@caltech.
edu
A large Mw 7.1 earthquake struck eastern Turkey to the north of the city of Van
on 23 October 2011, causing extensive damage in Van and many surrounding
towns. We analyze geodetic images from synthetic aperture radar (SAR) data
acquired by the European Space Agency Envisat and Italian Space Agency
COSMO-SkyMed (CSK) satellites spanning the earthquake. We use both interferometric (InSAR) and pixel offset tracking or sub-pixel correlation of the SAR
images and GPS data to measure the coseismic deformation of the land surface.
The high spatial resolution and short 16-day time interval of the CSK (X-band,
3.1 cm radar wavelength) image pair (10-26 October) provide excellent coherence
and detail for the area it covers around the city of Van. The Envisat (C-band, 5.6
cm wavelength) SAR image pairs (two tracks) have coarser spatial resolution and
longer time intervals that may include snow cover that causes lower coherence,
but cover larger areas. The InSAR and pixel offsets in the along-track direction
(roughly north) show that the main rupture dips to the north and projects to the
surface near the southern edge of the mountains north of Van and optimization
of the fault geometry prefers dips near 52 degrees. Preliminary inversion for static
finite fault models using the geodetic data only indicates that nearly all of the
fault slip was at depths greater than about 8 km. Many smaller scale discontinuities or InSAR phase variations in the hills and mountains north of Van indicate
widespread slip on faults near the surface, including up to 1 m of offset on a short
segment, but the main deformation is essentially a blind thrust at depth. We are
planning to perform joint inversions of the geodetic data with teleseismic waveforms (body and surface waves) to estimate a fault slip evolution model for the
time history of slip.
The Source and Attenuation Characteristics of Ground Motions from the 23
October 2011 Van, Turkey Earthquake
Yenier, E., University of Western Ontario, Department of Earth Sciences,
London, ON, Canada, [email protected]; ATKINSON, G. M.,
University of Western Ontario, Department of Earth Sciences, London, ON,
A M7.1-earthquake hit the city of Van in eastern Turkey on 23 October 2011. Its
ground motions were recorded at distances up to 600 km in Turkey and neighboring countries. This study examines the source and attenuation characteristics
of the earthquake using empirical regression and stochastic ground-motion modeling techniques. Fourier amplitudes are regressed versus hypocentral distance
to determine ground motions at a reference distance of 100 km, due to the lack
of empirical data at closer distances. The rate of geometrical spreading is fixed at
-0.5. The quality factor defining the anelastic attenuation of ground motions is
expressed as logQ = 2.191 + 0.221(logf) + 0.448(logf)2 for frequencies between
0.1 and 20 Hz. This Q agrees well with typical values determined for western
North America at a wide range of frequencies. We also determined that there is
no evidence of regional variability of Q between eastern Turkey and neighboring
regions. The comparison of reference amplitudes at 100 km with a Brune source
model, constrained at long periods by the known seismic moment, suggests that
the ground motions of the Van earthquake decayed as Dhyp-1.07 within 100 km,
on average (where Dhyp is hypocentral distance). By playing back the geometric and anelastic attenuation effects, we infer an equivalent Brune stress drop for
this earthquake as 215 bars. A stochastic ground-motion model (equivalent point
source) using the determined source and attenuation parameters reproduces the
observed ground-motion amplitudes on average. The results of this study may be
used to guide the modeling and prediction of ground motions in eastern Turkey
and neighboring regions.
Session Chairs: Nilesh Shome and Mark D. Petersen
Seismic Sources at Surface, in Geologic Structures, and for Hazard Modeling:
Discrepancies and Uncertainties in Continental Environment
Okumura, K., Hirowhima University, Higashi-Hiroshima, Japan, kojiok@
mac.com
Both in unstable and stable continental areas, where large earthquakes occur
once in thousand or longer years, detection of fault geometry is usually challenging. It is, for example, because of seismic quiescence, slow strain rates, structural
complexities, or massive granitic crust. Seismic sources after long quiescence and
hence possible rupturing in the near future are invisible in such environment.
Remnants of past surface ruptures, namely active faults are in many cases only
evidence of earthquake potential. Mapping of active faults and paleoseismology
demonstrate the source area and probabilities, but the geometry and rupture
process at seismogenic depth are not determined unequivocally from the surface.
When there is sedimentary cover seismic profiling show upper a few kilometers
of the fault geometry, but it is usually above the seismogenic depth. Very thick
sediments are not often ruptured and the faults below are not visible in bedrocks.
The deformation of the sedimentary cover indirectly indicates the fault geometry. However, the deformation may be just a sum of various types of faulting
events. Detachments and low angle faults modeled by structural geology are also
equivocal. Kinetic interpretation of geologic section, for example the balanced
cross section, is a useful tool to understand geotectonic process. However, seismic
and geodetic observations do not always favor the interpretations. We need to
formalize the hard and complicated ways to reach to fault models from geologic
observations.
Active Faults, Geodesy and Seismic Hazard in the Northern Walker Lane
Wesnousky, S. G., University of Nevada, Reno, Reno, NV USA, wesnousky@
unr.edu; HAMMOND, W., University of Nevada, Reno, Reno, NV USA;
KREEMER, C., University of Nevada, Reno, Reno, NV USA, [email protected];
BORMANN, J., University of Nevada, Reno, Reno, NV USA, kreemer@unr.
edu; BRUNE, J. N., University of Nevada, Reno, Reno, NV USA, wesnousky@
unr.edu
Roughly 20-30 km of cumulative right-lateral crustal displacement and >5 mm/
yr of the ongoing relative right-lateral motion between the Pacific and North
American plates are observed in the northern Walker Lane. The right-lateral
shear has been accommodated in large part by the development of a set of discontinuous, en echelon, normal fault-bounded basins and perhaps significant vertical
axis rotations of the intervening crust. The observations provide an illustrative
example of how large amounts of crustal shear may be accommodated in the
absence of strike-slip faults and point to difficulties attendant to melding geologic and geodetic observations in the analysis of seismic hazard. In this particular case, the assumption that all geodetically observed shear across the area will be
recorded by earthquake displacements may be flawed.
Attenuation Relationships for HPGA: Sensitivity Analysis and Applications
Mebarki, A., University Paris Est, Marne la Vallee, France, Ahmed.Mebarki@
univ-paris-est.fr; Laouami, N., National Centre for Applied Research on
Earthquake Engineering, Algiers, Algeria, [email protected]; BENOUAR,
D., University of Science & Technology Houari Boumediene (USTHB), Algiers,
Algeria, [email protected]; Gherboudj, F., National Centre for Applied
Research on Earthquake Engineering, Algiers, Algeria, gherboudj_faouzi@
yahoo.fr
A large number of empirical relationships might be used for seismic hazard studies. Actually, the HPGA values are usually predicted on the basis of several objective parameters such as distances to the site under study, depth of the quake hypocenter and magnitudes, for instance, and error models that describe the difference
between theoretical and observed HPGA.
Furthermore, various probabislistic distributions might be adopted in
order to describe the uncertainties that affect the predicted HPGA values since
Log-Normal, Gaussian or Gamma distributions are the most widely used for this
purpose.
The present study provides a sensitivity analysis of the HPGA values provided by several existing attenuation relationships. A special attention is devoted
to the class of relationships that consider a coupling effect between the magnitudes (moment magnitude, mainly) and the distances to the considered sites (distances to the fault, epicentral or hypocentral distances, etc).
Recent earthquakes and several relationships are considered for this study.
Whereas Gaussian and Log-Normal distributions for the error model might be
adopted, it is however shown that considering Gamma distributions for the error
model that affects the HPGA and models coupling between magnitudes and
distances provide acceptable predictions of the HPGA values, for various soils
conditions.
An improved attenuation relationship is also proposed and its results are
compared to the observed results for various kinds of faults, soils (various countries from Asia, Europe, America, Africa) and a large range of magnitudes (even
strong eartquakes) and distances (a few kilometers up to hundreds of hypocentral
kilometers). Adaptations of these form of relationships to predict the spectral values (acceleration, velocity, etc) are under development.
Sensitivity analysis of the seismic hazard according to the attenuation relationships, errors model and uncertainties that affect the governing parameters is
reported.
Comparison of the NGA Horizontal Ground Motion Prediction Models to the
Turkish Strong Ground Motion Database
Gulerce, Z., METU, Ankara, Turkey, [email protected];
Abrahamson, N. A., PG&E, San Francisco, CA, [email protected];
Kargioglu, B., METU, Ankara, Turkey, [email protected]
The objective of this study is to evaluate the regional differences between the
worldwide based NGA ground motion models and available Turkish strong
ground motion data. Turkish strong ground motion data may show a divergence
from the NGA model predictions since only six earthquakes from Turkey out of
a total of 173 earthquakes were included in NGA data base (Chiou et al., 2008).
A strong motion data base using parameters consistent with the NGA ground
motion models (Abrahamson et al., 2008) is developed by including strong
motion data from earthquakes occurred in Turkey with at least three recordings
per earthquake. The dataset consists of 1204 recordings with rupture distances
range from 2 to 300 km from 284 earthquakes with magnitudes from 3–7.6.
VS30 values were estimated for each station and range from about 180 to 900 m/s.
The depth to rock (Z1.0 and Z2.5) parameters are not available for any ground
motion station, therefore default values for these parameters are estimated based
on VS30. The depth to top of the rupture values in the selected data set goes up
to 30 km, providing a broader range of depths than was available in the NGA
data set. Average horizontal component ground motion is computed for response
spectral values at periods of 0.0, 0.2, 0.5, 1.0, and 3.0 seconds using the GmrotI
definition consistent with the NGA models (Boore et al, 2006). A random-effects
regression with a constant term only is used to evaluate the systematic differences
in the average level of shaking. Plots of the residuals are used to evaluate the differences in the magnitude, distance, site amplification, and depth scaling between
the Turkish data set and the NGA models. Results of this study will provide a
basis for the applicability of horizontal component NGA models in probabilistic
seismic hazard assessment (PSHA) studies conducted in Turkey.
Capturing Epistemic Uncertainties in PSHA within a Logic Tree Framework:
Summing the Branch Weights to One is not Enough
Scherbaum, F., Earth and Environmental Sciences, University of Potsdam,
Potsdam, Germany, [email protected]; KUEHN, N. M., Earth and
Environmental Sciences, University of Potsdam, Potsdam, Germany, nico@geo.
uni-potsdam.de
Logic trees have become the most popular tool for the quantification of epistemic
uncertainties in probabilistic seismic hazard assessment (PSHA). In a logic-tree
framework, epistemic uncertainty is expressed in a set of branch weights, by
which an expert or an expert group assigns degree-of-belief values to the applicability of the corresponding branch models. Despite the popularity of logic-trees,
however, one finds surprisingly few clear commitments to what logic-tree branch
weights are assumed to be (even by hazard analysts designing logic trees). Here we
argue that it is important for hazard analysts to accept the probabilistic framework from the beginning for assigning logic-tree branch weights. In other words,
to accept that logic-tree branch weights are probabilities in the axiomatic sense,
independent of one’s preference for the philosophical interpretation of probabilities. We demonstrate that interpreting logic-tree branch weights merely as a
numerical measure of “model quality, ” which are then subsequently normalized
to sum up to unity, will with increasing number of models inevitably lead to an
apparent insensitivity of hazard curves on the logic-tree branch weights, which
may even be mistaken for robustness of the results.
Uncertainty in Site Amplification Estimation for Urban Seismic Hazard
Mapping
memphis.edu
Urban seismic hazard mapping projects incorporate the effects of local geology
into probabilistic and scenario earthquake ground motion and liquefaction
hazard maps to provide more realistic estimates of hazard. The St. Louis Area
Earthquake Hazards Mapping Project (SLAEHMP) is releasing the first 17
of 29 urban hazard maps this year, and urban hazard maps have already been
released for Memphis, TN (2004) and Evansville, IN (2011). Care must be taken
in discussing sensitivity (variation due to unrestricted range of possible values)
versus uncertainty (variation due to the observed range at a specific location).
Uncertainties in site response estimation add to the uncertainties in hazard
calculations and increase overall uncertainty at a site. The focus of this paper is
on the contribution to overall uncertainty of the site response calculations for
urban hazard estimates, which involve hazard calculations at a point and not site
differential or distributed portfolio calculations. Key sources of uncertainty in
site response calculations are (1) selection of input time series, (2) Vs profile and
depth-to-bedrock, (3) dynamic soil properties, and (4) the choice of site response
modeling computer program. Examples from St. Louis and Memphis illustrate
the impact of these uncertainties.
Statistical Study of Ground Motion Amplification in the Mississippi
Embayment
Malekmohammadi, M., The University of Memphis, Memphis, TN,
[email protected]; PEZESHK, S., The University of Memphis,
Effect of soil on frequency content and amplitude of ground motions (GM) has
long been under investigation. Structural engineers are especially interested in
the amplification of the GM amplitude and the spectral acceleration of earthquake waves propagating from the bedrock to the soil surface. In current study,
we focus on the Mississippi embayment area which has a pronounced yet not
fully understood influence on the amplification of GMs associated with the New
Madrid seismic zone. The goal of this study is to statistically investigate both the
linear and the nonlinear GM amplifications in the Mississippi embayment due
to the effects of site properties such as depth of sediment, geology, and the soil
profile as well as earthquake properties such as PGA, earthquake magnitude, and
the spectral acceleration at the bedrock.
Different sites are selected in the Mississippi embayment area. Sample sites
are selected to represent all range of soil thicknesses, PGAs, and geologic structure. Since the study area is poor in real data, stochastic point source model is
used to simulate GMs. Generic seismological parameters of the study region are
used as input for the computer program SMSIM which simulates GMs based on
the stochastic point source method. Deagreggation analyses are conducted for
each site to determine the dominant earthquake scenarios and use these scenarios
to generate GMs. Generated GMs are then propagated to the surface using program SHAKE91. Results are compared and verified with the computer program
NOAH, which computes the nonlinear wave propagation of saturated soil. GM
amplification for each site is calculated as the ratio of the spectral acceleration of
motion on the soil surface to the bedrock spectral acceleration.
Can Current New Madrid Seismicity Be Explained as a Decaying Aftershock
Sequence?
Page, M. T., U.S. Geological Survey, Pasadena, CA, [email protected];
HOUGH, S. E., U.S. Geological Survey, Pasadena, CA; FELZER, K. R., U.S.
Geological Survey, Pasadena, CA.
It has been suggested that continuing seismicity in the New Madrid, central U.S.
region is primarily composed of the continuing long-lived aftershock sequence
of the 1811-1812 sequence, and thus cannot be taken as an indication of presentday strain accrual in the region. We examine historical and instrumental seismicity in the New Madrid region to determine if such a model is feasible given
1) the observed protracted nature of past New Madrid sequences, with multiple
mainshocks with apparently similar magnitudes; 2) the rate of historically documented early aftershocks from the 1811-1812 sequence; and 3) plausible mainshock magnitudes and aftershock-productivity parameters. We use ETAS modeling to search for sub-critical sets of direct Omori parameters that are consistent
with all of these datasets, given a realistic consideration of their uncertainties,
and current seismicity in the region. The results of this work will help to determine whether or not future sequences are likely to be clusters of events like those
in the past, a key issue for earthquake response planning.
A New Likelihood Method for Estimating Recurrence Interval Parameters
from Paleoseismic Event Series
Biasi, G., University of Nevada-Reno, Reno, NV, [email protected];
SCHARER, K., USGS, Pasadena, CA, [email protected]
We developed a new method for estimating recurrence interval mean and distribution width parameters from paleoseismic event series. The approach overcomes
several difficulties in earlier approaches. We now include true dating uncertainties, naturally incorporate censored intervals, and identify the correlated ranges
of the distribution parameters. Because the results are in units of probability, our
new approach also permits quantitative comparisons between recurrence distribution functional forms. We develop recurrence parameter estimates for the
paleoseismic event series on a grid relating the interval mean and uncertainty
(“sigma”) space. Each grid point is considered as if it were the true distribution
mean and sigma. To estimate the probability of any single event series (one series
of exact event dates picked from paleoseismic event dates), we first take the analytical shape of the distribution and slice it into bins of some width, say 5 years.
Thus, each bin is the probability of a recurrence interval falling in that 5 year
period. The product of these probabilities over the intervals in the paleoseismic
series is the probability of that set of intervals given the model mean and sigma.
By sampling often from the actual event probability distribution functions, an
ensemble of probabilities is developed for that grid point, and the mean probability is taken. Repeating this on the grid of mean and standard deviation yields a
surface that is contoured to indicate the full range of means and sigmas that could
account for an observed paleoseismic event series, including radiocarbon-derived
uncertainties. This approach is readily extended to include the open interval since
the most recent event by adding one more interval drawn at random from the
grid point mean and sigma, but discarding any result less than the open interval.
We illustrate the approach with current event series from the San Andreas fault
system.
Uncertainties in Characterizing the Cascadia Subduction Zone and Their
Seismic Hazard Implications
Wong, I., URS Corporation, Oakland, CA, [email protected];
KULKARNI, R., URS Corporation, Oakland, CA; ZACHARIASEN, J.,
URS Corporation, Oakland, CA; DOBER, M., URS Corporation, Oakland,
CA; THOMAS, P., URS Corporation, Oakland, CA; YOUNGS, R., AMEC
Geomatrix, Oakland, CA.
We have evaluated the impacts of uncertainties in a seismic source model for the
Cascadia subduction zone on seismic hazard in the Pacific Northwest. The five
most significant seismic source parameters and their uncertainties have been
addressed using a logic tree approach: the eastern edge of the megathrust rupture
zone, segmentation, recurrence models, recurrence intervals, and maximum magnitudes. We have adopted the eastern rupture extent from the model of Wang and
Hyndman (2011). We have assumed that M 9 rupture extends down to (1) the
base of the coseismic transition zone (CTZ), (2) 30 km downdip, and (3) 10 km
updip of the base of the CTZ. We consider three possible modes of rupture for
the megathrust: (1) full rupture events around M 9; (2) intermediate-sized earthquakes of M 8 to 8.8, which rupture one of two possible segments in the southern
half of the subduction zone; and (3) smaller earthquakes (M < 8). Segmentation
of the Cascadia subduction zone is based on the model of Goldfinger et al. (2012).
Paleoseismic evidence supports full rupture and intermediate magnitude earthquakes but there is very little evidence for smaller earthquakes with the possible
exception of the 1992 M 7.2 Cape Mendocino earthquake. Time-independent
and time-dependent recurrence intervals have been estimated for full rupture
events based on the Holocene turbidite history of Goldfinger et al. (2012).
Temporal clustering of the M 9 earthquakes was addressed by including intercluster and intracluster recurrence intervals. Only time-independent recurrence
intervals have been estimated for the two southern rupture scenarios. We have
investigated the sensitivities to probabilistic hazard at several cities in the Pacific
Northwest by calculating the hazard along branches of our logic tree. The most
significant impact on the hazard for most of the Pacific Northwest was due to the
uncertainty in full rupture recurrence intervals.
Fault Slip Rate Variability and Consequences for Seismic Hazard and Seismic
Risk in Japan Resulting from Static Stress Changes Following the M 9.0
Tohoku Earthquake
Apel, E., Risk Management Solutions, Newark, CA, [email protected];
NYST, M., Risk Management Solutions, Newark, CA; WILLIAMS, C., Risk
Management Solutions, Newark, CA.
We calculate regional static stress changes following the M 9.0 Tohoku Japan
earthquake using twelve published models of co-seismic slip for the 11 March
2011 megathrust event. The published slip models all solve for the distribution
of slip along the ruptured megathrust interface using various data sets, seismic,
GPS, and tsunami, or some combination thereof. We model stress changes on
the subduction zones and crustal faults in northern Honshu to estimate regional
seismicity rate changes, fault slip rate changes, and the consequent impact on
earthquake hazard and risk in the area. We explore the sensitivity of the elastic
parameters on fault stress changes and the range of stress changes predicted by
these slip models on individual faults and subduction zones, the so-called receiver
faults. Generally, the slip models have consistent rupture area geometry and contain patches of high slip in similar areas, although the maximum amount of slip
per model varies between 20 and 60 meters. Patterns of stress change predicted
by the 12 slip models are similar; the range of the magnitude of stress changes on
receiver faults is significant in general and can be as high as 30 bars. Variability
in stress changes due to the various slip models appear to be most dependent on
the proximity of the receiver fault to the highest slip patches. Predicted stress
changes are also sensitive to changes in elastic parameters (i.e., the coefficient of
friction). We apply the 12 different calculated stress change models to our hazard
model seismic rates using both the clock reset and the recurrence rate methodology (Parsons, 2005). We then compare a suite of metrics between the original
model and the models with updated rates to assess 1) the impact on hazard and
risk from static stress changes and 2) the uncertainty associated with this type of
implementation.
Calculating Earthquake Recurrence Rates from Partially Complete
Earthquake Catalogs with Uncertain Magnitudes—from M* to N*
Youngs, R. R., AMEC Environment & Infrastructure, Oakland, CA, bob.
[email protected]
Two studies in the 1980s provided approaches for assessing unbiased earthquake
recurrence relationships from earthquake catalogs with uncertain magnitudes.
Tinti and Mulargia (1985) proposed an adjustment factor to apply to the computed recurrence rate, exp[–β2σ 2/2], where σ is the standard in the catalog magnitudes and β is the b-value in natural log units, β = bln(10). EPRI (1988) developed
an alternative approach in which the magnitudes are shifted by a factor before
computing the earthquake recurrence parameters. EPRI designated the shifted
magnitude as M* = M – βσ 2/2. For earthquake catalogs with homogeneous
magnitude uncertainty, the two approaches are equivalent. The advantage of the
EPRI approach is that it allows treatment of catalogs with variable magnitude
uncertainty. Furthermore, EPRI showed that the sign of the magnitude shift
depends upon whether the magnitudes are measured in the magnitude scale of
interest or obtained by a regression relationship from some other size measure.
Simulation testing demonstrated the equivalence of the Tinti and Mulargia
and EPRI approaches and also verified the change in sign of the M* that is necessary when the magnitudes are estimated from other size measures. However, this
testing indicated that the EPRI M* approach produced biased estimates when
applying the Weichert maximum likelihood approach to catalogs with magnitude dependent completeness. The proposed solution is to apply the Tinti and
Mulargia adjustment individually to each earthquake by computing an equivalent earthquake count N* = exp[β2σ 2/2] and using the sum of N* values for earthquakes in each magnitude bin in the Weichert algorithm. Simulation testing
demonstrates that the N* approach leads to unbiased recurrence parameters in
catalogs with magnitude dependent completeness and magnitudes derived from
a mixture of size measures.
The Use of Multi-Layer Source Zones in Assessing Uncertainty in the Spatial
Distribution of Earthquakes
Leonard, M., Geoscience Australia, Canberra, ACT, Australia, mark.
[email protected]; CLARK, D., Geoscience Australia, Canberra, ACT,
Australia, [email protected]; BURBIDGE, D., Geoscience Australia,
Canberra, ACT, Australia, [email protected]; COLLINS, C.,
Geoscience Australia, Canberra, ACT, Australia, [email protected]
The effect of ground motion models, site response and recurrence parameters (a,
b, Mmax) on the uncertainty in estimating earthquake hazard have been widely
discussed. There has been less discussion on the effect of the choice of source
zones and the implied seismicity model. In order to capture the variability in spa-
tial distribution of the seismicity the current Australian National Seismic Hazard
has adopted a multi-layer source zone model. This model attempts to capture the
variability of the spatial in the stable continental crust of Australia.
PSHA has an implied assumption that the spatial distribution of earthquakes within a source zone is either uniform or random—with the random distribution approaching uniformity as it becomes sufficiently dense. In no area of
Australia does the seismicity conform to either a random (single Poisson model)
or a uniform distribution, at almost any scale considered—in contrast it is highly
clustered. Generally, at least three Poisson models are required to match the
observed spatial statistical distribution in Australia; typically zones of low, moderate, and high seismicity. Using the full (not declustered) catalogue at least four
Poisson models are required.
In order to account for this uncertainty in seismic source zones we use a
three-layer source zone model, consisting of: 1) a Background layer, with three
zones covering 100% of the continent, based on geological and geophysical properties; 2) a Regional layer, of 25 zones covering ~50% of the continent, based on
the pattern of earthquake density; and 3) a Hotspot layer, of 44 zones covering
2% of the continent, based on the areas of sustained intense seismicity. In the
final hazard model the maximum of the three hazard values is used, rather than a
weighted average of the three layers. Additionally, the Hotspot layer has a lower
Mmax and so significantly reducing the affect of this layer for return periods of
2500+ years.
Probabilistic Seismic Hazard Assessment in Europe: Uncertainty Treatment
for a Harmonized Approach
Woessner, J., Swiss Seismological Service, ETH Zurich, Zurich, Switzerland,
[email protected]; DANCIU, L., Swiss Seismological Service, ETH
Zurich, Zurich, Switzerland, [email protected]; GIARDINI, D., Institute of
Geophysics, ETH Zurich, Zurich, Switzerland, [email protected]; and the
SHARE Consortium
Probabilistic seismic hazard assessment (PSHA) aims to characterize the best
available knowledge on seismic hazard of a study area, ideally taking into account
all sources of uncertainty. Results from PSHAs form the baseline for informed
decision-making and provide essential input to each risk assessment application.
Seismic Hazard Harmonization in Europe (SHARE) is an EC-FP7 funded
project to create a testable time-independent community-based hazard model for
the Euro-Mediterranean region. SHARE scientists are creating a model framework and infrastructure for a harmonized PSHA. The results will serve as reference for the Eurocode 8 application and will provide homogeneous input for
state-of-the art seismic safety assessment for critical industry.
Harmonizing hazard is pursued on the input data level and the model
building procedure across all tectonic features of the European-Mediterranean
region. We require transparent and reproducible strategies to estimate parameter
values and their uncertainties within the source model assessment and the contributions of the ground motion prediction equations (GMPEs).
The SHARE model accounts for uncertainties, whether aleatory or epistemic, via a logic tree. Epistemic uncertainties within the seismic source-model
are represented by four source model options including area sources, fault sources
and kernel-smoothing apporaches, aleatory uncertainties for activity rates and
maximum magnitudes. Epistemic uncertainties for predicted ground motions
are considered by multiple GMPEs as a function of tectonic settings and treated
as being correlated. For practical implementation, epistemic uncertainties in
the source model (i.e. dip and strike angles) are treated as aleatory, and a mean
seismicity model is considered. The final results contain the full distribution of
ground motion variability. The present contribution will feature preliminary
results and sensitivity analyses of the new Euro-Mediterranean hazard model.
Assessing Earthquake Source Models Under Uncertainty with Bayesian
Analysis and Parallel MCMC Algorithms
Cruz Jimenez, H., King Abdullah University of Science and Technology,
Thuwal, Kingdom of Saudi Arabia, [email protected]; Mai, P.
M., King Abdullah University of Science and Technology, Thuwal, Kingdom
of Saudi Arabia, [email protected]; Prudencio, E. E., Institute for
Computational Engineering and Science, U. Texas, Austin, TX, prudenci@ices.
utexas.edu
Recent destructive earthquakes such as those in Haiti and Chile (2010), and
Japan (2011), highlight the importance of computational earthquake seismology
and advanced ground-motion simulations for mitigating human and economical
losses. Reliable ground motion predictions, with quantified uncertainty, are critical for designing large civil structures (e.g. bridges, dams, buildings) and response
plans. With the advent of HPC, comprehensive uncertainty quantification of
the expected shaking levels when considering a large set rupture models is now
becoming possible.
In this feasibility study, we use Bayesian analysis to quantitatively rank candidate rupture model classes under uncertainty. The initially highly simplified
candidate models represent a Mw=6.5 earthquake with strike-slip fault mechanism with homogeneous slip on a vertical fault plane, for which ground-motions
are computed at a dense virtual seismic network. Different model classes are
proposed by choosing certain fault characteristics as random, e.g. width, and/or
length, and/or depth.
The ranking returns the model class that best simulates (among the proposed candidates) peak ground velocities with respect to the Boore and Atkinson
(2008) empirical attenuation relation.
Stochastic Event Sampling for M 9 Cascadia Megathrust Earthquakes:
Capturing the Uncertainties in the Potential Event Characterization
Williams, C. R., RMS, Newark, CA, [email protected]; GROSSI,
P., RMS, Newark, CA, [email protected]; MOLAS, G. L., RMS, Newark,
To capture the risk posed by M9 Cascadia megathrust earthquakes, a risk model
needs to include a stochastic event set that covers a wide range of potential realizations of future megathrust earthquakes. The Tohoku earthquake showed
that very rare events outside of historical event constraints should be considered
(i.e., expect the unexpected). The 2008 version of the National Seismic Hazard
Maps produced by the USGS limited the seismogenic rupture to the locked (elastic layer) and transition zones based on Flück and others (1997) through three
source models: the lock zone alone, the locked plus 1/2 transition zones and the
locked plus full transition zones. USGS researchers, as part of the next version
of the hazard maps (to be released in early 2014), have been examining the latest research into the down-dip extent of the seismogenic zone of the Cascadia
Subduction Zone. Constraints for the extent of rupture include surface deformation, observed seismicity (including episodic tremor and slip events, ETS) and
rheological limits to brittle rupture (based on the temperature and pressure seen
at depth). Examination of the risk (i.e., property loss estimates) posed by the alternative models in the 2008 version of the maps shows a two fold increase in the
risk with each expansion of the down-dip extent. This study examines a suite of
additional source characterizations to understand the potential risk implications
of down-dip extension of the Cascadia megathrust source including expansion
down to the upper extent of the ETS events as well as into the ETS zone. While
these source characterizations push the sources deeper, the eastern extent of the
rupture will be closer to the exposure concentrations of Seattle and Portland
potentially increasing the risk to these regions.
Quantification of Uncertainty in Seismic Hazard Assessment
Wang, Z., University of Kentucky, Lexington, KY, [email protected]
How to quantify uncertainty is a key element in any seismic hazard assessment.
In probabilistic seismic hazard analysis (PSHA), uncertainties are separated into
two types: epistemic and aleatory. Epistemic uncertainties are caused by lack of
knowledge or scientific understanding, whereas aleatory uncertainties are caused
by randomness. These two types of uncertainty are treated differently in PSHA.
Uncertainty in earthquake data and models cannot easily be separated, and may
be impossible to separate, however. For example, ground-motion uncertainty
(sigma) is treated as an aleatory uncertainty in PSHA, but it depends on the
ground-motion model, which is treated as an epistemic uncertainty. Thus, this
separation of uncertainty may not be meaningful in practice, and causes additional problems in seismic hazard assessment.
Alternative approaches for characterizing uncertainty in seismic hazard
assessment are needed. One such approach is to derive a ground motion hazard
curve at a site of interest directly from the input database in a way similar to the
flood hazard analysis. This approach characterizes uncertainty explicitly. It could
be used to derive ground-motion hazard curves from the input database of the
national seismic hazard maps. The hazard curves derived from this approach
could be compared with and constrained by instrumental, historical, and geological observations.
A New Tool for Trimming the Logic Tree: Assessing the Value of Hazard
Information
Porter, K. A., SPA Risk LLC, Denver, CO, [email protected]; FIELD,
E. H., US geological Survey, Golden, CO, [email protected]; MILNER, K.,
University of Southern California, Los Angeles, CA, [email protected]
We developed a tool based on OpenSHA (http://www.OpenSHA.org) that allows
one to quantify the risk implications of various hazard model components. For
example, the Uniform California Earthquake Rupture Forecast version 2.0 has
480 branches on its logic tree of 9 modeling decisions, often called epistemic
uncertainties. In combination with 4 next-generation attenuation (NGA) rela-
tionships, UCERF2 has 1, 920 branches. While each uncertainty has scientific
importance, it also has a socioeconomic significance. For example, greater uncertainty in an insurer’s economic risk translates to greater need for and higher cost
of reinsurance. From an economic viewpoint, there can be greater value in reducing some uncertainties than others through scientific investigation. We studied
the sensitivity of a statewide risk metric to each of UCERF2’s modeling alternatives, plus the NGA relationships. While many ways to examine the importance
of each modeling alternative can be implemented, the metric used here is expected
annualized loss to an estimated statewide portfolio of single-family woodframe
dwellings. The results are depicted in a so-called tornado diagram. The uncertainties that matter most to this risk metric are the earthquake recurrence model
(empirical vs. Poisson vs. elastic-rebound renewal) and the choice of attenuation
relationship, probably because these are the epistemic uncertainties that have significant statewide impact and the direction of the effect is fairly consistent. Risk
is much less sensitive to the other modeling decisions, probably because they are
regi

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