2006 Annual Meeting Seismological Society of America San

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2006 Annual Meeting Seismological Society of America San
2006 Annual Meeting
Seismological Society of America
San Francisco, California
2006 Annual Meeting
• Meeting Information
100th Anniversary Earthquake Conference
18–22 April
Convened jointly by
Seismological Society of America,
Earthquake Engineering Research Institute,
and Disaster Resistant California
Location
Technical sessions and tutorials: Moscone Center, 747 Howard St., San Francisco
Field trips: Depart from and return to Moscone Center
SSA conference hotel and side events: Palace Hotel, 2 New Montgomery St, San Francisco
Hosted by
U.S. Geological Survey, Menlo Park
Berkeley Seismological Laboratory, University of California, Berkeley
Key Dates and Deadlines
Palace Hotel Reservation Cutoff
16 March—www.1906eqconf.org or phone the hotel, (800) 325-3589
Current registration, session and field trip information Ongoing—www.1906eqconf.org/
Due to the joint nature of this conference, nothing is quite the
same as in past years. Details are available at the conference Web
site, www.1906eqconf.org/.
A Unique Conference
• The 2006 Annual Meeting will be unlike any in SSA history. Because SSA was founded in the fall of 1906 following the San Francisco earthquake, the 2006 annual meeting
will kick off SSA’s centennial commemoration.
• The 2006 Annual Meeting will commemorate the 100th
anniversary of the 1906 earthquake with this historic conference jointly convened by the Seismological Society of
America, the Earthquake Engineering Research Institute,
and Disaster Resistant California. It will bring together
earth scientists, structural engineers, and emergency planners concerned with earthquake science, engineering, and
emergency management. We expect more than 2500 participants.
This major conference will feature six concurrent activities:
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Seismological Research Letters
Volume 77, Number 2
1. The co-convened technical conference, including joint
plenary sessions and discipline-oriented sessions on special
topics, with presentations in both oral and poster formats;
2. Tutorials for professionals, teachers, and the public;
3. A wide variety of field trips during and after the conference;
4. Exhibits and demonstrations with a variety of vendors and
organizations;
5. Participation by community groups including the
Association of Bay Area Governments;
6. Daily press briefings to communicate scientific results, hazard assessments, and mitigation information to national
and regional policy makers and the public.
In addition to presentations on current earthquake research,
this conference will provide a forum to review what we have
learned, assess our current level of understanding and envision
future direction. Because SSA is joined this year by EERI and
DRC, the conference presents a unique opportunity for crossdisciplinary communication. A particular focus will be the
effort to extend the lessons learned since 1906 into the arena of
public policy.
March/April 2006
Headquarters Hotel
The historic Palace Hotel will serve as SSA headquarters during the conference. A bridge from the old world to the modern
city, the Palace debuted in 1875 with its vaulted ceilings and
Austrian crystal chandeliers to recreate the elegance and glamour of 19th century high society. The Palace survived the 1906
earthquake but was damaged in the fires that followed, then
lavishly restored. The hotel is within walking distance of the
Moscone Center.
Make your reservation before 16 March, 2006, to receive
the special rate of $159 (for either a king or double/double).
Register through the conference website (www.1906eqconf.
org/) or directly with the hotel at (800) 325-3589; identify the
group as the Seismological Society of America.
• Simon Winchester, author of A Crack in the Edge of the
World: America and the Great California Earthquake of
1906, will be the keynote speaker.
SSA Meeting Chairs
Carol Prentice and William Ellsworth
U.S. Geological Survey
Menlo Park
[email protected], [email protected]
Peggy Hellweg
Berkeley Seismological Laboratory
University of California, Berkeley
[email protected]
Special Events
Press Information
A large number of memorable special events will be included in
the registration fee. Please consult the Special Events section of
the conference website for details.
For SSA sessions: Mary George, [email protected]
For the joint meeting: Solem Associates, [email protected]
Of particular interest to SSA participants:
Additional Information
Registration: online at www.1906eqconf.org/
SSA Icebreaker—Monday, 17 April, Palace Hotel
Exhibitor registration: online at www.1906eqconf.org/
SSA annual luncheon—Wednesday, 19 April, Moscone Center
• Nicholas Ambraseys will receive the Harry Fielding Reid
Medal
• Emily Brodsky will receive the first Charles F. Richter Early
Career Award
• P. Patrick Leahy, Director of the U.S. Geological Survey,
will be the President’s Invited Speaker
Gala SSA Centennial Reception and Banquet—Thursday, 20
April, Palace Hotel
• Frank Press will receive the first SSA Public Service
Award.
Schedule at a glance: www.1906eqconf.org/schedGlance.htm
Field trips: see http://www.1906conf.org/fieldtrips.htm
Tutorials: see http://www.1906conf.org/tutorials.htm
If you do not have web access, or cannot use the conference
website to register, please contact Joy Troyer by telephone at
510-559-1784, fax at 510-525-7204, or email: [email protected]
org.
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March/April 2006
161
• Meeting Program
Overview of Technical Program
Sessions held jointly with the Earthquake Engineering Research Institute (EERI) and Disaster Resistant California (DRC) are indicated.
ORAL SESSIONS
Tuesday, 18 April
9–11:30 am
Plenary Session: Commemoration of the 1906 San Francisco Earthquake
2–3:30 pm
The Impact of the 1908 Lawson
Report on Earthquake Science
Nuclear Explosion Monitoring
Anniversary Session I
Earthquake Science in the 21st
Century: Understanding the Processes
that Control Earthquakes I
4–5:30 pm
The Northern San Andreas Fault: Nuclear Explosion Monitoring
100 Years of Scientific Study
Anniversary Session II
Earthquake Science in the 21st
Century: Understanding the Processes
that Control Earthquakes II
Wednesday 19 April
8:30–10 am Plenary session: Learning from the Past
10:30–12
The Giant Sumatran
Earthquakes of 2004
and 2005 (with
EERI)
Near-fault Ground
Motions from Large
Earthquakes (with
EERI)
Beyond the San
Andreas, the Other
Active Faults of
Northern California
How Seismologists,
Engineers and
Emergency Planners
Can Work with
Policymakers to
Improve Disaster
Planning and
Mitigation (EERI
session with SSA and
DRC)
2–3:30
The Giant Sumatran
Earthquakes of 2004
and 2005 (with
EERI)
Extending ANSS:
Next Generation
Earthquake
Monitoring I (with
EERI)
The M 7.6 Kashmir
Earthquake of 8
October 2005 (with
EERI)
Next Generation
of Ground Motion
Attenuation Models
(EERI session with
SSA)
4–5:30
Tsunamis
Extending ANSS:
Next Generation
Earthquake
Monitoring II (with
EERI)
Advances in Volcano
Seismology: Enhanced
Monitoring Capability
Through Application
of Complementary
Methods
Advances in
Liquefaction
Evaluation (EERI
session with SSA)
Thursday, 20 April
8:30–10 am Plenary Session: Assessing the Present
10:30–12
Paleoseismic
Characterization
of Earthquake
Recurrence and
Hazard Assessment I
Broadband
Simulations of the
1989 Loma Prieta and
1906 San Francisco
Earthquakes I
2–3:30
Paleoseismic
Characterization
of Earthquake
Recurrence and
Hazard Assessment II
Broadband
Constraints on
Simulations of the
Transonic Rupture
1989 Loma Prieta and Propagation
1906 San Francisco
Earthquakes II
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Seismological Research Letters
Volume 77, Number 2
Crossing the Fault
from Seismology to
Engineering: Bruce
Bolt Memorial
Session (with EERI)
March/April 2006
The Future of
Earthquake Research
(EERI session with
SSA and DRC)
Surface Fault Rupture Scenario for a M6.7
(EERI session with
Earthquake on the
SSA)
Seattle Fault (EERI
session with SSA)
4–5:30
Integrating Geology
and Geodesy in
Studies of Active
Faults
Global Seismicity and
Wave-speed Structure
of Earth’s Deep
Mantle and Crust:
Sessions in Honor
of the Seismological
Contributions of E.
Robert Engdahl
Using Regional
Velocity Structures
to Estimate Seismic
Hazard
Friday, 21 April
8–9:30
Faults Exposed!
Earthquake Warning and
Applications of ALSM data Alerting Systems: New
Technologies for Hazard
Mitigation and Emergency
Response (with DRC)
10–12
Plenary Session: Preparing for the Future
12:00
Closing Session
Ground Motions for
Engineering Design
(EERI session with
SSA)
Advances in Geodetic
Studies of Seismic Sources
The Earthquake
Professionals’ Top Ten
Initiatives (EERI session
with SSA and DRC)
POSTER SESSIONS
All posters should be in place at 8:00 am and will be displayed all day.
A. Modeling the Tectonic Evolution of the San
Tuesday PM
Andreas Transform Boundary through Time
B. Beyond the San Andreas, the Other Active Faults of
Northern California
C. The M7.6 Kashmir Earthquake of 8 October 2005
(with EERI)
D. Earthquakes and Seismicity Around the World
E. One Hundred Years and More: Historical
Instruments and their Recordings of Earthquakes
Wednesday AM J. Advances in Volcano Seismology: Enhanced
Monitoring Capability Through Application of
Complementary Methods
K. Recent Results from the 28 September 2004, M6.0
Parkfield, California, Earthquake
L. Paleoseismic Characterization of Earthquake
Recurrence and Hazard Assessment
F. Extending ANSS: Next Generation Earthquake
Monitoring (with EERI)
G. Monitoring and Modeling the Seismic Wavefield
H. Earthquake Sources: Theory and Practice
I. Earthquake CORE: Culture, Outreach, Resources
and Education
M. The Northern San Andreas Fault: 100 Years of
Scientific Study/The Impact of the Lawson Report on
Earthquake Science
N. Integrating Geology and Geodesy in Studies of
Active Faults
Q. Near Fault Ground Motions from Large
Wednesday PM O. Earthquake Science in the 21st Century:
Understanding the Processes that Control Earthquakes Earthquakes (with EERI)
P. Nuclear Explosion Monitoring Anniversary Session R. Hazard and Risk
Thursday AM
S. The Giant Sumatran Earthquakes of 2004 and 2005
(with EERI)
T. Tsunamis
U. Advances in Geodetic Studies of Seismic Sources
V. Global Seismicity and Wave-speed Structure of
Earth’s Deep Mantle and Crust: Sessions in Honor of
the Seismological Contributions of E. Robert Engdahl
W. Using Regional Velocity Structures to Estimate
Seismic Hazard
Thursday PM
X. Ground Motion: Assessment and Effects
Y. Broadband Simulations of the 1989 Loma Prieta
and 1906 San Francisco Earthquakes
Z. Crossing the Fault from Seismology to Engineering:
Bruce Bolt Memorial Session (with EERI)
AA. Earthquake Warning and Alerting Systems: New
Technologies for Hazard Mitigation and Emergency
Response (with DRC)
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Volume 77, Number 2
March/April 2006
163
Program for 2006 SSA Annual Meeting
Presenter is indicated in bold.
TUESDAY, 18 APRIL
PLENARY SESSION: Commemoration of the 1906 San Francisco Earthquake (see page 191)
9:00
Chris Poland: Introduction
9:30
Kevin Starr: The 1906 San Francisco Earthquake: an Historical Overview
10:00 Mary Lou Zoback: The 1906 Earthquake: Birth of Earthquake Science
10:30
Coffee Break
11:00 Thomas D. O’Rourke: The 1906 San Francisco Earthquake: An Overview of Ground Failure and Associated Lifeline/Fire
Impacts
11:30 Stephen Tobriner: The 1906 San Francisco Earthquake Physical Impacts
Concurrent SSA Oral Sessions
The Impact of the 1908 Lawson
Report on Earthquake Science
Presiding: Jack Boatwright and Carol
Prentice (see page 191)
Nuclear Explosion Monitoring
Anniversary Session I
Presiding: Bill Walter and Brian Stump
(see page 192)
Earthquake Science in the 21st
Century: Understanding the
Processes that Control Earthquakes I
Presiding: Bill Ellsworth and Greg van
der Vink (see page 194)
2:00
Location and Tectonics of the Focal
Region of the California Earthquake
of 18 April 1906: Evidence from the
Lawson Report and Later Studies.
Lomax, A.
The CTBT—a Treaty with Two Faces.
Dahlman, O.
Earthquake System Science: What It
Means and Where It’s Going. Jordan,
T.
2:15
Re-evaluating the Intensity
Seismic Source Location and Test Ban
Distribution of the 1906 San Francisco Verification. Douglas, A.
Earthquake. Boatwright, J. and
Bundock, H.
Paleoseismology in the 21st Century.
Weldon, R.
2:30
Triangulation Surveys, Elastic
Rebound, and Models of Slip in the
1906 Earthquake. Segall, P., Song, S.,
and Lisowski, M.
Earthquake Dynamics at the Crossroad
between Seismology, Mechanics and
Geometry. Madariaga, R. and AddaBedia, M.
2:45
The Lawson Report and Geologic
Development and Future of Explosion Fault Segmentation Effects on
Research Along the Northern San
Source Theory. Stevens, J.
Sequences of Dynamic Events. Shaw,
Andreas Fault. Prentice, C. and Niemi,
B.
T.
3:00
Mining the Lawson Report. Hoose, S. Frontiers and New Opportunities for
Remotely Triggered Earthquakes.
Seismic Monitoring Research. Ammon, Hough, S.
C.
3:15
A CAMEL-Based Assessment of
Earthquake-Induced Landslide
Hazards in the San Francisco Bay
Region, California. Keefer, D., S.
Miles, M. Swank, and J. Blair
3:30
Coffee Break
164
Seismological Research Letters
Experimental Research Programs
Designed for Improving Nuclear Test
Monitoring: Historical Aspects and
Future Considerations. Bonner, J. and
Stump, B.
Seismic Instrumentation—Past and
New Frontiers. Berger, J.
Volume 77, Number 2
March/April 2006
Panel Discussion
The Northern San Andreas Fault:
100 Years of Scientific Study
Presiding: Carol Prentice and Tina
Niemi (see page 195)
Nuclear Explosion Monitoring
Anniversary Session II
Presiding: Brian Stump and Bill Walter
(see page 196)
Earthquake Science in the 21st
Century: Understanding the Processes
that Control Earthquakes II
Presiding: Bill Ellsworth and Greg van
der Vink (see page 198)
4:00
Application of New Technology to
Mapping the Northern San Andreas
Fault. C. Prentice, Zachariasen, J.,
Koehler, R., Baldwin, J., Hall, N., and
Wright, R.
Improving Magnitude Detection
Thresholds Using Multi-event, Multistation, and Multi-phase Methods.
Schaff, D. and Waldhauser, F.
Overview of SAFOD Phases 1 and 2:
Drilling, Sampling and Measurements
in the San Andreas Fault Zone at
Seismogenic Depths. Hickman, S.,
Zoback, M., Ellsworth, W., Boness, N.,
Solum, J., and Malin, P.
4:15
The 1906 Earthquake and Northern
San Andreas Fault: Significant Source
of Near-Future Hazard? Wong, I. and
Zachariasen, J.
SH-Wave Generation by an Explosion
in a Complex Scattering Medium.
Toksoz, M. N., Chi, S., and Lu, R.
Observations of Fault Zone
Deformation, In Situ Stress and Pore
Pressure in SAFOD Phases 1 and 2:
Implications for Fault Zone Processes.
Zoback, M., Hickman, S., Ellsworth,
W., Boness, N., and Day-Lewis, A.
4:30
H.F. Reid, Elastic Rebound, and
Seismic Gaps. Jackson, D. and Kagan,
Y.
Source Scaling Analyses of Frequency
Dependent Energy Partition For
Regional P and S Phases From
Explosion Sources. Murphy, J. and
Barker, B.
Energy Partition of the 1999 Chi-Chi,
Taiwan, (Mw 7.6) Earthquake. Ma,
K.-F.
4:45
Paleoseismic Records of Earthquakes
on the Northern San Andreas Fault:
How Characteristic is the Great 1906
San Francisco Earthquake? Niemi, T.,
Zhang, H., Hall, N., and Fumal, T.
Observations of Pn-Lg Coda
Scaling and Implications for Seismic
Discrimination and the Explosion
Source. Patton, H. and Taylor, S.
Earthquakes Triggered by Silent Slip
Events: Improved Understanding of
Earthquake Process by Joint Analysis
of Seismic and Geodetic Data. Segall,
P.
5:00
Deep-Water Turbidites as Holocene
Earthquake Proxies along the Northern
San Andreas Fault System. Goldfinger,
C., Morey, A., Nelson, H.
A Lower Bound on the Standard
Error of an Amplitude-based Regional
Discriminant. Anderson, D., Walter,
W., Carlson, D., and Mercier, T.
A Decade of Episodic Tremor and Slip
observations in the Northern Cascadia
Subduction Zone. Rogers, G., Kao,
H., and Dragert, H.
5:15
How Space-time Interactions Organize Fundamental Limitations in Resolving Panel Discussion
the Northern San Andreas Fault
Power of Q Tomography. Xie, J.
System: Analysis Based on Recreating
Great Earthquakes in the Computer.
Rundle, J.
Tuesday PM, 18 April Poster Sessions
A3
A Proposed Model for Lithospheric Evolution during
Development of the Pacific-north American Plate
Boundary. Biasi, G.
Modeling the Tectonic Evolution of the San Andreas
Transform Boundary through Time (see page 198)
A4
Geologic Constraints on the Evolution of the San
Andreas Fault System—implications for Transform
Boundary Models. Powell, R.
A5
Scientific Visualization and Collaboration Tools
Enhance Understanding of Seismological Data. Kilb,
D., Nayak, A., and Smith, B.
A6
A Comparison between the Transpressional Plate
Boundaries of the South Island, New Zealand, and
Southern California, USA. Fuis, G., Kohler, M.,
Scherwath, M., ten Brink, U., and Van Avendonk, H.
A1
A2
Implications of Slab-window Volcanism in Coastal
California for Evolution of the San Andreas
Transform. McCrory, P., Wilson, D., and Stanley, R.
Making the San Andreas Plate Boundary in the Wake
of the Mendocino Triple Junction. Furlong, K.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
165
A7
A8
A9
A10
Giant Low-angle Faults Beneath the Palos Verdes
Anticlinorium, California. Sorlien, C., Broderick,
K., Seeber, L., Luyendyk, B., Fisher, M., Sliter, R., and
Normark, W.
B8
Geophysical Piercing ‘Features’ Defining Offset in
the San Andreas Fault System, Northern California.
Jachens, R., Wentworth, C., McLaughlin, R., and
Graymer, R.
GPS-derived Fault Slip Rates along the Northernmost
Segments of the Maacama and Bartlett Springs Fault
Zones, Northwestern California. Williams, T., Kelsey,
H., and Freymueller, J.
B9
Near-surface Geophysical Surveying of East San
Francisco Bay faults. Craig, M., Kimball, M., and
Lienkaemper, J.
B10
Potential Earthquake Hazards Associated with
Previously Unrecognized Blind Thrust Fault: Analysis
of the Marin County–Mt. Tamalpais Region. Johnson,
C., Furlong, K., and Kirby, E.
B11
A New 3D Finite-Element Model of the Hayward
Fault. Barall, M. and Simpson, R.
B12
Mapping the Deformational Behavior and Mechanical
Properties of the Hayward Fault. Furlong, K.,
Malservisi, R., and Gans, C.
B13
Fault-zone Discontinuities along the Hayward Fault,
Northern California, and Their Implications on
Earthquake Hazards. Ponce, D., Hildenbrand, T., and
Jachens, R.
B14
A 3-Dimensional Geologic Map of the Hayward
Fault. Phelps, G., Graymer, R., Jachens, R., Ponce, D.,
Simpson, R., and Wentworth, C.
B15
Earth Structure and Site Response in the Northern
San Francisco Bay Area. Lin, H.-I., Chen, Y., Sell, R.,
Mooney, W., Detweiler, S., Fletcher, J., and Boatwright,
J.
B16
The Evolution of a Plate Boundary System—Crustal
Structure, Seismicity and Volcanism in Northern
California. Hayes, G. and Furlong, K.
B17
Digital Compilation of Thrust and Reverse Fault Data
along the Northeastern Range Front of the Santa
Cruz Mountains, Southern San Francisco Bay Region,
California. D. Kennedy
B18
Analysis of the Seismicity of the San Gregorio and
Monterey Bay Fault Zones, Monterey Bay Region,
California. Simila, G., Stakes, D., Begnaud, M., and
McNally, K.
B19
Commemorate the 1906 Earthquake at the Bottom
of an Active-fault Trench. Stenner, H., Zoback, M.,
Lienkaemper, J., Wells, D., and Schwartz, D.
Insights into the Evolution of Faulting along the
Rodgers Creek-Healdsburg-Maacama Fault Zones,
Northern California, as Revealed by Gravity and
Magnetic Data. Langenheim, V., McLaughlin, R., and
Jachens, R.
Geologic Constraints on Long-term Displacements
along the Rodgers Creek, Healdsburg and Maacama
Fault Zones, Northern California. McLaughlin, R.,
Langenheim, V., Jachens, R., Sarna-Wojcicki, A., Fleck,
R., Wagner, D., and Clahan, K.
County. Lippincott, C., Merritts, D., Walter, R.,
Muller, J., and Springer, D.
Beyond the San Andreas, the Other Active Faults of
Northern California (see page 201)
B1
B2
Kinematics and Future Seismic Sources of the
Hayward Fault, California, from ERS and
RADARSAT PS-InSAR. Funning, G., Bürgmann, R.,
Ferretti, A., Novali, F., and Schmidt, D.
Late Holocene Slip Rate Investigation of the Maacama
Fault at the Haehl Creek site, Willits, California.
Larsen, M., Prentice, C., and Kelsey, C.
B3
Seismicity Rate Changes and Earthquake Forecasting
Beyond the San Andreas. Bowman, D., Colella, H.,
and Tiampo, K.
B4
Seismic-reflection Profiles in the Stepover Region
of the Southern Hayward Fault Reveal a NortheastDipping Hayward Fault and West-Directed Blind
Thrusting. Williams, R., Wentworth, C., Stephenson,
W., Simpson, R., Jachens, R., and Odum, J.
B5
B6
B7
166
A New Campaign GPS Network and Alinement Array
on the Bartlett Springs Fault. Murray, J., Svarc, J.,
Lienkaemper, J., Langbein, J., McFarland, F., Nishenko,
S., and Page, W.
Active Tectonic Deformation East of the San Andreas
Fault System—Sacramento-San Joaquin Delta Area,
California. Weber, J.
The Pacific Star Fault Zone—A Significant Newly
Recognized Structure in the San Andreas Fault System
on the Northern California Coast of Mendocino
Seismological Research Letters
Volume 77, Number 2
March/April 2006
B20
Faults and Potential Hazards Beneath the AlluvialCovered, Highly Populated Areas of the San Francisco
Bay Area Revealed by Seismic Images. Catchings, R.,
Goldman, M., Rymer, M., and Gandhok, G.
B21
Fault length and Implications for Seismic Hazards in
California. Black, N. and Jackson, D.
B22
Distribution of Aseismic Slip along the San Andreas
and Calaveras Faults from Repeating Earthquakes.
Templeton, D., Nadeau, R., and Bürgmann, R.
B23
Expected Fault Displacements along the BART
Concord-Bay Point Line, Alameda and Contra Costa
Counties, California. Kelson, K., Thompson, S., and
Matsuda, E.
The M 7.6 Kashmir Earthquake of 8 October 2005 (Joint
with EERI) (see page 205)
C1
C2
C10
Probabilistic Seismic Hazard Assessment of
Muzaffarabad, Azad Kashmir. Khwaja, A. and
MonaLisa
C11
Environmental Issues Relating to the 8 October 2006
South Asia Earthquake. Kelly, C.
C12
The Kashmir Earthquake of 8th October 2005, and
Landslides. Sinvhal, A., Pandey, A., and Pore, S.
Earthquakes and Seismicity Around the World (see page
209)
D1
Seismicity Northeast of the New Madrid Seismic
Zone and its Implications on the Hazard of the Area.
Shumway, A.
D2
Recent Microearthquake Swarms in the Yakima Fold
Belt, Southeastern Washington. Rohay, A.
D3
Location and Slip Distribution of the 2005 October
8 Kashmir Earthquake Rupture using Envisat SAR
Analysis. Fielding, E., Pathier, E., and Wright, T.
Shallow Seismicity of the Prince William Sound,
Alaska Region (1971–2001). Doser, D. and Veilleux,
A.
D4
The March 6, 2005, Magnitude 5.4 Charlevoix
Earthquake and Related Seismic Activity January
2000—December 2005. Peci, V., Drysdale, J.,
Halchuk, S., Bent, A., and Hayek, S.
D5
The 26 July 2005 Mw 5.6 Dillon, Montana
Earthquake. Stickney, M.
D6
Static Stress Change from the 8 October, 2005 M =
7.6 Kashmir Earthquake. Parsons, T., Yeats, R., Yagi,
Y., and A. Hussain.
The Damas (Mw 6.4), Costa Rica, Earthquake,
of November 20, 2004; Aftershocks and Slip
Distribution. Pacheco, J., Quintero, R., Vega, F.,
Segura, J., Jiménez, W., and González, V.
D7
The 2004 December 23 M8.1 Macquarie Earthquake.
Murphy, K., Abercrombie, R., and Antolik, M.
The Pattan, Pakistan, Earthquake of 1974.
Pennington, W.
D8
The Pulumur and Bingol Earthquakes of 2003
Provide Evidence for the Internal Deformation of the
Karliova Block between the North Anatolian and East
Anatolian Faults. Gulen, L., Kalafat, D., Gunes, Y.,
Pinar, A., Kuleli, S., and Toksoz, M. N.
D9
Seismic Activities of an Intra-continental Strikeslip Fault System: Kuhbanan Fault, Central Iran.
Shahpasandzadeh, M. and Shafiei, A.
Surface Ruptures of the 8th October 2005 Kashmir
Himalayan Quakes: Bridges as Strain Gauges? Grasso,
J.-R. and Mughal, M.
C4
Geodetic Constraints and Tectonic Implications of
the Mw = 7.6, 8 October 2005, Kashmir Earthquake.
Bendick, R., Bilham, R., Feldl, N., Khan, S. F., and
Khan, M. A.
C6
Kashmir (Muzaraffabad) Earthquake of October 8,
2005: Damages to Non-engineered Constructions.
Pore, S., Pandey, A., and Sinvhal, A.
Surface Ruptures and Rupture Kinematics of the
2005, Mw 7.6 Kashmir Earthquake from Sub-pixel
Correlation of ASTER Images and Seismic Waveforms
Analysis. Avouac, J.-P., Ayoub, F., Leprince, S., Konca,
O., and Helmberger, D.
C3
C5
C9
C7
Surface Features of the Mw 7.6, 8 October 2005
Kashmir Earthquake, Northern Himalaya, Pakistan:
Implications for the Himalayan Front. Yeats, R. and
Hussain, A.
C8
Damage to the Engineered Constructions Due to
Kashmir Earthquake of October 8, 2005. Pandey, A.,
Pore, S., and Sinvhal, A.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
167
D10
Fault Segment with a Maximum Offset of 10-meter
in the 1931 Fuyun Surface Rupture, NW China—An
Interim Report. Awata, Y. and Fu, B.
E9
Historical Earthquakes from Turkey and Neighboring
Countries. Meral Ozel, N., Bergeroglu, A., Kara, M.,
Bekler, F., and Kalafat, D.
D11
Preliminary Understanding of the Dynamics of the
1999 Chi-Chi Earthquake. Chen, X. and Zhang, H.
E10
Climate Change Investigations Using Historical
Seismograms. Uhrhammer, R. and Bromirski, P.
D12
Estimation of Frequency-magnitude Distribution
Based on Interevent-time Statistics. Hainzl, S.,
Scherbaum, F., and Beauval, C.
E11
D13
Moderate and Large Earthquake Activity along
Oceanic Transform Faults. VanDeMark, T. and
Ammon, C.
A Reexamination of the 1964 m 9.2 Alaska
Earthquake Rupture Process from the Combined
Inversion of Seismic, Tsunami, and Geodetic Data and
a Comparison with the 2004 Sumatra Earthquake.
Ichinose, G; Graves, R; Sommerville, P., and Thio, H.
Extending ANSS: Next Generation Earthquake
Monitoring (Joint with EERI) (see page 214)
D14
Theory of Transform-fault Trends. Rance, H.
D15
Variability of Atmospheric Circulation—an Initiator
of Strong Earthquakes. Bokov, V.
F1
Continuous Microtremor Monitoring: One Possible
Approach for Early Detecting the Damage of the Dam.
Chiu, H. C.
One Hundred Years and More: Historical Instruments and
their Recordings of Earthquakes (see page 212)
F2
The Kentucky Vertical Strong-motion Network.
McIntyre, J., Wang, Z., and Woolery, E.
E1
SeismoArchives at the IRIS DMC: Seismograms of
Significant Earthquakes of the World. Benson, R.,
Lee, W., Knight, T., Hutt, B., and Ahern, T.
F3
An Earthquake Detection, Identification and Location
System for the Northeastern U.S. Based on the Wavelet
Transform. Ebel, J.
E2
TESEO2: Turn the Eldest Seismograms into the
Electronic Original Ones. Pintore, S. and Quintiliani,
M.
F4
Observational Technologies Implemented for
USArray. Alvarez, M., Busby, R., and Fowler, J.
F5
E3
Monitoring Earthquakes Since 1887: The Berkeley
Seismographic Stations/Seismological Laboratory.
Uhrhammer, R., Hellweg, M., and Romanowicz, B.
Characterization of Near-surface Geology at StrongMotion Stations in the Vicinity of Reno, Nevada.
Pancha, A., Anderson, J., and Louie, J.
F6
E4
Seismic Recording and Instrumentation at the
Hawaiian Volcano Observatory. Nakata, J., Okubo, P.,
and Koyanagi, R.
New Computational Approaches for Structural
Damage Identification Using the Densely
Instrumented 17-Story Moment-Resisting Steel
Frame Factor Building. Kohler, M., Heaton, T., and
Bradford, C.
E5
74 Years of Southern California Earthquake Catalog.
Hutton, K., Hauksson, E., Jones, L., and Givens, D.
F7
99 Years of Earthquake Recording in the Utah Region
(1907–2006): Remaining Big Questions and Future
Instrumentation Strategies. Arabasz, W. and Pankow,
K.
F8
Earthquake Detection and Data Processing Systems at
the Alaska Earthquake Information Center. Ruppert,
N., Hansen, R., and Robinson, M.
F9
Analysis of Recent Earthquake Monitoring
Improvements in the United States. McNamara, D.,
Anderson, K., Gee, L., Earle, P. Leeds, A., Buland, R.,
Benz, H., Hutt, C., and Butler, R.
F10
Shake Table Tests of a Full Scale Reinforced Concrete
Wall Building: Real Time 50 Hz GPS Displacement
E6
MMI Attenuation and Historical Earthquakes in the
Basin and Range Province of Western North America.
Bakun, W.
E7
A Modern Re-examination of the Locations of
the 1905 Calabria and the 1908 Messina Straits
Earthquakes. Michelini, A., Lomax, A., Nardi, A.,
Rossi, A., Balombo, B., and Bono, A.
E8
168
The Stress Triggering Role of the 1923 Kanto
Earthquake, Japan. Nyst, M., Pollitz, F., Nishimura, T.,
Hamada, N., and Thatcher, W.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
Measurements. Bock, Y., Panagiotou, M., Yang, F.,
Restrepo, J., and Conte, J.
M., Abbott, R., Symons, N., Bartel, L., and Aldridge,
D.
F11
Spatial Gradient Analysis for Areal Seismic Arrays: A
New Method for Seismic Array Processing. Langston,
C.
G10
A New Finite-difference Method for Seismic
Applications. Nilsson, S., Petersson, A., Sjögreen, B.,
Rogers, A., and McCandless, K.
F12
Antelope-based Alarm Systems for Earthquake
Monitoring. Lindquist, K., Stachnik, J., Hansen, R.,
and Ruppert, N.
G11
Modeling Seismic Wave with Free Surface Topography
Using Traction Image Method. Zhang, W. and Chen,
X.
F13
Implementation of a Linear Shaker Using the Zero
Friction Air Bearings. Vrcelj, N.
G12
Effects of Ground Surface on Rupture Dynamics of an
Earthquake. Zhang, H. and Chen, X.
F14
Digital Accelerometer. Vrcelj, N.
Earthquake Sources: Theory and Practice (see page 219)
F15
The Mutual Benefit of Seismograph Installation at
Naval Hospital, Bremerton. Wilson, D., Kent, R.,
Swanson, D.
H1
Test of the Split Nodes Fault Model for Faulting in
Staggered Finite Difference Scheme. Dalguer, L. and
Day, S.
Monitoring and Modeling the Seismic Wavefield (see page
217)
H2
Optimal Seismic Station Placement for Source
Inversion. Page, M. and Carlson, J.
G1
Surface and Body Waves from Hurricane Katrina
Observed in California. Fehler, M., Gerstoft, P., and
Sabra, K.
H3
Resolving Fault Plane Ambiguity Using 3D Synthetic
Seismograms. Chen, P., Zhao, L., and Jordan, T.
H4
G2
Observations of Infragravity Waves at the Monterey
Ocean Bottom Broadband Station (MOBB).
Romanowicz, B., Dolenc, D., McGill, P., Neuhauser,
D., and Stakes, D.
Friction Laws and Complexity in Earthquake Rupture
Dynamics. Daub, E. and Carlson, J.
H5
Scaling Law of Slip Pinned by Fault Bends. Ando, R.
and Yamashita, T.
G3
The Earth’s Hum, Microseisms and Ocean Waves.
Rhie, J. and Romanowicz, B.
H6
Fault Interaction in Alaska: Coulomb Stress Transfer
and Periodic Clustering. Bufe, C.
G4
A Search for Tremor Using the Southern California
Earthquake Data Center (SCEDC) Continuous Data.
Cochran, E. and Shearer, P.
H7
Homogeneity of Small-Scale Earthquake Faulting,
Stress and Fault Strength. Hardebeck, J.
H8
G5
Monterey Ocean Bottom Broadband Station
(MOBB): Data Analysis and Noise Removal.
Dolenc, D., Romanowicz, B., Stakes, D., McGill, P.
Uhrhammer, R., and Neuhauser, D.
Pulverized Rocks in the San Andreas Fault Zone. Dor,
O., Sisk., M., Ben-Zion, Y., Rockwell, T., and Girty, G.
H9
Structural and Wave Phenomena Effects on Double
Couple Focal Mechanisms. Preston, L. and von
Seggern, D.
Q of the Mexican Volcanic Belt. Iglesias, A., Singh, S.,
García, D., Ordaz, M., and Pacheco, J.
H10
A New Paradigm for Inferring Stress Using Focal
Mechanism Orientations. Smith, D. and Heaton, T.
New Madrid Seismic Zone VP/VS Ratios. Powell, C.,
Withers, M., Dunn, M., and Vlahovic, G.
H11
Fault Mechanisms of Recent Earthquakes in the
Aegean Region Inferred From Regional Moment
Tensor Inversions. Meral Ozel, N. and Yilmazer, M.
H12
Twelve Years and Counting: Regional Moment
Tensors in and around Northern California. Hellweg,
M., Dolenc, D., Gee, L., Templeton, D., Xue, M.
Dreger, D., and Romanowicz, B.
G6
G7
G8
High Fidelity Seismic Imaging for Steep Reflectors.
Wu, R.-S. and Cao, J.
G9
Evaluation of Statistical Techniques for Seismic
Wavelet Extraction via 3D Elastic Modeling. Haney,
Seismological Research Letters
Volume 77, Number 2
March/April 2006
169
H13
The Real-time SCSN Moment Tensor Solution:
Robustness of Mw, and Style of Faulting. Clinton, J.
and Hauksson, E.
I2
The COSMOS VDC (http://db.cosmos-eq.org/): A
Search Engine for World-wide Strong-motion Data.
Archuleta, R., Steidl, J., and Squibb, M.
H14
Local and Moment Magnitude Scales in the Iranian
Plateau Based on Strong Motion Records. ShojaTaheri, J., Naserieh, S., and Ghofrani, H.
I3
USGS Earthquake Hazards Program Unveils
Redesigned Website. Wald, L.
I4
H15
Size Scaling of Signals in the Early Portion of P
Waveforms. Lewis, M. and Ben-Zion, Y.
The Station Information System (SIS) at the Southern
California Earthquake Data Center (SCEDC). Appel,
V. and Clayton, R.
H16
Energy Partition and Scaling Relations during
Earthquake Rupture Processes. Shi, Z., Needleman,
A., Ben-Zion, Y., and Coker, D.
I5
Summary of the ISC Bulletin of Events of 2003.
Storchak, D. and Bolton, M.
I6
H17
Can Seismic Energy Radiation be Estimated from
Near-fault Ground Motion and Mapped over
Earthquake Fault Zones? McGarr, A. and Fletcher, J.
Updating Default Depths in the ISC Bulletin. Bolton,
M., Storchak, D., and Harris, J.
I7
Aftershock Abundance: Forecasting Aftershock
Rates When Catalog Completeness Is High.
Christophersen, A. and Gerstenberger, M.
Public Education—Disaster Preparedeness Education
Program in Turkey. Cakin, O., Petal, M., Sezan, S., and
Turkmen, Z.
I8
What’s Shaking? Teaching about the Hazard of
Earthquakes in Public High Schools. Iversen, E.
I9
Evolution of the Catfish (Namazu) as an Earthquake
Symbol in Japan. Smits, G. and Ludwin, R.
I10
Earthquake Catfish ( Jishin Namazu): Alive and Well
in Japan. Berglof, W.
H18
Earthquake CORE: Culture, Outreach, Resources and
Education (see page 223)
I1
International Seismological Centre—An Update.
Aspinwall, M., Botlon, M., Dawson, P., Harris, J.,
Shapira, A., and Storchak, D.
WEDNESDAY, 19 APRIL
Plenary Session: Learning From the Past (see page 225)
8:30
William B. Joyner Memorial Lecturer: Norm Abrahamson: Lessons Learned From Ground Rupture and Strong Ground
Motion
9:00
Mary Comerio: Losses in the Built Environment
9:30
Richard Andrews: Emergency Management: Lessons From the Past
10:00
170
Coffee Break
Seismological Research Letters
Volume 77, Number 2
March/April 2006
Concurrent SSA Oral Sessions
The Giant Sumatran
Earthquakes of 2004 and
2005 (Joint with EERI) (see
page 225)
Presiding: Kerry Sieh and
Aron Meltzner
Near Fault Ground
Motions from Large
Earthquakes (Joint with
EERI) (see page 226)
Presiding: Paul Spudich and
David M. Boore
Beyond the San Andreas,
The Other Active Faults of
Northern California (see
page 228)
Presiding: Jim Lienkaemper
and John Baldwin
How Seismologists,
Engineers and Emergency
Planners can Work with
Policymakers to Improve
Disaster Planning and
Mitigation (EERI Session
joint with SSA and DRC)
(see page 229)
Presiding: Linda Rowan,
Brian Pallasch and Ray
Willeman
10:30
Teleseismic Relocation and
Assessment of Seismicity
(1918–2005) in the
Region of the 2004 MW 9.0
Sumatra-Andaman and 2005
MW 8.6 Nias Island Great
Earthquakes. Engdahl, E.,
Villasenor, A., and DeShon,
H.
Near-Fault Strong-Motion
from the M6.0 Parkfield,
California Earthquake of
28 Sept 2004. Shakal, A.,
Haddadi, H., and Huang, M.
The Earthquake Cycle on
a Plate Boundary Fault
System: San Francisco Bay
Area 1600–2006. Schwartz,
D., Lettis, W., Lienkaemper,
J., Hecker, S., Kelson, K.,
Fumal, T., Baldwin, J., Seitz,
G., and Niemi, T.
Global Natural Hazard
Risk Identification and
International Development:
Linking Mitigation to
Regional Economic
Development. Lerner-Lam,
A. and Chen, R.
10:45
Reverse-time Migration
of Teleseismic P Waves:
Imaging the 28 March
2005 Sumatra Earthquake.
Walker, K., Shearer, P., and
Ishii, M.
Variation of Recorded
and Simulated NearFault Ground Motion
Considering Fault Rupture
Processes. Pitarka, A.,
Somerville, P., Collins, N.,
Graves, R., and Thio, H.
The Relationship of the
1911 Calaveras Earthquake
to Static Shear Stress
Changes Following the 1906
San Francisco Mainshock.
Doser, D., Stein, R., Toda,
S., and Grunewald, E.
CISN Display: Enhanced
Delivery of Real-time
Earthquake Hazards
Information for Critical
Users. Scheckel, N.,
Vinci, M., Hauksson, E.,
Oppenheimer, D., and
Frieberg, P.
11:00
Rupture Kinematics and
Strong Ground Motion
Estimates of the 2005,
Mw 8.6, Nias- Simeulue
Earthquake from the Joint
Inversion of Seismic and
Geodetic Data. Konca, A.,
Hjorleifsdottir, V., Song, A.,
Helmberger, D., Sieh, K.,
and Avouac, J.-P.
High Frequency Earthquake
Radiation Inferred from
Near-fault Ground Motions:
Contraints from a Dynamic
Rupture Model and
Empirical Green’s Tensor
Derivatives. Pulido, N. and
Dalguer, L.
New Quaternary Fault
Map Database for the San
Francisco Bay Region,
California. Graymer, R.
CAPSS: Involving the San
Francisco Community in the
Community Action Plan for
Seismic Safety. Comerio, M.
11:15
The “Simeulue Saddle” and
Rupture Overlap in the
2002, 2004, and 2005 Sunda
Megathrust Earthquakes.
Meltzner, A.J., Briggs, R.W.,
Sieh, K., Konca, A.O., Hsu,
Y.-J.
Influence of Fault Dip
and Near-Fault Crustal
Heterogeneity on NormalFaulting Rupture Dynamics
and Ground Motions.
O’Connell, D., Ma, S., and
Archuleta, R.
New Coastal Strike-Slip
Faults with Relatively
High Rates of Slip and
Deformation between
the Offshore San Andreas
and Onshore Maacama
Faults, Northern Coastal
California, Mendocino
County. Merritts, D.,
Springer, D., Walter, R.,
Lippincott, C., and Muller, J.
Geography of Earthquake
Risk in the South of Market
District of San Francisco:
People, Place and Policy.
Wilson, J.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
171
11:30
Seismic Activity in the
Sumatra-Java Region Prior
to the December 26, 2004
(MW = 9.0–9.3) and March
28, 2005 (MW = 8.7)
Earthquakes. Mignan, A.,
King, G., Bowman, D.,
Lacassin, R., and Dmowska,
R.
Site Effects for NearFault Forward-Directivity
Motions. RodriguezMarek, A.
Structure of the Hayward
Fault, California, from
Relocated Seismicity
and Focal Mechanisms.
Hardebeck, J., Michael, A.,
and Brocher, T.
A Hint for Improving
Disaster Plans and
Developing Better
Earthquake Mitigation
Strategies: Partnership.
Weaver, C.
11:45
Interseismic Strain
Accumulation and Future
Giant Earthquake Scenarios
in the Mentawai, Central
Sumatra, Subduction Zone.
Chlieh, M., Avouac, J.-P.,
Sieh, K., Natawidjaja, D.,
and Galetzka, J.
Constraints on Near-Fault
Motions from Unstable
Landform Features in New
Zealand. Stirling, M. and
Anooshehpoor, R.
A 1650-Year Record of
Large Earthquakes on the
Southern Hayward Fault.
J. Lienkaemper and P.
Williams
Reduced Earthquake Risk
and Losses as Consequences
of Improved Seismic
Monitoring. Somerville, P.
and Leith, W.
12:00
SSA Annual Luncheon
Concurrent SSA Oral Sessions
The Giant Sumatran
Earthquakes of
2004 and 2005
(Joint with EERI)
(see page 231)
Presiding: Lori
Dengler and Emile
Okal
Extending ANSS:
Next Generation
Earthquake
Monitoring I (Joint
with EERI) (see page
232)
Presiding: William
Leith and Robert
Nigbor
The M7.6 Kashmir
Earthquake of 8
October 2005 (Joint
with EERI) (see page
233)
Presiding: Roger
Bilham and Saif
Hussain
2:00
Two Earthquakes
and Tsunamis
that Changed the
Perspective of
Indonesian People.
Prasetya, G.
Future Seismic
Instrumentation for
ANSS.
Evans, J., Savage,
W., Hutt, C., and
Oppenheimer, D.
Geology of the
2:00 The “Next
Kashmir Earthquake
Generation of
and its Geomorphic
Ground Motion
Consequences.
Attenuation
Khan, M., Khattak,
Models” (NGA)
G., Shafique, M., and
Project: An
Owen, L.
Overview. Power,
M., Chiou, B.,
Abrahamson, N.,
Roblee, C.
2:00 Do We Have It
Right? Holzer, T.
2:15
Tsunami Generation
from the Andaman
Segment of the
M>9.0 December
26, 2004 SumatraAndaman
Earthquake. Geist,
E.
The “GeoNet”
Monitoring System
of New Zealand.
H. Cowan and K.
Gledhill
The Blinding of
2:06 NGA Database.
the Himalayan
Chiou, B.
Arc at the Western
Syntaxis. Seeber, L.,
Armbruster, J., and
Jacob, K.
2:10 Update of Fieldbased Methods
for Evaluating
Liquefaction
Potential.
Idriss, I.M. and
Boulanger, R.
172
Seismological Research Letters
Volume 77, Number 2
March/April 2006
Next Generation
of Ground Motion
Attenuation
Models (EERI session joint with SSA,
see page 235)
Presiding: Yusef
Bozorgnia and
Norm Abrahamson
Advances in
Liquefaction
Evaluation (EERI
session joint with
SSA)
Presiding: Ross
Boulanger and
Thomas Holzer
2:30
The Cataclysmic
2004 Tsunami on
NW Sumatra—
Preliminary Evidence
for a Near-field
Secondary Source
along the Western
Aceh Basin. Plafker,
G., Nishenko,
S., Cluff, L., and
Syahrial, M.
ANSS
Accelerometer
Data—Not Just For
“The Big One”
(Anymore).Pankow,
K., Pechmann, J.,
and Arabasz, W.
Surface Faulting dur- 2:20 The Abrahamsoning the October 8th,
Silva NGA Model.
2005, Muzaffarabad
Abrahamson, N.
Earthquake and
Coulomb Stress
2:34 Boore-Atkinson
Increase on the
NGA Model.
Jhelum Fault.
Atkinson, G.
Tapponnier, P, King,
G., Bollinger,L., and
Grasso, J.-R.
2:45
The impact of the
December 26, 2004
MW 9.2 Sumatra
Earthquake and
Tsunami on Utility,
Bridge, and Highway
Systems in Aceh
Province, Sumatra.
Cluff, L., Nishenko,
S., Plafker, G.
IRIS Collaborations
with the ANSS
Backbone Network.
Butler, R. and
Anderson, K.
The October
2005 Kashmir
Earthquake—EERI
Reconnaissance
Report. Hussain,
S., Khazai., B., and
Ahmed, N.
3:00
Port and Harbor
Damage from the
December 26,
2004 Tsunami and
Earthquake—south
India and the
Andaman Islands.
Eskijian, M.
Probabilistic
Estimates of
Monitoring
Completeness of
Seismic Networks.
Schorlemmer, D.,
Woessner, J., and
Bachmann, C.
Performance of
3:02 PEER-NGA
2:40 Liquefaction and
Engineered &
Empirical Ground
Deformation
Non-engineered
Motion Model for
Potential of FineStructures in
Horizontal Spectral
grained Soils.
Northern Pakistan
Accelerations from
Youd, T. L.
& Azad Kashmir
Earthquakes in
during Oct 8
Active Tectonic
Earthquake. Syed,
Regions. Chiou, B.
A., Naeem, A., Ali,
and Youngs, R.
Q., Naseer, A., Javed,
M., Ashraf, M., and
Hussain, Z.
3:15
Ancillary Records
of the 2004 Sumatra
Tsunami: New
Challenges and
Opportunities for
Geophysicists. Okal,
E.
How to Install
More Strong
Motion Stations
for Less Money
More Quickly.
Oppenheimer, D.,
Evans, J., Savage, W.,
and Hutt, C.
Pakistan Earthquake 3:16 Idriss NGA Model. 2:50 Panel Discussion
of October 8,
Idriss, I.
2005 (Mw7.6):
A Preliminary
Report on Source
Characteristics and
Recorded Ground
Motions, Singh.
S., Iglesias A.,
Dattatrayam, R.,
Bansal, B., PerezCampos, X., and
Suresh, G.
3:30
Coffee Break
2:20 Recent
Advances in Soil
Liquefaction
Engineering.
Seed, R.
2:48 Campbell2:30 Fines Content
Bozorgnia Next
Correction
Generation
Factors. Green, R.
Attenuation (NGA)
Relations for PGA,
PGV and Spectral
Acceleration: A
Progress Report.
Campbell, K., and
Bozorgnia, Y.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
173
Tsunamis (see page 235)
Presiding: Rob Witter and Brian
Atwater
Extending ANSS: Next Generation
Earthquake Monitoring II (Joint with
EERI) (see page 237)
Presiding: William Leith and Robert
Nigbor
Advances in Volcano Seismology:
Enhanced Monitoring Capability
Through Application of
Complementary Methods (see page
238)
Presiding: Charlotte Rowe and
Heather DeShon
4:00
Sedimentary Differences in Nearsource Deposits of the 2004 South
Asia Tsunami and Hurricane Katrina.
Moore, A., McAdoo, B., and Fritz, H.
A New Low Complexity Real-time
Ground Motion Reporting Network.
Rosenberger, A., Rogers, G., and
Cassidy, J.
Using Tiltmeters, GPS Receivers,
Time-lapse Photography and
Photogrammetry as Aids for
Interpreting Volcanic Seismicity during the Ongoing Eruption of Mount
St. Helens. Moran, S., Dzurisin, D.,
LaHusen, R., Lisowski, D., Major, J.,
Schilling, S., and Shermod, D.
4:15
Evidence of Combined Entrainment
and Suspension Deposition as
Recorded in Tsunami Sand Sheets
from the Recent SE India Tsunami
and the 1700 AD Cascadia Tsunami.
Peterson, C., Jol, H., and Yeh, H.
DamageMap Prototype Using Realtime GPS Point Positioning. Hudnut,
K., Safak, E., Borsa, A., Langbein, J.,
Stark, K., Barseghian, D., Aspiotes, A.,
Acosta, A., Stubailo, I., Kohler, M., and
Davis, P.
Improvements to Absolute Locations
from an Updated Velocity Model
at Mount St. Helens, Washington.
Thelen, W., Malone, S., Qamar, A.,
and Pullammanappallil, S.
4:30
Numerical Modeling of Submarine
Landslide-generated Tsunamis at
Seward and Valdez, Alaska, with
Constraints from Recent Multi-beam
and High-resolution Seismic Surveys.
Suleimani, E., Lee, H., Haeussler, P.,
and Hansen, R.
Monitoring Civil Structures Using
Small Scale Attenuation Structure
a Network of Wireless Sensors.
at Mt. Vesuvius, Italy. Del Pezzo, E.,
Govindan, R., Caffrey, J., Johnson, E., Bianco, F., and De Siena, L.
and Masri, S.
4:45
A Comprehensive Study of Tsunami
Risk in New Zealand, Including
Probabilistic Estimates of Wave
Heights from All Sources, Damage
to Buildings, Deaths and Injuries.
Berryman, K. and Smith, W.
Using Networked Wireless Structural
Arrays for Urban Damage Detection.
Kohler, M., Davis, P., and Govindan,
R.
Anamolous Thin Crust and High
Attenuation Beneath the Taupo
Volcanic Region of North Island,
New Zealand from 3-D Tomographic
Inversion of Short-period and
Broadband Data. Chiu, J.-M.,
Reyners, M., and Pujol, J.
5:00
Tsunami Monitoring and Warning
in Puerto Rico and the Caribbean.
Von Hillebrandt-Andrade, C. and
Huérfano, V.
Real-Time Structural Health
Monitoring Incorporating Soil
Structure Interaction Effects. Soyoz,
S., Feng, M. Q., and Safak, E.
Infrasound from Strombolian
Eruptions at Mount Erebus Volcano.
Jones, K., Aster, R., Johnson, J., Kyle,
P., and McIntosh, W.
5:15
Seaside Tsunami Awareness Program.
Wilson, J.
Establishing Connectivity between the Large Scale Ground Deformation of
COSMOS Geotechnical Virtual Data Etna Observed by GPS between 1994
Center and the COSMOS Virtual
and 2001. Houlie, N.
(Strong Ground Motion) Data Center.
Swift, J., Squibb, M., Archuleta, R.,
Steidl, J., and Stepp, C.
174
Seismological Research Letters
Volume 77, Number 2
March/April 2006
Recent Results from the 28 September 2004, M6.0
Parkfield, California Earthquake (see page 242)
Wednesday AM, 19 April Poster Sessions
Advances in Volcano Seismology: Enhanced Monitoring
Capability Through Application of Complementary
Methods (see page 240)
J1
Separation of Qi and Qs from Passive Data at Mt.
Vesuvius: A Reappraisal of Seismic Attenuation. Del
Pezzo, E., Bianco, F., and Zaccarelli, L.
J2
3-D Scattering Image of Mt. Vesuvius, Preliminary
Results. Tramelli, A., Fehler, M., Del Pezzo, E., and
Bianco, F.
J3
Multiple Denoising and Classification Methods for
Improving Seismic Surveillance: Applications at Guagua
Pichincha, Soufriere Hills and Redoubt Volcano. Rowe,
C., Garcia-Aristizabal, A., and White, R.
J4
Can 4D Seismic Tomography Forecast Volatile-rich
Magma Intrusions and Explosive Activity at Mt. Etna?
Patane, D., Barberi, G., Cocina, O., De Gori, P., and
Chiarabbar, C.
J5
Volcano-tectonic Earthquake Sequences near Active
Volcanoes and Their Use in Eruption Forecasting.
White, R. and Rowe, C.
K1
Comparing the 1966 and 2004 Parkfield Events.
Hellweg, M. and Dreger, D.
K2
Small Magnitude Source Parameters in the Parkfield
Region. Allmann, B., Shearer, P., and Lin, G.
K3
Detecting Stress-induced Spatiotemporal Variations of
Scatterers, Parkfield, CA. Taira, T., Silver, P., Niu, F.,
and Nadeau, R.
K4
Co-seismic and Post-mainshock Variations in Seismic
Velocity on the San Andreas Fault at Depth and
Implications from the 2004 M6 Parkfield Earthquake.
Li, Y.-G., Vidale, J., Chen, P., and Cochran, E.
K5
Apparent Changes in Repeating Earthquake Depths
Associated with the 28 September 2004, M6.0
Parkfield Mainshock. Siegel, J. and Nadeau, R.
K6
Parkfield Earthquakes and Micro-repeater Recurrence
Times. Goltz, C.
K7
Seismicity Precursor Modeling of M6.0 2004 Parkfield
Earthquake. Korneev, V.
J6
Broadband Characteristics of Volcanic Earthquakes
Recorded during 2004–2005 at Mount Saint Helens,
Washington. Horton, S.
K8
Kinematic Rupture Model for the 1966 Mw 6
Parkfield Earthquake with Assessment of Resolution.
Custodio, S., Archuleta, R., and Liu, P.
J7
Seismo-acoustic Monitoring at Tungurahua Volcano.
Ruiz, M., Lees, J., and Jonson, J.
K9
Kinematic Modeling of the 2004 Parkfield Earthquake.
Kim, A. and Dreger, D.
J8
Seismicity Related to the 2005 Explosive Events at
Volcán de Fuego, México. Nunez-Cornu, F., VargasBracamontes, D., and Suarez-Plascencia, C.
K10
The Effect of Lateral Refraction on Estimates of the
Rupture Velocity of the 2004 Parkfield Earthquake
from Observations at UPSAR. Fletcher, J., Spudich,
P., Baker, L., and Sell, R.
J9
Cross-correlation Analysis Reveals Waveform
Similarity in Long-period Events Prior to Eruptive
Activty at Mt. Spurr Volcano, Alaska. Brown, J.,
DeShon, H., Prejean, S., Thurber, C., and Power, J.
K11
Cross-correlation and Double-difference Techniques used
in Earthquake Relocations at Shishaldin Volcano, Alaska.
Meyer, N., DeShon, H., Thurber, C., and Prejean, S.
Subsurface Structure of the San Andreas Fault Zone
near Parkfield, California, Inferred from HighResolution Reflection and Refraction Profiling.
Rymer, M., Catchings, R., Goldman, M., and
Steedman, C.
K12
High-precision Earthquake Location and Three-dimensional P-wave Velocity Determination at Redoubt
Volcano, Alaska. DeShon, H., Rowe, C., and Thurber, C.
On the Strong Ground Shaking at the Fault Zone 16
and Nearby Stations of Parkfield Array. Haddadi, H.,
Shakal, A., Kalkan, E., and Roffers, P.
K13
Seismic Input Energy of Ground Motions During
the 2004 (M6.0) Parkfield, California Earthquake.
Kalkan, E., Haddadi, H., and Shakal, A.
J10
J11
J12
High-precision Earthquake Locations at Great Sitkin
Volcano, Alaska using Waveform Alignment and
Double-Difference Techniques. Pesicek, J., DeShon,
H., Thurber, C., and Prejean, S.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
175
K14
Simulation of Strong Ground Motion from the 2004
Parkfield Earthquake. Sesetyan, K., Madariaga, R.,
Durukal, E., and Erdik, M.
K15
The San Fernando Valley, California High School
Seismograph Project: 2004 Parkfield Earthquake.
Simila, G.
Paleoseismic Characterization of Earthquake Recurrence
and Hazard Assessment (see page 245)
The Northern San Andreas Fault: 100 Years of Scientific
Study/The Impact of the Lawson Report on Earthquake
Science (see page 247)
M1
Timing of Late Holocene Paleoearthquakes on the
Northern San Andreas Fault at the Fort Ross Orchard
Site, Sonoma County, California. Kelson, K., Streig,
A., Koehler, R., and Kang, K.
M2
A 3000-year Record of Earthquakes on the Northern
San Andreas Fault at the Vedanta Marsh Site, Olema,
California. Zhang, H., Niemi, T., and Fumal, T.
L1
Earthquake Surface Slip Distributions. Wesnousky, S.
L2
Using Pollen to Constrain the Age of the Youngest
Rupture of the San Andreas Fault at San Gorgonio
Pass. Yule, D., Maloney, S., and Cummings, L. Scott
M3
Stratigraphic Evidence for Major Earthquakes at
Bolinas Lagoon, Marin County, California. Byrne, R.
and Reidy, L.
L3
Slip Rates, Recurrence Intervals and Earthquake
Event Magnitudes for the Southern Black Mountains
Fault Zone, Southern Death Valley, California, Using
Optically Stimulated Luminescence. Mahan, S., Sohn,
M., Knott, J., and Bowmen, D.
M4
Preliminary Earthquake Record of the Peninsula
Section of the San Andreas fault, Portola Valley,
California. Baldwin, J., Prentice, C., Wetenkamp, J.,
and Sundermann, S.
M5
L4
The Study and Revision of Probabilistic Seismic
Hazard Map of Taiwan. Cheng, C., Lee, C., Lin, P.,
Chiou, B., and Chern, J.
Tectonic deformation and coastal change associated
with the offshore San Andreas fault zone west of the
Golden Gate. Ryan, H. and Parsons, T.
M6
L5
An Example of Time-dependent Seismic Hazard
Analysis from West Central Taiwan. Lin, P., Lee, C.,
and Cheng, C.
Utilization of LiDAR / ALSM Point Cloud Data
for Earthquake Geology and Tectonic Geomorphic
Mapping, Analysis, and Visualization. Crosby, C. and
Arrowsmith, R.
L6
A Preliminary Seismicity Model for Southwest
Western Australia Based on Neotectonic Data. Clark,
D. and Schneider, J.
M7
Simulation- and Statistics-Based Analysis of the 1906
Earthquake and Northern California Faults. Glasscoe,
M., Donnellan, A., Granat, R., Lyzenga, G., Norton,
C., and Parker, J.
L7
Geomorphic Evolution of the Cadell Fault,
Southeastern Australia: Implications for Intraplate
Fault Behaviour and Seismic Hazard Assessment.
Prendergast, A., Clark, D., Collins, C., and Schneider,
J.
M8
Significance of Damaging San Francisco Bay Region
Earthquakes Before and After the Major 1906
Earthquake. Toppozada, T. and Branum, D.
M9
Using the Lawson Report and Other Historical
Documents to Investigate Fault Morphology and
Coseismic Slip of the 1906 Earthquake in Marin
County. Daehne, A. and Niemi, T.
L8
Precariously Balanced Rock Methodology and Shake
Table Calibration. Purvance, M., Anooshehpoor, R.,
and Brune, J.
L9
Geologic Constraints on Extreme Ground Motions.
Brune, J.
L10
WITHDRAWN: Earthquakes and Archeology:
Neocatastrophism or Science? Nur, A. and Kovach, R.
L11
176
Estimating Historical Earthquakes Parameters Using
Archeology and Geology in Um-El-Kanatir, Dead Sea
Transform. Wechsler, N., Katz, O., and Marco, S.
Seismological Research Letters
Volume 77, Number 2
M10 High-resolution Analysis of 1906 Earthquake
Intensities in the City of San Jose, California. Shostak,
N.
M11 Effects and Response of Nevada to the Great 1906 San
Francisco, California Earthquake. dePolo, C. and Earl,
P.
March/April 2006
Integrating Geology and Geodesy in Studies of Active
Faults (see page 250)
N1
Earthquake Cycle Models and Interseismic Strain:
A Test of Effective Friction Evolution and Transient
Mantle Rheology. Hearn, E., Ergintav, S., Reilinger,
R., and McClusky, S.
N2
Variability of Long-term Fault Activity along the
North Anatolian Fault, Turkey. Okumura, K. and
Kondo, H.
N3
The Comparison of Long-term and Short-term Slip
Rates of a Major Active Strike-slip Fault System: Mosha
Fault, Central Alborz, Iran. Shahpasandzadeh, M.
N4
N5
N6
Preliminary Paleoseismic Observations along US
Highway 50, Basin and Range Province, Central
Nevada. Koehler, R., and Wesnousky, S.
Slip Rate of the San Andreas Fault near Littlerock,
California. Sickler, R., Weldon, R., Fumal, T.,
Schwartz, D., Mezger, L., Alexander, J., Biasi, G.,
Burgette, R., Goldman, M., and Saldana, S.
Improving the Slip Rate Estimate at Pitman Canyon,
Southern San Andreas Fault. Bemis, S., Weldon, R.,
and Burgette, R.
F., Zuzlewski, S., Murray, M, Dietz, L., Houlié, N.,
Oppenheimer, D., and Romanowicz, B.
O6
Accessing SAFOD Data Products: Downhole
Measurements, Physical Samples and Long-term
Monitoring. Weiland, C., Zoback, M., Hickman, S.,
and Ellsworth, W.
O7
Associating Southern California Seismicity with Late
Quaternary Faults. Woessner, J., Hauksson, E., Plesch,
A., Shaw, J., and Wesson, R.
O8
Relationship of Seismicity to Fault Structure in
California. Powers, P. and Jordan, T.
O9
Seismic Probing of InSAR Anomalies to Understand
Fault Zone Compliance. Cochran, E., Li, Y.-G.,
Shearer, P., Vidale, J., and Fialko, Y.
O10
Quantifying Heterogeneities in the Surface Traces of
Strike-slip Faults. Wechsler, N., Ben-Zion, Y., and
Christofferson, S.
O11
Fault Geometry and Rupture Dynamics in the
Marmara Sea, Turkey. Oglesby, D., Mai, P., Atakan,
K., Pucci, S., and Pantosti, D.
O12
Nonuniform Prestress on Branched Fault Systems and
the Effects on Dynamic Fault Branching. Duan, B.
and Oglesby, D.
O13
Clusters of Earthquakes in the Southern of Iberian
Peninsula. Posadas, A., Navarro, M., and Vidal, F.
O14
Locally Induced Seismicity in the Swiss Alps Following
the Large Rainfall event of August 2005. Husen, S.,
Deichmann, N., and Kissling, E.
O15
Causes of Intraplate Earthquakes in Greenland, Plate
Motion or “Post” Glacial Uplift. Gregersen, S., Voss,
P., and Larsen, T.
O16
Direct Test of Static Stress versus Dynamic Triggering
of Aftershocks. Pollitz, F. and Johnston, M.
O17
Dynamic Stresses, Coulomb Failure, and Remote
Triggering. Hill, D.
O18
Dynamic Triggering of Earthquakes Caused by Surface
Waves. Hernandez, S., Velasco, A., and Pankow, K.
O19
The June 2005 Southern California Anza Earthquake:
An Examination of the Extended Aftershock Zone
and Intermediate Range Triggering of the Yucaipa
Earthquake. Felzer, K. and Kilb, D.
Wednesday PM, 19 April Poster Sessions
Earthquake Science in the 21st Century: Understanding
the Processes that Control Earthquakes (see page 251)
O1
O2
O3
O4
O5
Study of Near-Field Earthquake Processes: Progress of
the NELSAM Project in Tautona Mine, South Africa.
Reches, Z., Jordan, T., Johnston, M., Zoback, M,
Heesakkers, V., Zechmeister, M., Murphy, S., and van
Aswegen, G.
Drilling the Megathrust: The Nankai Trough Seismogenic
Zone Drilling Project. Tobin, H. and Kinoshita, M.
Construction of the EarthScope Plate Boundary
Observatory: Two Years Down and Three to Go.
Jackson, M., Prescott, W., Andeson, G., Feaux, K.,
Mencin, D., and Blume, F.
EarthScope Data Management at the IRIS DMC.
Trabant, C., Johnson, P., Templeton, M., Benson, R.,
and Ahern, T.
Diverse Continuous Seismic, Geophysical, and
Geodetic Data at the Northern California Earthquake
Data Center (NCEDC). Neuhauser, D., Klein,
Seismological Research Letters
Volume 77, Number 2
March/April 2006
177
O20
Anomalous Omori and Inverse Omori’s Law around
the Time of Main Shocks. Peng, Z. and Vidale, J.
O21
Source Properties of Earthquakes in the Aftershock
Zones of the 1999 Izmit and Duzce Earthquakes from
Iterative Spectral Stacking for Common Source and
Receiver Terms. Yang, W., Peng, Z., and Ben-Zion, Y.
O22
O33
Teleseismic Receiver Functions Study On The Velocity
Structure Beneath Yanqing-Huailai Basin, NW
Beijing. Zhou, R.-M., Stump, B., Herrmann, R.,
Chen, Y. T., and Yang, Z.-X.
O34
Detailed Seismic Velocity Structures in the Focal Areas
of Recent Large Inland Earthquakes in Japan by DD
Tomography. Okada, T., Yaginuma, T., Suganomata,
J., Hasegawa, A., Zhang, H., and Thurber, C.
O35
Detailed Crustal Shear-wave Splitting Observations
Along the POLARIS-BC Array. Al-Khoubi, I.,
Cassidy, J., and Bostok, M.
O36
Testing the 1st-Generation RELM Models.
Schorlemmer, D., Field, E., and Jordan, T.
O37
Implementing the Collaboratory for the Study of
Earthquake Predictability: Challenges and Solutions.
Schorlemmer, D., Zechar, J., Maechling, P., and
Jordan, T.
O38
Testing Alarm-based Earthquake Prediction Strategies.
Zechar, J. and Jordan, T.
O39
When the Earth Speaks. Freund, F., Lau, B., and
Takeuchi, A.
O40
Ongoing Accelerating Seismicity in California.
Colella, H. and Bowman, D.
Marked Co-seismic Fault Weakening in the Presence
of Melt Lubrication. Nielsen, S., Di Toro, G., Hirose,
T., and Shimamoto, T.
O41
Precursory Accelerating Moment Release: Fact or
Data-Fitting Fiction. Michael, A., Felzer, K., and
Hardebeck, J.
Thermal Pressurization of Pore Fluids Due to
Frictional Heating during Earthquakes. Vredevoogd,
M., Oblesby, D., and Park, S.
O42
Earthquake Forecasting in Northern California
Based on Temporal Variations in the Strain Field at
Seismogenic Depths. Sipkin, S.
Structure, Composition and Strain of the San Andreas
Fault-zone at Tejon Pass, California. Reches, Z.,
Verrett, J., Borges, G., Dewers, T., Witten, A., and
Brune, J.
Nuclear Explosion Monitoring Anniversary Session (see
page 259)
Source Properties of Repeating Earthquakes in the
Aftershock Zones of the 1999 Izmit and Duzce
Earthquakes Based on a Stacked Spectral-ratios and
Moving Time-window. Peng, Z., Ben-Zion, Y., and
Yang, W.
O23
How Much Does P-wave Coda Bias S-wave Spectral
Estimates? Prieto, G., Thomson, D., Vernon, F., and
Shearer, P.
O24
Variability in Source Parameters, as Measured
Downhole at Parkfield, CA. Sonley, E. and
Abercrombie, R.
O25
Characterization of Co-seismic Strain Release in
Southern California Based on Earthquake Catalog
Data. Bailey, I., Becker, T., and Ben-Zion, Y.
O26
Combing Noisy Waveforms for Signal: Application of
Matched Filters to Identify and Locate Earthquakes in
35-500 s GSN Data. Walker, K. and Shearer, P.
O27
O28
O29
O30
Earthquake Scaling and Near-source Ground-motions
from Multi-cycle Earthquake Simulation (with
Heterogeneity in Rate-and-State Friction). Mai, P.,
Hillers, G., Ampuero, J.-P., and Ben-Zion, Y.
O31
Scale Seismology. Results. Problems. Possibilities.
Chesnokov, E.
O32
Full Form Synthetic Seismogram Calculations And
Determination of Focal Mechanism Of Frac Events
Based On 3-C Seismic Array Observations. Vikhorev,
A., Ammerman, M., Brown, R., Abaseyev, S., and
Chesnokov, E.
178
Seismological Research Letters
Volume 77, Number 2
P1
The Seismic Networks of the International Monitoring
System of the Comprehensive Nuclear-Test-Ban Treaty
Organization. Barrientos, S. and Suarez, G.
P2
On the Detection of Low Magnitude Seismic Events
Using Array-based Waveform Correlation. Gibbons,
S., Ringdal, F., and Kvaerna, T.
P3
A Bayesian Hierarchical Approach to Multiple-event
Seismic Location. Myers, S., Johannesson, G., and
Hanley, W.
P4
Regional Body-Wave Attenuation Using a Coda Source
Normalization Method: Application to MEDNET
March/April 2006
Records of Earthquakes in Italy. Walter, W., Mayeda,
K., Malagnini, L., and Scognamiglio, L.
P5
Developing Pn attenuation models for Eurasia. Yang,
X., Taylor, S., and Phillips, W.
P6
Regional Calibration of Peak Envelope Arrival Time.
Phillips, W. and Stead, R.
P7
Joint Inversion for Three-Dimensional Velocity
Structure of North Africa and the Middle East.
Flanagan, M., Matzel, E., Pasyanos, M., van der Lee,
S., Marone, F., Rodgers, A., Romanowicz, B., and
Schmid, C.
P8
Improving Ms Estimates by Calibrating Variable Period
Magnitude Scales at Regional Distances. Pasyanos,
M., Hooper, H., and Bonner, J.
P9
Modeling of the May 21, 1997 Jabalpur Earthquake in
Central India: Regional Path Calibration. Saikia, C.
P10
A New Approach for Wave Propagation Simulation
in Irregular Multilayered Earth Model with Boundary
Element Method. Ge, Z. and Chen, X.
P11
Source Phenomenology Experiment in Arizona:
Amplitude Ratio Analysis of Regional Arrivals for
Production Mining and Single-Fire Sources. Zeiler, C.,
Velasco, A., and Hernandez, S.
P12
P13
Source Features and Scaling of Calibration Explosions
in Middle East/Eastern Mediterranean for CTBT
Monitoring. Hofstetter, A., Gitterman, Y., and Pinsky, V.
Infrasound Waveguide. Herrin, E., Kim, T., and
Stump, B.
Near Fault Ground Motions from Large Earthquakes (Joint
with EERI) (see page 261)
Q1
Q2
Q3
Q4
Effects of Directivity and Supershear Rupture Speed
on Near-Fault Ground Motion. Bykovtsev, A. and
Quazi, H.
The Relationship of Near-fault Velocity Pulse to the
Source Parameters. Liu, Q., Yuan, Y., and Jin, X.
Effects of Directivity on Shaking Scenarios: An
Application to the 1980 Irpinia Earthquake, M 6.9,
Southern Italy. Pacor, F., Cultrera, G., Emolo, A.,
Gallovic, F., Cirella, A., Hunstad, I., Piatanesi, A.,
Tinti, E., Ameri, G., and Franceschina, G.
An Efficient Method for Simulating Near-fault Strong
Motions at Broadband Frequencies in Layered Halfspaces. Hisada, Y.
Q5
Analysis and “Prediction” of the M = 6.2, 1991 and M
= 7.2, 1992 Cape Mendocino Earthquakes by Ground
Motion Modeling with Empirical Green’s Functions.
Hutchings, L., Kane, D., O’Boyle, J., Scognamiglio, L.,
and Tremi, M.
Q6
Do Weak (Strong) Motion Empirical Models Predict
Strong (Weak) Ground Motion? Results from the
Kik-Net Records in Japan. Pousse, G., Cotton, F.,
Scherbaum, F., and Bonilla, L.
Q7
Near-fault Broadband Ground Motions from
a Megathrust Earthquake: A Case of the Great
1923 Kanto Earthquake. Miyake, H., Koketsu, K.,
Kobayashi, R., Tanaka, Y., and Ikegami, Y.
Q8
Inclusion of Stress Distribution on the Fault in
Stochastic Finite Fault Modeling: Application to the
M6, 2004 Parkfield Earthquake. Assatourians, K. and
Atkinson, G.
Q9
Event Location and Source Complexity as Derived
from Strong Motion Data. Porter, L. and Leeds, D.
Q10
Thermal Pressurization Explains Enhanced Long-Period
Motion in the Chi-Chi Earthquake. Andrews, J.
Q11
Scaling of High-Frequency Ground Motions for the
Sumatra, Chi-Chi, and Kocaeli Earthquake Sequences.
Frankel, A.
Q12
Ground-Motion Scaling in Western Anatolia Region
(Turkey). Akinci, A., Akyol, N., D’Amico, S.,
Malagnini, L., and Mercuri, A.
Q13
Use of mb vs. MW in the Search for High-Stress
Earthquakes. Dewey, J. and Boore, D.
Q14
Damage Potential of Near-source Ground Motion
Records. Bazzurro, P. and Luco, N.
Q15
Near-fault Ground Motion Destructiveness: The
Inadequacy of Some Popular Intensity Measures.
Georgarakos, P., Kourkoulis, R., and Gazetas, G.
Q16
Simulated Nonlinear Response of High-Rise Buildings
for the 2003 Tokachi-Oki Earthquake MW 8.3. Yang,
J., Heaton, T., and Hall, J.
Hazard and Risk (see page 265)
R1
Earthquake Risk Estimates for Residential
Construction in the U.S. and Canada. Windeler, D.,
Rahnama, M., Baca, A., Hall, L., Molas, G., Morrow,
G., Onur, T., Seneviratna, P., and Williams, C.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
179
R2
R3
R4
R5
Comparing Site-specific Probabilistic Seismic Hazard
in Southern California with the USGS National
Hazard Maps. Terra, F., Wong, I., Zachariasen, J.,
Dober, M., Hill, J., and Robb, B.
R9
Use of Rupture End-Point Characteristics in Seismic
Hazard Assessment. Knuepfer, P.
R10
Seismic Response Of Adjacent Buildings Under
Pounding Effects. Gholipour, Y.
R11
Seismic hazard evaluation on the Thai Peninsula,
Thailand. Dober, M., Wong, I., Zachariasen, J.,
Fenton, C., Thongsoi, A., Sutiwanich, C., and
Harnpattanapanich, T.
Insured Losses for Repeats of the 1906 San Francisco
and 1811/1812 New Madrid Earthquakes: How
Does the Hazard Relate to Risk? Hall, L., Rahnama,
M., Windeler, D., Baca, A., Molas, G., Onur, T., and
Seneviratna, P.
R12
A Study on Calibration and Validation of Building
Vulnerability to Earthquake. Byeon, J.
Correlating Earthquake Risk and Urban Development:
Case of Istanbul. Gencer, E.
R13
A Study on Seismic Resistance of R/C Multi-Story
Buildings with Slab Irregularity. Gulay, G., Ayranci,
M., and Sahbaz, U.
R14
The Instable Dynamics of the Earth Energy: The
Methods and Possibilities of Control Thereof.
Kerimov, I. and Kerimov, S.
New Seismic Hazard Assessment for Guam and the
Northern Mariana Islands. Mueller, C., Haller, K.,
Frankel, A., and Petersen, M.
R6
A New Seismic Zonation of Latium Region. Colombi,
A., Meloni, F., and Orazi, A.
R7
Earthquake Hazard Maps for County Level Disaster
Prevention. Chao, S.
R8
State-of-the-Art of the research on Lifeline Earthquake
Engineering in China. Han., Y. and Sun, S.
THURSDAY, 20 APRIL
Plenary Session: Assessing the Present (see page 268)
8:30
Greg Beroza: “Ground Motion Simulations for a Repeat of the 1906 Earthquake”
9:00
Charlie Kircher: HAZUS Analysis of a Repeat of the 1906 Earthquake
9:30
Richard K. Eisner: Emergency Response and Post-event Recovery After “The Big One”
10:00
Coffee Break
Concurrent SSA Oral Sessions
10:30
180
Paleoseismic Characterization
of Earthquake Recurrence
and Hazard Assessment I (see
page 269)
Presiding: Ray Weldon and
Tom Rockwell
Broadband Simulations of the
1989 Loma Prieta and 1906 San
Francisco Earthquakes I (see page
270)
Presiding: Brad Aagaard and
Thomas Brocher
Crossing the Fault from
Seismology to Engineering:
Bruce Bolt Memorial Session
(Joint with EERI) (see page
272)
Presiding: Norm Abrahamson,
Nick Gregor
High Resolution Paleoseismic
Records at Three Sites on the
Northern San Andreas Fault.
Fumal, T., Niemi, T., and
Zhang, Z.
Three-Dimensional Geologic
Map of Northern and Central
California: A Basic Model for
Supporting Earthquake Simulations
and Other Predictive Modeling.
Jachens, R., Simpson, R., Graymer,
R., Wentworth, C., and Brocher, T.
Crossing the Seismology—
Engineering Interface.
Abrahamson, N. and Gregor,
N.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
The Future of
Earthquake
Research (See
EERI program
for details)
10:45
New and Extended
Paleoseismological Evidence
for Large Earthquakes on the
San Andreas Fault at the Bidart
Fan Site, California. Akciz, S.,
Grant, L., and Arrowsmith, R.
The New USGS 3D Seismic
Velocity Model for Northern
California. Brocher, T., Aagaard,
B., Simpson, R., and Jachens, R.
Recommendations for
the Selection and Scaling
of Ground Motion Time
Histories for Building Code
Applications. WatsonLamprey, J., Abrahamson, N.,
and Bachman, R.
11:00
Reid’s Elastic Rebound
Theory in Light of the
Long Paleoseismic Record
at Wrightwood. Scharer,
K., Biasi, G., Fumal, T., and
Weldon, R.
A New Regional Seismic
Tomography Model for Northern
California. Zhang, H., Thurber, C.,
Brocher, T., Liu, Y., and Evangelidis,
C.
Incorporation of Earthquake
Source, Propagation Path,
and Site Uncertainties into
Assessment of Liquefaction
Potential. Darragh, R., Gregor,
N., and Silva, W.
11:15
New Insights to Earthquake
Behavior of the Southernmost
San Andreas Fault. Williams,
P. and Seitz, G.
A Unified Source Model for the
1906 San Francisco Earthquake.
Song, S. G., Beroza, G., and Segall,
P.
On the Use of Bayesian
Updating to Combine
Seismic Hazard Results
and Information from the
Geological Record. Toro, G.
and Cornell, A.
11:30
Rupture Histories from
Paleoseismic Records on the
Southern San Andreas Fault.
Biasi, G., Weldon, R., and
Scharer, K.
Regional and Global Scale
Modeling the Great 1906 San
Francisco Earthquake. Rodgers, A.,
Petersson, A., Nilsson, S., Sjogreen,
B., McCandless, K., and Tkalcic, H.
“Did You Feel It?” and
ShakeMap: A New Interface
between Seismological and
Engineering Data. Atkinson, G.
and Wald, D.
11:45
The Long Record of San Jacinto
Fault Paleoearthquakes at Hog
Lake: Implications for Regional
Patterns of Strain Release in the
Southern San Andreas Fault
System. Rockwell, T., Seitz, G.,
Dawson, T., and Young, J.
Large Scale Seismic Modeling
and Visualization of the 1906 San
Francisco Earthquake. Petersson,
A., Rodgers, A., Duchaineau,
M., Nilsson, S., Sjogreen, B., and
McCandless, K.
Making Waves: Seismologists
and Engineers Collaborating at
the NEES Experimental Field
Sites. Steidl, J.
12:00
Lunch
Concurrent SSA Oral Sessions
2:00
Paleoseismic
Characterization
of Earthquake
Recurrence and
Hazard Assessment II
(see page 273)
Presiding: Ray Weldon
and Tom Rockwell
Broadband
Simulations of the
1989 Loma Prieta and
1906 San Francisco
Earthquakes II (see
page 275)
Presiding: Brad Aagaard
and Thomas Brocher
Constraints on
Transonic Rupture
Propagation (EERI
session joint with SSA)
(see page 276)
Presiding: Ralph
Archuleta and Michel
Bouchon
Surface Fault Rupture
(EERI session joint with
SSA) (see page 277)
Presiding: Suzanne
Hecker and Jerry
Treiman
A Synergistic Approach
to Earthquake Science
and Forecasting:
Assimilating
Paleoseismic, Geodetic,
and Historic Data into
Numerical Simulations
of Earthquake Fault
Systems. Rundle, J.
Broadband Ground
Motion Simulations for
Earthquakes in the San
Francisco Bay Region.
Graves, R.
Dynamic Rupture
Propagation and
Radiation along
Kinked Faults. Vilotte,
J.P. and Festa, G.
Characteristic Fault
Rupture: Implications
for Fault Rupture
Hazard Analysis.
Abrahamson, N. and
Hecker, S.
Seismological Research Letters
Volume 77, Number 2
Scenario for a M6.7
Earthquake on the
Seattle Fault
Presiding: Don
Ballantyne and
Craig Weaver (EERI
session joint with
SSA) (see page 325)
March/April 2006
181
2:15
Holocene Paleoseismic
Activity on the Nephi
Segment of the
Wasatch Fault Zone,
Utah. DuRoss, C.,
McDonald, G., and
Lund, W.
Simulations of the
1906 San Francisco
Earthquake using
High Performance
Computing. Larsen,
S., Dreger, D., and
Dolenc, D.
Guidelines for
Predicting the
Occurrence
of Supershear
Earthquakes. Dunham,
E.
Estimating Fault
Displacement Hazard
for Strike-Slip Faults.
Petersen, M., Cao, T.,
Dawson, T., Wills, C.,
and Schwartz, D.
2:30
A Longer and More
Complete Paleoseismic
Record for the
Provo Segment of
the Wasatch Fault
Zone, Utah. Olig, S.,
McDonald, G., Black,
B., DuRoss, C., and
Lund, W.
Finite-element
Simulations of
Ground Motions in
the San Francisco
Bay Area from Large
Earthquakes on the
San Andreas Fault.
Aagaard, B.
The Effect of
Supershear Rupture
Speed on the High
Frequency Content
of Ground Motions.
Spudich, P., and
Bizzarri, A.
Coseismic Ground
Deformation at San
Bernardino Valley
College, California.
Gath, E., Gonzalez, T.,
and Sieh, K.
2:45
Multi-method
Paleoseismology:
Combining on and
Offshore Data to Build
a Basin Wide Record
of Earthquakes at Lake
Tahoe. Seitz, G., Kent,
G., Smith, S., Dingler,
J., Driscoll, N., Karlin,
R., Babcock, J., and
Harding, A.
Flexible Steel Building
Responses to a 1906
San Francisco Scenario
Earthquake. Heaton,
T., Olsen, A., and Hall,
J.
On the Correlation
of Slip and Rupture
Velocity and Its
Effect on Ground
Motion. Schmedes,
J., Archuleta, R., and
Liu, P.
Understanding Surface
Fault Rupture Hazards
to Mitigate Fault
Rupture Risks. Cluff,
L.
3:00
Fault Interactions
and Paleoearthquake
Clustering in the
Active Taupo Rift, New
Zealand. Villamor, P.,
Nicol, A., Robinson,
R., Berryman, K., and
Walsh, J.
Predicted Liquefaction
of East Bay Fills During
a Repeat of a 1906 San
Francisco, California,
Earthquake. Holzer,
T., Blair, L., Noce, T.,
and Bennett, M.
An Observational
Mitigation of the
Link between Rupture Surface Fault Rupture
Velocity and Fracture Hazard. Bray, J.
Energy: The Case of
the Bam Earthquake.
Bouchon, M.
3:15
Feasibility of Longterm Earthquake
Prediction Using
Global Data Sets:
Implications for
California. Sykes, L.,
and Menke, W.
Simulation of Longperiod Ground
Motions in the Los
Angeles Basin from
the Great 1906 San
Francisco Earthquake.
Kimura, T., Ikegami,
Y., and Koketsu, K.
Radiation Pattern
Peculiarities for
Transonic and
Supersonic Complex
Rupture Propagation.
Bykovtsev, A. and
Quazi, H.
3:30
Coffee Break
182
Seismological Research Letters
Volume 77, Number 2
March/April 2006
Structures Near a
Fault—Can They
Survive? Wyllie, L.
Integrating Geology and
Geodesy in Studies of
Active Faults (see page 278)
Presiding: Sally McGill and
Liz Hearn
Global Seismicity and
Wave-speed Structure of
Earth’s Deep Mantle and
Crust: Sessions in Honor
of the Seismological
Contributions of E. Robert
Engdahl (see page 279)
Presiding: Mike Ritzwoller
and Steve Kirby
Using Regional Velocity
Structures to Estimate
Seismic Hazard (see page
281)
Presiding: Fred Pollitz and
Jeanne Hardebeck
Ground Motions for
Engineering Design
Presiding: Gail Atkinson and
Jon Stewart (EERI session
joint with SSA. See page 282)
4:00
Constancy of strain accumulation and release on
strike-slip faults in Turkey
and California. Dolan, J.,
Kozaci, O., Frankel, K., and
Finkel, R.
The Management of
Data from International
Seismographic Networks:
Activities at the IRIS DMC.
Ahern, T. and Benson, R.
Integrated Modeling
and Waveform Tuning
of Regional 3-D Velocity
Structures. Koketsu, K.,
Tanaka, Y., Hikima, K.,
Miyake, H., Kobayashi, R.,
and Ikegami, Y.
Do Scaled and Spectrummatched Near-Source
Records Produce Biased
Nonlinear Structural
Responses? Bazzurro, P. and
Luco, N.
4:15
Lithospheric elasticity promotes episodic fault activity.
Chery, J., and Vernant, P.
Two Decades of Mantle
Tomography With Routinely
Processed Travel Time Data.
van der Hilst, R.
Details of Earth Structure in
the San Francisco Bay Area as
Revealed by a Network of 2-D
Controlled-Source Seismic
Imaging Profiles. Catchings,
R. D., Goldman, M. R.,
Rymer, M .J., and Gandhok, G.
Evaluation of Two Ground
Motion Scaling Methods to
Estimate Mean Structural
Demands. Kalkan, E. and
Kunnath, S.
4:30
Relationship between
geodetic and geologic fault
slip-rates with more realistic rheologies and rupture
histories. Hetland, E., and
Hager, B.
High-resolution seismic
tomography and hypocenter
relocations for the NE Japan
subduction system -An overview. Hasegawa, A.
Ground Predictions Using
The USGS Seismic Velocity
Model of the San Francisco
Bay Area: Evaluating
the Model and Scenario
Earthquake Predictions.
Rodgers A., Petersson, A.,
Nilsson, S., Sjogreen, B., and
McCandless, K.
Biases Caused by Use of
Spectrum-compatible
Motions. Watson-Lamprey,
J. and Abrahamson, N.
4:45
Discrepancies Between Fault
Slip Rates Obtained by Block
Modeling of GPS Data and
Surface Exposure Age Dating
of Strike-Slip Fault Offsets in
Tibet. Thatcher, W.
Earthquake Location and
Seismic Tomography:
Pushing the Envelope for
Subduction Zone Studies.
Thurber, C., Zhang, H.,
Brudzinsk, M., DeShon, H.
and Engdahl, E.R.
Simulated Ground Motion
in Santa Clara Valley
and Vicinity from M6.7
and Greater Scenario
Earthquakes. Harmsen, S.,
Hartzell, S., and Liu, P.
A Computationally
Intelligent Method of
Ground Motion Selection
for Structural Design.
Alimoradi, A., Naeim, F.,
and Pezeshk, S.
5:00
Geodetic versus geologic slip From precision to accuracy:
rate along the Dead Sea Fault. recent advances in seismic
Le Beon, M., Klinger, Y.,
location. Myers, S.
Agnon, A., Dorbath, L., Baer,
G., Meriaux, A.-S., Ruegg,
J.-C., Charade, O., Finkel, R.,
and Ryerson, F.
TeraShake: Strong Shaking
in Los Angeles Expected
From Southern San Andreas
Earthquake. Olsen, K., Day, S.,
Minster, J., Cui, Y., Chourasia,
A., Faerman, M., Moore,
R., Hu, Y., Zhu, J., Li, Y.,
Maechling, P., and Jordan, T.
Ground Motion Intensity
Measures for Collapse
Capacity Prediction: Choice
of Optimal Spectral Period
and Effect of Spectral Shape.
Haselton, C. and Baker, J.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
183
5:15
Latest Pleistocene Slip
Rate of the San Bernardino
Strand of the San Andreas
fault in Highland: Possible
Confirmation of the Low
Rate Suggested by Geodetic
Data. McGill, S., Weldon, R.,
Kendrick, K., and Owen, L.
Fine-scale Seismicity of
Earth’s Interior: Regionaland Global-scale Double-difference Applications to Study
Plate-tectonic Processes.
Waldhauser, F., Abend, H.,
Bohnenstiehl, D., Kim, W.,
Richards, P., Schaff, D. and
Tolstoy, M.
Thursday AM, 20 April Poster Sessions
Effects of Large-Scale
Topography on the Ground
Motions and Rupture
Dynamics in the Simulation
of the 1812 Wrightwood,
California, Earthquake. Ma,
S., and Archuleta, R.
S9
A Cumulative Broadband Body-wave Magnitude
for Quick Reliable Estimation of the Size of Great
Earthquakes. Bormann, P., Wylegalla, K., and Saul, J.
S10
9.3—An Orchestral Composition Commemorating
the 2004 Sumatra Earthquake and Tsunami. Barker, J.
and Rolls, T.
S11
Outreach in Western Sumatra: Educating Citizens
on How to Live with Their Natural Tectonic
Environment. Stebbins, C., Sieh, K., Natawidjaja, D.,
and Suwargadi, B.
S12
Risk Communication in a Networked Society.
Comfort, L.
S13
Tsunami Damage Detection Using Moderate-resolution Satellite Imagery. Yamazaki, F., Kouchi, K., and
Matsuoka, M.
S14
Evaluation of Tsunami Damage in the Eastern Part
of Sri Lanka Due to the 2004 Sumatra Earthquake
Using Remote Sensing Technique. Miura, H.,
Wijeyewickrema, A.C., and Inoue, S.
S15
Geotechnical Damages on the Indian Coast Due
to Tsunamis Caused by Dec. 26, 2004 Sumatra
Earthquake. Maheshwari, B., Sharma, M.L., and
Narayan, J. P.
S16
Role of Mangrove Ecosystem with reference to
Tsunami Seismic Hazard. Gokhale, V.
The Giant Sumatran Earthquakes of 2004 and 2005 (Joint
with EERI) (see page 283)
S1
S2
S3
Coseismic Land-level Changes Caused by 26
December, 2004 Sumatra Earthquake and Evidence of
Paleotsunami Deposits (?) in Andaman and Nicobar
Islands, India. Malik, J., and Murty, C. V. R.
Constraining the Co-seismic Fault Slip of Large
Subduction Earthquakes Using both Teleseismic
Body and Surface Waves and an Update of the 2004
Sumatra-Andaman Earthquake. Ji, C., Hjorleifsdottir,
V., and Song, T.-R.
Kinematic Analysis of GPS Data in SE Asia during the Sumatra-Andaman and Nias Earthquakes.
Hashimoto, M., Hashizume, M., Takemoto, S.,
Fukuda, Y., Fujimori, K., Takiguchi, H., Sato, K.,
Otsuka, Y., Saito, S., Miyazaki, S., and Satomura, M.
S4
Earthquake Rupture Variations along the SumatraAndaman Subduction Zone. Bilek, S.
S5
Joint GPS and Satellite Measurements of Atmospheric
Processes Related to the Northern Sumatra Earthquake
Sequence of Dec 2004–Apr 2005. Ouzounov, D.,
Pulinets, S., Cervone, G., Kafatos, M., Ciraolo, L., and
Taylor, P.
S6
Estimation of Path Characteristic of the Great Sumatra
Earthquake by Multipulse Method. Routray, A., and
Kumar, V.
S7
A CUSUM Based Phase Detector for Seismic Signals
Using an Adaptive Markov Model. Mohanty, W.
S8
Development of Attenuation Relationship for Far
Field Earthquakes Caused by Dip Slip Mechanism for
the Application of Sumatran Earthquake Effects to the
Peninsula of Malaysia. Adnan, A., Hendriyawan, H.,
Marto, A., and Irsham, M.
184
Seismological Research Letters
Volume 77, Number 2
Design Ground Motion
Library. Youngs, R., Power,
M., and Chin, C.
Tsunamis (see page 286)
T1
Tsunamis along the Eastern Mediterranean Coast: The
Past Is the Key to the Future. Salamon, A., Ward, S.,
and Rockwell, T.
T2
Late Prehistoric Tsunami(s) in the Tasman Sea:
Evidence from Tasmania and Flinders Island.
Hutchinson, I. and Ellison, J.
March/April 2006
T3
In Search of Past Tsunami Deposits along the
Sumatran Subduction Zone, Padang, Western
Sumatra. Logsdon II, M., Yulianto, E., Rubin, C., and
Witter, R.
T4
Paleotsunami Study in Simelue Island, a Preliminary
Result. Yulianto, E. and Dengler, L.
T5
Landform and Marsh Deposits Provide Evidence for
the Probable Occurrence of Prehistoric Earthquakes
and Tsunamis for the Last 5,000 Yr BP on the Pacific
Coast of Mexico, Guerrero State. Ramirez-Herrera,
M.-T., Kostoglodov V., and Cundy, A.
T6
Tsunami Deposit Grading as a Record of Changing
Tsunami Flow. Higman, B. and Jaffe, B.
T7
Modeling Tsunami Erosion and Deposition.
Gelfenbaum, G., Lesser, G., Jaffe, B., and Moore, A.
T8
Tsunami Whirlpools—Observed in 2004 and
Remembered in First Nations Art and Myth. Ludwin,
R. and Colorado, A.
T9
T10
T11
T12
Submarine Geologic Constraints on Central
California Tsunami Hazards. Nishenko, S., Cluff, L.,
Page, W., Hanson, K., Angell, M., Rietman, J., Thio,
H., and Ichinose, G.
Joint Contribution of Historical and Geological Data
for Tsunami Hazard Assessment in Gargano and
Eastern Sicily (Italy). De Martini, P., Pantosti, D.,
Barbano, M., Gerardi, F., Smedile, A., Azzaro, R., and
Del Carlo, P.
Source Parameters Analysis of the Regional Moment
Tensor Inversion in the Caribbean Region. Cameron,
A., Asencio, E., von Hillebrandt-Andrade, C.,
Huerfano, V., Mendoza, C.
U3
Postseismic Deformations Following the SumatraAndaman and Nias Earthquakes Detected by
Continuous GPS Observations in Southeast Asia.
Hashimoto, M., Hashizume, M., Takemoto, S.,
Fukuda, Y., Fujimori, K., Takiguchi, H., Satomura, M.,
Otsuka, Y., and Saito, S.
U4
Post-seismic Deformation after the 2003 Bam, Iran
Earthquake from Time Series Analysis of Envisat
InSAR. Fielding, E., Funning, G., Lundgren, P., Li, Z.,
and Bürgmann, R.
U5
Near Real-time Source Parameters for Earthquake Loss
Estimates: Bam, 26 December 2003. Wang, R., Wyss,
M., Zschau, J., and Xia, Y.
U6
Over a decade monitoring a mature seismic gap: how
much longer do we have to wait? Protti, M., Gonzalez,
V., Schwartz, S., Dixon, T., Kato, T., Kaneda, Y., and
Lundgren, P.
U7
Interseismic Geodetic Strain around Continental
Faults and Equivalent Elastic Thickness. Chery, J.
U8
Aseismic Creep Associated with Seismic Swarms in the
Salton Trough, CA. Lohman, R. and McGuire, J.
U9
Joint Inversion of GPS and Leveling Data for the
Coulomb Stress Evaluation in the Mexicali-Imperial
Valley. Glowacka, E., Sarytchikhina, O., Nava
Pichardo, F., and Gonzalez, J.
U10
Using InSAR for the Observation of Large-scale
Deformation over the Western Basin and Range.
Gourmelen, N. and Amelung, F.
U11
A GPS Anomaly, Probably Related to Hydrology, in
the San Gabriel Valley, California. King, N., Argus,
D., Langbein, J., Agnew, D., Dollar, R., Bawden, G.,
Liu, Z., Reichard, E., Yong, A., Bock, Y., Stark, K., and
Barseghian, D.
U12
Motion of upper plate faults during subduction zone
earthquakes: The curious case of the Atacama Fault
in northern Chile. Loveless, J., Pritchard, M., and
Allmendinger, R.
Probabilistic Tsunami Hazard Analysis. Thio, H.,
Ichinose, G., Polet, J., and Somerville, P.
Advances in Geodetic Studies of Seismic Sources (see page
289)
U1
High-rate GPS Data—When Are They Useful?
Clinton, J., Bilich, A., Larson, K., Miyazaki, S., and
Yamagiwa, A.
U2
Kinematic Inversion of the 2004 Mw 6 Parkfield
Earthquake from Strong Motion Seismic Data and
High-rate GPS Data. Custodio, S., Liu, P., Archuleta,
R., and Larson, K.
Global Seismicity and Wave-speed Structure of Earth’s
Deep Mantle and Crust: Sessions in Honor of the
Seismological Contributions of E. Robert Engdahl (see
page 291)
V1
Calibrated Earthquake Data Sets for Regional and
Global Seismology. Bergman, E. and Engdahl, E.R.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
185
V2
GLASS: A New Approach to the Global Phase
Association Problem. Johnson, C., Benz, H., and
Buland, R.
Recorded by LASA. Peng, Z., Vidale, J., Leyton, F.,
and Koper, K.
V3
Development of a Direct Search Software Package for
Locating Poorly Constrained Earthquakes. Lee, W.
and Baker, L.
V4
Dueling Slabs Revealed by the Engdahl/van-der-Hilst/
Buland (EHB) Earthquake Catalogue. Kirby, S.,
Engdahl, E. R., and Villaseñor, A.
V5
Accurate Relocated Earthquake Hypocentres Reveal
Structure of Subducted Indian Plate under Burma.
Stork, A., Selby, N., Heyburn, R., Woodhouse, J., and
Searle, M.
V6
MesoAmerican Seismic Experiment: Imaging the
Subducting Slab. Pérez-Campos, X., Clayton, R.,
Iglesias, A., Singh, S., Husker, A., Davis, P., ValdésGonzález, C., and Stubailo, I.
Development of a Three-dimensional Velocity Model
for the Greater Barents Sea Region. Ritzmann, O.,
Faleide, J., Bungum, H., Maercklin, N., Mooney, W.,
Detweiler, S., and Myklebust, R.
V8
Progress in Broad-band Continental Scale Ambient
Noise Tomography. Ritzwoller, M., Barmin, M.,
Bensen, G., Levshin, A., McCoy, C., Moschetti, M.,
Lin, F., Yang, Y., and Shapiro, N.
V9
Sn Tomography in China. Sun, Y., Toksoz, M. N., Pei,
S., Zhao, J., and Liu, H.
V10
Crustal Structure of the Northeastern Margin of the
Tibetan Plateau from the Songpan-Ganzi Terrane to
the Ordos Block. Liu, M., Mooney, W., Li, S., Okaya,
N., and Detweiler, S.
Full Waveform Inversion of Seismic Velocity
and Anelastic Losses in Highly Heterogeneous
Sedimentary Valleys. Akcelik, V., Askan, A., Bielak, J.,
and Ghattas, O.
V12
Implications of Precise Tremor Event Location for the
Mechanism of Deep Nonvolcanic Tremor. Shelly, D.,
Beroza, G., Ide, S., and Nakamula, S.
V13
Investigating Upper Mantle Structure Beneath New
Zealand with Receiver Functions. Boyd, O., Savage,
M., Sheehan, A., and Jones, C.
V14
Investigating Fine-scale Heterogeneity of the Innercore Structure Using Inner-core Scattered Waves
186
Seismological Research Letters
Volume 77, Number 2
The Western Quebec Seismic Zone (Eastern Canada):
Seismic Clustering along an Ancient Hotspot Track.
Ma, S., Eaton, D., and Dineva, S.
V16
Georgian Bay (Ontario) Earthquake with Magnitude
mN 4.3 (October 20, 2005) and Its Foreshock–
Aftershock Sequence: Tectonic Implications. Dineva,
S., Eaton, D., Ma, S., and Mereu, R.
V17
A Global Search for Repeating Earthquakes:
Preliminary Results and Application to the Inner Core.
Zhang, J., Richards, P., and Schaff, D.
Using Regional Velocity Structures to Estimate Seismic
Hazard (see page 295)
V7
V11
V15
W1
Modulus Based Quantification of Seismic Hazards.
Dickson, W.
W2
Probabilistic Seismic Hazard Assessment for the Urban
Area of Evansville, Indiana, Incorporating Laterally
Varying Site Effects. Haase, J., Choi, Y. S., and
Nowack, R. L.
W3
A Matter of Scale: Understanding Nevada’s
Sedimentary Basins for Seismic Hazard Assessment.
Louie, J. N., Heimgartner, M., Pancha, A., Thelen, W.,
Scott, J. B., and Lopez, C. T.
W4
Characterizing the Yucca Mountain Site for
Developing Seismic Design Ground Motions.
Upadhyaya, S., Wong, I., Kulkarni, R., Stokoe, K. H.,
Dober, M., Silva, W., and Quittmeyer, R.
W5
Waveform Inversion of the Strong Motion Data from
Anchorage Basin, Alaska. Dutta, U., Sen, M. K.,
Biswas, N., and Yang, Z.
W6
Shear-velocity Profile across the Evergreen Basin (CA)
Using Microtremor Array Studies. Asten, M. and
Boore, D.
W7
Regional Attenuation Method Comparison for
Northern California. Ford, S., Dreger, D., Mayeda, K.,
Walter, W., Malagnini, L., and Phillips, W. S.
W8
Fully 3D Waveform Tomography for the L. A. Basin
Area Using SCEC/CME. Chen, P., Zhao, L., and
Jordan, T.
W9
3-D Velocity Models and Earthquake Locations in
Southern California using a New Cross-correlation
Location Method. Lin, G. and Shearer, P.
March/April 2006
W10 Shear Wave Velocity of California’s Strong Motion
Recording Stations. Kayen, R., Thompson, E.,
Minasian, D., and Carkin, B.
W11 Joint Inversion of Surface Wave Velocity and Gravity
Observations and its Application to Central Asian
Basins Shear Velocity Structure. Maceira, M. and
Ammon, C. J.
W12 Crustal Structure for Eastern and Central Canada
from an Improved Neighborhood Algorithm
Inversion. Bent, A. and Kao, H.
X9
The Preliminary Study of Next Generation GroundMotion Attenuation Relationship for Taiwan Crustal
Earthquakes. Lin, P., Lee, C., Chiu, H., Cheng, C.,
Chiou, B., and Chern, J.
X10
Three Dimension Velocity Imaging of Seismic Pseudo
Wave in North China with Seismic Anomaly. Li, D.
Broadband Simulations of the 1989 Loma Prieta and 1906
San Francisco Earthquakes (see page 299)
Y1
Acceleration Response Spectra for the 1906 San
Francisco Earthquake Inferred from Modified Mercalli
Intensity. Seekins, L., Boatwright, J., and Bundock, H.
Y2
The Great 1906 San Francisco Earthquake: Simulation
of Broad-Band Strong Ground Motion. Mavroeidis,
G., Halldorsson, B., Zhang, F., and Papageorgiou, A.
Y3
3D Simulations of Ground Motions in Northern
California Using the USGS SF06 Velocity Model.
Dolenc, D., Dreger, D., and Larsen, S.
Y4
Uncertainty Estimates of Losses for a Repeat of the
1906 San Francisco Earthquake. Molas, G., Anderson,
R., Seneviratna, P., and Winkler, T.
Correlation of Casualties with Various Ground
Motion Parameters in the 1999 Chi-Chi, Taiwan
Earthquake. Sullivan, M. and Onur, T.
Y5
The 2004 Mid-Niigata Earthquake: The effect
of ground motion on triggering of Catastrophic
Landslides and Soil–Structure Interaction.
Kourkoulis, R., Gerolymos, N., Georgarakos, P., and
Gazetas, G.
Dynamic Failure Stress for the Great 1906 San
Francisco Earthquake as a Predictor For Later Events.
Olsen, K., Eddo, J., Jimenez, R., Lippincott, C.,
Wimmer, L., and Winther, P.
Y6
Near-field Broadband Ground-motions Based on Lowfrequency Finite-difference Synthetics Merged with
High-frequency Scattering Operators. Mai, P. and
Olsen, K.
W13 Site Classification and Amplification in the Mississippi
Embayment for Regional Seismic Risk Estimations.
Onur, T., Hall, L., and Molas, G.
Thursday PM, 20 April Poster Sessions
Ground Motion: Assessment and Effects (see page 297)
X1
X2
X3
X4
Ground Motion Scaling for Large Subduction
Earthquakes: The September 26, 2003, M 8.1 Tokachioki Earthquake Sequence (Hokkaido, Japan). Macias,
M. and Atkinson, G.
Building Settlement in the Artificial Fill of Old
Mission Creek Marshland, San Francisco Bay.
Sullivan, R.
Crossing the Fault from Seismology to Engineering: Bruce
Bolt Memorial Session (Joint with EERI) (see page 301)
X5
Flexible Steel Building Responses to Scenario
Earthquakes in the Los Angeles Basin. Olsen, A.,
Heaton, T., and Hall, J.
X6
Effects of Rainfall on Soil-structure System Frequency:
Examples Based on Poroelasticity and a Comparison
with Full-scale Measurements. Todorovska, M. and Al
Rjoub, Y.
X7
X8
Instrumental Criteria for Seismic Intensity
Assessment: Alternative Definitions and Applications.
Sandi, H., Borcia, S., Vlad, I., and Vlad, N.
Damping-adjustment Factors for Spectral
Accelerations. Malhorta, P.
Z1
Accelerograms Selection for Structural Response
Analysis Accounting for the Intrinsic Seismic Motion
Variability. Berge-Thierry, C. and Rey, J.
Z2
Time Histories for SHAKE Analysis—Spectra
Matching or Scaled. Zafir, Z. and Boardman, T.
Z3
Using Random Vibration Theory to Predict Site
Response. Rathje., E., Ozbey, M., and Kottke, A.
Z4
Australia’s Earthquake Hazard and Risk. Schneider, J.,
Leonard, M., Allen, T., Robinson, D., Clark, D., Dhu,
T., Cummins, P., Edwards, M., Burbidge, D., Dale, K.,
Mullaly, D., and Milne, M.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
187
Z5
Potential Impact of Earthquakes on the Cadell Fault
Scarp, Southeastern Australia, on Regional Australian
Communities. Dhu, T., Clark, D., Allen, T., and
Schneider, J.
Z6
National Site Classification Map for Australia.
McPherson, A. and Hall, L.
Z7
Balloons to Satellites: A Century of Progress in
Geotechnical Site Characterization. Yong, A., Hough,
S., Cox, H., Tiampo, K., Braverman, A., Harvey, J.,
Hook, S., Hudnut, K., and Simila, G.
Z8
SCEC Cybershake Platform: Incorporating
Deterministic 3D Waveform Modeling into
Probabilistic Seismic Hazard Curves. Graves, R.,
Maechling, P., Zhao, L., Mehta, G., Gupta, N.,
Mehringer, J., Deelman, E., Kesselman, C., Callaghan,
S., Cui, Y., Field, E., Gupta, V., Jordan, T., Okaya, D.,
and Vahi, K.
Z9
The Working Group on California Earthquake
Probabilities (WGCEP) Plan for Developing a
Uniform California Earthquake Ruture Forecast
(UCERF). Field, E.
Z10
A Probabilistic Analysis of Extensional Ground
Cracking along the MacArthur Park Escarpment,
Los Angeles. Thio, H., Roth, W., Dawson, E., and
Somerville, P.
Z11
A Preliminary Look at Multiple Gas Pipeline
Crossings of the Eastern Castle Mountain-Caribou
Fault System, Alaska. Darigo, N., and Rajah, S.
Z12
Extreme Magnitude Earthquake Modeling and Its
Impact on Mexico’s City Seismic Hazard Estimation.
Chavez, M., Madariaga, R., Mai, M., Cabrera, E., and
Perea, N.
Z13
Seismic Hazard Data for the New, Italian Building
Code Based on European Standard. Montaldo, V.,
Meletti., C., Stucchi, M., Faccioli, E., Calvi, G., Boschi,
E., Di Pasquale, G., and Gomez Capera, A.
Z14
Ground Motion Scenarios for Urban Areas and
Infracstructures: the Case of Istanbul, Turkey.
Cultrera, G., Akinci, A., Lombardi, A., Pacor, F.,
Ameri, G., Cocco, M., Franceschina, G., Pessina, V.,
and Zonno, G.
Z15
Z16
188
Herrero, A., Cultrera, G., Piatanesi, A., Rovelli, A.,
Cirella, A., Hunstad, I., and Tinti, E.
Z17
Characteristics of Radiated Energy and Apparent
Stress for Continental Strike-slip Earthquakes. Choy,
G. and McGarr, A.
Z18
Analysis of Strong Ground Motion Source Scaling
and Attenuation Models from Earthquakes Located in
Different Source Zones in Taiwan. Sokolov, V., Loh,
C.-H. and Jean, W.-Y.
Z19
A Retrospect of Two Strong Motion Networks by and
for Seismologist and Engineers: the SMART1 Array
and the TSMIP Networks in Taiwan. Tsai, Y.-B.
Z20
Post-earthquake Response Spectra for Evaluating
Building Performance from a Structural Engineer’s
Viewpoint. Freeman, S.
Z21
Urban Seismology: City Effects on Earthquake
Ground Motion and Effects of Spatial Distribution of
Ground Motion on Structural Response. Fernandez,
A. and Bielak, J.
Z22
Decision Tools for Earthquake Risk Management,
including Net Present Value and Expected Utility.
Smith, W.
Z23
Insurance Earthquake Risk Management: 100 Years
of Progress. Guatteri, M., Castaldi, A., Bertogg, M.,
Dodo, A., Grollimund, B., Tschudi, S., and Haase
Straub, S.
Z24
Improved and Simplified Hazard Maps a Common
Task for Earth Scientists and Engineers. Kuroiwa, J.
Z25
The Great (Ms8.5) Haiyuan Earthquake of 1920,
Northwest China. Zhang, K. and Liu, S.
Z26
The Research and Suggestion of Extent Value of
Physical Measure in Seismic Intensity Scale of China.
Hao, M. and Xie, L.-L.
Earthquake Warning and Alerting Systems: New
Technologies for Hazard Mitigation and Emergency
Response (Joint with DRC) (see page 306)
Characteristics of Seismic High Frequencies of Strong
Motion Accelerograms. Saragoni, G. and Ruiz, S.
AA1
The Fastest P-wave Warning System FREQL, UrEDAS
and Compact UrEDAS with Actual Situations.
Nakamura, Y., Saita, J., Araya, T., and Sato, T.
AA2
Station Density and Its Role in the Evolution of
Earthquake Early Warning Estimates. Cua, G. and
Heaton, T.
Directivity Influence on Displacement Response
Spectra at Low Frequency in Near Source Range.
Seismological Research Letters
Volume 77, Number 2
March/April 2006
AA3
AA4
AA5
AA6
AA7
Implementation of Real-time Testing of Earthquake
Early Warning Algorithms: Using the California
Integrated Seismic Network (CISN) Infrastructure
as a Test Bed. Hauksson, E., Solanki, K., Given, D.,
Maechling, P., Oppenheimer, D., Neuhauser, D., and
Hellweg, M.
Earthquake Warning Systems from the User
Perspective. Grasso, V. and Allen, R.
AA11 Shakemap Estimation Based on Empirical Site
Correction Model. Wen, K.-L., Chang, Y.-W., Jean,
W.-Y., Lin, C.-M., and Chang, C.-L.
AA12 Relationships between Instrumental Ground Motions
and Felt Intensity for the Central United States.
Atkinson, G. and Kaka, S.
AA13 Seismic Network Conversion at the Geological Survey
of Canada, Sidney, BC. Mulder, T. and Lindquist, K.
The Crywolf Issue in Seismic Early Warning
Applications. Iervolino, I., Convertito, V., Giorgio,
M., Manfredi, G., and Zollo, A.
The Irpinia Seismic Network: A New Monitoring
Infrastructure for Seismic Alert Management in
Campania Region, Southern Italy. Iannaccone, G.,
Weber, E., Bobbio, A., Cantore, L., Corciulo, M.,
Convertito, V., DiCrosta, M., Elia, L., Emolo, A.,
Lancieri, M., Martino, C., Romeo, A., Satriano, C., and
Zollo, A.
Advanced Digital Seismic Network for Earthquake
Hazard Mitigation in Bulgaria. D. Solakov, S.
Nikolova, P. Passmore, Zimakov, L., Rozhkov, M.,
Kushnir, A., and Khaikin, L.
AA8
Development of a Shakemap Methodology Based on
Fourier Amplitude Spectra. Sokolov, V., Wenzel, F.,
and Böse, M.
AA9
Attenuation Relations for Intermediate-depth Vrancea
(Romania) Earthquakes Based on Fourier Amplitude
Spectra. Sokolov, V., Bonjer, K.-P., Wenzel, F., and
Grecu, B.
AA10 a Study of Spectral Intensity Scales in Taiwan. Ueong,
Y.-S., Yeh, Y., and Shih, R.-C.
AA14 Canada’s Automated Natural Hazard Alert Service—
Earthquakes. Wetmiller, R., Halchuk, S., and
Woodgold, C.
AA15 Rapid Post-earthquake Information Tools from the
Advanced National Seismic System (ANSS). Wald, D.
AA16 Prompt Assessment of Global Earthquakes for
Response (PAGER): A System to Estimate Impact
Following Significant Earthquakes Worldwide. Earle,
P., Wald, D., and Lin, K.-W.
AA17 Earthquake Loss Estimates: Real-time and Scenario
Mode. Wyss, M.
AA18 International Cooperation for an Indian Ocean
Tsunami Warning System (IOTWS). Detweiler, S.,
Mooney, W., Hudnut, K., Atwater, B., and Sipkin, S.
AA19 The Local Tsunami Warning System in Hawaii. Fryer,
G., Hirshorn, B., Cessaro, R., Shiro, B., Koyanagi, S.,
McCreery, C., and Weinstein, S.
AA20 Investigating the Damage Potential of Seismic Seiches
in the Puget Lowland. Barberopoulou, A., Pratt, T.,
and Titov, V.
FRIDAY, 21 APRIL—ORAL SESSIONS
8:00
Faults Exposed! Applications
of ALSM Data (see page 311)
Presiding: Ken Hudnut and
Judith Zachariasen
Earthquake Warning and
Alerting Systems: New
Technologies for Hazard
Mitigation and Emergency
Response (Joint with DRC) (see
page 312)
Presiding: Richard M Allen,
James Goltz, and David Wald
Advances in Geodetic Studies
of Seismic Sources (see page
314)
Presiding: Roland Bürgmann
and Gareth Funning
Seeing through the Redwoods:
Mapping the Northern San
Andreas Fault in Dense
Forest Cover Using LiDAR.
Zachariasen, J., Prentice, C.,
Koehler, R., and Baldwin, J.
Applications and Benefits of
Earthquake Early Warning:
Implementation and Alert
Times across California. Allen,
R. M.
Coseismic Slip and Afterslip of
the Mw9.15 Aceh-Andaman
Earthquake. Chlieh, M.,
Avouac, J.-P., Sieh, K.,
Hjorleifsdottir, V., Song, T.-R.,
Ji, C., Sladen, A., Hebert, H.,
Natawidjaja, D., and Galetzka, J.
Seismological Research Letters
Volume 77, Number 2
The Earthquake
Professionals’
Top Ten
Initiatives (EERI
session joint with
SSA) (see EERI
program for
details)
March/April 2006
189
8:15
The B4 LIDAR Survey of the
Southern San Andreas and
San Jacinto Faults. Bevis, M.,
Hudnut, K., Brzezinska, D.,
Sanchez, R., and Toth, C.
Applications and Limitations
of Earthquake Early Warning:
Inferences from ShakeMap Uses
and Users. Wald, D.
Coupled Seismic and Geodetic
Studies of Six Subduction Zone
Earthquakes. Pritchard, M., Ji,
C., Simons, M., Norabuena, E.,
Dixon, T., and Boroschek, R.
8:30
New Looks at Active Faults:
Tectonic Geomorphology Using
Airborne Laser Swath Mapping
(ALSM). Arrowsmith, J. and
Crosby, C.
Early Warning Systems for Large
Earthquakes: Extending the
Virtual Seismologist to Finite
Ruptures. Yamada, M. and
Heaton, T.
Modeling the Rupture Process
of Large Earthquakes with 1 Hz
GPS. Larson, K., Miyazaki, S.,
Choi, K., Hikima, K., Koketsu,
K., Haase, J., Emore, G., and
Yamagiwa, A.
8:45
Systematic Landform Response
to Uplift along the Dragon’s
Back Pressure Ridge, Carrizo
Plain, California, Imaged
Using High-resolution LiDAR
Topographic Data. Hilley, G.
and Arrowsmith, J.
ElarmS Earthquake Alarm
Systems: Early Results in
Northern California. Wurman,
G. and Allen, R.
Did the 2003 San Simeon
Earthquake Influence the
Hypocenter Location and
Rupture Pattern of the 2004
Parkfield Earthquake? Johanson,
I. and Bürgmann, R.
9:00
Use of Airborne Laser Swath
Mapping in Slip-Rate Studies of
the San Bernardino Segment of
the San Andreas Fault, Southern
California. McGill, S. and
Pierce, L.
The Seismic Alert System of
Oaxaca. Cuéllar, A., EspinosaAranda, J., Palomino, M., and
Ramos, S.
Along-track Differential InSAR:
A New Look at the 1999 Hector
Mine Earthquake. Bechor Ben
Dov, N. and Zebker, H.
9:15
GeoEarthScope: Imagery and
Geochronology to Support
Investigations into the Structure
and Evolution of the North
American Continent and the
Physical Processes Controlling
Earthquakes. Phillips, D.,
Prescott, W., Jackson, M., and
Meertens, C.
Real-time Estimation of
The Next Big Earthquake on a
Earthquake Location and
San Andreas Fault. Fialko, Y.
Magnitude for Seismic Early
Warning in Campania
Region, Southern Italy. Zollo,
A., Satriano, C., Lancieri, M.,
Lomax, A., Bobbio, A., Cantore,
L., Convertito, V., Corciulo, M.,
De Matteis, R., Di Crosta, M.,
Elia, L., Emolo, A., Iannaccone,
G., Martino, C., Romeo, A., and
Weber, E.
9:30
Coffee Break
Plenary Session: Preparing for the Future (see page 315)
10:00 Kerry Sieh: A Bleak Prognosis for Greater Human Suffering from Earthquakes
Greg Deierlein: Challenges and Innovations in a Sustainable World
Henry Renteria: TBA
Closing Session
12:00 Chris Poland: A Centennial Challenge to Earthquake Professionals Worldwide
190
Seismological Research Letters
Volume 77, Number 2
March/April 2006
SSA 2006
Abstracts of the Annual Meeting
• Abstracts
• Abstracts Index
Tuesday, 18 April—Oral Sessions
Plenary Session: Commemoration of the 1906 San
Francisco Earthquake
The 1906 Earthquake—Lessons Learned, Lessons Forgotten, and Looking
Forward in Earthquake Science
M. Zoback, USGS, Menlo Park, [email protected]
At the turn of the century, San Francisco had a population of 400,000 and was the
richest, the most powerful, and the most important city on the Pacific. Seismology
was at its infancy. There was not general agreement among scientists as to the cause
of earthquakes. The 1906 Mw7.8-7.9 earthquake on the northern San Andreas
Fault and its subsequent study marked the birth of modern earthquake science.
For the first time, the effects and impacts of a major seismic event were systematically investigated, documented and interpreted as a recurring process. The resulting
publication, the so-called “Lawson report” (named for the principal investigator),
contained many “firsts”:
• The San Andreas Fault, recognized previously in small segments, was identified and mapped as a continuous geologic structure transecting nearly the entire
state
• The entire 300-km-long surface rupture was mapped, surface offsets documented, and co-seismic surface displacements inferred from geodetic measurements
• Analysis of local seismic data yielded an epicenter ~40 km NW of the current best location offshore from San Francisco—impressive considering how little
was known of local velocity structure and that P and S waves had only been identified by seismologists <10 yrs before
• Comprehensive mapping of intensity showed the strongest shaking
occurred in areas of “made land” (fill) and soft sediment including China Basin
and present day Marina district-two San Francisco neighborhoods heavily damaged
again in 1989
• Surveys of damage to structures showed destruction was closely related to
building design and construction—a painful lesson oft repeated around the world
• Interpretation of the pre-and co-seismic deformation patterns led Henry
Reid to propose the elastic rebound hypothesis—that earthquakes represent sudden release of elastic energy along a fault resulting from a cycle of slow strain accumulation produced by relative displacements of neighboring portions of the crust.
It is still accepted today with minor modifications, even though the basis
for large-scale horizontal displacements wasn’t established until the plate tectonic
revolution five decades later. As earthquake science evolves, reanalysis of the 1906
earthquake data continues to yield new insights about that event and the behavior of large strike-slip faults in general. A ~60 yr period of seismic quiescence in
N. California after 1906 remains the best example of a regional “stress shadow”
resulting from reduction of stress on adjacent subparallel faults by slip in a major
earthquake. Looking to the future, a dense array of continuous GPS recorders in N.
California, part of EarthScope’s Plate Boundary Observatory, can search for fault
interactions and determine if an acceleration of strain rate precedes the next big
earthquake as it may have prior to 1906.
The Impact of the 1908 Lawson Report on Earthquake
Science
Presiding: Jack Boatwright and Carol Prentice
Location and Tectonics of the Focal Region of the California Earthquake of
18 April 1906: Evidence from the Lawson Report and Later Studies
A. Lomax, Anthony Lomax Scientific Software, [email protected]
We investigate the location and tectonics of the focal region of the 18 April 1906
California Earthquake. Applying modern, probabilistic relocation to arrival observations from the Lawson report, we place the 1906 hypocenter to the west of San
Francisco near the offshore San Andreas Fault system; we associate this focus with
a dilatational right-bend in the San Andreas Fault system, in agreement with previous work. Using seismological, geological and marine evidence from the Lawson
report and from later studies, we propose a 10-15 km long focal region in a zone of
sea floor subsidence and complex faulting extending northwestwards from offshore
Daly City to offshore of the Golden Gate. We characterize the geometry of 1906
rupture in this region by normal faulting on a steeply west-dipping structure trending about 20° clockwise to the San Andreas Fault zone, and by strike-slip rupture
along the San Andreas Fault system around and away from the west-dipping structure: rupture to the north on a vertical, currently a-seismic fault structure under
the Golden Gate Fault, and rupture to the south under the San Francisco Peninsula
along a steeply southwest-dipping structure showing present day extensional tectonism. All three of these structures extend from the near-surface to about 10 km
depth. We also identify a 20 km long, linear trend of clustered seismicity at 1013 km depth which connects the northern part of the proposed focal region with
the south end of the southwest-dipping, San Francisco Peninsula structure. We suggest that this trend reveals faulting at the base of a brittle, upper crust in response to
an underlying shear zone in a ductile, lower crust. Motion across this hypothesized,
deep shear zone, rotated about 6° clockwise relative to the strike of the San Andreas
Fault, may explain the present day extensional tectonism found along the northern
San Francisco Peninsula. These new interpretations on the focal region of the 1906
earthquake have implications for seismotectonic understanding, earthquake monitoring and seismic hazard assessment in the San Francisco Bay Area.
Re-evaluating the Intensity Distribution of the 1906 San Francisco
Earthquake
J. Boatwright, US Geological Survey, [email protected]; H. Bundock, US
Geological Survey, [email protected]
The damage descriptions and felt reports for the 1906 San Francisco earthquake
comprise a remarkable chapter of the 1908 Lawson Report. At a time when seismology was largely a foreign science, a group of geologists who were relatively untrained
in assessing earthquake damage produced the most thorough documentation of
earthquake effects to that time, and evolved much of the methodology for isoseismal studies still in use today. Although there were disagreements (notably between
Lawson and Wood regarding intensity scales), their work laid the foundation for
modern seismic hazard studies: in particular, they established important relations
between strong ground shaking, fault rupture, and soft soils. Ninety-eight years after
it was first published, the 1908 Lawson Report still yields critical intensity information. Boatwright and Bundock (2005) recently re-evaluated Modified Mercalli
Intensities (MMI) for more than 600 sites described in Lawson (1908) and plotted
these intensities using ShakeMap (Wald et al., 1999). Although their intensities are
similar to those of Stover and Coffman (1993), the two-fold increase in sites and
the use of the ShakeMap interpolation scheme significantly improve the resolution.
Plotted as a function of distance from the rupture, the intensities confirm both the
saturation of near-fault ground motion and the decrease of geometrical spreading
for very large earthquakes obtained by recent PEER/NGA strong-motion regressions. More interesting, however, are the anomalies of the intensity map: we will
discuss three of them. The angle between the fault strike and the zone of high intensity that extends NNE from Tomales Bay to Sebastopol and Santa Rosa suggests
that these high intensities were caused by a rupture velocity approaching the P-wave
speed. Similarly, the offset of damage and ground failure near Cape Mendocino
from the offshore San Andreas fault suggests that the rupture velocity of the fault
segment beyond Shelter Cove was also transonic. Finally, the marked decrease of
intensity along the rupture segment between Loma Prieta and San Juan Bautista
suggests that this segment may have been relatively unloaded and the slip on this
segment driven by the stress pulse from the prior, more energetic, rupture of the
Peninsula segment.
Triangulation Surveys, Elastic Rebound, and Models of Slip in the 1906
Earthquake
P. Segall, Stanford University, [email protected]; S. Song, Stanford
University, [email protected]; M. Lisowski, U.S.G.S. Cascade
Volcano Observatory, [email protected]
Deformations accompanying the 1906 earthquake displaced existing triangulation stations. “It was thus decided to repair the old triangulation, damaged by the
Seismological Research Letters Volume 77, Number 2 March/April 2006 191
earthquake, by doing new triangulation” (Hayford and Baldwin, 1907). These data
led Harry Fielding Reid to conclude that “external forces must have produced an
elastic strain in the region about the fault-line, and the stresses thus induced were
the forces which caused the sudden displacements, or elastic rebounds when the
rupture occurred” (Reid, 1908). Elastic rebound remains central to our understanding of earthquake physics to this day.
Hayford and Baldwin (1907) determined displacements by differencing station positions before and after the earthquake, assuming several stations northeast
of the fault remained stationary. Combined with inevitable survey errors, this led to
displacements that diverged with distance from the fixed stations.
Thatcher, in his pioneering studies of the earthquake, used only changes in
repeated angles, which can be directly related to displacements. Combined with
elastic dislocation theory, Thatcher and coworkers were able to use the angle
changes to estimate the fault-slip distribution. The use of repeated angles avoids
errors associated with uncertainties in absolute positions, but ignores non-repeated
observations.
Yu and Segall (1996) developed an approach that makes use of all observations,
but avoids the pitfalls of differencing positions. They used this approach to determine displacements in the 1868 Hayward fault earthquake, finding a 52-km long by
10-km deep rupture, considerably longer than the 30 km of surface breakage.
More recently, Song, Beroza, and Segall (this meeting) reexamined the 1906
geodetic data in an effort to resolve the discrepancy between slip models based on
triangulation and teleseismic body waves. They apply the Yu and Segall approach
to determine the displacement field along the fault north of Point Arena where
the geodetic and seismic inversions diverge. Displacements of ~ 2+ meters at two
stations near the fault remain fault parallel through a significant bend in the fault
trace, strongly supporting a tectonic origin. Slip near Mendocino is ~5 m, less than
the 8 + m inferred by Thatcher. The discrepancy between the geodetic and seismic
models is removed if the fault is allowed to rupture at speeds in excess of the local
shear wave velocity.
The Lawson Report and Geologic Research Along the Northern San Andreas
Fault
C. Prentice, US Geological Survey, 345 Middlefield Rd., MS 977, Menlo
Park, CA 94025, [email protected]; T. Niemi, Department of Geosciences,
University of Missouri, Kansas City, Missouri 64110, [email protected]
The Report of the State Earthquake Investigation Commission, commonly known
as the Lawson Report (1908), and historical documents associated with the Lawson
Report, have informed geologic studies of the northern San Andreas Fault (NSAF),
including efforts to make more detailed maps of active fault traces, paleoseismic
investigations, and research into the 1989 Loma Prieta earthquake. Studies in five
areas along the fault have especially benefited from historical data contained in the
Lawson Report and associated documents: the Southern Santa Cruz Mountains,
the San Francisco Peninsula, Olema, Fort Ross, and Shelter Cove. In the Southern
Santa Cruz Mountains, data from the Lawson Report and other historical sources
were re-examined to determine the nature of the surface rupture and amount of
slip there in 1906, allowing comparison between the 1906 and 1989 earthquakes.
Significant differences between the slip in 1989 and 1906 suggest the 1989 earthquake did not occur on the NSAF. Along the San Francisco Peninsula where the
fault has been intensely urbanized, 1906 photographs and other historical data
were crucial elements in producing a detailed and accurate GIS database showing
the locations of active fault traces. Near Olema, G.K. Gilbert’s measurements of
offset cultural features provide important evidence for new studies suggesting that
the penultimate earthquake in this area may have involved significantly less slip than
that 1906 earthquake. In the Fort Ross area, F. Matthes’s detailed, 5-ft-contourinterval map of the rupture traces (surveyed with a plane table and alidade in 1906)
has been particularly important to paleoseismic studies because the construction of
Highway 1 has obscured the location of the fault and the details of the offset geomorphic features. In the Shelter Cove area, the long-standing controversy on the
location of the NSAF and the nature of the surface rupture reported in the area in
1906 has been resolved using historical and paleoseismic data. The Lawson Report
is a singularly remarkable document, and contains data of great value to scientific
research a century after its publication.
Mining the Lawson Report
S. Hoose, Retired, [email protected]
The Lawson Report is a gold mine of detailed data on the effects of the 1906 earthquake. The report is an amazing compilation of observations and facts that were
reported by geologists who spread out over the countryside to collect the ephemeral
information. The descriptions are very precise and detailed. The accuracy and clarity of the observations allowed the identification of features caused by liquefaction
during the 1970s, even when the original observers did not understand the process.
One of the issues surrounding the Lawson Report is the modern research approach
that results in ignoring paper based references in favor of what is easy to find “online”. Often the seminal reports and investigations are older references and maps still
on paper. Not including these references results in negligent geological work. We all
need to remember to help the developing geologists among us to know, recognize,
and use these fundamental papers and maps. It is not automatically true that the
most recent report is the best report. The Lawson Report completely changed the
way we look at earthquakes, which are no longer considered weather phenomenon
as was the case before the 1906 earthquake. How did we mine the Lawson Report?
We used road maps and historic and current topographic maps to locate the place
names, follow the route of the geologists, and plot the descriptions. Colored dots
were used to indicate various types of observations. Numbers were used to track
the location, phenomenon type, and original quote from the report. This approach
was applied to numerous other historical research methods All told it was lots of
fun to ferret out the details from the Lawson Report! Today this data is being used
to develop liquefaction and landslide hazard maps. The Lawson Report is the key
to a safer future.
A CAMEL-Based Assessment of Earthquake-induced Landslide Hazards in
the San Francisco Bay Region, California
D. Keefer, US Geological Survey, [email protected]; S. Miles, Consensus
Building Institute, [email protected]; M. Swank, San Jose State University,
[email protected]; J. Blair, US Geological Survey, [email protected]
The 1906 San Francisco earthquake produced thousands of landslides throughout
the San Francisco Bay Region. These landslides caused at least 40 deaths and significant property damage. The 1989 Loma Prieta earthquake, though substantially
smaller than the 1906 event, still generated at least 1500 landslides, which caused
one fatality and more than $30 million in direct economic losses. Landslides from
both earthquakes also blocked roads and damaged other infrastructure, greatly
complicating post-earthquake rescue and relief efforts. These types of landslide
damage and hazards to life have also occurred in other historical earthquakes in the
San Francisco Bay region and are expected in future earthquakes. To assess these
hazards, a new model has been developed for mapping seismic landslide hazard.
The model-the Comprehensive Areal Model of Earthquake-Induced Landslides, or
CAMEL-is the first to provide separate output concerning the very different kinds
of hazards that result from different types of landslides. CAMEL incorporates the
variables empirically determined to be most important for earthquake-induced
landslide occurrence, including slope angle, soil moisture, material strength, slope
height, soil depth, shaking intensity, terrain roughness, artificial slope disturbance,
and vegetation condition. The model is based on fuzzy set theory (also called “computing with words)” and deals with the inevitable uncertainties in the input data by
providing ranges in the output data. Output is given as predicted ranges of landslide
concentrations (numbers of landslides per unit area) for six categories of landslides.
Incorporating CAMEL into Geographic Information Systems (GIS) technology
can produce map-based regional hazards assessments. Beginning with a prototype
test area in the Southern Santa Cruz Mountains, around the epicenter of the Loma
Prieta earthquake, we are currently applying CAMEL to produce maps of earthquake-induced landslide hazards for the San Francisco Bay region.
Nuclear Explosion Monitoring Anniversary Session I
Presiding: Bill Walter and Brian Stump
The CTBT—A Treaty with Two Faces
O. Dahlman, Chairman of CTBT Preparatory Commission WG on
Verification, [email protected]
Like Chagall’s famous painting “David et Bethsabée”, the CTBT has two closely integrated faces. Chagall’s faces are both bright, CTBT has one darker political and one
brighter technical. Soon to celebrate its tenth anniversary, it is now signed by 176
States but is still a long way from entering into force. This political stalemate started
on 13 October 1999 when the US Senate rejected ratification. The treaty has, however, created a valuable norm of non-testing among the signatory States. The global
verification system, the most extensive ever created, with more than 300 observing
stations in some 90 countries, is rapidly approaching the final stage of implementation. Large volumes of data are on-line transferred to a high capability data-center in
Vienna for automatic and interactive analysis. To build such a technically complex
system on a global scale and in a political environment is a real challenge and it is
also a significant confidence building measure. Testing and evaluation have started
and we have high hopes that the system might prove most capable. The Treaty has
also a most intrusive on-site inspection regime to clarify events on which States may
have doubts. Also this part is unprecedented as it provides for the inspection of large
areas. The treaty organization and its Secretariat in Vienna are faced with two future
192 Seismological Research Letters Volume 77, Number 2 March/April 2006
challenges. The first is political: What to do when you have a verification system that
is ready for operation and you do not have treaty in force? The second is scientific
and technical: How can you connect to the scientific world and recapitalize knowledge to prevent the system and the organization from being obsolete?
Seismic Source Location and Test Ban Verification
A. Douglas, AWE Blacknest, [email protected]
The Comprehensive Test Ban Treaty has provision for an international team to
inspect the area around the estimated epicenter of any suspicious seismic disturbance
(i.e. carry out an on-site inspection, OSI) to determine if a nuclear test really took
place. For an OSI to be effective it is essential that the area of search cover the true
epicenter, which requires reliable estimates of source location. This in turn requires
that reading error in P times be small and estimates of the path effects reliable; a
path effect being the difference between the true travel time and the time predicted
from standard travel-time tables. The paper reviews recent estimates of reading error
and how this error: (i) varies with signal-to-noise ratio; (ii) differs for analyst and
automatic picks; and (iii) differs for earthquakes and explosions. Estimates of path
terms is straight forward for former test sites where the true epicenters of the explosions are available. For P times for explosions recorded at teleseismic distances, it
appears that with correction for path terms, epicenters can be estimated with an
accuracy of a few kilometres with small numbers of stations. For areas away from
test sites earthquake times have to be used. The most effective method for estimating path terms is group analysis of the times from clusters of earthquakes (at least
one of which has a well-determined epicenter) using times read by a single analyst
or a number of analysts trained to a common standard, rather than by automatic
systems. Group methods assume that path effects are correlated for all sources in a
cluster. The power of group methods is that statistical tests can be applied to determine the area over which the path effects can be assumed to be constant.
Experimental Research Programs Designed for Improving Nuclear Test
Monitoring: Historical Aspects and Future Considerations
J. Bonner, Weston Geophysical Corporation, [email protected];
B. Stump, Southern Methodist University, [email protected]
General Leslie R. Groves wrote a memo to J. Robert Oppenheimer on 27 April
1945 initiating the planning for the first ever seismic measurements of a nuclear
explosion, Trinity detonated on 15 July 1945. This initial work has been followed
by an extensive history of experimental research programs that have increased our
understanding of the nuclear explosion source. We present a review of the programs
that have increased the knowledge of coupling and material property effects, decoupling, depth-of-burial effects, free-surface interactions, and travel-time calibration.
We also discuss the future directions for these experimental programs.
Coupling experiments going back to first underground explosion, Rainier, and
including other tests such as Piledriver/Hardhat in granite have improved research
in nuclear monitoring efforts significantly in particular the relationship between
yield and seismic amplitudes or magnitude. Theoretical models of decoupling in
cavities motivated experiments such as Cowboy (1959) and Diamond Beech/Mill
Yard (1985) that are still used today. The Non-Proliferation Experiment (1993)
provided the experimental basis to demonstrate the near equivalence of the nuclear
and chemical explosion sources, which provided the foundation for many future
nuclear monitoring research experiments including the Wyoming Regional Seismic
Experiment (1996).
Recent phenomenology experiments have focused on the generation of shearwave energy from chemical explosion with particular emphasis on regional observations. Local recordings of Rg from the Shagan Depth-of-Burial Experiment (1997)
were used to provide one explanation for regional Lg observations. Moment tensor
analysis of explosions in the Arizona Source Phenomenology Experiments (2003)
showed that the isotropic chemical explosions had little or no shear waves; however,
shear waves were generated and observed within one second of the blast origin.
Recently, there has been increased interest in calibration experiments for improved
location accuracy as well as characterization of regional propagation path effects.
The Dead Sea Calibration Experiment (1999) allowed the calibration of regional
seismic phase travel times as far away as Germany. A similar series of explosions
conducted in central Anatolia and eastern Turkey (2002) were used to calibrate
regional and IMS networks in the Middle East.
Development and Future of Explosion Source Theory
J. Stevens, SAIC, [email protected]
The goal of explosion source theory is to develop a physical model for the source
that can predict the observed seismic phases. Source theory has progressed from
spherically symmetric source models that reproduce near-field waveforms and farfield compressional waves, to more complex models that predict shear waves generated by an explosion buried at finite depth.
The simplest model for an explosion is an instantaneous high-pressure source
in an infinite medium. As the high-pressure region expands, the external material
deforms through expansion and subsequent rebound. Seismic source functions
derived from empirical data, such as the Mueller/Murphy source model, provide
a source representation parameterized by yield, depth and material type. Near field
deformation time history can be calculated using nonlinear spherically symmetric
finite difference codes, with material models developed from near field observations
of underground nuclear tests.
The main asymmetries in an explosion come from the effects of gravity and
the free surface. The decrease in pressure at shallow depth causes much stronger
nonlinear deformation above the explosion than below it. One result of this asymmetry is direct generation of shear waves, which would not be generated by a spherically symmetric source. Axisymmetric finite difference calculations including gravity permit modeling of this asymmetry and show that in some cases the explosion
source is closer to conical in shape than spherical.
A longstanding nuclear monitoring problem is prediction of the regional Lg
phase. Observed Lg is generally larger than predicted from a point source in a planelayered earth model, particularly in high velocity source regions. Direct generation
of shear waves by a realistic explosion source is a likely explanation of the Lg amplitudes, although other explanations such as scattering of Rg into Lg have also been
proposed, and to date it has not been possible to conclusively and quantitatively
resolve the mechanisms responsible. In general, explosions generate more shear
waves than are predicted from numerical or empirical models, and shear waves are
observed even in the near field of cavity-decoupled explosions. These observations
suggest the need for simulation of additional physical mechanisms, such as excitation of nonspherical modes of cavity vibration.
Frontiers and New Opportunities for Seismic Monitoring Research
C. Ammon, Penn State, [email protected]
For decades, seismological techniques have been a critical component of nuclear
explosion monitoring efforts. Since Gutenberg’s 1946 landmark paper on the
Trinity explosion, earthquake and nuclear-explosion monitoring seismology have
benefitted from a synergistic relationship that has led to rapid advances in each field.
With the end of the Cold War, the focus changed from large explosions at specific
test sites to potential small explosions globally, producing a new set of challenges.
The focus shift resulted in a dramatically increased number of events that must be
categorized and an increased importance for earth-structure variations, which now
more strongly affect monitoring efforts. The field has adapted well, but ongoing
developments in data availability and access suggest that exciting results wait on
the horizon. The rapid and accelerating increase in the amount of new, high-quality
seismic observations has only begun to affect monitoring research. The addition of
historic data online will facilitate novel data mining efforts that may expose undiscovered patterns in both the old and new observations. Effective use of these vast
quantities of data requires the development of new analysis approaches. Continued
computational advances will allow integrative analyses of seismic events, including
simultaneous global event location, moment-tensor estimation, and tomography;
exploiting measurements from the growing number of seismic stations. The power
to re-analyze older data will facilitate the most effective extraction of information
from the seismic wavefield. While combining diverse and complementary observations from seismograms will remain an important research frontier, more work
is needed on intelligently integrating the information. Recent explorations of the
advantages of wavelet or multi-objective norms shows promise for helping to define
new measures of modeling success. Simple L2 and L1 norms should yield to more
formal and complete probability metrics to assess models, origins, and to form a
basis for the decisions that are part of the monitoring solution. Computational
efficiency will also allow more thorough investigations and estimations of realistic
uncertainties, and the combination of probabilistic-based constraints to solve existing and future problems. Ready access to seismic monitoring data and the inexpensive availability of increasing computational power have the potential to spark
considerable innovation as we work to advance seismic monitoring capability and
reliability.
Seismic Instrumentation—Past and New Frontiers
J. Berger, Scripps Instition of Oceanography, UCSD, [email protected]
Nuclear Monitoring by seismological methods, the detection and characterization of
signals from nuclear explosions, provided much of the impetus for the development
of modern seismological instrumentation. In the 60s and 70s the VELA Program,
the US Government’s research effort managed by ARPA, sponsored many developments including instrumentation for the WWSSN, HGLP, and SRO networks,
wide-band, fedback seismometers, tri-axial and borehole seismometers, strain seismometers and digital recording techniques. The culmination of these efforts and
parallel developments in data processing may be seen today in the International
Monitoring System of the CTBT Organization headquartered in Vienna.
Seismological Research Letters Volume 77, Number 2 March/April 2006 193
As a result of these advances, seismologists began to see the scientific advantages of large deployments of wide-band, digitally recorded seismometers. These
efforts culminated in the mid 80’s with the organization of the IRIS GSN and
PASSCAL programs.
While the last decade has seen the gradual wind-down of Vela program and
governmental support of seismic instrument development in general, commercial
development of portable 3-component wide-band seismometers has increased and
a number of innovative new sensors are under development. The same cannot be
said of the development of seismic sensors with low noise and high resolution in the
normal mode frequency band (1-100 mHz). The older generation of low-noise sensors has become obsolete and the newer instruments are less capable. Some modest
development programs of such instruments are underway but a more serious problem is the decline in training of the next generation of seismological instrumentalists in departments of earth sciences.
misinterpreted, leading to earthquake series that have too many or too few events.
The quality of different kinds of paleoseismic indicators must be quantified, so high
quality evidence can be distinguished from low, and the completeness of paleoseismic records rigorously evaluated.
Finally, paleoseismology needs to be directed towards answering well-defined
questions about earthquake behavior rather than simply addressing the activity of
individual faults. Because paleoseismology is the only way to determine the timing
and size of long series of large earthquakes on a fault, future efforts must determine
what fundamental questions about earthquake recurrence can be best answered by
paleoseismology and effort focused on designing investigations to answer them.
Earthquake Science in the 21st Century: Understanding the
Processes that Control Earthquakes I
Presiding: Bill Ellsworth and Greg van der Vink
Earthquake dynamics has made substantial progress in recent years as more and
more seismic events are carefully modelled using seismological, geodetic and tectonic information. Most of these inversions are relatively low frequency, but they
have enough resolution so that many details of rupture are beginning to emerge.
Although rupture processes differ substantially from one earthquake to another,
several features appear systematically: slip complexity, fast supershear ruptures exist
but are rare, energy and rupture process zones scale with earthquake size, etc. What
is missing from these models is high frequency seismic radiation, an essential component of energy balance. There are currently two approaches to understand the
detailed energy balance that controls rupture propagation. One, mainly mechanical, looks at the details of steady state rupture growth considering increasingly
sophisticated friction models that take into account fault gouge, pore fluids and
pressure build up. The other approach, more in line with statistical physics, tries to
understand the rôle of fault geometry on the mechanics of rupture. Both approaches
are complementary, of course. In this talk I will discuss energy balance with simple
models of rupture that have been solved by different authors using a combination
of numerical and exact techniques. It appears that the concept of energy release rate
as originally defined for flat faults needs to be revisited in order to take into account
small-scale fault geometry. Simple non flat fault models produce complex stress distributions around the fault, energy release rate increases dynamically, while rupture
speeds are reduced. A significant part of the available energy that would otherwise
be available for rupture propagation is used instead to produce seismic radiation.
Earthquake System Science: What It Means and Where It’s Going
T. Jordan, Southern California Earthquake Center, [email protected]
The study of earthquake dynamics concerns interactions among many fault-system
components, which themselves are often complex subsystems. The success of this
research enterprise depends critically on the ability to construct system-level models that describe earthquake behaviors and to test them against multiple datasets.
This presentation will focus on two aspects of earthquake system science in which
new IT tools developed by the Southern California Earthquake Center (SCEC)
are facilitating model-based inference. The first is ground-motion prediction using
three-dimensional structural models that incorporate sedimentary basins and other
geological complexities. We have developed two terascale computational platforms,
TeraShake and CyberShake, to support such calculations, and they are beginning
to deliver new insights into seismic hazards in Southern California (see Olsen et al.
and Graves et al., this meeting). The second area is the study of earthquake predictability. SCEC is attempting to accelerate prediction research by creating a virtual,
distributed laboratory with a cyberinfrastructure adequate to support a global program of research on earthquake predictability. This Collaboratory for the Study
of Earthquake Predictability (CSEP) will have rigorous procedures for registering
prediction experiments, community-endorsed standards for assessing probabilistic
predictions, access to authorized data sets and monitoring products, and software
support to allow researchers to participate in prediction experiments and update
their procedures as results become available (see Schorlemmer et al., this meeting).
CSEP will encourage research on earthquake predictability by providing researchers with adequate infrastructure and resources to conduct scientific prediction
experiments, and it will allow the predictive skill of proposed algorithms to be compared with reference methods, such as the long-term, time-independent forecasts of
the National Seismic Hazard Map.
Paleoseismology in the 21st Century
R. Weldon, University of Oregon, [email protected]
The clarity of the relationship between the earthquake, elastic strain release, and
characteristics of the surface rupture in 1906 provided an important foundation for
the field of paleoseismology. Since 1906, paleoseismology has focused on determining the presence and width of rupture along potentially active faults, the average
recurrence interval of surface ruptures, and the average slip rate over multiple earthquake cycles. While these properties have been invaluable to informing seismic hazards, paleoseismology can provide a great deal more in the 21st century.
To realize its full potential, progress needs to be made in 3 main areas. First,
paleoseismology must focus more on determining the amount and style of individual displacements produced by prehistoric earthquakes. This will require greater
reliance on multiple or 3d excavations, and improving the understanding of the
microgeomorphology of paleoseismic sites, aided by the integration of trenching
and increasingly detailed DEMs provided by LiDAR and other emerging microtopographic techniques. In conjunction with displacement studies, we must better
understand the relationship between earthquake size and the deformation found
in trenches or surface microgeomorphology. Second, there must be a much greater
focus on quantifying uncertainties in the recognition, dating, and size of paleoearthquakes. While substantial progress has recently been made in quantifying dating
uncertainty, we are only beginning to understand uncertainties associated with the
recognition of paleoearthquakes. Evidence for paleoearthquakes may be poorly preserved or missed, and many features inferred to represent paleoearthquakes can be
Earthquake Dynamics at the Crossroad between Seismology, Mechanics
and Geometry.
R. Madariaga, Ecole Normale Supérieure, [email protected]; M.
Adda-Bedia, Ecole Normale Supérieure, [email protected];
Fault Segmentation Effects on Sequences of Dynamic Events
B. Shaw, Columbia University, [email protected]
One of the biggest assumptions, and a source of some of the biggest uncertainties in
earthquake hazard estimation is the role of fault segmentation in controlling large
earthquake ruptures. We have developed a model which spontaneously produces
complex segmented fault geometries, and on this complex fault network generates long sequences of dynamic rupture events. Using this model, we have studied
a number of aspects of ruptures relevant to hazard questions. We have examined
the cascading of large events across segments, finding support for a modified segmentation hypothesis whereby segments both break in power law small events
and occasionally participate in cascading multisegment larger ruptures, but also
predominantly break as a unit. We have looked at the variation of ruptures, finding an increase in variation at the ends of segments and a decrease in variation for
the longest segments. We have examined the initiation, propagation, and termination of ruptures, and their relationship to fault geometry and shaking hazard. We
find concentrations of epicenters near fault stepovers and ends; concentrations of
terminations near fault ends; and persistent propagation directivity effects. Taking
advantage of long sequences of dynamic events, we directly measure shaking hazards, such as peak ground acceleration exceedance probabilities, without need for
additional assumptions. This provides a new tool for exploring shaking hazard from
a physics-based perspective.
Remotely Triggered Earthquakes
S. Hough, U.S. Geological Survey, [email protected]
First recognized by the seismological community only in 1992 (although discussed
by Charles Richter in 1955), remotely triggered earthquakes represent a unique
opportunity to investigate earthquakes for which the immediate triggering mechanism is known. That is, triggered earthquakes that occur during the initial S/surface
wave arrivals are known to have been triggered by the dynamic, transient stress associated with the passing seismic waves. These triggered earthquakes, and the local
sequences that sometimes follow them, occur in a wide range of tectonic settings,
following small as well as large mainshocks. Yet even dense monitoring networks,
for example at Parkfield, have revealed no evidence of triggering on the San Andreas
fault, along which significant strain is presumably stored. One explanation for this
194 Seismological Research Letters Volume 77, Number 2 March/April 2006
is that the stored stress on a major fault such as the San Andreas is never close to failure according to a classic stress failure criterion. I suggest that, taken together, the
triggered earthquake observations provide support for the interpretation that major
faults are brittle—i.e., statically strong but dynamically weak—and that triggered
earthquakes occur on locally weak patches of faults. Triggered earthquakes essentially represent experiments in earthquake nucleation: although we cannot control
the timing of these experiments, through dense monitoring and careful quantification of triggered earthquake statistics we can exploit these experiments fully.
The Northern San Andreas Fault: 100 Years of Scientific
Study
Presiding: Carol Prentice and Tina Niemi
Application of New Technology to Mapping the Northern San Andreas Fault
C. Prentice, US Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park,
CA 94025, [email protected]; J. Zachariasen, URS Corporation, 1333
Broadway, Suite 800, Oakland, CA 94612-1924, [email protected]m;
R. Koehler, Center for Neotectonic Studies/MS 172, University of Nevada
Reno, NV 89577, [email protected]; J. Baldwin, William Lettis &
Associates, Inc., Inc. 1777 Botelho Drive, Suite 262, Walnut Creek, CA 94596,
[email protected]; N. Hall, Consulting Engineering Geologist, 3586 Spirit
Lane, Pollock Pines, CA 95726, [email protected]; R. Wright, Geomatrix
Consultants, 2101 Webster Street, 12th Floor, Oakland, California 94612,
[email protected]
The northern San Andreas Fault was first recognized and mapped as an integrated
feature as a result of the 1906 San Francisco earthquake. The Report of the California
State Earthquake Investigation Commission (commonly referred to as the Lawson
Report, 1908) contains the first complete mapping of this fault. In the 1960’s and
1970s, advances in mapping techniques led to the first generation of “strip maps”
in the 1960’s and 1970’s that portrayed the active traces of the San Andreas Fault
in detail. These maps, typically at a scale of 1:24,000, commonly included detailed
annotation documenting the locations of tectonically produced geomorphic features that were used to delineate Holocene faults. With the recent advent of GIS
technology and ALSM data, a new generation of fault maps is being produced for
the northern San Andreas Fault. These maps represent substantial improvements
in both the accuracy and detail of mapped fault features. Because the products are
digital, they also provide users with greater flexibility, access to a variety of datasets, and can be easily used as the basis of many diverse products for different user
groups. New fault maps for the section of the fault between Fort Ross, in Sonoma
County, and Point Arena, in Mendocino County, are being prepared using ALSM
data collected in 2003. ALSM data provides detailed images of the ground surface
through the forest cover unlike any previous remote sensing technique. Along the
San Francisco Peninsula, where no ALSM data are currently available, we have
relied on historical data from the 1906 earthquake and historical, pre-development
aerial photography to produce a new, GIS-based map of active fault traces. Included
in the GIS database are the 1906 photographs of the ground rupture, modern and
historical aerial photographs, pertinent passages from the Lawson Report, and previous mapping of fault traces along this section of the fault.
The 1906 Earthquake and Northern San Andreas Fault: Significant Source of
Near-future Hazard?
I. Wong, URS Corporation, [email protected]; J. Zachariasen,
URS Corporation, [email protected]
Three large earthquakes (M ≥ 6.7) have ruptured portions or all of the northern
San Andreas fault in 1838 and 1898 (M 6.8), and 1906 (M 7.9). Despite this relatively robust historical record, characterization of the behavior of the northern San
Andreas fault remains highly uncertain in large part because paleoseismic data are
still relatively sparse and very uncertain. Based on a paleoseismically-determined
mean recurrence interval of about 260 years, the Working Group on California
Earthquake Probabilities (WGCEP, 2003) estimates that a repeat of the 1906
earthquake, which ruptured the entire northern San Andreas fault, has a probability of less than 5% of occurring in the 30-year period from 2002 to 2031. In contrast, the probability of one or more M ≥ 6.7 earthquakes occurring on the northern
San Andreas fault from 2002 to 2031 is 21% (WGCEP, 2003). This somewhat
surprisingly high value is due to the large uncertainties in defining rupture scenarios
for the fault, which include smaller events occurring as single segment, multi-segment, and floating earthquakes. The current building code in California is based
on the USGS National Hazard Map estimates of probabilistic hazard, which are
largely controlled by the 1906 earthquake. These hazard estimates, however, assume
a Poissonian behavior and do not account for the elapsed time since the last events
on the faults. We calculate the time-dependent probabilistic hazard for the San
Francisco Bay region and elsewhere along the northern San Andreas fault using
the recently developed PEER Next Generation of Attenuation (NGA) relationships and compare these estimates with current USGS estimates from the National
Hazard Maps. The use of the NGA relationships themselves results in decreases in
short-period ground motions of at least 20%. We also assess the sensitivities of the
hazard to uncertainties in the WGCEP (2003) characterization of the northern
San Andreas fault including the ranges of rupture scenarios and recurrence intervals. Given the relatively short elapsed time since the 1906 earthquake, which is
dominant in all the WGCEP (2003) rupture models, the time-dependent hazard
should be lower than the time-independent hazard. Hazard contributions from the
smaller scenarios (e.g., 1838), however, also need to be properly accounted for.
H.F. Reid, Elastic Rebound, and Seismic Gaps
D. Jackson, UCLA, [email protected]; Y. Kagan, UCLA, [email protected]
edu.
In revolutionary lectures and publications in 1910 and 1911, Reid articulated the
idea that earthquakes result from pre-established stresses, posited that the times of
large earthquakes could be predicted by the time when strain reaches a threshold,
and suggested a specific numerical threshold for the San Francisco Bay area. Using
geodetic measurements after 1911, we estimate the date for a repeat earthquake
implied by Reid’s ideas, compare that date with more recent forecasts, and examine
the consistency of Reid’s assumptions with modern understanding of earthquake
occurrence and tectonic geodesy.
Reid’s ideas have been extended and quantified in the seismic gap hypothesis,
which has been used to make many forecasts of earthquake occurrence. We examine
the track record of those forecasts specific and comprehensive enough to test, and
comment on the degree to which Reid gets credit or blame.
Paleoseismic Records of Earthquakes on the Northern San Andreas Fault:
How Characteristic Is the Great 1906 San Francisco Earthquake?
T. Niemi, University of Missouri-Kansas City, [email protected]; H. Zhang,
University of Missouri-Kansas City, [email protected]; N. Hall, Pollock Pine,
CA, [email protected]; T. Fumal, U.S. Geological Survey, [email protected]
The great 1906 San Francisco earthquake ruptured a 470-km section of the northern
San Andreas fault (NSAF) along four primary segments including the Santa Cruz
Mountain (SCM), the Peninsula (Los Gatos to the Golden Gate), the North Coast
(NC), and the Offshore segments. Historical and recent earthquakes indicate that
some segments of the NSAF are capable of rupturing in earthquakes smaller than
1906. Furthermore, coseismic slip in 1906 was larger north of the Golden Gate
than south of it. Of critical importance to all earthquake probability estimations is
whether the NSAF fundamentally repeats in 1906-type (4 segments) earthquakes
or whether other rupture models are likely. A growing amount of paleoseismic
data at multiple sites along the 1906 rupture allows a preliminary evaluation of the
NSAF rupture history. The Vedanta paleoseismic site on the NC segment yielded
evidence for twelve earthquakes over the past 3000 years with recurrence intervals
ranging from 53 to 605 years. The penultimate event (Ev2) at Vedanta occurred in
the late 17th to early 18th century, with earlier earthquakes occurring in the 14th
and 12th centuries. Other NC sites corroborate the Vedanta record. At Bodega
Harbor, coseismic subsidence from the Ev2 occurred in 1470-1850 A.D. and a
third-event-back during 900-1390 A.D. Re-analyses of the Dogtown site data suggest the Ev2 occurred 1695-1776 A.D. Sites in Fort Ross and Point Arena on the
northern NC segment indicate that the Ev2 also occurred at these sites in the late
17th to early 18th century, with earlier events occurring in the 13th-14th and 11th12th centuries. Together these data suggest that the NC segment may have ruptured over three cycles as a single segment, or with closely timed earthquakes. A 3mslip measurement for the Ev2 at the Vedanta site indicates that the earthquake was
smaller than 1906. Paleoseismic data from the SCM sites suggest multiple earthquakes with short recurrence, possible related to proximity to the central creeping segment. Paleoseismic data on the Peninsula indicate this segment ruptured in
the1838 earthquake. Additional data, especially on the Peninsula, are needed in
order to determine if 1906-type earthquakes have occurred during the past.
Deep-water Turbidites as Holocene Earthquake Proxies along the Northern
San Andreas Fault System
C. Goldfinger, Oregon State University, COAS, Ocean Admin. 104, Corvallis
OR 97331, [email protected]; A. Morey, Oregon State University,
COAS, Ocean Admin. 104, Corvallis OR 97331, [email protected];
H. Nelson, Instituto Andaluz de Ciencias de la Tierra,CSIC,Universidad de
Granada, Granada, Spain, [email protected]
New core data show that continental margin channels in Northern California
have recorded a Holocene history of regional submarine landslides slides possibly
Seismological Research Letters Volume 77, Number 2 March/April 2006 195
triggered by great earthquakes. The field program was completed in 2002 during
a month of at-sea coring with an international science party of 37 on the Scripps
vessel R/V Roger Revelle. Thus far in our analysis of the data, we have first tested
the turbidite record, applying multiple tests for synchronous triggering of turbidity
currents. We use 14C ages, relative dating tests at channel confluences, and stratigraphic correlation to determine whether turbidites deposited in separate channel
systems are synchronous, that is they were triggered by a common event. The events
recorded along the Northern California margin can be correlated with multiple
proxies from site to site between Noyo Channel and the latitude of San Francisco.
The evidence that the Holocene turbidite record is primarily an earthquake proxy,
is now quite strong. Preliminary comparisons of our event ages with existing and in
progress work at onshore coastal sites show correspondence to a remarkable degree,
further circumstantial evidence that the offshore record is primarily earthquake
generated.
Matching physical property records requires synchronous timing because of
the rapid settling time for turbidites, an in some cases the lack of direct connection
between the separate channel systems that are sampled. We have recently tested XRay fluorescence (XRF) analysis of selected cores to augment existing heavy mineral analysis to “fingerprint” the source provenance, and thus identify simultaneous
arrival at a confluence from multiple locations along the fault.
Hemipelagic sediment thickness between events is used as a semi-independent measure of time between events, and thickness patterns down core are also
used as a correlation criteria along with multiple other datasets. Hemipelagic thickness is also used to identify event-specific erosion among multiple cores at a single
site. If correct, our initial correlations along strike imply rupture lengths for many
events of at least 270 km.
We are using OXCAL to build an age model for each key site along the
margin, using both 14C results, the timing constraints provided by hemipelagic
sedimentation between events, and correlation constraints. OXCAL uses a rigorous Bayesian technique for refining event ages with multiple constraints which can
be stratigraphic, historical or other timing, rate limiting, or correlation criteria.
Testing this method for 1906 yields 1902 (1880-1910), and 1690 (1660-1720) for
the penultimate event. .
This work has great societal relevance for the San Francisco Bay Area, where
Holocene recurrence intervals for great San Andreas earthquakes are presently elusive. Results from the turbidite record combined with land paleoseismology can
address long term recurrence, possible patterns of recurrence, segmentation, and
segment interaction along the Northern San Andreas.
How Space-time Interactions Organize the Northern San Andreas Fault
System: Analysis Based on Recreating Great Earthquakes in the Computer
J. Rundle, University of California, [email protected]
The San Francisco earthquake and fire of April 18, 1906 killed more than 3,000
persons, and destroyed much of the city leaving 225,000 out of 400,000 inhabitants
homeless. The 1906 earthquake occurred on a km segment of the San Andreas fault
that runs from the San Juan Bautista north to Cape Mendocino and is estimated
to have had a moment magnitude m ~ 7.9. Observations of surface displacements
across the fault were in the range 2-5 m. As we approach the hundredth anniversary of the great San Francisco earthquake, a timely question is the extent of the
hazard posed by another such event, and how this hazard may be estimated. We
are particularly interested in the influence of the fault-fault interactions between
the Northern San Andreas and the surrounding faults on the dynamics of large and
great earthquakes that occur on the plate boundary. We present an analysis of this
problem based upon a numerical simulation, Virtual California, that include many
of the physical processes known to be important in earthquake dynamics. These
include elastic interactions among the faults in the model, driving at the correct
plate tectonic rates, and frictional physics on the faults using the physics obtained
from laboratory models with parameters consistent with the occurrence of historic
earthquakes. Models such as Virtual California represent “numerical laboratories” in
which the event statistics and precursory patterns can be determined directly from
simulations, rather than by assumption. Of particular relevance is the opportunity
to assess the importance of elastic interactions and stress transfer in organizing the
dynamics of the fault system. Processes of stress roughening and stress smoothing
can clearly be seen in the simulations as result of activity on neighboring fault segments. Space-time patterns of activity can be defined based upon Karhunen-Loeve
expansions (Principal Component Analysis) that lead to deeper understanding
of fundamental patterns of correlated activity in the fault system. An example of
this type of result is our discovery that the two most significant modes of activity
represent coordinated events on 1) the Northern San Andreas-Haward-Calaveras
system; and on the Big-Bend region of the San Andreas together with the Garlock
fault. We also find that the creeping section tends to decouple activity in northern
and southern California.
Nuclear Explosion Monitoring Anniversary Session II
Presiding: Brian Stump and Bill Walter
Improving Magnitude Detection Thresholds Using Multi-event, Multistation, and Multi-phase Methods
D. Schaff, Columbia University, [email protected];
Waldhauser, Columbia University, [email protected]
F.
We present results for research that has been conducted on techniques for generating a multi-phase detection bulletin derived by two means—station array processing (multi-station) and source array processing (multi-event). Comparison and
quantification of improvement over standard P-wave, single-event, single-station
processing is evaluated. The methods can be applied to any seismic network but
are being tailored with a nuclear monitoring interest in mind. Semi-empirical tests
were conducted for the multi-event correlation method for signals with increasing amounts of background seismic noise showing detection magnitude thresholds
could be lowered by one full unit. A comparison of two dissimilar traces was shown
to produce a false detection if only correlation coefficients were used. If an STA/
LTA filter was applied to the correlation traces these false detections could be eliminated. Using all three components shows a SNR enhancement for the correlation
coefficient similar to that achieved by beam forming. A test of the multi-station
method by stacking STA/LTA traces was performed for a hypothetical case of two
concurrent events 175 m apart. Problems of correctly associating phases for the two
events were alleviated compared to standard processing. The method automatically
gives a location estimate along with the detection. All this is accomplished with out
making any phase picks. It is demonstrated that the technique is able to separate
events close in time and space.
SH-Wave Generation by an Explosion in a Complex, Scattering Medium
M. N. Toksoz, Earth Resources Laboratory, Department of Earth, Atmospheric
and Planetary Sciences, MIT, [email protected]; S. Chi, Earth Resources Laboratory,
Department of Earth, Atmospheric and Planetary Sciences, MIT, [email protected]
edu; R. Lu, Earth Resources Laboratory, Department of Earth, Atmospheric and
Planetary Sciences, MIT, [email protected]
Explosions often are conducted in complexes with chambers, tunnels, and shafts
used for access and instrumentation. These structures can act as strong scatterers
of seismic waves and complicate the radiation patterns from explosions. In this
study we evaluate the effects of these near-source scatterers on seismic waves radiated from explosions by 3-D finite difference modeling. We use a rotated-grid finite
difference code with capability to include: (1) free surface, (2) topography, and (3)
strong scatterers. A perfectly matched layer (PML) is incorporated into the code to
improve the absorption at the boundaries.
Forward modeling was done for a reference model with an explosive source
in a plane, layered half-space. Then, calculations were carried for an explosion near a
finite length horizontal tunnel and for models of surface topographic features. The
tunnel produces P to P and P to S scattering and a complicated radiation pattern. P
to S scattering is amazingly strong and the tunnel acts as a virtual shear wave source.
Because of shallow depth, surface waves dominate the seismograms and significant
SH waves are generated by the presence of the tunnel. The effects of wave scattering
due to various topographical features are investigated. Realistic and smooth topographic features do not contribute much to scattering. However, features with sharp
gradients or corners, such as a mesa or a canyon, act as strong scatterers of seismic
waves, especially of surface waves.
To determine the properties of a complex source, such as an explosion and
a tunnel, we applied a wavelet domain moment tensor inversion. The moment
tensor shows significant shear components due to the presence of a scatterer. We
also tested the applicability of the Time Reversed Acoustics (TRA) approach for
detecting the presence of a tunnel near the source. In this approach, the recorded
seismograms are time-reversed and sent back into the earth at each station. The
back-propagating wavefields focus at the source. The P wave focuses strongly at the
explosion while the S wave at the tunnel. TRA has great potential for determining
the seismic source properties.
Source Scaling Analyses of Frequency Dependent Energy Partition for
Regional P and S Phases from Explosion Sources
J. Murphy, SAIC, [email protected]; B. Barker, SAIC, [email protected]
saic.com.
Research conducted over the past 20 years has demonstrated that the most reliable
of the regional discriminants considered to date are those based on high frequency
spectral ratios of the amplitudes of the shear phases Sn and Lg to those of the corresponding P phases Pn and Pg. While much observational evidence supporting
196 Seismological Research Letters Volume 77, Number 2 March/April 2006
the general applicability of these regional discriminants has now been accumulated,
a problem remains in that there is currently no physical model of shear wave generation by explosions that can be shown to be quantitatively consistent with the
wide range of Sn and Lg observations from underground explosion sources. In an
attempt to provide better constraints on the various proposed shear wave generation mechanisms, we are conducting frequency dependent source scaling analyses
of the regional phases Pn, Pg, Sn and Lg using data recorded from underground
explosions at a variety of nuclear test sites. Our initial analysis has focused on
regional phase data recorded from underground nuclear explosions at the Degelen
Mountain and Balapan testing areas of the Semipalatinsk test site. Digital data
recorded at the Borovoye Geophysical Observatory in North Kazakhstan from
selected Semipalatinsk explosions have now been processed and analyzed to define
frequency dependent source scaling relations for these observed regional P and
S wave data. The source scaling results indicate that both the Sn/Pn and Lg/Pn
spectral ratios show some modest yield dependence in the 1-3 Hz band, but no
statistically significant yield dependence at the higher frequencies typically used for
discrimination purposes. These yield scaling observations have been shown to be
remarkably consistent with a simple explosion S wave source which is directly proportional to that for P, except that the corner frequency is reduced by the S/P velocity ratio of the source medium. That is, using the Mueller/Murphy explosion source
model to predict S/P spectral ratios as a function of yield over the yield range of the
observed Semipalatinsk data samples leads to predicted frequency dependent yield
scaling exponents which agree very closely with the corresponding experimentally
derived exponent values.
Observations of Pn-Lg Coda Scaling and Implications for Seismic
Discrimination and the Explosion Source
H. Patton, Los Alamos National Lab, [email protected]; S. Taylor, Los
Alamos National Lab, [email protected]
Multi-frequency observations of the scaling of Lg coda waves with respect to Pn
have been made for nuclear explosions at the Nevada Test Site (NTS) and the former Soviet test site at Semipalatinsk (STS). These observations are for the scaling
slope when plotting narrowband log Lg coda amplitudes (abscissa) against log Pn
amplitudes (ordinate) for a broad range of explosive yields at a specific recording
station: Kanab or Elko for NTS, and Borovoye for STS. Both Lg coda and Pn
amplitudes have been filtered with an identical bank of narrowband filters. The
results for both test sites show that Pn scales 10-30% higher than Lg coda waves
do for frequencies between 2-8 Hz, indicating that Pn/Lg Coda amplitude ratios
are yield dependent. For NTS explosions, the scaling contrast is even greater (as
much as 50%) for frequencies less than 2 Hz, except in the lowest band, 0.3-0.5
Hz, where the slopes at both stations are not different from 1.0 at the 2-sigma level.
On the other hand, scaling slopes for STS explosions are not significantly different from 1.0 for any of the lower frequency bands. To the extent that the source
generation mechanisms for Lg and Lg coda waves are in common, these observations have implications for the behavior of widely-used regional discriminants and
their physical basis. Furthermore, the use of relative scaling slopes facilitates the
investigation of generation mechanisms because path effects, such as the nearfield
scattering transfer function, are transparent as long as they are held in common to
all the explosions at a given test site. Preliminary attempts to model amplitude and
frequency dependence of the observed scaling slopes will be presented.
A Lower Bound on the Standard Error of an Amplitude-based Regional
Discriminant
D. Anderson, [email protected]; W. Walter, [email protected]; D.
Carlson, [email protected]; T. Mercier, [email protected]
Wave path, magnitude and signal processing corrections made to observed regional
amplitudes ensure that what remains is fundamentally information about the seismic source. Such corrected amplitudes can then be used in ratios to discriminate
between earthquakes and explosions. However, there remain source effects such as
those due to depth, focal mechanism, local material property and apparent stress
variability that cannot easily be determined and applied to amplitude corrections.
These effects establish a lower bound on the amplitude variability for new events,
even after path and magnitude corrections are applied. We develop a general strategy to account for amplitude correction inadequacy by appropriately partitioning
error. The proposed mathematics are built from random effects analysis of variance
(ANOVA) and have application potential to a variety of amplitude correction
theories (for example see Taylor and Hartse (1998), Taylor et al. (2002), Walter
and Taylor (2002)). The error components from random effects ANOVA are the
basis for a general station-averaged regional discriminant formulation. The standard error of the discriminant has a lower bound of amplitude correction error. The
developed methods are demonstrated for a suite Nevada Test Site (NTS) events
observed at regional stations.
Fundamental Limitations in Resolving Power of Q Tomography
J. Xie, Air Force Research Laboratory, [email protected]
Imaging lateral variations of seismic Q is much more difficult than imaging those
of velocity. The foremost reason for the difficulty is that individual Q measurements are prone to large errors caused by the imprecisely compensated effects of the
Earth’s 3D velocity structure on seismic amplitudes. Less attention has been paid
to another fundamental limitation in Q tomography caused by the inherently large
variability of Q. In both velocity and Q tomography, the laterally varying quantities
that are solved for by linear equations are the inverse of velocity or Q (i.e., slowness or attenuation coefficient). The resolution of tomography, which is controlled
by the data sampling density, is naturally measured by how well the variations of
slowness or attenuation coefficient can be recovered. The velocity in the Earth
typically only deviates by a small fraction from a mean or reference value. In this
case, variation of slowness is to a good approximation linearly converted to that of
velocity, and vice versa. The resolution of a velocity model is about the same as that
of a slowness model and a dense data sampling can ensure both models to be well
resolved. The Q values in the Earth, on the other hand, vary drastically, by up to an
order of magnitude. The conversion between such large variations of Q and attenuation coefficient are highly non-linear, resulting in different resolution in models
of attenuation coefficient (or inverse of Q) and Q. High Q values tend to be recovered much more poorly than low Q values, although the high and low attenuation
coefficients can be recovered equally well. This limitation means the usual “checker
board” resolution test used in velocity tomography yields a less satisfying result in
Q tomography. Taking into account that the errors in Q models also tend to grow
with Q values, we conclude it is much more difficult to recover the true Q values
in high Q regions in tomography. Increased data sampling density lead to limited
improvement to this situation.
Earthquake Science in the 21st Century: Understanding
the Processes that Control Earthquakes II
Presiding: Bill Ellsworth and Greg van der Vink
Overview of SAFOD Phases 1 and 2: Drilling, Sampling and Measurements
in the San Andreas Fault Zone at Seismogenic Depths
S. Hickman, U.S. Geological Survey, [email protected]; M. Zoback,
Stanford University, [email protected]; W. Ellsworth, U.S. Geological
Survey, [email protected]; N. Boness, Stanford University, [email protected]; J. Solum, U.S. Geological Survey, [email protected]; P. Malin, Duke
University, [email protected];
The San Andreas Fault Observatory at Depth main borehole was drilled vertically
to a depth of 1.5 km and then deviated at about 55 deg to vertical, passing beneath
the surface trace of the San Andreas Fault at a depth of 3.2 km. Repeating microearthquakes on the San Andreas define the main active fault trace at depth, as well
as a secondary active fault about 250 m to the SW. SAFOD is located at the transition between the creeping and locked sections of the fault, 9 km NW of Parkfield,
California. In this talk and the talk by Zoback et al. (this session) we will provide an
overview of results from drilling, sampling and downhole measurements associated
with the first two Phases of SAFOD.
The SAFOD main borehole was rotary drilled, comprehensive cuttings were
obtained and a real-time analysis of gases in the drilling mud was carried out. Spot cores
were obtained at three depths (at casing set points) in the shallow granite and deeper
sedimentary rocks penetrated by the hole, augmented by over fifty side-wall cores.
Continuous coring of the San Andreas Fault Zone will be carried out in Phase 3 of the
project in the summer of 2007. Real-time geophysical measurements were made while
drilling through most of the San Andreas Fault Zone and a suite of open-hole geophysical measurements were also made over essentially the entire depth of the hole.
Geophysical logs define the San Andreas Fault Zone to be relatively broad
(~250 m) containing several discrete zones with anomalous geophysical or mineralogical properties that may represent active shear zones. The most dramatic of these
is a zone at 3.30-3.33 km measured depth exhibiting low P- and S-wave velocities
that is now undergoing casing deformation. This zone is also associated with the
sudden appearance of serpentine, a mineral thought to be important in controlling frictional strength and the stability of sliding. Continuing measurements of
casing deformation, as well as monitoring of microearthquakes using seismometers directly within the fault zone, will pinpoint the exact location of the actively
deforming fault trace(s) prior to continuous coring in Phase 3.
Construction of the multi-component SAFOD observatory is well underway, with seismometer, accelerometer and tiltmeter sondes operating at 1.1 km
depth in the pilot hole and at 2.9 km in the main hole, as well as a fiber-optic laser
strainmeter cemented behind casing in the main hole. We are now preparing to
Seismological Research Letters Volume 77, Number 2 March/April 2006 197
install a variety of seismic and tilt sensors in the SAFOD borehole where it crosses
the actively deforming zone, which will allow unprecedented near-field observations of earthquake source processes.
Observations of Fault Zone Deformation, In Situ Stress and Pore Pressure in
SAFOD Phases 1 and 2: Implications for Fault Zone Processes
M. Zoback, Stanford University, [email protected]; S. Hickman,
U.S. Geological Survey, [email protected]; W. Ellsworth, U.S. Geological
Survey, [email protected]; N. Boness, Stanford University, [email protected]
stanford.edu; A. Day-Lewis, Stanford University, [email protected]
Geophysical logs define the San Andreas fault zone at depth to be relatively broad
(~250 m) with apparently multiple active shear zones characterized by anomalous
geophysical properties. Repeated measurements of the shape of the cased hole since
drilling ended indicates creep-related casing deformation associated with a ~15 m
wide zone exhibiting very low P- and S-wave velocities. There appears to be casing
deformation at other locations in the fault zone as well, but this will become more
clear as monitoring continues in the future. Our best estimate of the depth at which
we passed through the strand of the fault producing repeating microearthquakes is
also associated with a relatively narrow zone of anomalously low P- and S- velocities, but interestingly, no localized casing deformation. Stress (and temperature)
measurements in the SAFOD main hole (and co-located pilot hole) indicate that
the San Andreas Fault is a relatively weak fault in an otherwise strong crust, confirming three decades of inferences about fault strength from heat flow and stress
orientation measurements at shallower depth and greater distance from the fault.
As viewed with depth in the SAFOD pilot hole and vertical section of the main
hole (1.8 km southwest of the mapped surface trace) and relative position (crossing
the active fault zone at depth), the average direction of maximum horizontal stress
is at a high angle to the San Andreas. The notable exception to this is directly within
the active shear zone where the stress rotates to a more oblique orientation, as predicted by theoretical models of a weak fault in a strong crust. Measurements of the
stress magnitude indicate an increase in the magnitude in the vicinity of the active
fault trace, also as theoretically predicted. There is no thermal evidence of frictionally-generated heat on the San Andreas fault. Statistical characterization of stressinduced wellbore failures in the pilot hole exhibit fractal scaling over wavelengths
spanning five orders of magnitude. The sizes of observed stress rotations scale in
approximately the same manner as the local fault-size/frequency distribution for
nearby earthquakes, implying that local stress fluctuations are closely related to the
distribution of active slip patches on the San Andreas rather than to crustal heterogeneity. There are no indications of anomalous pore pressure in the core of the fault
zone. Rather, the fault zone appears to separate distinct hydrologic regimes, with
elevated pore pressure and anomalous geochemical signatures on the north east side
of the fault. During Phase 3 of the project, to be carried out in 2007, direct measurement of pore pressure in the core of the fault zone will be attempted.
Energy Partition of the 1999 Chi-Chi, Taiwan, (Mw7.6) Earthquake
K. Ma, Institute of Geophysics, NCU, [email protected]
Earthquake energy budget is composed of radiated energy, fracture energy, and frictional energy. The radiated energy could be determined from the analysis of seismic
data. Fracture energy had been estimated from seismologic, experimental rock deformation data, and the quantify structural observations of the fault core related to the
earthquake rupture. The heat generated during an earthquake due to the frictional
sliding of the fault is thought to be a major portion of the total energy release. The
well resolved spatial-temporal slip distribution of the 1999 Chi-Chi earthquake,
along with the recent complete drilling of Taiwan Chelungpu-fault Drilling Project
provide the unique opportunity to understand the energy partition of a large earthquake. The seismic fracture energy estimated from seismic data was compared to the
surface fracture energy estimated from the grain sizes in the gouge zone of the fault
sample, which was identified as the slip zone related to the Chi-Chi earthquake. This
comparison, thus, provide the quantify contribution of the seismic fracture energy to
the formation of the fault gouge. The frictional heat was estimated directly from the
measurements in a borehole penetrating the identified slip zone of 8 m slip during the
1999 Chi-Chi earthquake. A local increase in the temperature profile across the fault
is interpreted to be the residual heat generated during the earthquake. These results
would give the first quantify values of the energy partition of a large earthquake.
Earthquakes Triggered by Silent Slip Events: Improved Understanding of
Earthquake Process by Joint Analysis of Seismic and Geodetic Data
P. Segall, Stanford University, [email protected]
Advances in understanding the physics of earthquakes will increasingly require analysis of multiple data types. For example, joint analysis of teleseismic body wave and
triangulation data from the 1906 earthquake reconciles both data types, if the rupture velocity is supershear (Song, et al., this meeting). Similarly, geodetic data alone
provide insufficient constraints on interseismic deformation, leading to a spectrum
of models ranging from simple dislocations, which fit data with few parameters but
do not incorporate known physics, to fully numerical models that involve more
parameters than can be reasonably estimated from data. One approach is to include
paleoseismic slip-rates as prior information, restricting the acceptable model space
and allowing inversion with more realistic models (Segall, Int. Geol. Rev., 2002).
Combined analysis of seismic and geodetic data is also yielding insights into
slow slip events. The detection of aseismic, transient slip in subduction zones is arguably the most exciting new discovery in earthquake science in a decade. Depths of
these events have been difficult to determine from deformation measurements, and
while it is assumed they are located on the megathrust this has not been possible to
prove. Slow slip may be associated with non-volcanic tremor, however tremor is difficult to locate and may be distributed over a broad depth range. We have found that
swarms of high frequency earthquakes accompany otherwise silent slip events on
Kilauea volcano, Hawaii (Segall, Desmarais, Shelly, Miklius, Cervelli, Fall AGU).
Time dependent inversion of the GPS data shows that slow slip begins before the
seismicity. The temporal evolution of seismicity is well explained by increased stressing caused by accelerated slip, demonstrating that the events are triggered. The earthquakes, well located at depths of 7-8 km, constrain the slow slip to be at comparable
depths, since they must fall in zones of positive Coulomb stress change. Triggered
earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low. Detection of such events would help constrain the
depth of slow slip, and could lead to a method for quantifying hazard during slow
slip, since triggered events have the potential to grow into destructive earthquakes.
A Decade of Episodic Tremor and Slip observations in the Northern
Cascadia Subduction Zone
G. Rogers, Geological Survey of Canada, [email protected]; H. Kao,
Geological Survey of Canada, [email protected]; H. Dragert, Geological
Survey of Canada, [email protected]
For southern Vancouver Island, located in the northern Cascadia subduction zone,
we have accumulated ten years of ETS data observed simultaneously with continuous GPS and digital seismic records. The motions of GPS stations are characterized by sloped saw-tooth functions consisting of accelerated north-eastward displacements for periods of 13 to 16 months, followed by transient south-westward
displacements over periods of one to two weeks, superimposed on steady, linear
north-eastward trends. These motions have been modelled by a combination of
long-term locking on the shallow subduction interface and temporary locking
and repeated slip of a few centimetres on the deeper plate interface between the
subducting oceanic plates and overlying continental plate. The episodes of slip are
invariably accompanied by distinct low-frequency tremors, hence the naming of
the phenomena as “Episodic Tremor and Slip” (ETS). Short tremor sequences from
a few minutes to a few days occur in most months and comprise one-third of all
the observed tremor activity. The other two-thirds of the tremor activity occurs
in extended episodes (5 to 30 days) that are correlated with the transient crustal
motions resolved by continuous GPS. For southern Vancouver Island, the return
periods for extended ETS sequences are sufficiently regular that we have been able
to successfully forecast them and deploy temporary additional seismic and GPS
instruments for more detailed observations. Recent analysis of the detailed seismic
data using the newly developed Source-Scanning Algorithm reveals that tremors
migrate along strike, often haltingly, and occur over a wide depth range of 40 km
in a region overlying the modelled transient slip interface. This vertical distribution of tremors suggests tremor and slip are separate, strongly linked phenomena.
Although the processes involved in ETS are not yet fully understood, it seems likely
that fluids emanating from the young subducting plates play a role.
Tuesday, 18 April—Poster Sessions
Modeling the Tectonic Evolution of the San Andreas
Transform Boundary through Time
Poster Session
Implications of Slab-window Volcanism in Coastal California for Evolution
of the San Andreas Transform
P. McCrory, US Geological Survey, [email protected]; D. Wilson,
University of California, Santa Barbara, [email protected]; R. Stanley, US
Geological Survey, [email protected]
The geologic record of coastal California includes evidence of numerous volcanoes
that erupted when ridge segments of the East Pacific Rise encountered the North
198 Seismological Research Letters Volume 77, Number 2 March/April 2006
American subduction zone. By correlating these volcanoes with slab windows predicted from analysis of magnetic anomalies on the Pacific plate, we add new temporal and spatial constraints to tectonic reconstructions of North America since 30
Ma. We define our model for North American deformation more rigorously than
previous studies by specifying finite rotations of numerous fault blocks within the
San Andreas transform boundary in the same fashion as the major plates. The position of each continental fragment relative to the Pacific plate is an exact prediction
of the kinematic model; thus, relative positions of volcanoes and slab windows can
be used as direct tests of relative motion parameters. In current coordinates, older
volcanic units are generally northwest of younger units, but reconstruction of their
eruption positions indicates a west-to-east progression of activity compatible with
slab-window growth. The offsets we restore on major strike-slip faults in California
are widely accepted, and generally follow those of Dickinson [1996]. Many faults,
however, have poorly known offsets, and even the best constrained vertical axis rotations are uncertain by about 10°, so constructing a complete model requires some
subjective judgment. Information on timing of fault slip is often poor, and for simplicity we specify constant relative motion when possible, changing at plate-motion
reorganizations at 19.0 and 12.5 Ma triggered, by Pacific plate capture of Monterey
and Magdalena oceanic fragments. Our correlations, such as erupting the Morro
Rock-Islay Hill complex south of the Pioneer fracture zone and the Iversen Basalt
south of the Mendocino fracture zone, require larger displacements than advocated
by most previous authors. Specifically, we infer at least 315 km of motion between
Sierra Nevada and rigid North America at an azimuth of about N60°W, and at least
515 km between Baja California and rigid North America in a similar direction.
A consequence of inferring a large displacement of Baja California is that the San
Andreas transform must have developed most of its current form prior to 10 Ma.
Making the San Andreas Plate Boundary in the Wake of the Mendocino
Triple Junction
K. Furlong, Penn State University, [email protected]
Our understanding of the formation of the San Andreas plate boundary system
over the past 30 Ma provides an opportunity to link lithospheric-scale processes
to development of an important fault system that hosts damaging earthquakes. It
has long been recognized that the San Andreas system forms (and lengthens) in
response to the migration of the Mendocino triple junction (MTJ), yet our understanding of the mechanisms by which this occurs is still unfolding. Plate kinematics
provide the framework in which to analyze the large-scale structural development
of the plate boundary; and when that kinematics based model is coupled with thermal, deformational, and geomorphic modeling, we are able to better define our
understanding of how a subduction regime is transformed into a well-expressed
strike-slip fault system. In particular, the 3-dimensional ‘slab window’ that develops
in the wake of the MTJ provides not only a significant thermal effect to subsequent
plate boundary evolution, but also plays a direct role in the ongoing deformation
of the North American lithosphere. In association with MTJ migration, the plate
boundary forms in a regime of rapid but ephemeral crustal thickening, driven by
a viscous coupling within the slab window. The subsequent crustal thinning that
occurs 100-150 km south of the MTJ is associated with the coalescing of fault segments into well defined faults (e.g. the expression of the Maacama Fault in the vicinity of Willits, CA). The combination of significant systematic variations in crustal
thickness with the thermal effects of emplaced upper mantle lead to profound modifications to the middle and lower crust of the plate boundary region. The result is
an evolving plate boundary fault system that over a period of 5-10 Ma after MTJ
passage localizes into a well defined primary fault that acts as the principal structure
of the plate boundary. The fault-system complexity seen in the San Francisco Bay
region reflects the final stages of this fault system evolution after MTJ passage.
A Proposed Model for Lithospheric Evolution During Development of the
Pacific-North American Plate Boundary
G. Biasi, University of Nevada Reno Seismological Lab MS-174, Reno, NV
89557, [email protected]
A tectonically and mechanically consistent history of the Pacific-North American
plate boundary must include the evolution of the whole lithosphere, including its
upper mantle component. Geologic heterogeneities in the crust are well known.
Tomographic imaging indicates that the upper mantle is also heterogeneous and
has been throughout boundary development. This heterogeneity has exerted
mechanically important controls on large-scale structures in California. The tomographic images used in this research are more complete than previously published
versions because they include better station coverage above and east of the Sierra
Nevada, and because first-order crustal thickness corrections have been applied specifically to improve imaging in the mantle. The origin of key mantle structures and
the mechanical relationship between surface and subsurface are most readily seen
beneath the Sierra Nevada block. We note first that Sierra Nevada terrain is not
distinguished at the surface from faulted and even shattered batholithic rocks in
southern California. It does differ in the upper mantle, because the Sierra Nevada
is underlain by a high-velocity root along almost its entire strike. Where that root
is missing, roughly south of the White Wolf fault, the surface rocks are deforming.
The root is interpreted as cold upper plate mantle lithosphere, which developed
during Laramide and earlier low-angle subduction, and was modified somewhat
during high-angle post-Laramide subduction. The relationship is self-evident near
39.5N latitude, where the subducting Gorda Slab and the Sierran mantle root can
be imaged directly. We interpret the southern Sierran “drip” as Sierran-style mantle
lithosphere that started beneath a southward extension of the range, perhaps from
beneath the Salinian Block, and is now being forced downward and maybe westward by compression from the south. The Transverse Ranges anomaly similarly is
interpreted as thermal mantle lithosphere scavenged from beneath the Peninsula
Ranges and sinking because of convergence. All the high velocity bodies imaged
in the upper mantle beneath ~100 km, including a small one along Garlock fault,
appear to have a single consistent interpretation as thermal lithosphere being forced
downward by convergence. Crust without this root has been vulnerable and the
locus of faulting and tectonic disruption.
Geologic Constraints on the Evolution of the San Andreas Fault SystemImplications for Transform Boundary Models
R. Powell, U.S. Geological Survey, [email protected]
Balanced palinspastic reconstruction of bedrock terranes in southern California
provides constraints on location, magnitude, and timing of displacements on successively older groups of faults in the overall San Andreas fault system over the last ~20
Ma. Domains of Proterozoic through Cenozoic crystalline rocks and superjacent
Late Cretaceous through earliest Neogene strata, when fully reconstructed along
all faults of the San Andreas system, show seamless paleogeologic patterns. The
coherence of these patterns across the reconstructed terranes appears to validate the
approach. If so, the necessary and sufficient sequence of major strike-slip faulting in
the evolution of the San Andreas system is as follows: (1) Right-lateral displacement
of about 100 km accumulated between 20-17 Ma and 13-12 Ma along the path
defined by the reconstructed Clemens Well-Fenner-San Francisquito-San Andreas
fault. (2) Right-lateral displacements of 42-45 km on the San Gabriel and 150 km
on the Rinconada-Reliz and San Gregorio-Hosgri faults accumulated between 1312 Ma and 6-4 Ma. (3) Since 6-4 Ma, right-lateral displacement accumulated along
the San Andreas fault, sensu stricto, in southern California, ranging from 180 km
along the Salton trough segment to 150-160 km along the Mojave Desert segment.
This variability in displacement along the fault was accompanied by and related
to accumulation of lateral displacements on faults disrupting the blocks bounding
the San Andreas. To the west, right-lateral displacements accumulated on faults in
the Peninsular Ranges, including 24-28 km on the San Jacinto and 5-10 km on the
Elsinore fault. To the east, left-lateral displacement totaled 55 km on the east-west
faults in the eastern Transverse Ranges and varied along the length of Garlock fault
from as little as 12 km along its western reach to as much as 60 km along its central reach. Coeval right-lateral displacements accumulated on the north-northwest
trending faults of the Mojave Desert. This evolutionary sequence of faulting constrains models for on-land development of the plate margin transform (e.g., oldest
strand of the southernmost San Andreas system is the farthest east) and it defines
distinct provincial kinematic regimes that reflect differing responses of various
crustal blocks to the underlying dynamics of the transform boundary.
Scientific Visualization and Collaboration Tools Enhance Understanding of
Seismologcial Data
D. Kilb, Scripps Institution of Oceanography, [email protected]; A. Nayak,
Scripps Institution of Oceanography, [email protected]; B. Smith, Scripps
Institution of Oceanography, [email protected]
Researchers at the Scripps Institution of Oceanography Visualization Center (http://
www.siovizcenter.ucsd.edu) use a combination of high-resolution display systems and
visualization software to gain a better understanding of the relationships between
multidimensional and heterogeneous geophysical data. For example, combining
temporal snapshots (representing calendar years 1900 to 2004) of 3D theoretical
models of deformation of the San Andreas Fault System generated by major quakes
(M>6), draped over the topography of California and the offshore bathymetry can
help highlight ‘hot spots’ where stress perturbations are largest. We also combine this
imagery with basic data such as ~35,000 earthquake locations (lat, lon, depth), roads
(major highways), and faults to create interactive visualizations that allow us to better
assess correlations within and between the data. Augmenting this even further, we
use two rectangles to represent the two nodal plane orientations (strike & dip) of the
associated first motion focal mechanism data from the NCEDC. This makes it easy
to pinpoint regions of fault complexity (e.g., Coalinga) and regions of relative simplicity (e.g., Parkfield). Many of these animations are also being used as educational
tools at the Birch Aquarium at Scripps. These visualizations can be viewed in stereo
on the Highly Immersive Visual Environment (HIVE), on very high resolution tiled
Seismological Research Letters Volume 77, Number 2 March/April 2006 199
displays like the Apple 50 megapixel tile display ‘iCluster’ developed at Scripps, or on
a simple laptop system. As these visualizations grow in size and number, transferring
these files between collaborators becomes an issue. The OptIPuter (an NSF funded
cyberinfrastructure project) solves this problem, using various computing, storage,
memory, and graphics resources linked together by multiple 10 gige lightpaths over
dedicated fiber optic networks. Using these cutting edge technologies to help keep
pace with seamlessly integrating and exploring the rapid collection of seismological
data is crucial to the overall advancement of the science.
A Comparison between the Transpressional Plate Boundaries of the South
Island, New Zealand, and Southern California, USA
G. Fuis, U.S. Geological Survey, Menlo Park, CA, USA, [email protected]; M.
Kohler, University of California, Los Angeles, Los Angeles, CA, USA, [email protected]
ess.ucla.edu; M. Scherwath, Victoria University of Wellington, Wellington,
New Zealand (now at IFM-GEOMAR, Kiel, Germany), [email protected]
de; U. ten Brink, U.S. Geological Survey, Woods Hole, MA, USA, [email protected]
usgs.gov; H. Van Avendonk, University of Texas, Austin, TX, USA, [email protected]
utig.ig.utexas.edu.
Although there are clear similarities between the Alpine Fault (AF) system of
New Zealand’s South Island and the San Andreas Fault (SAF) system of southern
California, USA, there are also notable differences. Both systems are transpressional, with similar right slip and convergence rates, similar onset ages (for the current traces), and similar total offsets. Differences exist in the dips of the faults and
in plate-tectonic histories.
Crustal structure surrounding the AF and SAF was investigated with active
and passive sources along transects known as South Island Geophysical Transect
(SIGHT) and Los Angeles Region Seismic Experiment (LARSE), respectively. The
AF appears to dip moderately southeastward (~50 degrees) at the SIGHT transects
based on surface outcrops. LARSE results indicate a steeply northeastward-dipping
to vertical SAF. On the South Island, the AF appears associated with a relatively wide
(40-50 km) upper-crustal low-velocity zone (LVZ), but in southern California, the
SAF is not associated with a significant upper-crustal LVZ. On the South Island, a
mid-crustal decollement, connecting to the AF, is required to explain both uplift of
rocks from limited (mid-crustal) depths along the AF and an active fold and thrust
belt on the Pacific plate (PAC). In southern California, observed highly reflective
zones, interpreted as fluid-lubricated decollements, connect the SAF to a fold and
thrust belt on the PAC. On the South Island and in southern California, crustal
roots of comparable width and relief are associated with convergence of the plates
across both faults.
On the South Island and in southern California, narrow (50- to 100-km
wide) upper-mantle bodies of relatively high P velocity extend obliquely across the
AF and SAF and extend from near the Moho to more than 200-km depth. The
fact that these bodies extend downward from near the Moho is consistent with an
origin by depression of upper-mantle isotherms, caused by compression and (or)
density instability. In southern California, the body appears to be largely or wholly
confined to the PAC, suggesting that the PAC is weaker than the North American
plate. On the South Island, the correlation of the high-velocity body with the PAC
is more ambiguous.
Giant Low-angle Faults Beneath the Palos Verdes Anticlinorium, California
C. Sorlien, University of California Santa Barbara, [email protected];
K. Broderick, Exxon Mobil, [email protected]; L. Seeber,
Lamont-Doherty Earth Observatory of Columbia U., [email protected];
B. Luyendyk, University of California Santa Barbara, [email protected]
edu; M. Fisher, U. S. Geological Survey, [email protected]; R. Sliter, U. S.
Geological Survey, [email protected]; W. Normark, U. S. Geological Survey,
[email protected]
Late Miocene plate motion changes and formation of the Mojave restraining double
bend in the San Andreas fault resulted in the widespread post-Miocene reactivation
of pre-existing normal faults into thrust faults, and the inversion of basins into anticlinoria. One of these active fault-fold structures, the Palos Verdes anticlinorium as
we define it (PVA), is critical for earthquake hazard because of its location and size.
The PVA is a regional NW-trending 70km-long structure between the L.A. Basin
and the Santa Monica-San Pedro Basins offshore and implies an active thrust-fault
system of similar dimensions. The onshore restraining trend of the Palos Verdes
fault contributes locally some contraction that may account for enhanced uplift
of the Palos Verdes Hills, but cannot account for the PVA. We have identified
faults that may account for the PVA. The NE-dipping San Pedro Escarpment fault
(SPEF) aligns in 3D with the Compton thrust ramp and may be the same fault.
The combined Compton-SPEF has twice the area of the Compton ramp alone,
and could generate a M7.3 earthquake. The fault area and maximum magnitude are
even larger if the Compton-SPEF is continuous down-dip with the lower Elysian
Park fault. Santa Monica and Los Angeles Basins have subsided respectively 4 km
and 5 km in the last 5 m.y., and this subsidence has probably continued through
Quaternary time. Thrust faulting and folding are required in order to keep the Shelf
Projection, Palos Verdes Hills, and San Pedro Shelf from sinking concurrently with
the adjacent basins. In a simple fault-bend fold model that assumes similar longterm and Holocene subsidence rates, slip=0.8 mm/yr/sin(dip), or ~2 mm/yr for
a Compton ramp dipping 22 degrees. Strain is accumulating beneath and north
of downtown Los Angeles (Argus et al., 2005), which may stem from creep on the
downdip part of the fault system. Despite different names for its different parts, a
single major thrust fault may account for the west flank of the LA Basin and be a
potential source of rare but catastrophic ruptures.
Geophysical Piercing “Features” Defining Offset in the San Andreas Fault
System, Northern California
R. Jachens, U.S. Geological Survey, [email protected]; C. Wentworth,
U.S. Geological Survey, [email protected]; R. McLaughlin, U.S. Geological
Survey, [email protected]; R. Graymer, U.S. Geological Survey, [email protected]
gov.
Geophysical anomalies produced by rock bodies truncated at strike-slip faults are
important in defining offsets across faults. Within the San Andreas Fault (SAF)
system, anomaly-producing bodies are mainly magnetic ophiolites and plutons,
dense Franciscan terranes, and light Tertiary basin deposits. Most of these units
are older than the onset of SAF movement and thus yield estimates of total offset.
Geophysical piercing ‘features’ are most effective when refining approximate offsets
based on geologic units because these ‘features’ (usually body boundaries) often can
be defined with high resolution (typically within 2-3 km) even where concealed.
Four critical piercing ‘features’ define the regional offset framework of the SAF
system in northern California: 1) magnetic ophiolitic gabbro at Eagle Rest Peak
(Tehachapi Mtns) correlated with gabbro at Logan Quarry (San Juan Buatista);
2) gravity anomalies (flanked by magnetic anomalies) of Franciscan Permanente
terrane (Parkfield)-Permanente terrane (Santa Cruz Mtns; 3) buried magnetic
ophiolitic Logan gabbro (western Santa Cruz Mtns)-Black Point ophiolite (Sea
Ranch); and 4) gravity anomaly at NW edge of Hames Valley syncline offset by
Reliz-Rinconada Fault (NW of Paso Robles). Other geologic and/or geophysical
correlations support each geophysical estimate. These four correlations constrain
the interrelated offsets to yield the following estimates of total offset: 1) 301 km
across central California SAF; 2a) 174 km across southern Calaveras F. feeding into
East Bay Fault system; 2b) 127 km across Santa Cruz Mtns SAF; 3) 175 km across
San Gregorio F. north of Monterey Bay; 4a) 25 km across Reliz-Rinconada F.; 4b)
150 km across San Gregorio-Hosgri F south of Monterey Bay; and 5) 302 across
SAF north from Pt. Reyes. Most east Bay offset (174 km) probably was accommodated by the Hayward F. system, but its partitioning north of San Pablo Bay is
unresolved. These estimates assume rigid block horizontal motions, an assumption
that appears approximately valid in the along-fault direction, but not in the crossfault direction. An unresolved problem with this reconstruction is the resulting
mismatch between isolated Salinian granitic rock at Montara Mtn (San Francisco
Peninsula) against Great Valley sequence (east) and inferred offshore ophiolite
(west).
Insights into the Evolution of Faulting along the Rodgers Creek-HealdsburgMaacama Fault Zones, Northern California, as Revealed by Gravity and
Magnetic Data
V. Langenheim, U S Geological Survey, [email protected]; R.
McLaughlin, U S Geological Survey, [email protected]; R. Jachens, U S
Geological Survey, [email protected]
The Rodgers Creek-Healdsburg Fault (RCHF) appears to connect via a right step
to the Maacama Fault east of the city of Santa Rosa, California. The ~5-km-wide
right step produces a pull-apart basin that is well expressed topographically but
poorly expressed in the gravity field, consistent with geologic evidence that the
basin formed only during the past 1 Ma. This scenario accounts for ~6km of the
28 km of total dextral slip on the RCHF since 6 Ma. We propose, based on analysis
of gravity and magnetic data, that prior to 1 Ma the RCHF transferred a portion of
the slip to the Maacama Fault via a connection north of the city of Santa Rosa. The
RCHF coincides with the boundary between a prominent, >10-km long gravity
and magnetic high on the east and gravity lows reflecting the Windsor and Cotati
basins beneath the Santa Rosa Plain on the west. North of the Larkfield-Wikiup
area, the RCHF no longer forms the northeastern margin of the Windsor basin
gravity low, but instead cuts across the gravity low without significant displacement of the gravity gradients marking the basin margin. The position of the fault
within the gravity low may signify a northeast dip and reverse slip on the RCHF.
Alternatively, we suggest that the position of the fault may reflect a young adjustment of the fault within an older right step in the fault. Gravity data filtered to
enhance subtle features show an 8-km long, 2-km wide gravity low that we speculate represents an older pull-apart subbasin superimposed on the northeastern mar-
200 Seismological Research Letters Volume 77, Number 2 March/April 2006
gin of the larger Windsor Basin gravity low. Closing this subbasin by restoring 8 km
of right slip brings displaced magnetic highs into alignment. The Quaternary fault
trace ( Jennings, 1994) cutting across the subbasin and seismicity indicating a steep
northeast dip and right-lateral slip on the fault are both consistent with the fault
having successfully propagated across the right step (as predicted by sandbox models of extensional stepovers). This analysis suggests that the transfer of slip from the
RCHF to the Maacama Fault has migrated in time and space.
Geologic Constraints on Long-term Displacements along the Rodgers Creek,
Healdsburg and Maacama Fault Zones, Northern California
R. McLaughlin, U.S. Geological Survey, [email protected]; V. Langenheim,
U.S. Geological Survey, [email protected]; R. Jachens, U.S. Geological Survey,
jachens @usgs.gov; A. Sarna-Wojcicki, U.S. Geological Survey, [email protected]
usgs.gov; R. Fleck, U.S. Geological Survey, [email protected]; D. Wagner,
California Geological Survey, [email protected]; K. Clahan, California
Geological Survey, [email protected]
The Rodgers Creek Fault Zone (RCFZ) extends north from San Pablo Bay to
Santa Rosa, where it transfers slip northeastward to the southern Maacama Fault
(MFZ) across the geomorphically youthful ~4 km x10 km Santa Rosa pull-apart
basin (SRPB). Basin opening since ~1.2—0.8 Ma produced ~6-8 km of slip on the
RCFZ and ~5 km on the MFZ, yielding slip rates of ~5—7 mm/yr for both faults.
Southeast of Santa Rosa, a distinctive ~6—8.0 Ma sequence of rhyodacite overlain
by fault scarp breccia and interbedded gravel, are offset ~28 km along the RCFZ.
These rocks are offset from the vicinity of Santa Rosa, along the east margin of the
Cotati basin and Santa Rosa Plain, to the Sears Point area. About 21 km of this
slip on the RCFZ occurred between ~1.2 and ~7 Ma, suggesting an average slip
rate of 3-4 mm/yr during this time. The Healdsburg Fault Zone (HFZ) north of
Santa Rosa, overlaps along-strike with the MFZ, forming a complex right-step with
a geometry different from the SRPB. Along the eastern side of the Santa Rosa Plain,
the HFZ displaces gravels of the ~2.8 Ma -1.2 Ma Glen Ellen Formation. These gravels, derived largely from volcanic sources in the Napa-Calistoga and Franz Valleys,
show no sedimentologic evidence for displacement along the MFZ or HFZ during
the time of their deposition. Only 4—8 km of the 28 km of total offset attributed to
the RCFZ south of Santa Rosa, appears to be taken up by the HFZ since ~1.2 Ma.
North of Santa Rosa, any older slip appears to be partitioned to faults other than
the HFZ. Partitioning of a part of this slip to buried ancestral faults of the HFZ, as
suggested by gravity and aeromagnetic data, would have pre-dated 2.8 Ma.
Beyond the San Andreas, the Other Active Faults of
Northern California
Poster Session
Kinematics and Future Seismic Sources of the Hayward Fault, California,
from ERS and RADARSAT PS-InSAR
G. Funning, University of California, Berkeley, [email protected];
R. Burgmann, University of California, Berkeley, [email protected]; A. Ferretti, Tele-Rilevamento Europa, [email protected]
com; F. Novali, Tele-Rilevamento Europa, [email protected]; D.
Schmidt, University of Oregon, [email protected]
Permanent Scatterer InSAR (PS-InSAR) is an advanced form of InSAR that allows
the use of isolated point radar scatterers on the ground that are coherent in every
interferogram to form deformation time series. As such, they offer a dense coverage of deformation observations on the ground, with the advantage of improved
coverage in areas where conventional InSAR often fails. One such location is the
East Bay Hills, on the east side of the Hayward Fault in the San Francisco Bay Area,
a heavily vegetated area where conventional InSAR methods such as interferogram
stacking provide very little constraint on the contemporary aseismic deformation
occurring on the fault.
Using the full archive (1992-2004) of ERS descending and RADARSAT
ascending data acquired over the Bay Area, we create the most complete spatiotemporal picture of deformation in the region yet assembled. We use this data, in
combination with GPS velocities and observations of surface fault creep rates, to
obtain, through a kinematic inversion, the distribution of slip rate over the fault
surface—and thus to identify where the fault is creeping, and where it is not. Two
connected areas are identified where the fault slip rates are negligible; these we infer
to contain locked asperities, likely loci of major fault slip in expected future earthquakes on the Hayward Fault. Using boundary element stress modelling, driven by
deep fault dislocations with velocities constrained by the GPS and InSAR data, we
then attempt to estimate the size and distribution of the fully-locked asperities, and
their potential moment release as future seismic sources.
Late Holocene Slip Rate Investigation of the Maacama Fault at the Haehl
Creek Site, Willits, California
M. Larsen, Department of Geology, Humboldt State University, Arcata, CA
95521, [email protected]; C. Prentice, U.S. Geological Survey, Middlefield
Road, MS 977, Menlo Park, CA 94025, [email protected]; H. Kelsey,
Department of Geology, Humboldt State University, Arcata, CA 95521, [email protected]
humboldt.edu.
The Maacama fault zone (Mfz) is one of three major fault zones that comprise the
San Andreas fault system in northern California. The fault is creeping near the
town of Willits, and determining a long term slip rate for the fault is critical in
order to evaluate whether stress on the fault is only released by ongoing creep or
whether large earthquakes occur on this fault as well. We investigated Holocene
sediments that were deposited across the Maacama fault near the western edge of
the Little Lake Valley in Willits, California. The Mfz in Little Lake Valley has been
creeping at a rate of 6.6 mm/yr for the last 11 years (Galehouse, 2002). We excavated multiple trenches parallel and perpendicular to the fault to provide exposures
of channel stratigraphy and channel margins on both sides of the fault. Detailed
study of these excavations allowed us to map the paths of two paleo-channels of
Haehl Creek where they are offset by the Maacama fault. The first channel, channel
A, is right laterally offset 4.6 m. Based on eight radiocarbon ages, the age of channel is less than or equal to 653-537 years, indicating a minimum slip rate of about
7 mm/yr. The second and older channel, channel B, is offset right laterally about
27 m. Based on one radiocarbon age, channel B is less than or equal to 3480-3350
ybp. From the offset and maximum limiting age, we infer a minimum slip rate for
channel B of about 8 mm/yr. Multiple sample ages are pending that may result in
a revised preliminary slip rate. Because radiocarbon ages are from detrital charcoal
that may well be older than the age of deposition of the host alluvium, the radiocarbon ages will tend to overestimate the age of the channels. The new radiocarbon
analyses may significantly reduce the channel ages, which would increase our slip
rate estimates. Nevertheless, the preliminary results are that over the last 650 years,
only fault creep has occurred at the site; however, over the last 3500 years, slip has
been accommodated by both creep and earthquakes with surface rupture.
Seismicity Rate Changes and Earthquake Forecasting Beyond the San
Andreas
D. Bowman, CalState Fullerton, [email protected]; H. Colella,
CalState Fullerton, [email protected]; K. Tiampo, University of Western
Ontario, [email protected]
Regional and local variations in seismicity rate have been proposed to be useful
proxies for exploring evolving correlations in the regional stress field before and after
large earthquakes. We have applied two related analysis techniques to explore seismicity in the San Francisco Bay Region. These techniques, the Pattern Informatics
(PI) Index and Accelerating Moment Release (AMR), explore complementary features of the evolving regional stress field. Both approaches are applied to seismicity in the Bay Area, and suggest activity consistent with precursory loading of the
Rogers Creek/Calaveras fault system.
Seismic-Reflection Profiles in the Stepover Region of the Southern Hayward
Fault Reveal a Northeast-dipping Hayward Fault and West-directed Blind
Thrusting
R. Williams, USGS, [email protected]; C. Wentworth, USGS,
[email protected]; W. Stephenson, USGS, [email protected]; R.
Simpson, USGS, [email protected]; J. Odum, USGS, [email protected]; R.
Jachens, USGS, [email protected]
Two high-resolution, P-wave reflection profiles in the southern San Francisco Bay
Area of California were located on the western edge of the stepover region between
the Calaveras and Hayward faults. Recent studies of this stepover region indicate
that the two faults are simple and continuous at seismogenic depths with more
complex shallower relations. Our reflection profiles support this direct connection
by indicating a northeast-dipping Hayward fault whose dip progressively shallows
along strike to the southeast, where it splays into a series of northeast-dipping thrust
faults. One profile across the creeping trace of the southern Hayward fault near
Fremont images the fault to a depth of 650 m. Truncated reflections define a fault
dip of about 70 degrees NE at 100-650 m depth that projects upward to the creeping surface trace, contrary to the previous assumption of a vertical fault. This fault
projects down dip to the Mission seismicity trend at 4-10 km depth about 2 km
east of the surface trace and suggests that the southern end of the fault is as seismically active as the part north of San Leandro. Our second profile crosses densely
populated east San Jose, terminates at the foot of the west side of the Diablo Range,
and shows a westward-thickening Quaternary sedimentary section that forms an
east-up stair-step ramp-and-flat structure beneath east San Jose. This structure, with
thickening of some sedimentary intervals and relatively constant thickness of oth-
Seismological Research Letters Volume 77, Number 2 March/April 2006 201
ers, suggests active, but episodic, deformation as young as about 100 ka or younger
(horizons above 50 m were not imaged). The deformed Quaternary section is
underlain by a prominent reflector that marks the top of a wedge of higher-velocity
(3150 m/s) rocks. Low-angle east-dipping reflectors in the wedge indicate at least
two previously unidentified westward-directed blind thrust faults, referred to here
as the Penitencia thrust system. This growing body of information about the relations between the Hayward and Calaveras faults may stimulate a reassessment of
potential event magnitudes that could occur on the combined fault surfaces, thus
affecting hazard assessments for the San Francisco Bay region.
A New Campaign GPS Network and Alinement Array on the Bartlett Springs
Fault
J. Murray, U.S. Geological Survey, [email protected]; J. Svarc, U.S.
Geological Survey, [email protected]; J. Lienkaemper, U.S. Geological
Survey, [email protected]; J. Langbein, U.S. Geological Survey, [email protected]
gov; F. McFarland, San Francisco State University, [email protected]; S.
Nishenko, Pacific Gas and Electric, [email protected]; W. Page, Pacific Gas and
Electric, [email protected]
The San Andreas fault system north of the latitude of Point Arena consists of three
main strands, the San Andreas, Ma’acama, and Bartlett Springs faults. Few geodetic
observations span the Bartlett Springs fault (BSF). The available data suggest, however, that the fault may creep at approximately 8 mm/yr at all depths (Freymueller et
al., 1999). The BSF may be the northern extension of the Green Valley fault which
has an estimated creep rate of 4.4 ± 0.1 mm/yr (Galehouse et al., 2003), but the
manner in which these two faults may connect and the extent to which creep transitions from one to the other is unknown.
Creeping behavior, if it extends to seismogenic depths, can reduce a fault’s
potential for generating damaging earthquakes. The rate and depth extent of fault
creep may be estimated using geodetic data given adequate station coverage. The distribution of GPS stations used in the Freymueller et al. (1999) study was sparse in the
vicinity of the BSF, consisting of only one pair of stations spanning the fault at moderate distances. The four existing continuous GPS sites within 50 km of Lake Pillsbury
and the eventual addition of approximately 7 more through the Plate Boundary
Observatory will be insufficient to image creep in the upper 12 km of the BSF.
We have established and made initial measurements of a spatially dense
network of 31 campaign GPS sites centered on the Lake Pillsbury area and an
alinement array spanning the fault at the north end of Lake Pillsbury to measure
near-surface creep. We plan to install six additional GPS sites in the coming year
to complete the network. The network will be remeasured in 2006, and then once
every two years. Future work will involve estimating site velocities from the position time series and inversion of these rates to assess whether significant fault creep
occurs at seismogenic depths or is confined to the near-surface. From this analysis,
the seismic hazard for the BSF can be better estimated.
Active Tectonic Deformation East of the San Andreas Fault System—
Sacramento-San Joaquin Delta Area, California
J. Weber, formerly of University of California at Berkeley, Dept of Geology &
Geophysics, [email protected]
The North-Central California Coast Ranges are dominated by a N40W structural
trend controlled by the major active strike slip faults related to the San Andreas
Fault system. This trend is modified or interrupted in several places along the eastern boundary of the Coast Ranges at the margin of the Central Valley. One area in
particular, the low-lying area at the confluence of the Sacramento and San Joaquin
Rivers known as the Delta, is recognized as structurally anomalous because of the
occurrence of N-S trending faults, E-W trending folds, and a broad area of relatively
flat-lying sedimentary units (Montezuma Hills) lying between strongly uplifted
strata to the north and south. This area is also important because of the extensive
system of earthen levees that control the water in the region.
Three historical earthquake events occurred in the Delta area: The 1889 m
6.3 Antioch earthquake and two earthquakes in 1892 in the Winters-Vacaville area
of M 6.0 to M 6.5. Understanding the structural relationships and relative seismic
activity of this area is an important part not only of making sense of the complex
region of deformation associated with the San Andreas Fault system, but also in
understanding the potential earthquake hazards associated with the levee system.
Based on geomorphic expression and features apparent in seismic reflection
profiles, the Pittsburg/Kirby Hills fault (renamed from Kirby Hills or Montezuma
Fault) and a north-south striking reach of the Midland fault appear to be active in
the Quaternary with apparent reversal of motion along ancient normal faults. Agedating of key stratigraphic horizons allow calculation of an approximate uplift rate of
about 2 mm/yr on both faults. Interestingly, focal mechanisms of recent microseismic events do not seem to relate directly to the faulting style apparent at the surface.
The Pacific Star Fault Zone—A Significant Newly Recognized Structure in
the San Andreas Fault System on the Northern California Coast of
Mendocino County
C. Lippincott, San Diego State University, [email protected]; D.
Merritts, Franklin and Marshall College, [email protected];
R. Walter, Franklin and Marshall College, [email protected]; J.
Muller, NASA Goddard Space Flight Center, [email protected]; D.
Springer, College of the Redwoods, [email protected]
We document the discovery of a previously unmapped zone of active faults—named
here the Pacific Star Fault Zone—that intersects the northern California coast
between the towns of Mendocino and Westport, approximately 240 km north of
San Francisco. These faults: (1) have a right-lateral strike slip component of motion,
with secondary faults also possessing a minor vertical component (normal or
reverse); (2) are either sub-parallel to the main trace of the San Andreas Fault (8 km
offshore to the west), or conjugate to its trend; (3) occur landward of the submarine
Noyo Canyon, which contains a detailed record of earthquake induced turbidites;
and (4) offset and deform the lowest marine terrace platform and overlying terrace
sediments, suggesting slip as recently as the late Pleistocene and possibly Holocene
epochs. At least one of these faults appears to have significant and recurrent horizontal displacement as shown by deflected and abandoned stream channels. This
fault cuts two Pleistocene fluvial deposits of different ages and appears to displace
them northward along the coast from their apparent source in Wages Creek. The
older offset paleochannel and its fluvial sediments are buried by (and hence predate) marine sediments of the lowest marine terrace, whereas the younger offset
fluvial deposits overlie the lowest marine terrace. A solitary coral (Balanophyllia
elegans), dated from the lowest marine terrace at Laguna Point north of Fort Bragg,
yields a U-Th (TIMS) age of 130.3 ± 0.9 ka. We tentatively correlate this dated
terrace with the lowest, deformed marine terrace at Wages Creek. This correlation
provides two calibration points for slip-rate measurements. In addition, we determined slip rates from a series of deflected streams carved into this same terrace.
In aggregate, these offset features span a distance of 6.4 km along a strand of the
Pacific Star Fault, and yield an average slip rate of 4-6 mm/yr (absolute range of
2.3 to 10.8 mm/yr). The range of plausible slip rates is comparable to slip on other
faults within the San Andreas fault system that lie to the east, such as the HaywardRodgers Creek faults (slip rate of about 9 mm/yr).
GPS-derived Fault Slip Rates along the Northernmost Segments of the
Maacama and Bartlett Springs Fault Zones, Northwestern California.
T. Williams, UNAVCO, Inc., [email protected]; H. Kelsey, Humboldt
State University, [email protected]; J. Freymueller, University of AlaskaFairbanks, [email protected]
GPS-derived velocities (1993-2002) in northwestern California indicate that the
northern San Andreas fault system is in part accountable for observed upper-plate
contraction near the Mendocino Deformation Zone (MDZ; Figure 1). Model
results inland of Cape Mendocino across the northern projections of the developing San Andreas fault system suggest that the Maacama fault zone is locked to
~13km depth, with a slip rate of ~14mm/yr, and the Bartlett Springs fault zone
is locked to ~5 km depth, with a slip rate of ~8 mm/yr. Comparing these results
to Freymueller et al. (1999) suggests that fault slip rates along the Maacama and
Bartlett Springs fault zones are consistent along strike from Pt. Arena (39oN) to
Cape Mendocino, CA (40.4oN). However, the Bartlett Springs fault zone shows
characteristics of a progressively deeper locked zone along strike south to north;
from creeping at the surface at 39oN, to ~ 13 km locking depth at 40.75oN, North
of the latitude of Cape Mendocino. The northernmost end of the strain field associated with the locked portion of the Bartlett Springs fault zone (41oN) trends
into the Mad River fault zone, which is a subaerial portion of the accretionary fold
and thrust belt of the Cascadia subduction zone. We conclude that: 1) the youthful, northernmost segments of the Maacama and Bartlett Springs fault zones are
locked and actively accumulating strain at 14 and 8 mm/yr, respectively; 2) the
northernmost segment of Bartlett Springs fault zone is active North of the latitude
of Cape Mendocino, and, 3) a significant portion (6-10 mm/yr) of the upper-plate
contraction observed near Cape Mendocino is not solely a result of subduction of
the Gorda plate, but also a consequence of impingement of the northernmost segments of the San Andreas fault system.
Near-surface Geophysical Surveying of East San Francisco Bay Faults
M. Craig, California State University, East Bay, [email protected]; M. Kimball, U. S. Military Academy, [email protected]; J.
Lienkaemper, U. S. Geological Survey, [email protected]
We conducted near-surface geophysical surveys of the Hayward and Green Valley
faults using seismic refraction and ground-penetrating radar (GPR). The Hayward
fault site is located at Tyson’s Lagoon, a pull-apart basin between two strands of the
202 Seismological Research Letters Volume 77, Number 2 March/April 2006
southern Hayward fault. The Green Valley fault site is at Mason Rd., 3 km NW of
Cordelia Junction. We prepared seismic velocity models using both time-term and
tomographic methods. The GPR lines show buried channel features at Mason Rd.
and a surface at Tyson’s Lagoon that is evidently the Holocene-Pleistocene boundary. Seismic data were recorded using a 24-channel spread, 3-5 m geophone spacing,
18-30 m shot spacing, and sledgehammer source. GPR data were recorded using 50
MHz antennas and a 0.5 m step size. At Tyson’s Lagoon, we recorded three seismic
lines totaling 228 m in length and two GPR lines totaling 240 m in length. In the
NE portion of the lagoon, seismic and GPR data both indicate an near-horizontal interface 7-9 m deep that evidently corresponds to the Holocene-Pleistocene
boundary previously inferred at the site based on borehole logs and penetration
tests. Both GPR lines show this surface to dip gently to the west, towards the center of the lagoon. The seismic data indicate a sharp discontinuity in velocities at
approximately this depth range, increasing from 300-1000 m/s in the overlying
material to 1700-1800 m/s beneath. Seismic velocity models also indicate a possible
cross fault that cuts across the lagoon and connects the two strands of the Hayward
fault that bound the lagoon. At the Green Valley site, we recorded a grid of eight
seismic refraction lines with a total length of 1245 m, and nine GPR lines with a
total length of 1440 m. Suspected paleochannels 5-10 m wide were identified at
three locations based on the GPR data. We augered one of these locations to 3.0 m
depth and collected soil samples at 30 cm depth increments. Sediments ranged in
size from clay to fine sand. Velocity models derived from the seismic lines recorded
at this site provide constraints on the location of the Green Valley fault.
Potential Earthquake Hazards Associated with Previously Unrecognized
Blind Thrust Fault: Analysis of the Marin County—Mt. Tamalpais Region
C. Johnson, Penn State, [email protected]; K. Furlong, Penn State,
[email protected]; E. Kirby, Penn State, [email protected]
The major strike slip faults of the San Andreas fault system are the primary earthquake hazard in the San Francisco Bay area. Complex fault geometries and discrepancies in fault slip rates, however, imply that there may be additional structures such
as blind thrusts in the region to transfer slip among the faults in the system. Blind
thrusts have often remained unrecognized hazards within the San Andreas fault
system until a damaging event occurs. Two recent examples are the 1994 Mw 6.7
Northridge and 2003 Mw 6.5 San Simeon events. We propose that a blind thrust
beneath the Mt. Tamalpais and Marin County region, just north of San Francisco,
is an active structure that solves a slip rate discrepancy and has produced the enigmatic elevations in the area, and can potentially host moderate earthquakes. We
have combined geomorphic analyses of stream channels and the landscape in the
Marin County—Mt. Tamalpais region with seismicity, fault behavior, and deformational modeling to assess the potential hazard from this proposed structure.
Geomorphic analyses of stream channels within the elevated region show
a systematic change in channel steepness with location. Exploiting relationships
between channel steepness and uplift rate, we can constrain models of blind thrust
deformation that can produce the modern landscape, when erosion is included.
This study, coupling deformational modeling with geomorphic constraints on erosion to analyze the potential for a blind thrust beneath Mt. Tamalpais, allows us to
place important constraints on rates and extent of fault slip.
From this integrated analysis of geophysical, geomorphic, geochronologic,
geodetic and geodynamic observations, we are able to estimate that a simple blind
thrust capable of producing Mt. Tamalpais could host a Mw = ~6.8 with recurrence of ~300 years. Such a fault poses an additional earthquake hazard beneath
Mt. Tamalpais and Marin County, with the potential for the majority of ground
shaking to occur up-dip of the structure, towards San Francisco.
A New 3D Finite-element Model of the Hayward Fault
M. Barall, Invisible Software Inc., [email protected]; R. Simpson,
U.S. Geological Survey, [email protected]
We are constructing a new 3D finite-element model of the Hayward fault, using 3D data
recently published by USGS. The model accounts for both non-uniform material properties and the 3D fault geometry. The fault geometry and the rock units near the fault
are obtained from the Hayward 3D geologic map (Graymer et. al.), which is a detailed
regional model designed by USGS to help seismological analysis of the Hayward fault.
Farther away from the fault, rock units and physical properties are obtained from the Bay
Area 3D geologic map (Jachens et. al.), and the Bay Area 3D velocity model (Brocher et.
al.). Initially we have assumed elastic behavior, but the 3D finite-element software that
we are developing also allows viscoelastic and plastic rheologies.
The 3D finite-element model and our 3D finite-element software are tools
that we are using to investigate a variety of questions about the Hayward fault, such
as: What are the effects and relative importance of fault geometry and non-uniform
physical properties? Can the model account for observed creep rates and geodetic
strain rates along the Hayward fault? What are the effects of simulating locked
patches and friction on the fault?
For our initial calculations, we allowed the fault to slide without friction, and
the finite-element software calculated the resulting patterns of deformation and
stress. We performed the calculations once with uniform rheology and once with
non-uniform rheology, which revealed that the pattern of deformation was determined primarily by the 3D fault geometry rather than rheology. This demonstrates
the utility of the model for evaluating the effect and importance of individual features of the model. Future calculations will add more complex fault behavior.
Mapping the Deformational Behavior and Mechanical Properties of the
Hayward Fault
K. Furlong, Penn State University, [email protected]; R. Malservisi,
LMU—Munich, [email protected]; C. Gans, University of
Arizona, [email protected]
The Hayward fault serves as a primary component of the Pacific—North America
plate boundary through the S.F. Bay area. It is recognized as the potential host
of damaging earthquakes, and is of particular concern because of its location in a
highly urbanized region. Fault kinematics indicates that the fault deforms (slips)
both by fault creep and with potentially damaging earthquake events. By combining observations of surface deformation, seismicity, and deformational modeling
we have been able to map out variations in fault behavior that can be linked to its
mechanical properties. In particular we have mapped those patches of the fault that
at present appear to be locked (non-creeping) and those regions of the fault surface
that creep (or have the potential to creep). This analysis indicates that (1) much of
the micro-seismicity associated with fault creep occurs in the transitions between
locked and creeping patches, (2) recurring micro-earthquakes appear to be associated with small ‘asperities’ on the fault surface within the creeping region, and (3)
there are significant transient effects on fault creep expected in response to moderate to large earthquakes on the fault. Results 1 and 2 allow us to utilize the pattern
of micro-seismicity to help define the pattern of fault patches, particularly at depth,
a region of the fault poorly constrained by surface observations of crustal deformation. One consequence of the third result is that the presently observed creep rate
reflects a background rate, since there has been more than 150 years since the last
significant earthquake on the fault. Our modeling indicates that during the first ~
50 years after a significant earthquake the creep rate will be accelerated. This also
implies that the rate at which the fault-slip deficit accumulates on the fault is not
constant through time, but rather reflects the combined effects of external/regional
fault loading (plate motions) and the transient creep response of the fault.
Fault-zone Discontinuities along the Hayward Fault, Northern California,
and their Implications on Earthquake Hazards
D. Ponce, USGS, [email protected]; T. Hildenbrand, USGS, [email protected]
gov; R. Jachens, USGS, [email protected]
We suggest that the Hayward Fault contains a number of fault-zone discontinuities based on geophysical, three-dimensional geologic, and seismicity evidence.
The Hayward Fault is predominantly a right-lateral strike-slip fault that forms the
western boundary of the East Bay Hills and separates Franciscan Complex basement rocks on the southwest from Great Valley Sequence basement rocks on the
northeast. The Hayward Fault extends for about 90 km from Fremont northwest to
San Pablo Bay, and together with its northern extension, the Rodgers Creek Fault,
is regarded as one of the most hazardous faults in northern California. Historically,
the Hayward Fault has been partitioned into two fault segments on the basis of the
1836 and 1868 earthquakes. However, the 1836 earthquake is no longer considered
to have occurred on the Hayward Fault and the 1868 earthquake ruptured beyond
an earlier defined segment boundary-this necessitates a re-evaluation of the twosegment model of the Hayward Fault.
The Hayward Fault is characterized by distinct linear gravity and magnetic
anomalies that correlate with changes in geology, structural trends, creep rates, and
clusters of seismicity. These inter-relationships suggest that the Hayward Fault may
include of a number of fault-zone discontinuities that probably reflect changes in
mechanical properties along the fault, some of which are more prominent than others and may play a role in defining fault segments-locations where recurring seismic
ruptures may tend to nucleate or terminate. The ability of an earthquake rupture to
propagate across these fault-zone discontinuities may, in part be related to the location, magnitude, and rupture propagation velocity of the earthquake. For example,
the approximate location of the 1868 intensity center near San Leandro (Bakun,
1999) combined with geophysical and geologic data suggests that the 1868 earthquake may have been located near San Leandro at or near a fault-zone discontinuity
associated with a large gabbro body and thus, propagated bilaterally. The northern
extent of the rupture related to the 1868 earthquake (Yu and Segall, 1996) combined with geophysical and three-dimensional geological information suggests that
the rupture may have terminated at a fault-zone discontinuity near Berkeley, Calif.
Seismological Research Letters Volume 77, Number 2 March/April 2006 203
A 3-Dimensional Geologic Map of the Hayward Fault
g. Phelps, USGS, [email protected]; R. Graymer, USGS, [email protected]
gov; R. Jachens, USGS, [email protected]; D. Ponce, USGS, [email protected]
gov; R. Simpson, USGS, [email protected]; C. Wentworth, USGS,
[email protected]
The Hayward Fault is one of the most dangerous faults in the California Bay Area,
with an estimated 27% chance of a magnitude 6.7 earthquake occurring along the
fault in the next 30 years (Working Group on California Earthquake Probabilities,
2003). The USGS has created a 3D geologic map of the volume surrounding
the Hayward Fault to serve as a basis for process modeling (such as seismic hazard modeling) of the fault (Graymer et al., 2005). The 3D map was built using
EarthVision(tm) software. Fault surfaces and the boundaries of rock bodies were
defined using information from geologic mapping, modeling of gravity and magnetic anomalies, seismicity and seismic sounding data, and a few shallow drill-holes.
The map is built around several core elements, as follows, each the result of a unique
scientific investigation.
A representation of the Hayward Fault, modeled as a surface in three dimensions, was constructed using the mapped creeping trace of the fault and hypocenters
of earthquakes at depth. The subsurface 3D geometry of the San Leandro gabbro,
a body of dense, magnetic rocks exposed on either side of the Hayward Fault, was
inferred from modeling of associated gravity and magnetic anomalies. The depth
and shape of the boundary between light Cenozoic cover and dense Mesozoic
Franciscan rocks was modeled using gravity analysis. The patterns and orientations
of complexly folded and faulted rock units east of the Hayward Fault, as revealed
by traditional geologic mapping, allow the use of standard cross section techniques
to model these units in the subsurface. Concealed Franciscan units west of the
Hayward Fault were modeled from geophysically inferred boundaries and a constant dip extrapolated from geologic mapping of the Franciscan rocks farther west,
outside of the model area.
The Hayward Fault 3D geologic map can be used for process modeling, for
example to examine fault behavior in an inhomogeneous environment. Finite element modeling that uses the Hayward Fault 3D geologic map to define geometries
and to assign properties and rheologies, to generate an inhomogeneous model and
study the fault behavior, is currently underway (Barall and others, 2006).
The Evolution of a Plate Boundary System—Crustal Structure, Seismicity
and Volcanism in Northern California
G. Hayes, Penn State University, [email protected]; K. Furlong, Penn
State University, [email protected]
The Pacific-North America plate boundary system has developed in response to the
northward migration of the Mendocino triple junction through northern California
over the past 10-15 million years. Related changes in plate geometry have created
the major faults and drive deformation and volcanism in the crust. How a fault
behaves in the future is dictated by how that fault evolved. The Ma’acama, Rodgers
Creek and Hayward Fault corridor form a major part of this plate boundary system,
and reflect its northward evolution, so we can use processes occurring in and on the
Ma’acama fault to understand how the Hayward fault evolved in the past, and thus
explain its characteristics today.
Along a transect from Covelo to Hopland, receiver function analyses reveal
rapid changes in crustal thickness, transitioning from thick crust south of the triple
junction to thinner crust north of San Francisco Bay. This thinning coincides with
a low P-wave velocity zone, with high Poisson’s Ratio’s (>0.30), in the lower-crust
(~14-19km), both characteristics of crustal melt, and suggests a link between the
rapid thinning and the initiation of crustal melting.
The Ma’acama fault exhibits the majority of seismic activity in the northern
Coast Ranges, and is well defined at the surface through Willits Valley via trenching, paleoseismology and creep analyses. Enigmatically though, precise earthquake
relocations reveal that the microseismicity is offset to the east, defining an almost
vertical structure up to 10km away from the mapped surface trace of the fault.
Further analysis of the relocated earthquakes has identified a period of anomalous seismicity on an unmapped structure slightly east of the Ma’acama Fault.
Over a 6-month period in 2000, there were more than three times as many events
as occurred in the preceding 15 years. More importantly, relocations resolve a systematic migration pattern, diagnostic of magma movement. This activity links the
lower crustal melt bodies inferred from receiver functions to diking events at midcrustal levels, suggesting that the region west of Lake Pillsbury is the likely focus
for the next occurrence of Coast Range volcanism. This is the first evidence for an
active link between volcanic and seismic systems in northern California, and is thus
an important step towards understanding how processes involved in the formation
of this plate boundary interact and evolve.
Earth Structure and Site Response in the Northern San Francisco Bay Area
H. Lin, U.S. Geological Survey, [email protected]; Y. Chen, U.S. Geological
Survey, [email protected]; R. Sell, U.S. Geological Survey, [email protected];
W. Mooney, U.S. Geological Survey, [email protected]; S. Detweiler,
U.S. Geological Survey, [email protected]; J. Fletcher, U.S. Geological Survey,
[email protected]; J. Boatwright, U.S. Geological Survey, [email protected]
Digital Compilation of Thrust and Reverse Fault Data along the Northeastern
Range Front of the Santa Cruz Mountains, Southern San Francisco Bay
Region, California
D. Kennedy, Sanders & Associates Geostructural Engineering, Inc., [email protected]
sandersgeo.com.
An important component of estimating the seismic hazard for the San Francisco
Bay area is to understand the effect the Earth’s crust has on seismic waves. Waves
diminish and change character as they propagate from the earthquake source to
regional seismographs. To study this phenomenon in the northern San Francisco
Bay Area, we deployed 13 intermediate-period seismic stations throughout the
region. We expect that waves are amplified as they propagate through basins or
through young soils at the Earth’s surface, but instead find that they lose high-frequencies. We also hope to determine the velocity structure of the upper crust of
the Earth in the region from the coast to around Santa Rosa, Napa, and Sonoma.
Once known, the velocity structure can be used to model synthetic seismograms
to get an estimate of predicted ground shaking and site response. However, existing velocity structure information was only available for bedrock and not the sediments, making it difficult for our synthetic seismograms to differentiate the basin
reverberations from distant arrivals. The seismographs in the area recorded local
and distant earthquakes. By comparing the times of different phases as they arrive
at each station, and from their different amplitudes, we were able to determine features of the velocity structure as well as which areas are affected by very near-surface
loose soils. One of our principal interests is whether large amplifications are found
at sites in the various valleys as have been found elsewhere, and this was found to
be true. Another interesting result is that two of the earthquakes that were used for
modeling purposes were located southeast of the seismographs, on the other side of
the San Francisco Bay. It is likely that the complex geometry in the San Francisco
Bay area caused a scattering of surface waves, as evidenced by their low amplitudes
in the northern San Francisco Bay area. This decrease in shaking in the North Bay
was also noted during the 1989 Loma Prieta earthquake. This aspect of the wave
propagation is particularly challenging to model.
Available fault data was compiled for a system of thrust and reverse faults mapped
along the northeastern range front of the Santa Cruz Mountains, from near Loma
Prieta to Daly City, California. The primary objective of this compilation effort
was to prepare a digital fault map and an associated database of Quaternary active
fault traces that the U.S. Geological Survey (USGS) will incorporate into the San
Francisco Bay Region (SFBR) Quaternary Fault Database. The southwest-dipping
thrust and reverse faults are of particular interest because of their proximity and
tectonic relationship with the nearby San Andreas fault, uncertainties regarding
their level of activity, and the increasing urban development along many of the fault
traces. The faults locally offset and deform late Quaternary sediments and geomorphic surfaces, as well as probable Holocene soils. Available existing published and
unpublished data for the faults was acquired from numerous sources, including the
USGS, the California Geological Survey, Santa Clara County, local municipalities, and geological consulting firms. Individual fault locations were compiled from
regional maps using GIS software, and were attributed to include fault name, fault
rank, recency of activity, and source. Where possible, the fault trace locations were
further refined using detailed mapping data from geomorphic investigations of the
thrust faults; city or town geologic maps for Woodside, Portola Valley, Los Altos
Hills, Cupertino, Saratoga, and Los Gatos; selected site-specific fault hazard investigations for development; and unpublished geologic mapping data contained in a
guidebook for an Association of Engineering Geologists field trip along the range
front in March 2004. From a digital database of more than 7,300 individual fault
segments, pre-Quaternary faults were vetted, leaving about 1,100 Quaternary active
fault segments. The digital fault map and database generated during this study will
be valuable for further defining fault behavior and characterizing potential seismic
sources.
Analysis of the Seismicity of the San Gregorio and Monterey Bay Fault
Zones, Monterey Bay Region, California
G. Simila, Calif. State Univ. Northridge, [email protected]; D. Stakes,
Monterey Peninsula College, [email protected]; M. Begnaud, Los Alamos
204 Seismological Research Letters Volume 77, Number 2 March/April 2006
National Lab, [email protected]; K. McNally, U. C. Santa Cruz, [email protected]
Since 1998, a temporary seismic network has operated in the Monterey Bay Region.
In 1998-99, nine land based PASSCAL Ref Teks (3 component) were deployed
along the coast of Monterey Bay from Pigeon Point to Carmel Valley to supplement
the permanent USGS array and to complement five ocean bottom seismic (OBS)
instruments deployed in the Monterey Bay as part of the “Margin Seismology
System Development Project” of the Monterey Bay Aquarium Research Institute
(MBARI). In addition, three (3-component) accelerocorders continue to monitor the seismicity of the area. The seismicity data (1926-99) were relocated starting with the recent data and progressing systematically to the historical events, and
were also processed with a new crustal velocity model (1 D) developed by Begnaud
et al. (2000). The analysis of the 1998-99 microseismicity data included waveform
correlation and horizontal component rotation for S-wave selection for high-precision locations and associated focal mechanisms. In addition, the seismicity data
(1980-98) along the active San Gregorio (SGFZ) and older Monterey Bay (MBFZ)
fault zones produced well constrained relocations and fault mechanisms which
indicated several significant features. The fault mechanisms and the depth distribution of seismicity through the west and central portion of the bay indicate that the
San Gregorio fault dips roughly 50 70 degrees downward to the east. Thrust faulting mechanisms are found for deeper (h=8 12 km) easterly events along the SGFZ
and the oblique right slip with strikes of about N20 40W on shallower westerly
events. In contrast, earthquakes along the reactivated MBFZ indicate vertical faults
with right lateral motion at N50W. Earthquakes during 1926-79 have been relocated using several methods. Small well recorded earthquakes from diverse source
areas within the Bay have been used as a series of Master Events. Also, P and S wave
travel times to historic UC Berkeley stations were calibrated for the various subareas within the Bay, and then were used to systematically relocate the largest historic
Monterey Bay events (M 4 6.1) since 1926. Specifically, the 1926 (M=6.1) doublet
events relocated eastward to the SGFZ and MBFZ (possibly triggered), respectively. The five aftershocks (M=4.+; 1926-27) located along both fault segments,
as well as two later events in 1938 (M=4.5) and 1947 (M=4.1). Our results suggest
that most historic energy release at scattered locations found in the old catalogs is
real and these events can be associated with both the younger San Gregorio and
older Monterey Bay fault zones. These results are particularly important for hazard
assessment of the San Gregorio fault segments (north, south) which have a floating
M=6.9 event (USGS Working Group 99).
Commemorate the 1906 Earthquake at the Bottom of an Active-fault Trench
H. Stenner, USGS, [email protected]; M. Zoback, USGS, [email protected]
gov; J. Lienkaemper, USGS, [email protected]; D. Schwartz, USGS,
[email protected]; D. Wells, Geomatrix Consultants, [email protected]
As part of the Bay Area-wide commemoration of the 1906 San Francisco earthquake, there will be a Trench Exhibit open in Fremont from April 1 to May 30,
2006.
Free and open to the public, the Exhibit will feature a 10- to 12-feet-deep
trench across the Hayward fault. The fault is easily visible within the sediments at
this location and visitors are encouraged to descend a staircase to meet the Hayward
fault face-to-face. For safety, the trench walls will be sloped to ~45 degrees following in the style of Japanese trenching.
The Hayward fault was chosen for the exhibit to highlight that the 1906
earthquake has not been the only damaging quake in the Bay Area. In 1868 a large
earthquake occurred along the Hayward fault, causing significant damage in San
Francisco as well as the East Bay. It was referred to as The Great San Francisco
Earthquake until the 1906 quake put it into perspective. The 2003 Probability
Report by the USGS lists the Hayward fault and its continuation to the north, the
Rodgers Creek fault, as the most hazardous fault system in the Bay Area (USGS
Open File Report 03-214, pubs.usgs.gov/of/2003/of03-214). Future large earthquakes along the Hayward fault will have devastating effects because of the great
concentration of homes, schools, hospitals, roads and other critical structures along
and across the fault.
Surrounding the trench will be exhibit space for educational displays and
posters. If your organization would like to have an educational display included
at the Exhibit, which is geared toward the public, please contact Heidi Stenner
([email protected]). The Exhibit will be located adjacent to the parking lot
off Sailway Drive in Fremont’s Central Park. Major cross streets are Paseo Padre
Parkway and Stevenson Boulevard. The trench will be open on weekends and by
appointment. Visit 1906centennial.org/activities/trench for more information.
We thank Risk Management Solutions and Swiss Re for their generous sponsorship and the City of Fremont for access to Central Park.
Faults and Potential Hazards Beneath the Alluvial-covered, Highly
Populated Areas of the San Francisco Bay Area Revealed by Seismic
Images
R. Catchings, U.S. Geological Survey, [email protected]; M. Goldman,
U.S. Geological Survey, [email protected]; M. Rymer, U.S. Geological Survey,
[email protected]; G. Gandhok, U.S. Geological Survey, [email protected]
com.
Many of the large-magnitude earthquakes that have occurred in California over the
past few decades were located on previously unknown or buried faults. Most of
these faults do not have strong geomorphic expressions because they are covered
at the surface by alluvial deposits and/or by urbanization, and many of the faults
also do not have appreciable seismicity associated with them prior to generating
large-magnitude earthquakes. Identifying these faults from the surface (geologic
mapping, geodesy, trenching, LiDAR, etc.) is often difficult, particularly for blind
faults. However, it is important to locate these faults and understand the hazards
associated with them, particularly beneath urban centers. High-resolution seismic
imaging techniques are among the best and most accurate techniques to locate subsurface faults and to define basin structures that affect strong shaking. High-resolution seismic imaging profiles that cross the western Santa Clara Valley and the East
Bay Plain (between the San Francisco Bay and the Hayward fault) show apparent
vertically offset strata at depths ranging from a few meters to hundreds of meters.
The offset strata, combined with seismic velocity perturbations, indicate recent
faulting beneath highly populated areas of the Santa Clara Valley and the East Bay
Plain. In the Santa Clara Valley, the seismic images show that a series of near-surface faults extend from the Santa Cruz Mountains to near downtown San Jose. In
the East Bay, the seismic images show a series of near-surface faults concentrated
between the San Francisco Bay and Highway 880, beneath the densely populated
areas of the East Bay Plain. The seismic images further show that the San Leandro
Basin is fault bounded on its eastern side, with strata offset hundreds of meters. The
lateral extent of faults beneath the Santa Clara Valley and the East Bay Plain is not
known, but these faults appear to be sub-parallel to the major faults that bound the
bay, and they may represent a significant seismic hazard.
Fault Length and Implications for Seismic Hazards in California
N. Black, UCLA, [email protected]; D. Jackson, UCLA, [email protected]
edu.
It is important to accurately define fault geometry in order to assess mx, the largest earthquake magnitude that can occur on the fault and mp, the largest magnitude that should be expected during the planned lifetime of a particular structure.
However, fault length is often poorly defined and multiple faults often rupture
together in a single event. Therefore, we have expanded the definition of a mapped
fault length to obtain a more accurate estimate of the maximum magnitude. In
previous work, we compared fault length vs. rupture length for post-1975 earthquakes in Southern California. In that study we found that mapped fault length and
rupture length are often unequal, and in several cases rupture continued beyond
the previously mapped fault traces. We expanded the geologic definition of fault
length by outlining several guidelines: 1) if a fault truncates at young Quaternary
alluvium, the fault line should be inferred underneath the younger sediments 2)
faults striking within 45 degrees of one another should be treated as a continuous
fault line and 3) a step-over can link together faults at least 5 km apart. We have
expanded the study to include faults greater then 75 km in length throughout the
entire state of California. First we will examine mapped fault length to rupture
length for earthquakes greater then magnitude 6.0 since 1975 to see if the above
guidelines still hold. Then we will apply the guidelines above (or the modified ‘new’
guidelines) to assess the maximum fault length and the maximum magnitude. For
risk management we are usually more concerned with mp. To calculate the planning
magnitude mp we assume a truncated Gutenberg-Richter magnitude distribution
with parameters a, b, and mx. We fix b and solve for the a-value in terms of mx, b,
and the tectonic moment rate. In the previous study we found that by increasing mx
the cumulative earthquake rate actually decreases for smaller magnitude (5 and 6)
events. Fewer magnitude 5 and 6 earthquakes are required to balance the moment
budget if larger, but highly infrequent, earthquakes can occur. This result will now
be tested for faults at least 75 km in length, within the entire state of California.
Distribution of Aseismic Slip along the San Andreas and Calaveras Faults
from Repeating Earthquakes
D. Templeton, Berkeley Seismological Laboratory, [email protected]
edu; R. Nadeau, Berkeley Seismological Laboratory, [email protected]
edu; R. Burgmann, Berkeley Seismological Laboratory, [email protected]
berkeley.edu.
We investigate the distribution of asiesmic slip along the San Andreas and Calaveras
faults using repeating earthquake data from 1984 to 2005. We identify these repeat-
Seismological Research Letters Volume 77, Number 2 March/April 2006 205
ing earthquake sequences by cross-correlating local Northern California Seismic
Network waveforms recorded at the surface. Assuming that these repeating earthquake sequences represent a stuck patch in an otherwise creeping fault, we estimate
the minimum amount of creep necessary to load each sequence location to failure over the observation period using an empirically derived relationship between
moment and slip at the sequence location. We also study the time evolution of these
repeating earthquake sequences to determine the effects of nearby and distant larger
earthquakes on the timing of individual events within a sequence. Preliminary
results show that the distribution of aseismic slip can be extremely heterogeneous at
depth with repeating earthquake sequences located within a kilometer of each other
having significantly different amounts of total slip.
Expected Fault Displacements along the BART Concord-Bay Point Line,
Alameda and Contra Costa Counties, California
K. Kelson, William Lettis & Associates, Inc., [email protected]; S.
Thompson, William Lettis & Associates, Inc., [email protected]; E.
Matsuda, Bay Area Rapid Transit District, [email protected]
The BART Concord Line is a primary component of the San Francisco Bay regional
transportation system, and assessment of surface-rupture hazards is important for
seismic mitigation, maintenance and post-earthquake response planning. Expected
coseismic displacements where BART crosses the active Hayward and Concord
faults and the potentially active Contra Costa Shear Zone (CCSZ) were developed for scenario earthquakes (475-yr return period; 10% in 50 yr). Because of
uncertainty in how active fault creep affects earthquake recurrence and magnitude,
we used two magnitudes for the 475-yr event for each fault based on (a) existing
frequency-magnitude relations and mean values of seismic scaling factor R, and
(b) recalculating with R=1 to remove creep from frequency-magnitude relations.
Updated empirical magnitude-displacement relations constrained displacements,
which were corrected by a scaling factor related to the historic creep rate and geologic slip rate. Probabilistic displacement curves were developed for each rupture
scenario, and the distribution of slip across each fault zone was estimated based
on local geologic conditions and observations from the 1906 and other strike-slip
surface ruptures.
Information from the three fault crossings is being used to assess the safety
and operability of BART’s Concord Line. The Berkeley Hills Tunnel (BHT)
crosses the Hayward fault, which has a 300-m-wide zone of multiple fault strands
that locally deform the tunnel by aseismic creep. Surface rupture during the scenario earthquake is expected to produce 2.0 m of dextral displacement (84% cumulative probability), which will impose some extension and likely will be distributed
unequally across the fault zone. Surface rupture on the 3.5-km-wide CCSZ, located
between the Lafayette and Walnut Creek stations, may produce offset of about
2.2 m (84%) distributed on four potentially active fault strands. Dextral fault slip
locally would impose compression on some BART structures. At the Concord
fault, aseismic creep imposes dextral shear and compression over about 400 m of
track. Creep accounts for most of the long-term slip rate on the Concord fault,
such that surface rupture is expected to produce only about 0.2 m of displacement
(84%). Retrofits, focused post-earthquake response, and maintenance (for creep)
will mitigate impacts of fault displacements.
The M7.6 Kashmir Earthquake of 8 October 2005 (with
EERI)
Poster Session
Surface Ruptures and Rupture Kinematics of the 2005, Mw 7.6 Kashmir
Earthquake from Sub-pixel Correlation of ASTER Images and Seismic
Waveforms Analysis
J. Avouac, Tectonics Observatory, Caltech, [email protected]; F.
Ayoub, Tectonics Observatory, Caltech, [email protected]; S. Leprince,
Tectonics Observatory, Caltech, [email protected]; O. Konca, Tectonics
Observatory, Caltech, [email protected]; D. Helmberger, Tectonics
Observatory, Caltech, [email protected]
We report on remote sensing and teleseismic investigations of the rupture kinematics of the October 8 2005, Mw 7.6 Kashmir earthquake. Ground deformation is
measured from the sub-pixel correlation of ASTER images acquired respectively
on November 14 2000 and October 27 2005 using a novel procedure defined by
Leprince et al. (submitted) adapted from a previous approach designed for SPOT
images (Van Puymbroeck et al., 1999). We first produced two orthorectified images
using an DEM computed from an ASTER stereo pair. Each pixel in the satellite
focal plane is first projected onto a ground reference system. The images are sampled
on a common grid with a 15m resolution and offsets are measured from cross-corre-
lation of the two images. Uncertainties on the imaging system (including orbits) and
the topography lead to mis-registrations of non tectonic origin. To minimize these
artefacts the satellite viewing parameters are optimized. This process removes in part
deformation at long wavelengths, which trade-off with satellite viewing parameters,
but significantly enhance the performance of the sub-pixel correlation technique for
the measurements of deformation at short wavelengths. Our measurements reveal
a well defined surface ruptures which can be traced over a distance of about 70km.
Surface displacements indicate nearly pure thrusting with about 5m of slip on average. The earthquake reactivated the Muzafferabad and Murree faults although the
observed surface ruprures follow only approximately the trace of the previously
mapped fault trace. The reactivation coincides with a geomorphological expression
of cumulative uplift on the northern flank of the Jhellum river and Kunhar valley.
This analysis show that the rupture did reach the surface, although field evidence for
fault ruptures were scant, and provide measurements of fault slip and fault geometry
with an accuracy not achievable from field measurements. We combine this information with the analysis of teleseismic waveforms to derive some finite source kinematic
model of the rupture following the procedure of Ji et al. (2001). We use the USGS
epicenter to estimate the rupture initiation point and the Harvard moment tensor
solution to estimate the fault dip angle (39°). Waveforms and surface displacements
are computed in a layered earth model with a 1-D crustal model interpolated from
CRUST2.0 (Bassin et al., 2000). This earthquake departs significantly from the Ms
7.0 1991 Uttarkashi and the Ms 6.8 1999 Chamoli earthquake which occurred in a
similar structural position in the Garwal Himalaya but presumably as blind ruptures
along the Main Himalyan Thrust fault. The 2005 Kashmir earthquake shows that in
this part of the Himalaya crustal shortening is in part absorbed by out-of sequence
thrusting at the front of the high range. Although the significance out-of-sequence
thrusting for mountain building in the long run is uncertain elsewhere along the
Himalaya, it might be a significant source of earthquake hazard.
Location and Slip Distribution of the 2005 October 8 Kashmir Earthquake
Rupture Using Envisat SAR Analysis
E. Fielding, Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA, USA, [email protected]; E. Pathier, COMET
(Centre for Observation of Earthquakes and Tectonics), University of Oxford,
Oxford, UK, [email protected]; T. Wright, COMET (Centre for
Observation of Earthquakes and Tectonics), University of Oxford, Oxford, UK,
[email protected]
The synthetic aperture radar (SAR) on the Envisat satellite acquired imagery of the
2005 October 8 earthquake area on different tracks. Preliminary analysis of two
tracks shows that both interferometric phase and pixel-scale image offsets measure
the deformation. Combination of SAR image offsets from two tracks maps threedimensional vectors of surface displacements with a spatial resolution of about 500
meters. The 2005 main rupture involved primarily thrust motion on a NE-dipping fault with slip magnitude > 5 meters between Muzaffarabad and Balakot. The
sharp change in image-offset measurements requires large slip within < 1 km of the
surface. The down-dip extent is not yet constrained in preliminary analysis but is
roughly 10 km depth. The rupture surface location is largely coincident with faults
previously identified on geologic maps recently published by the Geological Survey
of Pakistan, and now called the Balakot-Bagh (B-B) fault system (Yeats and Hussein,
2006). Numerous landslides occurred in the hanging wall of the thrust, especially in
carbonate formations near Muzaffarabad and northwest. The B-B fault system is
aligned with the zone of seismicity recorded by the Tarbela Seismic Network in
1973-1976, called the Indus-Kohistan Seismic Zone (IKSZ), that extends some
100 km to the NW of Balakot. The vast majority of aftershocks in 2005 are located
northwest of the main rupture, building upon the high seismicity rate of the IKSZ.
The Balakot-Bagh fault system that ruptured in 2005 cuts across the Hazara
Syntaxis, a hairpin turn of the MCT and MBT structures at the NW corner of the
Himalayas. Seeber et al. (1981) and Seeber and Gornitz (1983) suggested a midcrustal ramp structure along the IKSZ that connects with the ramp described in
Nepal from active seismicity and uplift measurements. This structure would follow
the sharp increase in elevation along the Himalayan front and belt of seismicity.
The 2005 earthquake rupture indicates that, at least in the Hazara region, the active
fault reaches the surface at the steepest topographic increase. The complicated 3D
geometry of the Hazara Syntaxis, however, makes it difficult to extend lessons from
the 2005 earthquake to the rest of the Himalayan megathrust.
Surface Ruptures of the 8th October 2005 Kashmir Himalayan Quakes:
Bridges as Strain Gauges?
J. Grasso, LGIT, Observatoire de Grenoble, France, [email protected];
M. Mughal, GSP, Islamabad, Pakistan, [email protected]
Surface ruptures for the Mw 7.6 Kashmir thrust earthquake is exhibited by a range
of surface features from mild diffuse thrust rolls with 30-50 cm of vertical offset, to
2- 3 m vertical offsets recorded by surface fault scarps. Our preliminary measure-
206 Seismological Research Letters Volume 77, Number 2 March/April 2006
ments of the dip-component of reverse slip are consistent with those inferred from
seismic models for mean fault slip at depth. Evidence for a component of strike slip
faulting revealed right lateral slip amounting to 30-50% of total local slip, and are
most evident on the south-eastern section of the fault.
The inferred location of the surface rupture follows, for much of its course,
the base of a slope that runs parallel to the Jhelum river. Many bridges across the
river are perpendicular to the fault and have accommodated permanent deformations that are not apparently caused by shaking dynamics. Because there is no evidence for surface fault rupture below the bridges, the buckling of the bridges in the
horizontal plane is caused by strain contraction in surface soils and river gravels. The
bridges have acted as strain gauges. For one bridge located 500 m westward of 1 m
of vertical surface rupture, the bridge records strain contraction of 1 part in 100,
i.e. 10,000 microstrain. This exceptional strain value is larger than linear strain predicted from seismic modeling (Bouchon and Aki, 1982, Simpson et al., 1989, King
et al. 1992, Cotton and Coutant, 1996). Other observations on how earthquake
dynamics and surface faulting interact with landslides will be discussed.
Geodetic Constraints and Tectonic Implications of the Mw=7.6, 8 October
2005, Kashmir Earthquake
R. Bendick, University of Montana, [email protected]; R. Bilham,
University of Colorado, [email protected]; N. Feldl, UNAVCO, [email protected]
unavco.org; S. F. Khan, NCEG, University of Peshawar, [email protected]
com; M. A. Khan, NCEG, University of Peshawar, [email protected]
Four points of the sparse westernmost Himalaya GPS network installed in 2001 in
Pakistan were within one rupture dimension of the 2005 Kashmir Earthquake. The
closest points in the footwall were displaced NW by 8 and 56 cm respectively: two
others provide null constraints indistinguishable from interseismic deformation.
The data are consistent with mean reverse slip of more than 3 m on a main fault
with average strike of 330° ± 15°. They provide a numerical calibration of the 2D
image of coseismic surface displacements observed with InSAR amplitude analysis.
The InSAR observations are modeled as a rupture plane of 80-90 km in length, 39°
dip, minimum depth of ~1 km (near Balakot), and maximum depth of 25 km.
Coulomb stress calculations indicate that aftershocks to the NW occur in a
region of enhanced failure. Coulomb stress also increased on strike-slip faults SW
of the epicenter bringing the Jhellum and Tarbela faults closer to failure. However,
few large aftershocks occur in a similar region of increased Coulomb stress to the
SE, although this region has not failed in a large event since 1555. Regional tectonic
velocities relative to Eurasia are oblique to the cosiesmic slip direction, suggesting that
the tectonic stress field must play a significant role in modulating Coulomb stress.
The 2001-2005 velocity for Peshawar indicates north-south directed convergence of 21±2 mm/year across the plate boundary between the Pamir and
Peshawar, and an additional 8 mm/yr between Peshawar and the Indian plate at the
southern edge of the Potwar plateau. Thus if no earthquakes are missing from the
seismic record, the Kashmir earthquake has released less than half of the 8.5 m slip
deficit accumulated since 1555. Moreover, its along-strike dimension (80-90 km)
falls at least 200 km short of removing the slip deficit from the apparently mature
seismic gap south and west of Kashmir. We conclude that an Mw=8.2 earthquake
is possible in the Pakistan/Indian Himalaya, contiguous with the recent earthquake
extending SE to the Kangra 1905 Mw=7.8 rupture.
In contrast to the inferred loading in this SE region, the 2005 rupture has
effectively reduced compressive stresses in a NE/SW direction that might otherwise
have driven a detachment-type earthquake near Islamabad. However, vergence of
the thin-skinned tectonics here is orthogonal to this stress regime and it is unclear
whether, or by how long, the Islamabad region has been reprieved from a future
shallow faulting event of the sort that possibly destroyed Taxila in the first century.
Static Stress Change from the 8 October, 2005 M=7.6 Kashmir Earthquake
T. Parsons, USGS, [email protected]; R. Yeats, Oregon State University,
[email protected]; Y. Yagi, University of Tsukuba, [email protected]
tsukuba.ac.jp; A. Hussain, Geological Survey of Pakistan, [email protected]
A devastating M=7.6 earthquake shook Kashmir on 8 October 2005. We calculated static stress changes by simulating this earthquake as a slipping dislocation
in an elastic half space. We mapped Coulomb stress change on target fault planes
oriented by assuming a regional compressional stress regime with greatest principal
stress directed orthogonally to the mainshock strike. We tested calculation sensitivity by varying assumed stress orientations, target-fault friction, and depth. Our
results showed no impact on the active Salt Range thrust southwest of the rupture.
Active faults north of the Main Boundary thrust near Peshawar fall in a calculated
stress-decreased zone, as does the Raikot fault zone to the northeast. We calculated
increased stress near the rupture where most aftershocks occurred. The greatest
increase to seismic hazard is in the Indus-Kohistan seismic zone near the Indus
River northwest of the rupture termination, and southeast of the rupture termination near the Kashmir basin.
The Pattan, Pakistan, Earthquake of 1974
W. Pennington, Michigan Tech , [email protected]
On December 28, 1974, a magnitude 6.0 (mb) earthquake occurred beneath the
mountains of northern Pakistan, killing approximately 1000 people. At the time,
it was the largest earthquake recorded instrumentally in the area. The 2005 earthquake occurred immediately to the east of the 1974 rupture zone.
The 1974 earthquake happened to occur near a network of seismographs
installed about 100 km south by Lamont-Doherty Earth (then Geological)
Observatory for the Tarbela Dam. Although the aperture provided by this network
for relative locations of aftershocks was poor, portable stations established in the
epicentral area provided additional constraint on the locations of events.
The zone of aftershocks and first-motion studies of the main event indicate
that the 1974 earthquake was a thrust event, with maximum compressional stresses
oriented NE-SW. All aftershock activity was limited to depths greater than 12 km.
The rupture zone defined by the aftershocks within the first 100 days is 10 km long,
later expanding to 13 km. There was no surface rupture.
The main front of the Himalaya trends NW-SE in the area of the 2005
earthquake, and the focal mechanisms of that event correspond to faulting along a
plane trending parallel to that direction. The western syntaxial bend occurs at the
point where the aftershock zone from the 1974 event abut those of the 2005 event.
The trend of the surface structures to the west of the bend, where the 1974 event
occurred, is perpendicular to this trend. The surface geology does not reflect the
major tectonic boundaries as indicated by seismicity associated with the 1974 event
at depths of 12 km and more, which appears to continue along the main trend.
This (1974) earthquake also provided an opportunity to witness animal
behavior associated with the frequent aftershocks. In the immediate epicentral area,
sounds were frequently associated with each of the larger aftershocks and shaking
was either simultaneous with or immediately following the sound. Dogs would
bark simultaneously in response to the sound, and to sounds that were inaudible to
the human ear, but which were associated with very small aftershocks.
Surface Features of the Mw 7.6, 8 October 2005 Kashmir Earthquake,
Northern Himalaya, Pakistan: Implications for the Himalayan Front
R. Yeats, Oregon State University, [email protected]; A. Hussain,
Geological Survey of Pakistan, Peshawar Pakistan, [email protected]
The largest historical earthquake on the Indus-Kohistan Seismic Zone (IKSZ)
in Pakistan was accompanied by rupture on the 65-km-long Balakot-Bagh (BB) reverse fault, locally reactivating the Murree (Main Boundary) thrust (MBT)
in the opposite sense. The B-B fault dips NE and, near Muzaffarabad, separates
Precambrian limestone and shale on the NE from Miocene Murree Formation on
the SW. Farther SE, along the Jhelum River, the fault is entirely in Murree. Large
landslides were most severe on the hanging-wall side of the fault. Heavy damage
extended NW from Balakot where the B-B fault may be blind NW to the Allai
Valley south of Besham. ENVISAT range offsets from the COMET website suggest uplift of the hanging wall, consistent with field observations. Coulomb stress
changes show increased stress to the NW near the Indus River, location of the 1974
Mw 6.2 Pattan earthquake, and to the SE into Indian-held Kashmir, site of a possible seismic gap between this earthquake and the 1905 Mw 7.8 Kangra earthquake.
Stress modeling shows a decrease in stress toward Islamabad-Rawalpindi
and the Salt Range thrust. In India and Nepal, great Himalayan earthquakes were
assumed to nucleate on the zone of moderate seismicity that is the SE continuation of the IKSZ marked by a sharp topographic gradient between the Lesser and
Greater Himalaya beneath the Main Central thrust (MCT). These earthquakes
then propagated to the Himalayan front. In Pakistan, the MCT (Panjal thrust)
and MBT are folded into the inactive Hazara syntaxis. The IKSZ cuts across this
syntaxis to a modern syntaxis west of the Indus River.. Wallace et al. (2005) found
that the 1905 rupture did not extend SW to the Himalayan front. Large surface
ruptures on the Himalayan Front thrust around 1100 AD in SE Nepal (Lavé et al.,
2005) and questionably 1404-22 AD in Garhwal and Kumaon, India (Kumar et al.,
in press) did not accompany earthquakes that were recorded historically, although
the Indian rupture might be the 1505 earthquake. These ruptures might not be
analogous to the 1905 and 2005 earthquakes. Were they slow earthquakes?
Damage to the Engineered Constructions Due to Kashmir Earthquake of
October 8, 2005
A. Pandey, Indian Institute of Technology Roorkee, India, [email protected]
ernet.in; S. Pore, Department of Earthquake Engineering, Indian Institute of
Technology Roorekee, India, [email protected]; A. Sinvhal, Department
of Earthquake Engineering, Indian Institute of Technology, [email protected]
Northern mountainous region of India i.e. the Himalayas is known to be seismically
active. Out of the seven great Indian earthquakes (M = 8), four had occurred in
this zone. To confirm the character another event occurred on 8th October 2005
Seismological Research Letters Volume 77, Number 2 March/April 2006 207
with epicenter near Muzaraffabad in Pakistan Occupied Kashmir (POK) recording a magnitude of 7.6 on the Richter Scale. In light of the seismotectonics of the
area, this earthquake was overdue with reference to its occurrence time and size.
The vibrations of the earthquake were felt over wide stretch in India, Pakistan and
Afghanistan, even exceeding the distance of 1000 km from the epicentre. The Uri
bowl and Tangdhar bowl near the Line of Control (LoC) had suffered the greatest
damage. Many of the habitats in these regions were virtually destroyed. Shaking due
to the earthquake and the subsequent landslides blocked off several mountain roads
and highways cutting off access to the region for several days.
Extensive damage survey carried was carried out in Uri Bowl, Tangdhar Bowl,
Kamalkot region, which comprise the rural locations, along with the urban locations such as Srinagar, Baramulla, Uri (town), Handawara, Kupwara, Pattan and
Sopore. To survey the changes in landform, select hilly locations were also visited
The performance of engineered structures was expected to offer benchmarking
observations since these were designed and constructed in accordance with the
established engineering principles, byelaws and codes of practices which may not
be mandatory but certainly are recommendatory of good practices backed up by
the experiences in the past. The damages in such structures provide further insight
into their behavior, with regards their strengths and weaknesses, so that remedial
measures, if any, can be adopted as good practice in future guidelines.
The performance of engineered construction was in general found to be satisfactory only in urban areas. There was no widespread damage observed and/or
reported unlike the rural and remote areas. However, there were ample number
of isolated cases where damage ranging from non-structural cracking to the severe
structural category was observed which could be attributed to the improper planning and design considerations for an otherwise highly seismic zone IV as per IS
1893 Part I ˆ 2002. The codes of practices alone were found to be insufficient to
generate the awareness of earthquake resistant constructions and there is dire need
to address the problem at ground level of implementation.
Kashmir (Muzaraffabad) Earthquake of October 8, 2005: Damages to
Non-engineered Constructions
S. Pore, Indian Institute of Technology Roorkee, India, [email protected];
A. PandeY, Indian Institute of Technology Roorkee, India, [email protected]
in; A. Sinvhal, Indian Institute of Technology Roorkee, India, [email protected]
ernet.in.
8th October 2005 witnessed a powerful earthquake shake in the Kashmir Valley
and devastation of the environment on both sides of Line of Control between India
and Pakistan. The shallow focus event set up the tremors that covered a wide swath
in South Asia reaching Jalalabad in Afghanistan and Ahemdabad in India crossing
the states of Jammu and Kashmir, Himachal Pradesh, Punjab, Uttaranchal, Uttar
Pradesh, Delhi and Gujarat. At many villages and towns in Jammu and Kashmir,
more than 90% of the building stock was claimed by the earthquake, rendering the
people injured, disabled, and homeless. As per preliminary estimates about 1400
people were killed which include 80 army personnel; more than 7500 people suffered the fatal injuries; about 45000 houses were destroyed and more than 75000
structures were damaged, most of this damage was concentrated in the rural and
outlying areas of Jammu and Kashmir.
Damage survey conducted in the Kashmir valley, aimed at surveying damages in the region as close to the epicenter as was possible within the confines of
the Line of Control (LoC) and indicated that most of the damage that occurred
was to the non-engineered constructions which constitute more than 70% of the
total constructions in the region. Primarily the residential structures come under
this category and were found being constructed without seemingly appropriate or
adequate planning, design or execution. The damages observed ranged from minor
in nature to the total collapse of structural systems. This observation was equally
valid for the different structural systems adopted in the region. However, traditional structural forms devised by the natives, such as “Dhajji Dewari” and “Taq”
performed better in contrast to the forms of construction in vogue in the region.
Since the penultimate great earthquake dates back to 1950, a dormant period of 55
years damped the awareness of seismic hazard, which was evident from the metamorphosed construction practices in the valley.
The remote hilly locations and adverse weather conditions may be the reasons behind lack or absence of modern construction materials like cement and
widespread use of the mud mortar. The reasons for the extensive damages range
from a lack of awareness of the appropriate technology available, inappropriate
planning and choice of construction form and materials to the poor workmanship
on account of non-availability of skilled labor. It was indeed surprising in contrast
to traditional forms of construction, which reflect a better understanding of the
basic principles of seismic resistant design. Rehabilitation and reconstruction in the
region is a mammoth task and if not addressed properly would see a similar damage
scenario repeated after the next major event.
Probabilistic Seismic Hazard Assessment of Muzaffarabad, Azad Kashmir
A. Khwaja, Dept. of Earth Sciences, Quaid-i-Azam University Islamabad,
[email protected]; . MonaLisa, 2Department of Earth Sciences, Quaidi-Azam University Islamabad, Pakistan, [email protected]
Muzaffarabad is located within the Hazara-Kashmir Syntaxis in close vicinity
of many seismically active surface faults like the Main Boundary Thrust (MBT),
Muzaffarabad Fault and strike slip Jhelum Fault. Besides, gravity has indicated the
presence of the Bagh Basement Fault in the subsurface. The Indus Kohistan Seismic
Zone probably extends south eastwards beneath Muzaffarabad.
Peak ground accelerations using a catalogue containing instrumentally
recorded events of magnitude 4 and greater have been used. Seismic source regions
are modelled to establish relationships between earthquake magnitude and earthquake frequency. Since Pakistan does not have an attenuation equation of its own,
an appropriate attenuation has been selected. Seismic hazard curves have been generated based on probable Peak Ground Acceleration (PGA) for 10% probability
of exceedance for time-spans of 50 years (return period of 475 years) using the EZ
FRISK software. Twelve faults have been selected as the critical seismogenic features
and their maximum potential magnitudes determined using four regression relations. MBT with the maximum potential magnitude of 7.8 and PGA value of 0.14g
is designated as the most critical tectonic feature for the site of Muzaffarabad.
Environmental Issues Relating to the 8 October 2006 South Asia Earthquake
C. Kelly, Benfield Hazard Research Centre, [email protected]
The South Asia Earthquake of 8 October 2005 led to the loss of over 74,000 lives, a
significant number of injured and extensive damage to housing and infrastructure in
Pakistan’s North West Frontier Province and Pakistan Administered Kashmir. Part
of the earthquake damage occurred in the natural environment, including numerous landslides. Possibly more significant environmental impacts arose from the
need to dispose of debris resulting from the destruction of buildings as well as from
relief operations. In many past earthquakes, these direct and indirect environmental
impacts were not considered early in the disaster response. Failure to recognize the
direct and indirect environmental impacts associated with earthquakes often leads
to future and more severe environmental problems than should be the case.
The presentation reports on a rapid environmental impact assessment (REA)
conducted in Pakistan in the weeks following 8 October earthquake. The assessment involve input from organizations providing relief assistance as well as from the
earthquake survivors themselves. The presentation will cover the conceptual basis
for the REA, the field work conducted in Pakistan and the conclusions reached.
The presentation will also discuss the commonalities between the Pakistan findings
and other earthquakes and similar disasters.
The Kashmir Earthquake of 8th October 2005, and Landslides
A. Sinvhal, Indian Institute of Technology, Roorkee, India, [email protected]
yahoo.com; A. Pandey, Indian Institute of Technology, Roorkee, India, [email protected]; S. Pore, Indian Institute of Technology, Roorkee, India, [email protected]
The Kashmir earthquake (epicenter, 34.40°N, 73.56°E, Mw 7.6) originated within
the continent—continent collision zone of the Kashmir syntaxis. The epicentral
region, defined by the Balakot—Muzaffarabad region, is on the southern flank of
this syntaxis. This tectonic instability, together with the shaking produced by this
inter plate earthquake gave rise to gigantic landslides of unusual dimensions. These
were spread in a wide geographical extent in the rugged Pir Panjal and Shamshabari
mountain ranges and in the valleys of the meandering Jhelum, Kishan Ganga and
their tributaries. Human settlements were buried, roads were blocked, and rivers
were partly obstructed. River cuttings, road cuttings and landslides showed exposures of boulders of sandstone, limestone, shale, conglomerate of rounded and
angular boulders, cobbles, pebbles, gravel, sand, silt, clay and fine powdery materials. Approach road to several bridges were damaged due to two reasons, damage to
super structure due to rock avalanche and partial failure of slope protection work
made in random rubble stone masonry. Several types of bridges were damaged; these
included steel truss bridges, stone masonry arch bridges, and suspension bridges.
However, this kind of damage hampered the flow of traffic only on two bridges on
the Indian side of the LOC, including the famous Aman Setu. In view of the extensive damage to stone houses, bridges, and roads and due to the huge and widespread
landslides, the Uri bowl and the Tangdhar bowl have been assigned preliminary
intensity XI on the twelve point Medvedev Sponheuer Karnik (MSK) scale. The
authors carried out a detailed damage survey in the Indian Side of the epicentral
area. The paper deals with the details of the damage observed in different kinds of
structures and bring out the importance of local geological conditions in the type
and extent of damage caused in the bridges, buildings, roads and other constructions. The lessons learnt and the wisdom of using old local time proven techniques
in constructions. References: www.iitr.ernet.in/departments/EQ/eqkashmir.htm
208 Seismological Research Letters Volume 77, Number 2 March/April 2006
Earthquakes and Seismicity around the World
Poster Session
The March 6, 2005, Magnitude 5.4 Charlevoix Earthquake and Related
Seismic Activity January 2000—December 2005.
Seismicity Northeast of the New Madrid Seismic Zone and Its Implications
on the Hazard of the Area
A. Shumway, University of Memphis, CERI, [email protected]
The New Madrid Seismic Zone (NMSZ) is an approximately 100 km long zone
of seismicity that runs from northwestern Tennessee to southeastern Missouri and
is typically shown as two northeast-trending arms (dextral, strike-slip faults) with
a central connecting northwest-trending arm (thrust fault). During the winter of
1811-1812, a series of three large earthquakes occurred in the NMSZ, including a
M7-8 event on January 23, 1812 northeast of New Madrid, MO. This earthquake
is believed to have ruptured along the northern arm of the NMSZ. Based on the
estimated size of this earthquake, the rupture length of the fault plane should extend
beyond the short northern arm of higher microearthquake activity. Thirty years of
seismic monitoring in the region reveal three lineations of earthquakes that run from
New Madrid, MO into western Kentucky toward southern Illinois and Indiana.
These lineations may represent alternate locations of the January 23, 1812 M7-8 rupture and therefore are important to the seismic hazard of the area. Seismic data from
this area was obtained through catalogs from the Center for Earthquake Research
and Information (CERI) at the University of Memphis and from the University
of Kentucky. Fault plane solutions were determined from the programs FPFIT
and FPPLOT (Reasenberg and Oppenheimer, 1985) using first-motion polarities
from selected seismic events that fell on or near these three northeast-trending lineations. The initial results show strike-slip focal mechanisms with north-northeast and
northeast trending fault planes, roughly parallel to the three lineations.
Recent Microearthquake Swarms in the Yakima Fold Belt, Southeastern
Washington
A. Rohay, Pacific Northwest National Laboratory, [email protected]
The occurrence of microearthquake swarms has generally been associated with the
heterogeneous strength of the Columbia River Basalts that form the uppermost layer
of the crust (0-5 km) in southeastern Washington. The multiple, thin flows have weak
zones at the top and bottoms due to rapid cooling and/or deposition of sedimentary
interbeds. Magnitudes are generally less than M 3 and the size distribution is characterized by a high b-value above 1.0. Most of these swarms occur near the northernmost
few anticlines (Saddle Mountains and Frenchman Hills) where the basalt is thinning.
Beginning in December, 2000, microearthquake swarms have been occurring
at greater depths (near 7-11 km), near the more southern Horse Heaven Hills anticline. At this depth, the events are occurring below the basalts, near the boundary
between a thick sub-basalt sedimentary sequence and crystalline basement, based
on seismic refraction measurements. The sub-basalt sediments are estimated to
occupy the 5-10 km depth range in this area. It is apparent that the explanation for
the basalt microearthquake swarms is not valid here, but the sub-basalt sediments’
physical properties are poorly known.
The temporal occurrence of microearthquake swarms, their magnitude and
depth distributions, and focal mechanisms, are being explored to determine the
similarities and differences between basalt and sub-basalt microearthquake swarm
activity.
Shallow Seismicity of the Prince William Sound, Alaska Region (1971-2001)
D. Doser, Univ. Texas at El Paso, [email protected]; A. Veilleux, Univ.
Texas at El Paso, [email protected]
We have relocated over 6900 events occurring between 1971-2001 within the Prince
William Sound, Alaska region (59 to 62 N, 144 to 148 W) at depths < 20 km using
the double-difference technique. Nearly half the events occur at < 14 km depth, and
thus occur above the plate interface within the North American plate. Similar to
previous seismicity studies with more limited data sets, we observe concentrations of
shallow seismicity in the Tazlina Glacier region, the northern end of Knight Island,
the northern edge of Prince William Sound between Unakwik Inlet and Valdez
Arm, and the Copper River delta region. All these regions have been persistently
active throughout the 30 year study period. Seismicity in southern Prince William
Sound appears to be concentrated in clusters associated with moment-magnitude
> 4.5 events occurring since 1964. Some of the seismicity appears to be related to
mapped offshore structures showing Neogene to late Pleistocene movement.
In particular, the seismicity suggests an extension of the Kayak Island fault
zone toward the southwest. We are currently inverting first motion data to determine regional stress field variations. We also will compare the alignments of relocated epicenters with focal mechanisms/moment tensors of magnitude > 4.5 events
to obtain a clearer picture of upper plate deformation.
V. Peci, Natural Resources Canada, Geological Survey of Canada, [email protected]
nrcan.gc.ca; J. Drysdale, Natural Resources Canada, Geological Survey of
Canada, [email protected]; S. Halchuk, Natural Resources Canada,
Geological Survey of Canada, [email protected]; A. Bent, Natural
Resources Canada, Geological Survey of Canada, [email protected]; S.
Hayek, Natural Resources Canada, Geological Survey of Canada, [email protected]
seismo.nrcan.gc.ca.
The Charlevoix seismic zone is the most seismically active region of eastern Canada
experiencing earthquakes greater than magnitude 6 in 1663, 1791, 1860, 1870, and
1925. The zone, located 100 km north of Quebec City along the St. Lawrence River
valley, has been monitored using a microseismic array since 1977.
On March 6, 2005, a magnitude 5.4 mN earthquake occurred at the northern edge of the Charlevoix seismic zone. It was felt throughout most of southern
Quebec and parts of the northeastern United States with a maximum intensity of
V. A thrust-fault mechanism, along a N-S trending nodal plane was determined
for the event. This mechanism is consistent with many other earthquakes that have
occurred within the zone. The average focal mechanism solution is strike 184, dip
65, rake 51.
Three methods have been applied to determine the focal depth of the main
shock: free depth calculation; regional depth phase method; and focal mechanism
solution depth estimate. The best overall depth determination is 14 km.
A series of 53 aftershocks were recorded in 35 days following the event with
the largest aftershock registering 2.3 mN. They occurred in a 6.6 by 4.4 km ellipse
with the long axis parallel to the St. Lawrence River. Depths ranged from 12 to
19 km. Using this aftershock sequence a correlation between ML and mN magnitude was calculated.
Examination of seismic activity in the Charlevoix seismic zone from January
2000 to December 2005 revealed that 1284 earthquakes were located, ranging in
magnitude from -1.0 to 5.4. Depths, using free depth calculations, ranged from 4 to
24 km, with most depths in the 8-15 km range. Epicentres were distributed in a 33
by 90 km ellipse with the long axis parallel to the river. The magnitude-recurrence
curve for the period gives a b value of 0.92 ± 0.15.
The 26 July 2005 Mw 5.6 Dillon, Montana Earthquake
M. Stickney, Montana Bureau of Mines & Geology, [email protected]
Abstract On 26 July 2005 at 04:08 UTC a magnitude 5.6 earthquake occurred
16 km north of Dillon in SW Montana. Intensity VI shaking at Dillon caused damage to some masonry structures; up to 60% of older chimneys were damaged. A
USGS strong motion instrument on the UM Western campus in Dillon recorded
a peak horizontal acceleration of 12.7% g. An Interstate 15 overpass 6.5 km southwest of the epicenter experienced sheared anchor bolts and spalled concrete but
remained in service. Ground cracks unrelated to primary faulting formed in alluvial soils 3 km SW of the epicenter and rock fall from steep slopes 10 km NE of
the epicenter was reported. The Community Internet Intensity Map received over
3800 reports from throughout western Montana and surrounding states; more than
60% came within two hours of the main shock. The main shock occurred 10.5 km
below the surface and was followed by over three thousand aftershocks including a
magnitude 4.2 that followed 35 hours later. A P-wave first motion fault plane solution determined from the Montana Regional Seismograph Network and moment
tensor solutions by the USGS, Harvard University, and St. Louis University for
the main shock all indicate oblique normal faulting with ENE-WSW-directed
extension, consistent with the regional stress field. The fault plane solutions and
aftershock hypocenter distribution suggest that the north-trending, east-dipping
nodal plane represents the fault plane. Most aftershock hypocenters lie between
7 and 15 km deep. Most early, large aftershocks lie along the inferred fault plane
but later aftershocks occupy a wedge-shaped volume in the upper crust directly
above the inferred fault plane. The Dillon earthquake occurred on a previously
unknown fault that apparently lacks surface expression. The 26 July 2005 event
provides a well-documented example of a damaging, background earthquake on a
blind structure in the Intermountain Seismic Belt. A new broadband seismograph
station (DLMT) installed in cooperation with the USGS on top of the aftershock
zone on August 12 has significantly improved hypocenter locations for the ongoing
aftershock sequence.
The Damas (Mw 6.4), Costa Rica, Earthquake, of November 20, 2004;
Aftershocks and Slip Distribution
J. Pacheco, UNAM, Instituto de Geofísica, [email protected]; R.
Quintero, OVSICORI-UNA, [email protected]; F. Vega, OVSICORIUNA, [email protected]; J. Segura, OVSICORI-UNA, [email protected];
Seismological Research Letters Volume 77, Number 2 March/April 2006 209
W. Jiménez, OVSICORI-UNA, [email protected]; V. González,
OVSICORI-UNA, [email protected]
The earthquake of November 20, 2004 was located north of Damas Island in the
Pacific coast of Costa Rica, within the Costa Rica Deformed Belt. The earthquake
was located at 24 km depth and reported with a magnitude (Mw) of 6.4 and a strikeslip mechanism with a large normal dip-slip motion. This mechanism agrees with
mapped faults in the area that suggest transtensional deformation on the fore arc
and the entire western boundary of the Panama micro-plate. Aftershock locations
do not delineate a preferable plane to distinguish between the two nodal planes,
and are distributed between 15 and 25 km depth. The slip distribution during the
main shock, modeled after teleseismic and local data, pictured a circular rupture
8 km in radius and 0.25 m of average displacement. The fault plane cannot be distinguished from the two nodal planes from the slip distribution due to the lack
of directivity and resolution for this magnitude earthquake. Weak evidence from
empirical green’s function analysis suggests that the dextral NW-oriented fault was
the causative fault. Depth to the top of the slab, hypocenter location of the main
shock, its slip distribution, depth distribution of the aftershocks and Quaternary
fault activity at the surface suggest that deformation takes place throughout the
whole thickness of the crust. This extended deformation might be caused by seamount subduction and strong basal friction on the upper plate, due to subduction
of a thick, young and buoyant oceanic plate, rough seafloor and under-plating of
large seamounts.
The 2004 December 23 M8.1 Macquarie Earthquake
K. Murphy, Boston University, [email protected]; R. Abercrombie, Boston
University, [email protected]; M. Antolik, Quantum Tecnology Services, Inc., [email protected]
The 2004 M8.1 Macquarie earthquake occurred to the west of the strike-slip
Macquarie ridge. It was the largest earthquake of 2004, until the Sumatra-Andaman
earthquake three days later. We investigate the source process to improve our knowledge of how oceanic faults slip and whether they differ significantly from large continental strike-slip faults, such as the San Andreas. Our goal is to determine the
fault plane and details of the rupture process. Slip in oceanic lithosphere is not well
understood. It is not clear what proportion of slip on oceanic strike-slip faults is
aseismic, and at what depth most seismic slip occurs. There is debate about whether
oceanic earthquakes begin with slow slip, have high or low radiated energy, or
rupture unusual fault geometries. Although oceanic earthquakes are controversial,
comparison with continental earthquakes could help us better understand factors
governing both. Few oceanic strike-slip earthquakes have been studied in detail, so
analysis of the 2004 earthquake provides important new data on the source process
and greater insight into the tectonics of this complex region.
The Macquarie Ridge Complex is very seismically active. Most seismicity
occurrs along the ridge, but there is significant intraplate seismicity in the area
as well, including the 2004 earthquake. The Mw8.1 earthquake in 1989 was well
studied, but the depth, stress drop, and possibility of a slow slip component remain
poorly constrained. We analyze the 2004 earthquake and aftershock sequence, and
compare them to the 1989 earthquake. We model teleseismic broadband body
waves of the 2004 mainshock and the largest aftershock (3 January 2005, Mw6.0)
recorded by GSN and Geoscope to constrain the focal mechanism, depth, fault
plane, and seismic moment. Bathymetric features appear to be oriented in both
nodal plane directions. Aftershock alignment suggests that left-lateral slip occurred
on the northwest-striking nodal plane. Investigation is ongoing, and future work
will include an inversion for slip distribution.
The Pulumur and Bingol Earthquakes of 2003 Provide Evidence for the
Internal Deformation of the Karliova Block between the North Anatolian and
East Anatolian Faults
L. Gulen, Massachusetts Institute of Technology, Cambridge, MA 02139,
[email protected]; D. Kalafat, Kandilli Observatory and Earthquake Research
Institute, Bogazici University, Istanbul, Turkey, [email protected]; A. Pinar,
Dept. Geophysical Engineering, Istanbul University, Avcilar, Istanbul, Turkey, [email protected]; Y. Gunes, Kandilli Observatory and Earthquake Research
Institute, Bogazici University, Istanbul, Turkey, [email protected]; S. Kuleli,
Massachusetts Institute of Technology, Cambridge, MA 02139, [email protected];
M. N. Toksoz, Massachusetts Institute of Technology, Cambridge, MA 02139,
[email protected]
The right-lateral strike-slip North Anatolian and the left-lateral strike-slip East
Anatolian Faults form the tectonic boundaries of the Anatolian Block which
escapes westward with a counter-clockwise rotation based on the GPS measurements in Turkey. The Karlıova Block occupies the eastern tip of the Anatolian
Block and it is situated between the Ovacık Fault and the Karlıova Junction. Two
major earthquakes occurred along previously unknown faults that are conjugate
to the North Anatolian and East Anatolian Faults within the Karlıova Block and
within a three months time span. The focal mechanism of the Pülümür Earthquake
(Mw=6.1) of Jan. 27, 2003, along with the alignment of the aftershocks in the NESW direction, gives dominantly left-lateral strike-slip faulting with minor thrust
component indicating a fault plane dipping with 80° angle to the southeast. This
fault plane is a conjugate to the North Anatolian Fault and the epicentral location
is 15 km away from the North Anatolian Fault. The earthquake source process
analysis utilizing teleseismic data suggest that the fault rupture propagated bilaterally, but asymmetrically and the propagation direction was skewed towards the SW
with an inferred total seismic moment of 1.15 x 1018 Nm. The Bingöl Earthquake
of May 1, 2003 (Mw=6.4) also occurred along a previously unknown fault that is
conjugate to the East Anatolian Fault within the Karlıova Block. The epicentral
location is 15 km away from the East Anatolian Fault trace and the focal mechanism together with the aftershock distribution indicates a predominantly right-lateral strike-slip earthquake. The fault plane has a strike of N26°W with a dip of 89°.
Additionally the recently established seismic stations in this region have made the
detection of microseismicity possible and have improved the earthquake location
accuracy. As a result the Kığı active fault zone which is also a conjugate fault to the
North Anatolian Fault within the Karlıova Block has been delineated. All these
newly identified active fault zones within the Karlıova Block indicate that the internal deformation of crustal blocks takes place at the front of the Arabian-Eurasian
continental collision zone and that the strain is released not only by earthquakes on
major fault zones, but also by earthquakes on their conjugate faults.
Seismic Activities of an Intra-continental Strike-slip Fault System:
Kuhbanan Fault, Central Iran
M. Shahpasandzadeh, International Institute of Earthquake Engineering
and Seismology, [email protected]; A. Shafiei, Islamic Azad University,
[email protected]
Central Iran is consisted of a mosaic of various tectonic blocks, known as Yazd,
Tabas, and Lut blocks from west to the east. Most of the seismic deformation has
been concentrated within the deformational zones among these “rigid” blocks.
About 20-25 mmyr-1 of the present-day shorting because of Arabia-Eurasia convergence, represented as N-S shear in eastern Iran, would be taken up as about
100-125 km of right-lateral slip on the faults east and west of Lut block. A few
earthquakes have been documented on the Kuhbanan fault zone, as the western
boundary of the Lut block with more than 300 km length, due to the sparse low
population and high distance from the trade routes. However, the Kuhbanan fault
has been associated with three earthquakes of Mw= 5.9- 6.4 in the 20-21st centuries as well as at least five catastrophic historical earthquakes. As the recent seismic
activity of this fault, the 22 February 2005 Zarand (Mw 6.4) earthquake ruptured
about 10 km of the Kuhbanan fault, with an average vertical slip of 80 cm but with
surface displacements up to 110 cm in places. Analysis of long-period seismic body
waves shows that the earthquake ruptured a reverse fault dipping north at ~110 °
to a depth of about 14 km. Two earlier large earthquake of the 19 December 1977
Bob-Tangol (Mw 5.9, I0~ VII+) and 28 November 1933 Bahabad (Mw 6.5) devastated various segments of the fault. The 1977 Bob-Tangol earthquake, occurred not
far from the region where the 1896 and 1933 earthquakes occurred; These latter
earthquakes were associated with about 19.5 km of right-lateral ruptures north of
Zarand, but with very small vertical and right-lateral displacements of up to 7 and
20 cm, respectively. The much larger 1933 Bahabad earthquake produced about
10 km of discontinuous right-lateral surface displacement. This devastating earthquake was followed by the earthquake of 24 May 1978 on the west of Behabad.
Among documented historical earthquakes, the 27 May 1897 Qobeh-e-Sabz
(Mw 5.4, I0~ VII+), the 27 May 1896 Chatrud (Mw 5.3, I0~ VII), the May 1875
Kuhbanan (Mw 6, I0~ VII+), the 4 August 1871 Chatrud (Mw 5.9, I0~ VII+),
and the 17 January 1864 Chatrud (Mw 5.9, I0~ VII+) earthquakes constitute the
prominent events of Kuhbanan fault activities.
Fault Segment with a Maximum Offset of 10-meter in the 1931 Fuyun Surface
Rupture, NW China—An Interim Report
Y. Awata, Geological Survey of Japan, [email protected]; B. Fu, Institute of
Geology and Geophysics, Chinese Academy of Sciences, [email protected]
ac.cn.
The M 8.0 Fuyun earthquake of August 10, 1931, on the western foot of the Altay
Mountains, NW China, was reported that the surface rupture produced by the
earthquake have a world-largest offset of 14.6 m. We have been re-investigating
the details of fault geometry, and amount and distribution of slip on the rupture,
to reveal the scale of maximum fault segment. Every part of the rupture has been
mapped using handy GPS. A set of high-resolution satellite image is also very helpful for field survey and mapping the strand. In 2004 and 2005, we have mapped
a 50-km-long northern central section of the NNW-SSE striking, 180-km-long
rupture, and made offset measurements at 430 sites. The maximum displacement
210 Seismological Research Letters Volume 77, Number 2 March/April 2006
is 10 m in right-lateral component and 2 m in normal-dip-slip component, on average along a 2-km-section in a 36-km-long segment. The rupture gradually decreases
the amount of displacement from 8 m to 2 m along a 10-km-long northern section
of the segment,, and is separated by a gap of 1km-long from a 15-km-long segment
on the north. Along a 10-km-lomg southern section, the rupture consists of a few
several hundred meter-wide fault zone, where slip is partitioned into a strand with
predominant-right-lateral slip and a strand with reverse-dip-slip. This 36-km-long
segment is separated from southern segment by a 6-km-long and 2 to 4-km-wide
area, where the rupture partitions into reverse-right-lateral, normal-right-leteral
and normal fault strands. The southern segment boundary occurs at a junction with
Paleozoic fault in the Altay Mountains. There is no clear difference between the
ratio of maximum displacement and length of studied segment and those of wellstudied rupture segments in the world.
Preliminary Understanding of the Dynamics of the 1999 Chi-Chi Earthquake
X. Chen, Peking University, [email protected]; H. Zhang, Peking University,
[email protected]
The 1999 Chi-Chi, Taiwan, earthquake (Mw7.6) is the most destructive and largest
earthquake occurring in Taiwan in the last century. Moreover, it is one of the most
well-recorded earthquakes in history. More than 600 digital strong-motion observations as well as more than 40 GPS stations in the vicinity of the focal region provided
unprecedent detail of the earthquake process. Post-seismic survey revealed that surface ruptures from the mainshock extended about 85 km along the Chenglungpu
fault with a significant static offset up to ~8 m. Numerous studies have been focused
on this event. Far-field data, near-source strong-motion records, as well as GPS data
are used to invert the rupture process of the event. Although the details are not
exactly the same in different studies, gross features are identical, such as the rupture
did not start to propagate outward significantly after some time (about 6 sec) and
the slip on the fault in the north is much larger than that in the south.
In this study, we performed a fully dynamic simulation by using an extended
boundary integral equation method (BIEM) for half-space medium model, which
is suitable to solving boundary problems with a concentrated stress distribution.
Although both the geometry of the fault and the prestress in the focal region is
rather complicated, we assumed a very simple model (planar fault in an elastic half
space) to investigate the asymmetrical geometry of the fault and the effect of free
surface. Effect of the non-planar geometry is carefully replaced by uniformly distributed shear strength and initial stress and no other heterogeneity is included.
Numerical results showed that although the model is extremely simple, main feature of the mainshock, such as the rupture history and the final slip distribution,
can be well reproduced. This result may help to gain insight into the effect of the
asymmetry of the fault geometry on the dynamic rupture process.
Estimation of Frequency-magnitude Distribution Based on Interevent-time
Statistics
S. Hainzl, Institut fuer Geowissenschaften, University of Potsdam, Germany,
[email protected]; F. Scherbaum, Institut fuer Geowissenschaften,
University of Potsdam, Germany, [email protected]; C. Beauval,
Géosciences Azur, Valbonne, France, [email protected]
The statistics of the time delays between successive earthquakes has been recently
claimed to be universal and to show the existence of clustering beyond the duration
of aftershock bursts. We show that neither of them is true. By analyzing the interevent-time distributions on different spatial and magnitude scales in California,
we find that the shape of the distribution is correlated to the percentage of mainshocks in the region which varies between 10% and 90%. Additionally, we analyze
simulations of the Epidemic Type Aftershock Sequence (ETAS) model which only
consists of a Poissonian background activity and triggered Omori type aftershock
sequences. We find that these simulations reproduce the observed interevent-time
distributions showing that the empirical distribution can be explained without any
additional long-term clustering. Furthermore, the investigation of the ETAS simulations indicates that the mainshock distribution can be better estimated through
the interevent-time distribution than with standard declustering algorithms.
Moderate and Large Earthquake Activity along Oceanic Transform Faults
T. VanDeMark, Penn State, [email protected]; C. Ammon, Penn
State, [email protected]
Oceanic transform faults provide an excellent opportunity to explore strike-slip
faulting processes in a relatively simple, but seismically productive faulting environment. Key parameters such as overall boundary geometry, plate age, and long-term
slip rates are readily available. A number of transforms are quite active and provide
plentiful data to investigate the effects of event clusters in time and space, and possibilities of earthquake interaction. The main drawback in such an investigation is
the near total lack of local observations necessary to produce high-quality event
locations, needed to complete detailed investigations. To circumvent this problem, we use a double-difference relocation method exploiting intermediate-period
Rayleigh waveforms to estimate precise relative earthquake centroids for moderate
and large magnitude events. Although a formal estimate of uncertainty is difficult
to demonstrate, direction examination of the observed time shifts and geometric
consistency suggest that many relative locations are accurate to better than five kilometers. The number of events available on each transform varies and the constraints
are best during the last 15 years, a time corresponding to the installation of the
current Global Seismic Network. We estimated improved relative locations for a
total of 130 strike-slip events that occurred along the Romanche and Challenger
transform fault systems. We observed spatial clustering of seismicity separated by
possible aseismic gaps along each transform. To complement these observations
made over a short observation time (about 15 years), we also investigated seismicity
patterns using earthquake catalogs. We examined 862 strike-slip events from the
Harvard CMT catalog distributed across 30 transforms accommodating movement
over a range of relative plate velocity (V) to investigate the moment distribution
along oceanic transforms. We compare the observed moment distribution with a
simple uniform distribution estimated using NUVEL-1A. We estimate the fraction of asesimic motion for each transform using the ratio of observed to predicted
cumulative seismic moment for each transform. All transforms with V ≥ 7.0 cm/yr
have are approximately 90% aseismic; transforms with a V < 7.0 cm/yr have apparent aseismic fractions of about 80%. Slower moving transforms, (V < 7.0 cm/yr)
have hosted all earthquakes of M ≥ 6.5. For Gutenberg-Richter analysis of the same
events, we classified the transforms into three groups based on their associated relative plate offset speeds, V (0.0 to 3.9 cm/yr, 4.0 to 7.9 cm/yr, and ≥ 8 cm/yr). We
find that as V increases, both the G-R slope and the corner magnitude decrease.
An examination of the USGS earthquake catalog suggests that foreshock and aftershock sequences are rare for oceanic transform events M ≥ 6.0, with the exception
of events along the Romanche Transform, which has aftershock sequences for 11
of 13 recent events. We are exploring the observed patterns in seismicity in concert
with more modern precise locations to investigate rupture and plate motion accommodation along these tectonically important structures.
Theory of Transform-fault Trends
H. Rance, QCC of CUNY, [email protected]
Transform faults linking ridge segments between two plates are typically modeled
as being small circles about a Euler pole of rotation. However, spherical shells under
torsion do not break this way.
Variability of Atmospheric Circulation—an Initiator of Strong Earthquakes
V. Bokov, RSHU, [email protected]
Several symposiums took place some years ago and the decision about impossibility of
short-term forecasting of earthquakes was made, and consequently in many countries
the scientific programs of this direction were closed. However it was a mistake, as the
problem is solved by its wider consideration. At the same time in Russia for several
years exists a site http://quake_vnb.rshu.ru, on which in an operative mode the skilled
short-term forecasts of earthquakes with the justifience about 70 % are exposed. The
given forecasts are developed on a basis of a seismo-synoptic method. The change of
circulation of an atmosphere is the basic rule of the given method, on which the shortterm forecasts of earthquakes are made [1-3]. The basic mechanisms of initiation by
an atmosphere of strong superficial earthquakes are submitted in the report. Also the
analysis of synoptic situations before strong earthquakes with M > 6 for several seismically active regions of the Earth is given. The variability of atmospheric circulation
influences the occurrence of the basic harbingers of earthquakes (allocation of lithosphere gases, a change of spatial intensity of radon, changes of a level of earth waters,
acoustic noise etc.). At the same time the analysis of synoptic conditions points out
precisely on occurrence of the specified harbingers, and also allows defining a place,
time and force of earthquake. The revealed functional dependence carries universal
character for all seismic regions of the Earth. Seismo-synoptic method is intended for
the forecast of strong earthquakes, but it also allows predicting moderate earthquakes.
The statistical estimations of justifience of short-term earthquakes for 3 years are presented in the report. 2347 earthquakes with magnitude from 4 up to 7 were predicted
during this time, from which 1641 were justified. The forecasts of last destructive
earthquakes Iran 2002, Algeria 2003, Morocco 27 of May 2003, Japan 23 of October
2004, California 4 of January 2006 and some others are also presented. The earthquakes of 26 of December 2004 & 28 of March 2005 at Sumatra were “obvious” 2-3
days beforehand. An estimated area of the earthquake was huge for the power of the
atmospheric processes was great. So the forecast was postponed for one day to find the
exact place of the epicenter. And on the 25 of December it was exhibited on the site.
1. Bokov V.N. Prospects of use of Solar-atmospheric connection in forecasting
the seismicity of Earth. // News of RGS of RAS, 2000. v.132,ed.4. p.38-46. 2. Bokov
V.N., Sytinskii ?.D. The operative short-term forecast of earthquakes on a basis of
a seismo-synoptic method (results of annual test). // Moscow, Russia Ministry of
Seismological Research Letters Volume 77, Number 2 March/April 2006 211
Emergency Situtation, Scientific—practical conference “ Problems of forecasting of
extreme situations and their sources “ on July 26-27 2001, Reports and statements,
p. 34-39. 3. Bokov V.N. Variability of atmospheric circulation—initiator of strong
earthquakes. // News of RGS of RAS, 2003. v.152, ed.6. p. 31-40.
One Hundred Years and More: Historical Instruments and
their Recordings of Earthquakes
Poster Session
SeismoArchives at the IRIS DMC: Seismograms of Significant Earthquakes
of the World
R. Benson, IRIS Data Management Center, [email protected]; W. Lee,
USGS, [email protected]; T. Knight, IRIS Data Management Center, [email protected]
iris.washington.edu; B. Hutt, USGS, [email protected]; T. Ahern, IRIS Data
Management Center, [email protected]
SeismoArchives at the IRIS DMC: Seismograms of Significant Earthquakes of
the World The SeismoArchives are being constructed under the auspices of the
Committee for the SeismoArchives Project of the International Association
of Seismology and Physics of the Earth’s (IASPEI), in collaboration with the
Data Management System (DMS) of the Incorporated Research Institutions for
Seismology (IRIS). The main purpose of these online SeismoArchives is to preserve
scanned images of seismograms and related materials of significant earthquakes of
the world in computer data files so that they are readily accessible online as source
materials for research. In constructing an earthquake archive, we attempt to host
relevant data and information of that earthquake in one website. Because no funding is yet available for constructing these SeismoArchives, we depend on volunteers
and donors of data files and/or financial support for scanning analog recordings of
seismograms that dated back to 1882. Although the IRIS DMC has been managing modern digital seismogram data since the 1980s, the bulk of the seismograms
recorded by seismic observatories and networks for over 100 years are in analog
form on either paper or microfilm. This poster will highlight the holdings currently
available at the IRIS Data Management Center (DMC), describe access methods,
(whether by individual earthquakes or by special projects), and provide information
about how to contribute to this important collection.
TESEO2: Turn the Eldest Seismograms into the Electronic Original Ones
S. Pintore, Istituto Nazionale di Geofisica e Vulcanologia, [email protected]; M.
Quintiliani, Istituto Nazionale di Geofisica e Vulcanologia, [email protected]
it.
Historical seismograms contain a rich harvest of information useful for the study of
past earthquakes. This requires proper digitization of the analog records if modern
analysis is sought. The digitization procedure usually involves the extraction of the
sample sequence directly from the image and, successively, a correction mapping
from the (x,y) image coordinates to the amplitude and time of the samples. We present here a different digitization approach that relies on an intermediate parametric vectorial representation of the seismogram trace using piecewise cubic Bezier
curves. Our proposed workflow standardizes the historical seismograms vectorization process into various stages insuring proper quality control. We have developed
a software for seismogram digitization/vectorization named Teseo2 within the
Sismos project (Michelini et al., Eos, Vol. 86, No. 28, 12 July 2005). Teseo2 is a
plug-in for GIMP—a multiplatform photo manipulation tool—that extends its
functionalities for seismological studies. Teseo2 allows primarily for:—additional
operations on the vectorized trace (i.e. resampling and alignment)—supervised vectorization algorithms (color weighted mean)—features of post-analysis of the trace
(curvature correction, time realignment)—trace import/export in several formats
(such as SAC, SVG, DXF, ASCII, Timemarks distances). In order to keep track of
the stages and parameters of a seismogram vectorization, Teseo2 is able to write this
information into the image saved in XCF format. Teseo2 is developed following the
“Open-Source” philosophy and it is freely distributed under GPL license. Finally, it
is cross-platform and the sources, the binaries for Linux, Windows and Mac OS X,
are periodically provided on the Sismos web site.
Monitoring Earthquakes Since 1887: The Berkeley Seismographic Stations/
Seismological Laboratory
R. Uhrhammer, UC Berkeley, [email protected]; M. Hellweg,
UC Berkeley, [email protected]; B. Romanowicz, UC Berkeley,
[email protected]
Holden of UC Berkeley. Now, the Berkeley Seismological Laboratory’s (BSL) network of stations continues to record earthquake signals in observatory mode and
thus provides the longest continuous earthquake archive in the U.S, which includes
seismograms of the 1906 San Francisco earthquake. Shortly after the earthquake,
the Ewing seismographs were replaced with more modern Wiechert instruments,
and the BSS/BSL developed its operating philosophy: to use the best instruments
and best observational practice available, to record and archive earthquake data
continuously, and to maintain a close relationship between research and the network operations. Over the years, the number of stations increased to about 50 and,
as seismic metrology evolved, the instrumentation has changed in stages from the
original inertial pendulums recording on smoked paper to the modern force feedback seismometers coupled to high-resolution digital data loggers. Of the 50 stations, 28, which form the Berkeley Digital Seismic Network (BDSN), are equipped
with very broadband seismometers and strong motion accelerometers. Data transmission has also evolved from postal delivery of paper and film records to analog
telemetry to the current digital telemetry. The continuous operation of seismic stations starting in the early 1900s provided the first reliable catalog of earthquakes in
and around Northern California. The Bulletin of the Seismographic Stations, first
published in 1910, reported on earthquakes until 1992, when it was replaced by online publication of earthquake data through the Northern California Earthquake
Data Center (NCEDC), operated jointly by the BSL and the USGS/Menlo Park.
Since 1999, a systematic effort has been underway to characterize the spatial and
temporal evolution of the Northern California seismicity during the initial part of
the earthquake cycle as the region emerges from the stress shadow of the great 1906
San Francisco earthquake. The effort involves reading of the seismograms, transcription of the reading/analysis sheets, and application of modern analytical algorithms
towards the problem of determining the location and magnitude of the historical
earthquakes in a uniform and internally consistent manner.
Seismic Recording and Instrumentation at the Hawaiian Volcano
Observatory
J. Nakata, USGS Hawaiian Volcano Observatory, [email protected]; P.
Okubo, USGS Hawaiian Volcano Observatory, [email protected]; R.
Koyanagi, USGS Hawaiian Volcano Observatory, [email protected]
For nearly 100 years, the Hawaiian Volcano Observatory (HVO) has operated seismographs for the study of active volcanism. These instruments have produced a vast
collection of recordings of volcanic events or unrest related to magma movement.
Seismograms of numerous tectonic events of interest, both local and teleseismic,
including the 1975 Kalapana M7.2, are also part of the archived collection.
The earliest recoverable seismograms, dating back to mid-1913, are smokeddrum records from instruments installed by Thomas A. Jaggar, founder of HVO.
The instruments, operated in the Whitney Laboratory of Seismology, included a
long-period Omori, installed for teleseismic detection, a two-component BoschOmori, and a three-component, self-starting Omori. The horizontal Bosch-Omori,
used for ground-tilt measurement, operated until the Uwekahuna watertube installation in the early 1960’s.
Network operations were established in1950, using drum recordings from 5
stations sites: Hilo, Kona, Mauna Loa and two Kilauea Summit sites. The number
of stations in the network increased over the years as recording capabilities evolved
from drum paper, to film, to FM magnetic tape, to digital recording systems.
Geologic and seismic monitoring interests requiring broader network coverage also
influenced network growth. Now, HVO maintains an extensive seismic network
of field sensors. Eighty-nine ground motion components, vertical only or multiple-component combinations, at 48 sites make up the current seismic network.
Seismograms presented in digital form are examined daily for routine processing
on computer workstations, building the HVO catalogs of Hawaiian seismicity.
Data from an array of 30 broadband components around Kilauea summit and from
broadband and low-gain units, installed around the island, are also examined and
archived for events of interest.
The seismograms are stored within the observatory building and in a humidity-controlled warehouse. Archived formats include drum recordings (photographic, ink, and heat stylus), magnetic media (9-track, 1-inch Bell and Howell,
magneto-optical disk, Digital Audio Tapes) and 16-mm Develocorder films. The
digital preservation of the drum recordings is an ongoing concern. Cost, manpower
and the condition of the records are problematic factors delaying an effort to preserve the deteriorating analog records.
74 Years of Southern California Earthquake Catalog
K. Hutton, Seismological Laboratory, California Institute of Technology,
[email protected]; E. Hauksson, Seismological Laboratory, California
Institute of Technology, [email protected]; L. Jones, Pasadena Field
In 1887 the first seismographic stations in the Western Hemisphere were installed
at the astronomical observatories at Mt. Hamilton and Berkeley by astronomer E.S.
212 Seismological Research Letters Volume 77, Number 2 March/April 2006
Office, U.S. Geological Survey, [email protected]; D. Given, Pasadena Field
Office, U.S. Geological Survey, [email protected]
The southern California earthquake catalog, covering 74 years from 1932 to the
present, is one of the longest instrumental earthquake catalogs in the world. Many
instrumental and data processing changes have occurred over the time period of
operation. For example, the number of stations recorded by the Southern California
Seismic Network grew from 4 stations in 1932 to about 380 stations in 2006, while
the detection treshold decreased from about M3.5 to below M1.8 (depending on
local station density). The number of earthquakes detected per year increased from
a few hundred to over 12,000 (in a quiet year). Location errors shrank from several
km (or more) to several hundred meters. Local magnitudes (ML) have improved
due to the increased number of stations and better azimuthal coverage. Moment
magnitudes (Mw) have been introduced, as well as other magnitude types (Md and
“Mh”) that allow reliable magnitudes for earthquakes of all sizes. In this poster, we
review the history of the instumentation and data processing aspects of the catalog,
the status of catalog improvement projects, and the seismicity itself.
MMI Attenuation and Historical Earthquakes in the Basin and Range
Province of Western North America
W. Bakun, U S Geological Survey, [email protected]
Earthquakes in central Nevada (1932-1959) were used to develop a modified
Mercalli intensity (MMI) attenuation model for estimating moment magnitude M
for earthquakes in the Basin and Range province of interior western North America.
Intensity magnitude MI is 7.4-7.5 for the 26 March 1872 Owens Valley, California,
earthquake and MI is 7.5 for the 3 May 1887 Sonora, Mexico, earthquake. MMI
at sites in California for earthquakes in western central Nevada apparently are not
much affected by the Sierra Nevada, except at sites in and near the Sierra Nevada
where MMI is reduced. This reduction in MMI is consistent with a shadow zone
associated with the root of the Sierra Nevada. In contrast, MMI for earthquakes
located in the eastern Sierra Nevada near the west margin of the Basin and Range
are greater than predicted at sites in California. These greater MMI values may
result from critical reflections from layering near the base of the Sierra Nevada.
A Modern Re-examination of the Locations of the 1905 Calabria and the 1908
Messina Straits Earthquakes
A. Michelini, INGV, Roma, Italy, [email protected]; A. Lomax,
Anthony Lomax Scientific Software, [email protected]; A. Nardi, INGV, Roma,
Italy, [email protected]; A. Rossi, INGV, Roma, Italy, [email protected]; B. Palombo,
INGV, Roma, Italy, [email protected]; A. Bono, INGV, Roma, Italy, [email protected]
it.
Reliable estimates of the locations of large historical earthquakes is critical for the
evaluation of seismic hazard. In this work we focus on hypocentral relocation of
two large events—the 1905 Calabria and the 1908 Messina Straits earthquakes.
Both events occurred in Southern Italy, featured similar maximum intensities (XI
MCS) and resulted in extensive damage and, in 1908 especially, many fatalities.
The data used in this work consists of the world-wide phase data prepared and
published by Rizzo in 1906 and 1910 for the two earthquakes. In addition, for
the 1908 event we have re-interpreted the Taranto station waveforms using the
scanned images of the original seismogram that are available in the INGV Sismos
earthquake database (http://sismos.ingv.it). For relocation of these two events we
use the fully non-linear, probabilistic earthquake location algorithm NonLinLoc
(Lomax, 2005; http://www.alomax.net/nlloc). We obtain multiple locations using
different assumptions on the errors and phase identifications for the reported readings. This process allowed us to investigate fully the resolving power of the data
set and the uncertainty in the resulting locations. Our preferred solution for the
1905 earthquake is about 30 km offshore of the Calabrian coast to the west of Capo
Vaticano. Our preferred solution for the 1908 event is in the southern part of the
Messina Straits mear the Calabrian coast. This latter result is consistent with previous investigations of the extension of the causative fault and with the northwards
direction of rupture determined by Pino et al. (2000) . Overall, this study shows
that application of modern and robust techniques can be extremely useful in the
investigation of past historical events and underlines the importance of preserving
historical data as performed at INGV (http://sismos.ingv.it).
Lomax, A. (2005), A Reanalysis of the Hypocentral Location and Related
Observations for the Great 1906 California Earthquake, Bull. Seism. Soc. Am., 95,
861-877.
Pino, N. A., D. Giardini, E. Boschi, The December 28, 1908, Messina
Straits, southern Italy, earthquake: Waveform modeling of regional seismograms, J.
Geophys. Res., 105(B11), 25473-25492, 10.1029/2000JB900259, 2000.
The Stress Triggering Role of the 1923 Kanto Earthquake, Japan
M. Nyst, RMS, Inc., USA, [email protected]; F. Pollitz, U.S. Geological
Survey, USA, [email protected]; T. Nishimura, GSI, Japan, [email protected]
go.jp; N. Hamada, MRI, Japan, [email protected]; W. Thatcher,
U.S. Geological Survey, USA, [email protected]
This study revisits the mechanism of the 1923 Ms=7.9 Kanto earthquake in Japan
and uses it to compute its influence on the static stress field in the Kanto region.
The focal mechanism is computed from a geodetic data set that consists of displacements from leveling and angle changes from first and second order triangulation
measurements obtained in surveys between 1883 and 1927. We apply a correction
to remove interseismic deformation. We use the low-angle fault plane, recently
observed in a seismic reflection study [Sato et al., Science, 2005], as a priori information in our modeling. The earthquake was located in the Sagami trough, where
the Philippine Sea plate subducts under Honshu. Our final uniform-slip elastic dislocation model consists of two adjacent low-angle planes accommodating reverse
dextral slip of about 7 m with azimuths of 145 degrees. Coseismic stress changes calculated under Coulomb failure assumptions show a general spatial consistency with
the regional seismicity rate changes associated with the 1923 earthquake [Hamada
et al., Zisin, 2001]. Positive changes in Coulomb failure stress in Odawara and central Boso coincide with clusters of aftershocks and a drop in Coulomb failure stress
around Tokyo agrees with the still ongoing seismic quiescence. We also compute
the coseismic Coulomb stress change on different sources of seismic hazard in the
Kanto region and find that active faults in the Tokyo Bay area were affected by the
1923 earthquake. The Coulomb stress level increased on Izu Peninsula, which may
have triggered the 1930 Ms=7.3 Kita-Izu earthquake. Furthermore, Coulomb stress
increase on the Western Sagami Bay fracture is inconsistent with this structure’s
presumed delayed rupture. Finally, Coulomb stresses were also raised on the downdip extension of the 1923 rupture plane, and on the 1703 earthquake fault plane
southeast of Boso Peninsula, bringing these structures closer to failure.
Historical Earthquakes from Turkey and Neighboring Countries
N. Meral Ozel, Bogazici University Kandilli Observatory and ERI, [email protected]
boun.edu.tr; A. Berberoglu, Bogazici University Kandilli Observatory and
ERI, [email protected]; M. Kara, Bogazici University Kandilli Observatory and
ERI, [email protected]; F. Bekler, Bogazici University Kandilli Observatory
and ERI, [email protected]; D. Kalafat, Bogazici University Kandilli
Observatory and ERI, [email protected]
The historical heritage of earthquake observations in Turkey is of great importance
for seismological research tradition and for identity of Turkish seismological community. Even Turkish destructive earthquakes have a great reputation in the world
its traces -instruments, seismic recordings, seismic bulletins and other related materials- are neglected, abandoned, scattered or left their bad fortune under the hard
conditions. It is necessary to recover and protect of this historical heritage to study
seismogenic patterns of the strong earthquakes that occurred in the 20th century,
and assessment of earthquake potential and seismic hazard of Turkey. We have been
retrieving and processing historical Turkish earthquakes that have been recorded by
Mainka, Wiechert, and Gallitzin seismographs located at Kandilli Observatory for
the years from 1933 to 1992 magnitude greater than 5. Our study is aimed to encompass the digitization of the historical records and associated any materials belong to
related earthquakes. A great effort was made to collect historical seismic recordings.
We have, so far, collected 479 historical records, and 374 of them have been scanned.
The scanned events and materials converted into digital form for storage on a computer at very high-resolution (1016 dpi) as digital raster copies are archived. Data set
consist of 479 relevant earthquakes; about 270 of them occurred on the Turkish territory, and the remaining mostly occurred in neighboring countries. An effort has been
initiated also to collect WWSSN recordings since early 1960 recorded by Turkish
stations -mostly located in Istanbul. 105 great earthquakes have been selected from
the archive and their digital image processes have also been continuing. As of now,
operational history of the seismological stations run by Kandilli Observatory has
been preparing as digital images archive to easily access for scientists.
Climate Change Investigations Using Historical Seismograms
R. Uhrhammer, UC Berkeley, [email protected]; P. Bromirski,
UC San Diego, [email protected]
Climate change studies examining interdecadal fluctuations require long time
series. Understanding the characteristics of wave energy variability are also important for improving the reliability of design wave criteria in coastal developments
and planning mitigation of ocean wave impacts on beaches and sea cliff erosion.
The buoy record is relatively short along the California coast, beginning about
1980. However, the ocean wave climate prior to 1980 can be reliably reconstructed from historical archived seismograms. Such reconstructions require digitizing analog seismograms archived at UC Berkeley since 1931. The archived data
Seismological Research Letters Volume 77, Number 2 March/April 2006 213
were recorded by Willip-Galitzin and Sprengnether long period seismometers. To
ensure that the trace amplitudes are consistent over time and that the seismic-towave transfer function developed using recent STS-1 digital seismometer records
and local buoy ocean wave data will give reliable historical wave height estimates,
we cross-calibrated the digitized traces against recent STS-1 data for selected high
amplitude earthquake surface wave arrivals. Spectral phase coherency analysis was
employed to characterize the transfer functions and useable bandwidths of the
different seismographs from digitized analog and from digitally recorded seismic
records which overlapped in time. The transfer functions of the seismographs are
represented by their complex poles and zeros and scaling factor. We found that
the calibration of the seismographs are internally consistent and that the calibration accuracy is of order 2 percent or better throughout their common passband. Spectrograms and reconstructed wave heights during the 1940-41 strong
El Nino winter compare well with local ocean wave variability during the 198283 and 1997-1998 El Ninos. [Work supported by the California Department of
Boating and Waterways and the California Energy Commission through its PIER
Program.]
A Reexamination of the 1964 M 9.2 Alaska Earthquake Rupture Process from
the Combined Inversion of Seismic, Tsunami, and Geodetic Data and a
Comparison with the 2004 Sumatra Earthquake
G. Ichinose, URS, [email protected]; R. Graves, URS, robert_
[email protected]; P. Somerville, URS, [email protected]; H.
Thio, URS, [email protected]
Until the 26 December 2004 (Mw 9.3) Sumatra-Andaman Island earthquake
there was little known about the range of source parameters and ground motions
from mega-thrust type earthquakes that limited our ability to predict their effects.
A detailed reexamination of the 28 March 1964 (M 9.2) Prince William Sound,
Alaska earthquake improves our understanding of the seismic hazard of southern
Alaska and the Pacific Northwest because rupture models are more useful for realistic scenario ground motion simulations than using completely stochastic methods. We develop a multiple time window kinematic rupture models from the least
squares inversion of World Wide Standard Seismograph Network seismic body
waves, National Oceanic and Atmospheric Administration tsunami tide gauge
records, and regional geodetic leveling survey observations. We estimate a seismic
moment of 4.3-6.2(1022 Nm (Mw 9.0-9.1) smaller than previous long-period surface wave estimate of (M 9.2). This is likely due to similar band-limiting circumstances with initially estimating the true size of the 2004 Sumatra earthquake. The
earthquake ruptured about 800 km from Valdez and Anchorage to Kodiak Island,
Alaska along the Aleutian Trench dipping 6-12(. All slip occurred above 50 km
depth and mostly < 15 km depth along the trench. The rupture duration was at least
300 sec. We identify 3 areas of major moment release, near Montague Island, along
the bend of the fault near the so-called “Kodiak Island asperity,” about 300 km from
the hypocenter and 100 sec after the origin time, and west of Kodiak Island (~
800 km and 240 sec). We compare and contrast the 1964 Alaska and 2004 Sumatra
M9+ earthquake rupture characteristics.
Extending ANSS: Next Generation Earthquake
Monitoring (Joint with EERI)
Poster Session
Continuous Microtremor Monitoring: One Possible Approach for Early
Detecting the Damage of the Dam
H. Chiu, Institute of Earth Sciences, Academia Sinica, [email protected]
This paper presents the analyses of microtremor data recorded at one of the strongmotion stations in the gallery of the Feitsui arch dam. Results show that the microtremor can excite the fundamental mode of the dam vibration, which is consistent
with the analyses of the strong-motion data. It implies that microtremor can be
used to monitor the resonant frequencies of the Feitsui Dam. This result leads to an
important implication for future installation of seismometers on some important
engineering structures such as dams, bridges, buildings and nuclear containment. If
we install high-resolution seismometers or dual-gain seismometers on such structures, the low-gain signal still can serve as the traditional purposes while the highgain signal can be applied for continuous monitoring the resonant frequency of
structure. This continuous monitoring can be further applied to the early detecting
the damage (cracks) of structure. Considering the Feitsui dam as an example, in
order to do that, we need remove all other factors that might modify the resonant
frequencies as well. Those major factors include water level of the reservoir, the
mud deposit near the dam, the temperature and the fatigue of the dam material.
Fortunately, the effects of these factors can be removed in a continuous monitoring
by comparing the resonant frequencies right before and right after the earthquake.
Then, any change in resonant frequency can be attributed the new damage of the
dam because all other factors could not has significant change within such a short
time period.
The decreasing rate of resonant frequency as the water level increasing in
Feitsui Dam is about 0.011Hz/m. This number only provides a rough changing
rate of resonant frequency due to the water level of the Feitsui Reservoir. The most
important data for developing this method is the quantitative relationship between
the damage and resonant frequency. Before the observed data being available,
numerical or experimental measurement such as measuring the resonant frequency
change of a numerical/scaled model due to the crack density might be the best way
to estimate the possible frequency change in a real structure. If this change of resonant frequency is significant and detectable, this kind of monitoring could be one
possible approach for early detecting the damage of engineering structure right after
a major earthquake.
The Kentucky Vertical Strong-motion Network
J. McIntyre, University of Kentucky-Kentucky Geological Survey, jonathan.
[email protected]; Z. Wang, University of Kentucky-Kentucky Geological
Survey, [email protected]; E. Woolery, University of Kentucky-Department of
Earth and Environmental Sciences, [email protected]
Ground-motion amplification by near-surface soft soils is a very important issue
for seismic hazard assessment, and direct observations provide the best method to
characterize it. Since 1989, the University of Kentucky has installed and operated a
strong-motion network in the northeastern part of the New Madrid Seismic Zone
. The strong-motion network includes four vertical strong-motion arrays: VSAB,
VSAP, VSAS, and RIDG. The arrays consist of one to two downhole accelerometers. The first vertical strong-motion recordings in the central and eastern United
States were recorded at station VSAP from the February 5, 1994, southern Illinois
earthquake. These arrays have started to accumulate recordings that will provide a
database for scientists and engineers to study the effects of the near-surface soils on
the weak and strong ground motion in the New Madrid Seismic Zone. For example,
the weak-motion records show interesting wave-propagation phenomena through
the soils, such as the effects of different incident angles on S-wave velocity estimation, the S-wave attenuation from 260 m to 30 m depth, and amplification from
30 m to the surface.
An Earthquake Detection, Identification and Location System for the
Northeastern U.S. Based on the Wavelet Transform
J. Ebel, Weston Observatory/Boston College, [email protected]
It is a significant technical challenge to monitor the widespread seismicity in the
New England region of the northeastern U.S. using a regional seismic network with
a relatively coarse station spacing of 70-150 km. In order to optimize the ability of
the New England Seismic Network (NESN) to detect all local earthquakes to the
smallest possible magnitude, Weston Observatory of Boston College has developed
an automated event detection and identification system based on the wavelet transform. This software system performs a wavelet transform on the data from each station being received via Earthworm and then uses the time, frequency content and
energy of the first arrival, the highest energy arrival, and the end of the detection
to compute the Bayesian probability that the detection was a teleseism, regional
earthquake, local earthquake, quarry blast, Rg wave from a quarry blast, or transient noise. At each station, these measured parameters are used to estimate the origin time, epicentral distance and magnitude (both coda-wave magnitude Mc and
Lg-wave magnitude MLg) for each detection. Several event associators have been
implemented that attempt to associate those detections from different stations that
have a common event identification. One event associator is designed to associate
teleseismic P wave arrivals. A second associator works on signals that have a high
probability of being a regional or local earthquake, where the association is based
on the estimated origin time of the event signal at each station. If three or more
stations are found to have associated origin times, an automatic event location and
set of Mc and MLg magnitudes are computed under the assumption that a local or
regional event has been detected. A third associator looks to accumulate the event
detections at different stations from a common quarry blast source. The seismic
processing system sends automatic text pages and emails to network staff for all successfully located events. Implementation of this wavelet-transform event detector
and identifier has greatly increased the sensitivity of detecting and locating small
earthquakes and quarry blasts in the New England region. Weston Observatory
intends to increase the number of regional seismic stations, especially in northern
New England, which will further enhance the capabilities of this system to detect
local and regional earthquakes.
214 Seismological Research Letters Volume 77, Number 2 March/April 2006
Observational Technologies Implemented for USArray
M. Alvarez, IRIS, [email protected]; J. Fowler, IRIS, [email protected]; R.
Busby, IRIS, [email protected]
The seismological component of the NSF funded Earthcope project, USArray, has
undertaken to apply modern observational, analytical and telecommunications
technologies to investigate the structure and evolution of the North American
continent. To date, over 130 of an eventual 2000 broadband stations have been
installed as part of the Transportable Array using near-real time data telemetry. In
addition, a pool of 2400 stations (a mixture of broadband, short period and high
frequency stations) designed for high-resolution, short-term observations are being
assembled as part of the Flexible Array component of USArray.
Real-time data telemetry, standardized station design and automated data
archiving techniques are essential elements for the realization of this project. In
order to keep up with the large amount of data generated by USArray, real-time
telemetry is required. No single technology has been relied on to accomplish this
task. Instead a combination of VSATs, ethernet radios, direct connections and cell
phone CDMA technologies are employed. Each of these communications methods has advantages depending on station location. The inherent flexibility of our
modern data acquisition systems allow us to adopt regionally specific communication systems as needed. The planned period for recording events at a single station is relatively short, not exceeding 2 years. The quality of the seismic sites, hence
needs to be as good as possible. We have designed broadband sensor vault systems
which provide excellent coupling to the earth, reduce cultural and environmental noise sources while protecting the instrumentation. When fully deployed, the
Transportable Array will be comprised of 400 real-time stations. Online tools for
managing a dynamic network of this size have been developed to aid the station
operators keep data returns high. Quality control and overall communications
management for USArray are based at the Array Network Facility at U.C. San
Diego. The data from USArray are archived at the IRIS Data Management Center
in Seattle as soon as they are available and can be attained using the standard data
request methods.
Characterization of Near-surface Geology at Strong-motion Stations in the
Vicinity of Reno, Nevada
A. Pancha, Nevada Seismological Laboratory, University of Nevada, Reno,
[email protected]; J. Anderson, Nevada Seismological Laboratory,
University of Nevada, Reno, [email protected]; J. Louie, Nevada Seismological
Laboratory, University of Nevada, Reno, [email protected]
The Advanced National Seismic System (ANSS) is an effort to modernize, expand,
and integrate earthquake monitoring and notification in the United States. Key
goals of ANSS include dense instrumentation in high risk urban areas to monitor strong ground shaking, providing emergency response personnel with real-time
earthquake information, and engineers data on the response of buildings and other
structures. Western Nevada is one of the locations targeted by this effort. The cities
of Reno and Sparks, Nevada, are located in a fault-controlled basin that is about
13 km wide and 21 km long. The small basin size, and the growing Advanced
National Seismic System (ANSS) accelerograph network within it, make this area a
very attractive location for improving modeling techniques to explain the relationship between basin structure, near-surface geology, and ground motions.
We evaluate site conditions at each of the ANSS strong motion stations in
the Reno-Sparks area. Shallow shear wave velocities are measured using the refraction microtremor (ReMi) technique (Louie, 2001). Average velocities to depths of
30m and 100m are compared with local geological and soil classifications. While
generalized geological classifications show a general correlation with the measured
velocities, predictions of site velocities are significantly better based on 1:24,000
map scale units. Site velocities are also weakly correlated with elevation, topographic slope, and basin depth.
New Computational Approaches for Structural Damage Identification Using
the Densely Instrumented 17-story Moment-resisting Steel Frame Factor
Building
M. Kohler, UCLA, [email protected]; T. Heaton, Caltech, [email protected]
caltech.edu; C. Bradford, Caltech, [email protected]
Wave propagation effects can be useful in determining the system identification of
buildings such as the densely instrumented UCLA Factor building. The density of
measurements makes it possible to observe subtle changes in dynamic characteristics between pairs of floors and to relate the measurements to system properties
such as changes in stiffness due to a column failure. The high dynamic range of the
24-bit digitizers allows both strong motions and ambient vibrations to be recorded
with reasonable signal-to-noise ratios. Waveform data from the 72-channel array in
the 17-story moment-resisting steel frame Factor building are used in comparison
with finite element calculations for predictive behavior. A three-dimensional model
of the Factor building has been developed based on structural drawings. Observed
displacements for 20 small and moderate, local and regional earthquakes were used
to compute the impulse response functions of the building by deconvolving the
subbasement records as a proxy for the free field. The impulse response functions
were then stacked to bring out wave propagation effects more clearly. The simulation results for travel times, mode shapes, and frequencies of vibration agree to
within a few small percent using the impulse response function of the subbasement
as ground history input. It can be shown that small but significant changes in the
travel times, mode shapes, and frequencies are observed in the simulation results for
strong ground shaking and for modifications to the structural model for hypothesized damage patterns such as broken welds on a particular floor. The Factor building is a prototype structure for use in emergency response and engineering research
applications. It represents how densely and permanently instrumented structures
can record data on small spatial scales for numerical simulation validation and damage detection analysis.
99 Years of Earthquake Recording in the Utah Region (1907-2006): Remaining
Big Questions and Future Instrumentation Strategies
W. Arabasz, University of Utah Seismograph Stations, [email protected];
K. Pankow, University of Utah Seismograph Stations, [email protected]
Earthquake recording in Utah has evolved from Bosch-Omori seismographs in
1907 to an ANSS real-time earthquake information system in 2006. The monitoring emphasis has been on regional and local earthquakes, including induced seismicity. We examine this 99-yr history and the resulting instrumental catalog for
the Utah region containing more than 36,000 earthquakes (M ( 6.6), first, to identify unanswered “big questions” and, second, to explore seismic instrumentation
strategies that can help resolve them. Seismic hazard in Utah is dominated by the
Intermountain Seismic Belt (ISB), within which the 340-km-long Wasatch normal
fault zone transects the Wasatch Front urban corridor in north-central Utah. The
presence of more than 75% of Utah’s population in the latter area heavily influences
the distribution of seismic instruments. Despite a relative abundance of small-tomoderate size earthquakes within the ISB, observational seismology in the Wasatch
Front area has been handicapped by the absence of any historical rupture on the
Wasatch fault and also by extremely low background seismicity on the fault itselfa trait shared by virtually all the major active faults in the Intermountain region,
except three that ruptured in historical time (NW Utah, 1934; Montana, 1959;
Idaho, 1983). These circumstances leave unanswered many key questions for earthquake risk reduction and science in the Utah region. For seismic hazard analyses,
first-order questions relating to seismic source characterization include: the subsurface geometry of the Wasatch and other major active faults, the correlation of diffuse background seismicity with geologic structure, and the frequency-magnitude
distribution for major fault sources. Critical questions for ground-motion prediction include: source dynamics for large normal-slip earthquakes, ground-motion
attenuation, and the importance of non-linear soil behavior in Wasatch Front valleys. To address these key questions, specific instrumentation strategies need to be
devised. Elements include (a) going beyond risk-based attention to population distribution, (b) capitalizing on both weak-motion and accelerographic recordings,
to the greatest extent possible, (c) relying on data capture for moderate-to-large
earthquakes throughout the Intermountain region, and (d) using portable arrays of
telemetered stations to strategically supplement existing fixed networks.
Earthquake Detection and Data Processing Systems at the Alaska
Earthquake Information Center
N. Ruppert, University of Alaska Fairbanks, [email protected];
R. Hansen, University of Alaska Fairbanks, [email protected]; M.
Robinson, University of Alaska Fairbanks, [email protected]
Alaska is situated in a unique tectonic setting. While the majority of the earthquakes occur along the faults associated with the North American/Pacific plate
boundary, numerous other faults and active volcanoes produce a large quantity of
earthquakes as well. The Alaska Earthquake Information Center (AEIC) receives
data from about 400 seismic sites located within the state boundaries and the surrounding regions and serves as a regional data center. The real-time earthquake
detection and data processing systems at AEIC are based on the Antelope system
from BRTT, Inc. This modular and extensible processing platform allows an integrated system complete from data acquisition to catalog production. All steps are
archived within a relational database, including final processing and both continuous and segmented waveform data. Multiple additional modules constructed with
the Antelope toolbox have been developed to fit particular needs of the AEIC. The
real-time earthquake locations and magnitudes are determined within 2-5 minutes
of the event occurrence. AEIC maintains a 24/7 seismologist-on-duty schedule.
Earthquake alarms are based on the real-time earthquake detections. Significant
events are reviewed by the seismologist on duty within 30 minutes of the occurrence with information releases issued for significant events. This information is
Seismological Research Letters Volume 77, Number 2 March/April 2006 215
disseminated immediately via the AEIC website, ANSS website via QDDS submissions, through e-mail, cell phone and pager notifications, via fax broadcasts and
recorded voice-mail messages. In addition, automatic regional moment tensors are
determined for events with M>=4.0. This information is posted on the public website. ShakeMaps are being calculated in realtime with the information accessible
via password-protected website. AEIC maintains an extensive computer network
to provide adequate support for data processing and archival. For real-time processing, AEIC operates two identical, interoperable computer systems in parallel.
These systems reside on different computers and include independent waveform
data archival capabilities, real-time arrival and earthquake detections, magnitude
calculations, alarm and earthquake information dissemination modules. The AEIC
personnel located and reported over 17,000 earthquakes in 2005, with the largest event of M6.8 in Rat Islands. The overall detection magnitude threshold of the
Alaska Seismic Network is about 3.0, with about 1.2-1.4 in the best instrumented
parts of the network.
Analysis of Recent Earthquake Monitoring Improvements in the United
States
D. McNamara, USGS, [email protected]; K. Anderson, IRIS, [email protected]
iris.edu; L. Gee, USGS, [email protected]; P. Earle, USGS, [email protected]; A.
Leeds, USGS, [email protected]; R. Buland, USGS, [email protected]; H.
Benz, USGS, [email protected]; C. Hutt, USGS, [email protected]; R. Butler,
IRIS, [email protected]
Over the past several years, the combination of developments in the USGS
Advanced National Seismic System (ANSS) and the Earthscope USArray backbone effort and have significantly enhanced earthquake monitoring in the US. This
improvement is owing to several factors: installation of additional broadband stations, selection of quiet sites, improved vault design and instrumentation upgrades.
We demonstrate improvements in individual station performance as lower short
and long period noise levels and investigate overall network improvements using
three different measures of network capability: 1) minimum Mw detection threshold; 2) response time of the automatic processing system and; 3) theoretical earthquake location errors. We also demonstrate that the technique used in this analysis
is valuable for quantifying seismic network capability improvements and a useful
tool for network design planning.
Shake Table Tests of a Full Scale Reinforced Concrete Wall Building: Real
Time 50 Hz GPS Displacement Measurements
Y. Bock, Scripps Institution of Oceanography, [email protected]; M.
Panagiotou, University of California San Diego, [email protected]; F.
Yang, Scripps Institution of Oceanography, [email protected]; J. Restrepo,
University of California San Diego, [email protected]; J. Conte, University of
California San Diego, [email protected]
We report on real-time 50Hz GPS displacement measurements on a full-scale 7story reinforced concrete wall building at the Large High-Performance Outdoor
Shake Table at University of California San Diego, funded by the National Science
Foundation under the NEES program. The overall objective of this research program is to verify the seismic response of reinforced concrete wall systems designed
for lateral forces that are significantly smaller than those currently specified in
building codes in United States. The first phase of experimental program investigated the response of the web cantilever wall configuration to different levels of
excitation. This included low amplitude 0.5-25 Hz band-clipped white noise tests,
a low intensity earthquake, two medium intensity earthquakes that were somewhat
above the site response spectra for the period of the building for 50% probability
of exceedance event and a large intensity earthquake whose spectral acceleration in
the period range of interest was above the site response spectra for 10% probability
of exceedance in 50 years. The low intensity earthquake record is the vnuy longitudinal component from the 1971 San Fernando earthquake. The two medium intensity records are the vnuy transverse component record from 1971 San Fernando
earthquake and the whox longitudinal component from the Northridge 1994
earthquake. The large intensity record is the Sylmar Olive View Med 360o component record from the 1994 Northridge earthquake. For all tests, we deployed 7
50 Hz Navcom GPS receivers and Dorne Margolin antennas with chokerings—3
on the roof of the 7-story building, 2 cantilevered on the 5th and 3rd floors, one
on the shake table, and one as a reference just off the shake table. We report on
instantaneous 50 Hz displacements computed in real-time with the Geodetics, Inc.
RTD-Net software for all tests, and compared these measurements with integrated
in situ accelerometer data, and with the induced earthquake motions. Our results
demonstrate consistent mm-level (one-sigma) accuracy for the measured displacements and the usefulness of very high rate GPS displacement measurements for
seismic monitoring of structures.
Spatial Gradient Analysis for Areal Seismic Arrays: A New Method for
Seismic Array Processing
C. Langston, CERI, University of Memphis, [email protected]
The displacement gradient of a seismic wave is related to displacement and velocity
through two spatial coefficients. One gives the relative change of wave geometrical
spreading with distance and the other gives the horizontal slowness and its change
with distance. The essential feature of spatial gradient analysis is a time-domain
relation between three seismograms that yields information on the amplitude and
phase behavior of a seismic wave. Filter theory is used to find these coefficients for
data from 2 dimensional areal arrays of seismometers. A finite difference star is used
to compute the displacement gradient for irregularly shaped seismic arrays and a
relation for the frequency-dependent error in the displacement gradient is obtained
and applied to ensure accurate estimates. This kind of array analysis is useful for
arrays at any distance from a source and yields a variety of time domain and frequency domain views of wave amplitude changes and horizontal phase velocity estimates across the array. For example, time-dependent horizontal slowness and wave
azimuth plots are natural results of the analysis. These time-domain maps may be
used in conjunction with time-distance and horizontal slowness-distance models to
locate seismic sources or may be used directly to study earth structure. These methods are demonstrated using data from a small aperture (~ 120m) seismic/acoustic
array and a larger aperture (~ 1.5km) broadband seismic array.
Antelope-based Alarm Systems for Earthquake Monitoring
K. Lindquist, Linsquist Consulting Inc., [email protected];
J. Stachnik, University of Alaska Fairbanks, [email protected]; R. Hansen, University of Alaska Fairbanks, [email protected], N.
Ruppert, University of Alaska Fairbanks, [email protected]
We have developed a new earthquake alarm program, called orb_quake_alarm,
which provides highly configurable earthquake notification capability for Antelope
platforms. This utility is optimized for communication with cell phones via Short
Message Service(SMS) email-gateways, though can also be configured to work with
other compatible technologies. A new database table extends the rt1.0 schema to
track alarms that are constructed and sent to seismology-lab personnel. Support
is included to track retroactive recognition of false alarms, metadata about each
alarm, the raw text of each alarm message and alarm-cancellation acknowledgments. A new handler for the mail_parser utility in the Antelope contributed-code
respository supports callback acknowledgment and alarm cancellation. ‘Calldown’
capabilities are implemented which allow messages to be forwarded to additional
recipients if they are not acknowledged in sufficient time.
We discuss the integration of this program into Antelope-based alarm notification procedures and alarm-response capabilities at the Alaska Earthquake Information
Center. Future expansion includes support for alarms based on strong-motion ground
monitoring (triggering based on raw accelerations) that update database table entries,
based on predetermined acceleration thresholds, as shaking intensity changes. This
additional functionality may communicate directly with a monitoring system hardware control panel, providing additional usefulness to industrial applications.
Implementation of a Linear Shaker Using the Zero Friction Air Bearings
N. Vrcelj, Terrascience Systems Ltd./Weir-Jones Engineering Group of
Companies, [email protected]
This paper discusses a new approach to the design of small horizontal high-linearity
shake table. In particular, the suitability of a linear motor with a zero-friction sliding plate for the shake table is evaluated. Additionally, a new method is proposed
to compensate for small signal misalignments proportional to a fraction of the sampling interval by precisely controlling the phase shift. The goal was to obtain highlinearity reference acceleration and displacement signals used in qualification of a
new generation of 24-bit strong motion seismic equipment as well as to develop a
methodology for accurate seismic instrumentation data analysis. Low signal distortion is achieved by relying on a zero friction linear stage supported by air bearings.
Experiments were carried out and performance of the system is investigated and
compared to that of an electro-magnetic shaker. The test results indicate significant improvement in the shaker’s capability to reproduce typical reference signals
used in seismic equipment qualification in the frequency range related to the strong
motion, thus providing a valuable tool for precise detection of main parameters of
seismic instrumentation
Digital Accelerometer
N. Vrcelj, Terrascience Systems Ltd./Weir-Jones Engineering Group of
Companies, [email protected]
This paper presents current accomplishments in the development of the digital
force balance type of accelerometer based on the discrete current driving. The newly
216 Seismological Research Letters Volume 77, Number 2 March/April 2006
proposed and patented PWM pattern is introduced to allow for a precise control
of the torque coil current as low as 1 LSB on a 24-bit system. Minimum number
of driving components and a self calibration mechanism provide stability of the
torque coil current over a wide temperature range. The self calibration is performed
in real time without interruption of the data acquisition process. Improved long
term and temperature stability allows for a wider frequency dynamic range providing capability to resolve low frequency components. Being performed on the sensor
side, the A/D conversion embedded in the sensor feedback loop itself significantly
changes the typical data acquisition system architecture by eliminating the cable
length as an issue due to the digital transmission. Experiments were carried out and
the performance of the digital accelerometer is compared to that of a reference high
performance linear torque-balance accelerometer.
The Mutual Benefit of Seismograph Installation at Naval Hospital Bremerton
D. Wilson, Reid Middleton, Inc., [email protected]; R. Kent, Naval
Hospital Bremerton, [email protected]; D. Swanson, Reid Middleton,
Inc., [email protected]
Naval Hospital Bremerton in Bremerton, Washington was originally instrumented
with a strong motion seismograph in the early 1980’s but the film based recorder was
largely forgotten about until the 2001 Nisqually Earthquake because of its limited
use to the building user, the engineering community, and seismologists. The system
has been subsequently upgraded to a 12-channel digital recorder for the building
sensors with a dial-up connection to USGS, and a 3-channel free field instrument
connected to USGS via the internet. The Hospital benefits through remote health
monitoring of their instrumentation and data archiving of event records. They are
also able to use the data as part of a post -event damage assessment program to expedite the evaluation and continued use of the essential facility following an earthquake. Seismologists have gained another free-field instrument as part of the Pacific
Northwest Seismograph Network, which increases the accuracy of the ShakeMaps
created following an event and increases our understanding of local seismicity. The
seismology and engineering community will also benefit though the future availability of an on-site free field record as well as the corresponding building response
of a nine story, 250,000 square foot steel moment frame building retrofitted with
fluid viscous dampers.
Monitoring and Modeling the Seismic Wavefield
Poster Session
Surface and Body Waves from Hurricane Katrina Observed in California
M. Fehler, Los Alamos National Laboratory, [email protected]; P. Gerstoft,
Marine Physical Laboratory, University of California San Diego, [email protected]
edu; K. Sabra, Marine Physical Laboratory, University of California San Diego,
[email protected]
Hurricane Katrina struck land on August 29, 2005 as one of the strongest storms
in the United States in the past 100 years. Over the ocean, it attained a category
of 5 on the Saffir-Simpson scale, the highest on that scale, and was a category 4 at
landfall. While seismic noise generated by hurricanes has been studied in the past,
the recent availability of continuous seismic data from a large number of stations
allows us to characterize features of hurricane and ocean-generated noise in significantly more detail. By beamforming noise recorded on a distributed seismic array
in Southern California consisting of 150 geophones with aperture 500 km, we are
able to observe and track both the surface and body P-waves generated by Katrina
in the 4-20 seconds period (0.05-0.25Hz) microseism band. As the hurricane made
landfall, the longer-period surface waves weakened, indicating that air/ocean/land
coupling was a major factor in their generation. We observed P-waves that have
propagated deep inside the Earth. The observed P-waves can be back-propagated
to the hurricane. These findings demonstrate that ocean microseisms can propagate
quite far and open the possibility of further use of seismic noise, even at very low
signal level.
Observations of Infragravity Waves at the Monterey Ocean Bottom
Broadband Station (MOBB)
B. Romanowicz, Berkeley Seismological Laboratory, [email protected]; D. Dolenc, Berkeley Seismological Laboratory, [email protected]; P. McGill, Monterey Bay Aquarium Research Institute, [email protected]
org; D. Neuhauser, Berkeley Seismological Laboratory, [email protected]; D. Stakes, MPC, [email protected]
Broadband seismic stations on the ocean floor experience higher noise levels than
on land, due to coupling between ocean waves and the solid earth. Understanding
the nature and characteristics of this coupling, in particular its location on the
ocean floor, is important for the study of energy dissipation in the oceans as well
as the study of earth’s “hum” and earth structure using noise data. MOBB was
installed 40 km offshore in the Monterey Bay at a water depth of 1000 m in April
2002 in collaboration between Berkeley Seismological Laboratory and Monterey
Bay Aquarium Research Institute (McGill et al., 2002). It comprises a three-component broadband seismometer with a temperature sensor, a water current meter
measuring current speed and direction, and a differential pressure gauge (DPG).
The station is continuously recording data which are retrieved, on average, every
three months. Infragravity waves can be observed at MOBB on stormy as well as
quiet days in the period band 20-300 sec. When compared to the energy of the
short-period ocean waves recorded at the local buoys, infragravity waves are found
to be mainly locally generated from shorter period waves by non-linear processes.
Two types of modulation of the infragravity signal are observed. First, the entire
infragravity band signal is modulated in-phase with tides, possibly as a result of the
nonlinear exchange of energy between the short-period waves and tidal currents.
Second, a longer-period modulation of the infragravity signal is observed and is
best correlated with the energy of the 14 s period ocean waves. This correlation
indicates that the mechanism of generation of double frequency microseisms and
infragravity waves are likely strongly related. Analysis of the previously recorded
data during the Oregon ULF/VLF experiment at 600 m water depth (courtesy of
Peter Bromirski), also indicates that infragravity waves are primarily locally generated. Preliminary analysis of data from a station further north and 200 km off shore
(Keck experiment, courtesy of Will Wilcock) indicates that the low frequency seismic noise is generated when storms reach the coast, and not when the storm passes
directly above the station.
The Earth’s Hum, Microseisms and Ocean Waves
J. Rhie, Berkeley Seismological Laboratory, [email protected]; B.
Romanowicz, Berkeley Seismological Laboratory, [email protected]
edu.
Using array data from two regional networks of VBB seismometers, in California
(Berkeley Digital Seismic Network) and in Japan (F-NET), we recently documented that the source of the earth’s low frequency “hum” is primarily in the oceans
(Rhie and Romanowicz, 2004). We proposed a mechanism for their generation,
involving the coupling of infragravity waves with the ocean floor. The precise mechanism of this atmosphere-ocean-seafloor coupling is however not yet well understood. Microseisms are also another type of seismic noise originating from ocean
waves, which dominates seismic records in the period range 0.1-1 Hz. In order
to gain further insight into these intriguing phenomena, we have focused on the
North Pacific region, where the dominant sources of hum appear to be located in
the northern hemisphere winter. We have assembled a dataset of significant wave
height recordings at buoys deployed by the National Oceanographic Atmospheric
Administration (NOAA) and Japan Meteorological Agency ( JMA) for a five day
period in 2000, during which two large storms develop and propagate across the
Pacific, there are no significant earthquakes, and the background “hum” level is
high. From the temporal correlations between the signature of the storms on the
buoy data and the seismic low frequency Rayleigh wave background noise, we infer
that the coupling with the seafloor most likely occurs near the coast, around the rim
of the north Pacific ocean. We also show that we can track the generated Rayleigh
waves as they propagate from West to East across the continental United States. We
haveassembled and processed 3 years of microseism data at stations of the BDSN,
F-NET arrays, and show a strong correlation of amplitude fluctations in the microseismic band with that in the “hum” band during the northern hemispheric winter,
but not during summer months, suggesting that in the winter, the microseisms and
hum have a common “regional” or “local” origin, whereas in the summer, the origin
of the hum is indeed distant (southern hemisphere) while the microseisms remain
local and have smaller amplitudes.
A Search for Tremor Using the Southern California Earthquake Data Center
(SCEDC) Continuous Data
E. Cochran, University of California, San Diego, [email protected]; P.
Shearer, University of California, San Diego, [email protected]
In recent years, reevaluation of continuous seismic data has revealed a myriad of
seismic signals that previously had been ignored because they did not fit into the
usual definition of an earthquake. Slow earthquakes and high-frequency tremor
have been observed in subduction zones for several years, and associated with the
deep down-dip extension of the subducting slabs. Recent observations by Nadeau
et al. [2005] of deep tremor on the San Andreas Fault near Parkfield prompted us
to extend the search for unusual seismic signals to all of southern California. We
look for evidence of unusual signals using continuous Southern California Seismic
Network (SCSN) data archived since 2001 by the Southern California Earthquake
Data Center (SCEDC) (continuous data are not as widely available prior to 2001).
Seismological Research Letters Volume 77, Number 2 March/April 2006 217
To rapidly examine the large volume of data, we apply a bandpass filter between
1 and 10 Hz, compute the root mean square (RMS) amplitude of the data, and
resample to 0.1 samples per second. This is similar to the method by Nadeau et al.
[2005] who examined the envelope of the data. We then visually scan the records
for evidence of unusual activity appearing on multiple stations that is not associated
with catalogued local, regional or teleseismic earthquakes. For candidate signals, we
perform cross-correlation of the RMS records to obtain travel-time constraints on
possible event locations. We then compare the signals at different frequency bands
with those from cataloged earthquakes in the same region to assess whether tremor
or previously undetected earthquakes are a more likely explanation for our observations. We plan to present the results of this analysis for about 3 years of SCSN
data.
Monterey Ocean Bottom Broadband Station (MOBB): Data Analysis and
Noise Removal
D. Dolenc, Seismological Laboratory, UC Berkeley, [email protected]
edu; B. Romanowicz, Seismological Laboratory, UC Berkeley, [email protected]
seismo.berkeley.edu; D. Stakes, Monterey Bay Aquarium Research Institute,
[email protected]; P. McGill, Monterey Bay Aquarium Research Institute,
[email protected]; B. Uhrhammer, Seismological Laboratory, UC Berkeley,
[email protected]; D. Neuhauser, Seismological Laboratory, UC
Berkeley, [email protected]
MOBB was installed 40 km offshore in the Monterey Bay at a water depth of
1000 m in April 2002 in collaboration between Berkeley Seismological Laboratory
and Monterey Bay Aquarium Research Institute (McGill et al., 2002). It comprises
a three-component broadband seismometer with a temperature sensor, a water current meter measuring current speed and direction, and a differential pressure gauge
(DPG). The station is continuously recording data which are retrieved, on average, every three months. In the past 4 years of continuous operation MOBB has
recorded numerous local, regional, and teleseismic events. MOBB provided important information in addition to the BDSN land stations that enabled us to better
determine locations and mechanisms of offshore earthquakes. It also enabled us to
observe infragravity waves and learn more about their generation in the near-shore
environment (Dolenc et al., 2005). When compared to the quiet land stations,
ocean bottom seismic station MOBB shows increased background noise in the
band pass of interest for the study of regional and teleseismic signals. This is mainly
due to the signal from the infragravity waves and ocean currents. Observations at
MOBB also show additional signal-generated noise due to the reverberations in the
shallow sedimentary layers as well as in the water layer. We present results of removing the long-period background noise from the seismic observations by subtracting the coherent signals derived from the pressure measurements. We also present
results of the modeling of the signal-generated noise in the near surface layers and
examples of removing the signal-generated noise using a deconvolution.
Q of the Mexican Volcanic Belt
A. Iglesias, Instituto de Ingeniería, UNAM, [email protected];
S. Singh, Instituto de Geofísica, UNAM, [email protected]; D.
García, Departamento de Geofísica y Meteorología,, Universidad Complutense
de M, [email protected]; M. Ordaz, Instituto de Ingeniería, UNAM, [email protected]
pumas.iingen.unam.mx; J. Pacheco, Instituto de Geofísica, UNAM, [email protected]
ollin.igeofcu.unam.mx.
As Lg waves propagate from the Pacific coast of Mexico to the Valley of Mexico they
get amplified in the Mexican volcanic belt (MVB). They suffer further amplification in the lake-bed zone of the valley. The fate of these waves after they cross the
MVB is less well known. Do the spectral amplitudes in the north of the MVB get
enhanced because of the amplification in the MVB? Or, does the expected lower
Q below the MVB dominate the effect of the amplification so that the observed
amplitudes to the north of the MVB are less than the predicted ones? Whether the
Q of the MVB is higher or lower than the Q of the region between the coast and
MVB still remains controversial. In this study, we analyze recordings of 7 shallow,
coastal, thrust events recorded by a pair of broadband stations which straddle the
MVB: PLIG to the south and DHIG to the north. The stations are 217 km apart.
Both stations are located on limestone and exhibit little site effect. We assume 1/
sqrt(R) geometrical spreading between the two stations. For each event, we obtain
Q-1 at 11 discrete frequencies between 0.25 to 8 Hz. We compute mean value and
standard deviation of Q-1 at each frequency. A weighted least square fit yields Q1(f )=(0.01024 ( 0.00066) f -(0.717 ( 0.050), or Q(f )= 97.6f0.72. This is the average Q for the MVB. The southern part of the MVB, which is presently active, may
have a much lower Q. We note that the average Q of the MVB is significantly lower
than Q(f )=273f0.66 reported for the region between the coast and PLIG. We use
the Q(f ) of the MVB to predict spectrum at DHIG from the recording at PLIG of
a recent event near Pinotepa Nacional, Oaxaca (14 Aug 2005, Mw5.4). The agreement is excellent. The earthquake of 14 Sep 1995 (Mw7.4) near Copala, Guerrero
was recorded by stations near PLIG and DHIG. Again the predictions based on the
recording near PLIG are in good agreement with the observed spectrum at the site
near DHIG. This gives us confidence in our estimate of Q(f ) of the MVB.
New Madrid Seismic Zone Vp/Vs Ratios
C. Powell, U of Memphis, [email protected]; M. Withers, U of
Memphis, [email protected]; M. Dunn, U of Memphis, [email protected]; G. Vlahovic, N C Central University, [email protected]
Unusually low Vp/Vs ratios are associated with the major arms of seismicity in the
New Madrid seismic zone to depths of at least 9 km. Vp/Vs ratios were determined
using new three-dimensional P and S wave velocity models based upon arrival times
recorded by the New Madrid seismic network and by the PANDA deployment. The
merged network and PANDA data sets yielded 11,656 and 8,579 P and S arrival
times, respectively, after imposing a requirement of at least 4 P and S phases for
each earthquake retained. The inversion algorithm inverts simultaneously for both
P and S velocities and hypocentral locations. Station corrections were incorporated.
Block size was 2 by 2 by 2 km. Model resolution was investigated using chessboards,
spike tests, and reconstruction tests; lateral resolution is excellent in the portion
of the model with dense ray coverage. The low Vp/Vs values cannot be attributed
to resolution differences in the P and S velocity solutions. Low Vp/Vs ratios are
produced by negative (-3.5%) Vp anomalies and positive (+3.5%) Vs anomalies.
These values could be produced by the presence of very felsic rocks or by variations
in the compressibility of pore contents. They are difficult to attribute to increased
temperatures or to highly fractured, fluid filled rocks. The reliability of the low Vp/
Vs values is being investigated using Vp/Vs smoothing and a different tomographic
approach that inverts simultaneously for Vp and Vp/Vs.
High Fidelity Seismic Imaging for Steep Reflectors
R. Wu, Unviversity of California at Santa Cruz, [email protected]; J. Cao,
Unviversity of California at Santa Cruz, [email protected]
Using beamlet decomposition of wave field we discuss the effect of acquisition
configuration to image amplitude for steep reflectors. The acquisition aperture correction is carried out using the local image matrix and acquisition dip response,
which includes both the effects of acquisition system and the propagation through
complex overburden. Two types of amplitude corrections can be performed for the
high-fidelity seismic imaging: One is the correction for common reflection-angle
image gathers to get the true angle-dependence of reflection coefficient; the other
is that for the final total scattering coefficient. Through the numerical examples
using synthetic data sets, we see that the distortion of image amplitude due to the
acquisition aperture effect can be much improved through the acquisition aperture
corrections, especially for steep reflectors. The other factors influencing the image
amplitude, such as the scattering and absorption loss, geometric spreading in complex media, noise interference, and propagator errors, are also discussed.
Evaluation of Statistical Techniques for Seismic Wavelet Extraction via 3D
Elastic Modeling
M. Haney, Geophysics Department, Sandia National Laboratories, [email protected]
sandia.gov; R. Abbott, Solid Dynamics and Energetic Materials Department,
Sandia National Laboratories, [email protected]; N. Symons, Geophysics
Department, Sandia National Laboratories, [email protected]; L. Bartel,
Geophysics Department, Sandia National Laboratories, [email protected]; D.
Aldridge, Geophysics Department, Sandia National Laboratories, [email protected]
sandia.gov.
Accurate knowledge of the waveform of a seismic energy source is necessary for
numerous data processing, interpretation, and inversion procedures, as well as for
realistic forward simulation of seismic wavefields within numerical earth models.
For example, various techniques for source signature deconvolution, multiple suppression, amplitude vs. offset analysis, full waveform inversion, attenuation estimation, and source magnitude determination require an estimate of the source
pulse. Statistical methods for extracting a wavelet from recorded data, developed
primarily in the petroleum exploration industry, rely on several simultaneous (and
stringent) assumptions. In general, the mean autocorrelation function of a set of
traces is considered proportional to the autocorrelation of the source waveform. A
minimum phase wavelet is then calculated from the source autocorrelation function or power spectrum.
We utilize 3D numerical modeling to investigate the efficacy of conventional
statistical wavelet extraction techniques. Full waveform synthetic seismograms are
generated for isotropic elastic earth models, utilizing a finite-difference algorithm
based on the velocity-stress equations of elastodynamics. Models include 1D layered sequences obtained from well logs, the structurally complex Marmousi model,
and randomly-heterogeneous media containing spatially-correlated perturbations
in seismic properties. Elastic wavefields are activated by force or moment body
218 Seismological Research Letters Volume 77, Number 2 March/April 2006
sources, or via time-varying surface tractions. A parameterized causal source pulse
called a Berlage wavelet is adjusted to be minimum, mixed, or maximum phase.
Calculated data (with and without additive noise) are processed by a standard wavelet extraction approach, and comparison with the known source wavelet reveals
limitations of the procedure.
We also extract waveforms from high-quality shallow subsurface field seismic
reflection dataset. These data consist of vertical-component particle velocity traces
recorded on a densely-sampled rectangular array of geophones. A mobile surface
impactor source is used. Wavelets are obtained from various offset, azimuth, and
temporal windows (including the coda of scattered arrivals). Numerical modeling of
the seismograms, using the extracted source wavelet and a velocity model obtained
from surface and body wave tomography, tests the consistency of the pulse extraction method. Sandia National Laboratories is a multiprogram science and engineering facility operated by Sandia Corporation, a Lockheed-Martin company, for the
United States Department of Energy under contract DE-AC04-94AL85000.
grid, i.e. the DRP/opt MacCormack scheme with 4-6 LDDRK time integration.
To validate this new method, we performed numerical tests in 2D to several complex models by comparing our results with those computed by other independent
accurate methods. In 3D, we compared our results with those computed by BEM
for a Gaussian hill model. Although some of the testing examples are quite tough,
e.g. with extremely sloped topography, all tested results showed an excellent agreement between our results with those by other methods, confirming the validity of
our method for modeling seismic waves in the heterogeneous media with arbitrary
shape topography. Numerical tests also demonstrated the efficiency of this method.
We found about 10 grid points per shortest wavelength is enough to preserve the
global accuracy of the simulation.
A New Finite-difference Method for Seismic Applications
S. Nilsson, LLNL, [email protected]; A. Petersson, LLNL, [email protected]
gov; B. Sjögreen, LLNL, [email protected]; A. Rodgers, LLNL, [email protected]; K. McCandless, LLNL, [email protected]
Modeling dynamic rupture on a fault within the earth is a typical boundary problem. Although the semi-analytic boundary integral equation method (BIEM) is
suitable for solving such problems with stress concentration on the tip of the crack,
it is limited to full-space medium model so far due to the complexity of Green’s
function. We extended the BIEM by applying the exact Green’s function, which
can be expressed as a double integral in the wavenumber-frequency domain. All the
hypersingularities related with the second derivative of the Green’s function in the
boundary integral equation are completely removed by separating the singular parts
in the integrals, which are canceled by the explicit infinite terms in the boundary
integral equation. Computation of the integral kernels and the dynamic process is
completely separated, making it possible to build a database in advance for a certain active fault. The extended BIEM was applied to investigate the influences of
geometrical and physical parameters, such as the dip angle (δ) and depth (h) of
the fault, radius of the nucleation region (Rasp), slip-weakening distance (Dc), and
stress inside (Ti) and outside (Te) the nucleation region, on the dynamic rupture
processes on the fault embedded in a 3-D half space. In order to gain insight into
the basic feature of the rupture with the influence of the ground surface, all the
heterogeneities are neglected. Numerical results show that (1) overall pattern of the
rupture depends on whether the fault runs up to the free surface or not, especially
for strike slip, (2) although final slip distribution is influenced by the dip angle of
the fault, the dip angle plays a less important role in the major feature of the rupture
progress, (3) different value of h, δ, Rasp, Te, Ti and Dc may influence the balance of energy and thus the acceleration time of the rupture, but the final rupture
speed is not controlled by these parameters. An interesting feature of the dynamic
process on a fault embedded in a 3-D half space is the appearance of a secondary
rupture front propagating at a supershear speed for a strike slip. Numerical simulations indicate that for a fault intersecting the ground surface, all strike-slip faults
can evolve with supershear rupture. However, a dip-slip rupture propagates always
with subshear speed. These features may attribute to the disturbance of shear stress
ahead of the rupture front in the in-plane direction, which is greatly enhanced by
the interaction between the dynamic rupture itself and the ground surface.
We present a finite difference method for computing seismic wave propagation.
While most modern computational methods are based on the elastodynamic equations written as a first order system, we have retained the second order formulation.
Traditionally methods using the second order formulation have suffered from stability problems for high ratios of Vp over Vs near stress free boundaries. We avoid
this problem by a special treatment of the discretized equations close to the boundary nodes. The method is second order accurate in space and time, and conserves a
discrete energy norm. It is therefore stable for all elastic materials where Vp>0 and
Vs>0 holds.
Since the seismic events often are approximated as source terms having the
form of the Dirac distribution and its derivatives in space the solutions are certain
to contain local singularities. We describe some observations we have made on the
convergence properties of the numerical solution and possible improvements in
modeling of the singular parts of the source terms.
Our finite difference method has been implemented in a new code intended
for general elastic wave propagation problems eventually, but so far mainly used
for seismic applications. The code has been written in C++ with occasional calls
to Fortran routines for the computational kernels. Parallelization has been carried
out using the C++ bindings to the MPI-2 libraries and we have observed good scalability for up to 1024 processors on a Linux cluster .
We have successfully carried out extensive verifications of the code on standard test cases with known solutions. Furthermore, we have simulated several small
earthquakes in the Bay area and compared the results to available measured data.
Finally, we have simulated the 1906 event, results from this will be reported elsewhere [Rodgers et al., Petersson et al.].
Some plans for extending the work to include more features will be reported.
Foremost among these is to allow topography on the surface by using an embedded
boundary method to discretize the stress free conditions.
Modeling Seismic Wave with Free Surface Topography Using Traction
Image Method
W. Zhang, Peking University, [email protected]; X. Chen, Peking
University, [email protected]
Finite difference method (FDM) is a popular and efficient numerical tool in seismological study. Both staggered and non-staggered finite difference can be used
to numerical solve the first-order velocity-stress elastic equations. Staggered finite
difference using Stress Image method is particularly efficient for arbitrary complex
medias with flat free surface. For the problems with irregular shape topography,
non-staggered finite difference using body-fitted grid to conform grid lines with
the surface shape is more considerable. But in such scheme, an accurate and efficient free surface numerical treatment method was absent. We developed a new
numerical method, named as Traction Image method, to accurately implement
traction-free boundary conditions in non-staggered finite-difference simulation
in the presence of surface topography. To accurately describe the irregular shape
surface, we applied boundary-conforming gridding which transforms the irregular
surface into a “flat” surface in general curvilinear coordinate. Such precise description of surface topography avoids the artificial scattering caused by the discretization error. To preserve the traction-free condition on surface in the finite difference
simulation based on the boundary-conforming grid, we developed the Traction
Image technique in which the tractions on the fiction image grids above the free
surface are set being antisymmetric to those on the corresponding grids below
free surface along longitude. These effective measures were integrated and implemented in an optimal higher order finite difference scheme with non-staggered
Effects of Ground Surface on Rupture Dynamics of an Earthquake
H. Zhang, Peking University, [email protected]; X. Chen, Peking
University, [email protected]
Earthquake Sources: Theory and Practice
Poster Session
Test of the Split Nodes Fault Model for Faulting in Staggered Finite
Difference Scheme
L. Dalguer, Department of Geological Sciences, SDSU, [email protected]
edu; S. Day, Department of Geological Sciences, SDSU, [email protected]
Traction-at-split node (TSN) fault model for spontaneous rupture simulation is
usually implemented in finite difference (FD) schemes that (1) employ second-order
spatial differencing, and (2) collocate all 3 velocity components at a common set
of grid vertices, with all 6 stress components collocated at the corresponding cell
centroids. Other schemes, such as the fourth-order velocity-stress staggered (VSSG)
FD, do not meet these criteria, because the VSSG scheme defines each component
of stress and particle velocities at different grid points. However, we show that the
TSN treatment can be quite easily adapted to the VSSG scheme if (1) the spatial differencing along the fault plane is reduced to second order, and (2) the nodes of velocities, as well as stresses components that lie on the fault plane are split into plus-side
and minus-side parts, resulting in a velocity-stress staggered traction-at-split node
(VSSG-TSN) fault model. We test this approach by solving a three-dimensional
(3D) problem of spontaneous rupture propagation on a planar fault governed by the
simple linear slip-weakening friction law. The numerical solution convergences rapidly (~dx3) with grid spacing reduction, in contrast to the much poorer convergencerates seen in all previous VSSG rupture models. The solution adequately resolves the
Seismological Research Letters Volume 77, Number 2 March/April 2006 219
cohesive zone (defined by the slip-weakening friction) with as few as 1.5 grid points,
as shown by its agreement with a well-validated reference solution. The proposed
VSSG-TSN model is very easy to implement in standard VSSG wave propagation
codes, and provides an efficient and accurate means of adding spontaneous rupture
capability to them while retaining their other computational advantages.
Optimal Seismic Station Placement for Source Inversion
M. Page, UC Santa Barbara, [email protected]; J. Carlson, UC Santa
Barbara, [email protected]
We investigate how seismic station placement affects earthquake source inversion
resolution. Using a singular value analysis, we search a large parameter space for
optimal station configurations that will result in the greatest amount of information recoverable in an inversion. In addition, we investigate the robustness of the
optimal configurations, both to errors in the response function (Green’s function)
and to changes in station placement. This analysis will help to determine to what
extent optimal choice of seismic arrays can improve the amount of source information recoverable in future inversions.
Resolving Fault Plane Ambiguity Using 3D Synthetic Seismograms
P. Chen, University of Southern California, [email protected]; L. Zhao,
University of Southern California, [email protected]; T. Jordan, University of
Southern California, [email protected]
We present an automated procedure to invert waveform data for the centroid
moment tensor (CMT) and the finite moment tensor (FMT) using 3D synthetic
seismograms. The FMT extends the CMT to include the characteristic space-time
dimensions, orientation of the source, and source directivity (Chen, et al. BSSA,
95, 1170, 2005). Our approach is based on the use of receiver-side strain Green
tensors (RSGTs) and seismic reciprocity (Zhao, Chen & Jordan, 2005). We have
constructed a RSGT database for 64 broadband stations in the Los Angeles region
using the SCEC CVM and K. Olsen’s finite-difference code. 3D synthetic seismograms can be easily computed by retrieving RSGT on a small source-centered
grid and applying the reciprocity principle. At the same time, we calculate the
higher-order gradients needed to invert waveform data for CMT and FMT. We
have applied this procedure on 40 small earthquakes (ML < 4.8) in the Los Angeles
region. Our CMT solutions are generally consistent with the solutions determined
by Hauksson’s (2000) first-motion method, although they often show significant
differences and provide better fits to the waveforms. For most small events, the
low-frequency data that can be recovered using 3D synthetics (< 1 Hz) are usually
insufficient for precise determination of all FMT parameters. However, we show
the data can be used to establish the probability that one of the CMT nodal planes
is the fault plane. For 85% of the events, we resolved fault plane ambiguity of our
CMT solutions at 70% or higher probability. As discussed by Zhao et al. (this meeting), the RSGTs can also be used to compute Fréchet kernels for the inversion of
the same waveform data to obtain improved 3D models of regional Earth structure. This unified methodology for waveform analysis and inversion is being implemented under Pathway 4 of the SCEC Community Modeling Environment.
Friction Laws and Complexity in Earthquake Rupture Dynamics
E. Daub, UC Santa Barbara, [email protected]sics.ucsb.edu; J. Carlson, UC Santa
Barbara, [email protected]
Constitutive laws play a central role in the predictions of dynamic rupture models.
Both the constitutive equations as well as the spatial distribution of parameters dictate the complexity of the resulting earthquake. This is of interest as friction gradients such as barriers give rise to wide ranges of behavior, including arrest, healing,
and transition to supershear. We investigate the dynamic rupture problem with a
variety of friction laws and allow heterogeneities in their parameters on the fault,
and assess the complexity in earthquake ruptures due to friction.
Scaling Law of Slip Pinned by Fault Bends
R. Ando, LDEO, Columbia University, [email protected]; T.
Yamashita, ERI, University of Tokyo, [email protected]
The existence of non-planar geometry such as bends is well known a characteristic of
natural faults with its fractal nature. It is also known that these bends arrest slip like
as pines on faults. In this study, we theoretically investigated this effect of pinning
on the scaling law of slip by taking account of local planarization of fault bends due
to slip in short wavelength. For the purpose of simplification to extract the effect
of the fault bends in an elastic media, we first assume a finite monotonically wavy
fault with no friction under a homogeneous confining load condition, and then we
investigate the effect of different wavelengths keeping a similar shape. As a result,
we find that the mean slip on the entire fault is a decrease function of the assumed
wavelengths of the fault bends with a rate larger than a linear function. In other
words, the overall behavior on the entire fault is sensitive to the geometry in shorter
wavelength; therefore it is crucial to consider how the geometrical irregularities in
the short wavelengths behave during slip events. In order to address this problem, we
next assume that wearing or plastic deformation associated with slip instantaneously
planarizes the bends up to an effective length λeff that is determined by the value of
mean slip S. As solutions of this model, we find that mean slip linearly increases with
fault lengths if λeff ∝ S and the fault has self-similar geometry although the value the
mean slip is smaller than the planar fault case. In this case, the value of mean stress
becomes also scale independent. On the other hand, if the above condition is not
satisfied, mean slip is shown to depend non-linearly on the fault length and then
mean stress drop becomes scale dependent. The former case seems to correspond
with observations in nature where many ones suggest stress drop is a scale invariant.
Fault Interaction in Alaska: Coulomb Stress Transfer and Periodic Clustering
C. Bufe, U. S. Geological Survey, [email protected]
Coulomb stress transfer has been modeled from the 9 largest (M 7.5 or greater)
earthquakes in eastern Alaska since 1900. Transferred stresses from these sources
were computed on 30 target fault segments, including 16 segments associated with
the above major source earthquakes. A map of cumulative Coulomb stress transfer
prior to failure indicates stresses in excess of 100 kPa preceded failure of the southern Gulf of Alaska, Denali-Totschunda, Sitka, and Kodiak segments. A map of
transfer since the last rupture, or since 1938 in the absence of rupture, indicates the
presence of transferred stresses in excess of 100 kPa, locally approaching 1 MPa, at
seismogenic depths on the west Yakataga gap, on the Castle Mountain fault, on the
Cross Creek fault, on the Nenana-Susitna and Denali Park segments of the western Denali fault, on the southern part of the Totschunda-Fairweather gap, on the
northern offshore segment of the Fairweather fault that ruptured in 1958, and on
the northern and Cape St. James segments of the Queen Charlotte fault. Coulomb
stresses transferred to the slowly slipping Denali—Totschunda fault system may
result in significant earthquake probability increases or decreases. On the other
hand, high tectonic loading rates on the Fairweather—Queen Charlotte transform fault system limit the advance toward (or retreat from) time of failure due to
stress transfer. Other relaxation or triggering mechanisms may explain the time lag
between static stress transfer and failure. Analysis of consecutive inter-event times
and distances for M 7.5 or greater earthquakes in a larger region extending from the
Queen Charlotte to the Rat Islands, over the period 1949-2003, shows a tendency
toward periodicity and temporal clustering of widely separated events, suggesting a
large scale periodic trigger mechanism such as the Chandler wobble.
Homogeneity of Small-Scale Earthquake Faulting, Stress and Fault Strength
J. Hardebeck, USGS, [email protected]
I find small-scale faulting at seismogenic depths in the crust to be more homogeneous
than previously thought, based on three new high-quality focal mechanism datasets
of small (M<~3) earthquakes in southern California, the east San Francisco Bay, and
the aftershock sequence of the 1989 Loma Prieta earthquake. I quantify the degree
of mechanism variability on a range of length scales by comparing the hypocentral
distance between every pair of events and the angular difference between their focal
mechanisms. Closely-spaced earthquakes (inter-hypocentral distance <~2 km) tend
to have very similar focal mechanisms, often identical to within the 1-sigma uncertainty of ~25 degrees. This observed similarity implies that in small volumes of crust,
while faults of many orientations may or may not be present, only similarly-oriented
fault planes have produced earthquakes over the past ~20 years. On these short
length scales, the crustal stress orientation and fault strength (coefficient of friction)
are inferred to be homogeneous as well, to produce such similar earthquakes. Over
larger length scales (~2-50 km), focal mechanisms become more diverse with increasing inter-hypocentral distance (differing on average by 40-70 degrees.) Mechanism
variability on ~2-50 km length scales can be explained by relatively small variations
(~30%) in stress or fault strength. It is possible that most of this small apparent heterogeneity in stress or strength comes from measurement error in the focal mechanisms, as negligible variation in stress or fault strength (<10%) is needed if each
earthquake is assigned the optimally-oriented focal mechanism within the 1-sigma
confidence region. This local homogeneity in stress orientation and fault strength is
encouraging, implying that these parameters are stable over large enough areas that it
may be possible to map stress and strength onto fault surfaces with enough precision
to be useful in studying and modeling large earthquakes.
Pulverized Rocks in the San Andreas Fault Zone
O. Dor, USC, [email protected]; M. Sisk, SDSU, [email protected]; Y. BenZion, USC, [email protected]; T. Rockwell, SDSU, [email protected]
edu; G. Girty, SDSU, [email protected]
Recent mapping of crystalline Pulverized Fault Zone Rocks (PFZR) along the
Mojave section of the SAF (Dor et al., EPSL, 06) shows that they occupy a ~100 m
220 Seismological Research Letters Volume 77, Number 2 March/April 2006
wide tabular zone parallel to the fault. About 70% of the cumulative area of the
outcrops was found NE of the principal slip zone, suggesting that the SAF has an
asymmetric structure with more damage on the NE side of the fault, consistent with
smaller scale mapping results of Dor et al. (Pageoph 06). Apparent pulverization of
sedimentary rocks, depositional contact between formations of different, successive
ages starting in the Miocene, small maximum exhumation depth inferred for sections of the fault and various other evidence suggest that the observed pulverization
occurred at relatively shallow depth. The results are compatible with expectations
for ruptures on an interface that separates different elastic media, with a preferred
propagation direction (e.g., Ben-Zion and Shi, EPSL 05; Shi and Ben-Zion GJI 06).
To better understand the properties of the PFZR and the generating mechanisms,
we performed laboratory measurements of PFZR including particle size distribution, bulk and grain density, porosity, mineral XRD, major and trace element
chemistry, thin section, and SEM. The main goals are to find out to what extent the
pulverization is a result of mechanical (dynamic) processes vs. in situ weathering; to
assess the control of the rock type on the pulverization intensity and pattern; and
to quantify the damage/pulverization level of sedimentary rocks that were never
deeply buried. This last item is significant for the question of the depth extent of
pulverization. Results from this laboratory work will be presented in the meeting.
Structural and Wave Phenomena Effects on Double Couple Focal
Mechanisms
L. Preston, University of Nevada Reno, [email protected]; D. von
Seggern, University of Nevada Reno, [email protected]
We have developed a focal mechanism estimator that utilizes P, SH, and SV
amplitudes in addition to P first-motions. The software interfaces with an existing
Antelope database and allows the user to pick/change polarities and amplitudes
and to guide the solution process by varying the relative weights between firstmotion and amplitude data. The solution is based on a grid search of strikes, dips,
and rakes assuming a double-couple mechanism in a layered earth model. Error
bounds of the P- and T-axes are also displayed based on statistical F-tests. As part of
the testing and qualification of the software for use in general network operations
at NSL, we are using the finite-difference full 3-D waveform generation program
E3D developed at Lawrence Livermore National Laboratory. E3D is able to operate using general 3-D models, topography, attenuation and general source models,
allowing us to assess the effects of these realistic earth properties on focal mechanism solutions up to about 1 Hz frequency. Although in many cases inadequate
station coverage is responsible for poorly resolved focal mechanism solutions, our
primary interest here is the effects of non-modeled structure and wave phenomena
not accounted for in standard ray theory. For our tests, we used the true station coverage within the Yucca Mountain seismic monitoring network within about 40 km
of Yucca Mountain, which yields nearly 60 stations. Even using homogeneous halfspace models with free surface corrections, wave phenomena, such as diffraction
along the free surface, wavefront healing effects, and interference cause significant
discrepancies between ray-theory-based amplitude predictions and E3D-calculated
waveforms, ranging up to or more than a factor of five near nodal planes. Although
first-motion data and SH amplitudes give the expected solution perfectly in this
noise-free simulation, P and SV amplitudes give the solution within several degrees.
We will present the results of the effects of topography, velocity models, and earthquake mislocation both individually and together. We will quantify what such
effects have on the first-motions and P, SV, and SH amplitudes and the resulting
ability to resolve focal mechanism solutions.
A New Paradigm for Inferring Stress Using Focal Mechanism Orientations
D. Smith, California Institute of Technology, [email protected]; T.
Heaton, California Institute of Technology, [email protected]
Increasing evidence suggests that stress is heterogeneous in the Earth, but very
little is known about its characteristics in 3D. This research focuses on producing
numerical models of heterogeneous stress in 3D, then exploring the consequences
on observables such as focal mechanism orientations, seismic clustering, and apparent stress rotations after mainshocks such as Landers. In generating the heterogeneity, we took great care to produce fractal deviatoric stress that has approximately no
orientation bias within our 3D grids. When we compare our synthetic focal mechanism catalogues (from our fractal heterogeneous stress) to the real Earth, we obtain
rough estimates for the characteristics of stress heterogeneity in different regions.
Two numbers describe the fractal heterogeneous stress: 1) Alpha, which is the
spectral falloff of any 1D cross-section through our 3D grid. If Alpha = 0, we have
approximately white noise, and as Alpha increases the stress is increasingly spatially
smoothed. 2) Heterogeneity Ratio, which describes the relative size of the heterogeneity (which has no mean value) to the background stress (a spatially homogeneous
mean stress). If Heterogeneity Ratio << 1, then there is little to no heterogeneity
and if Heterogeneity Ratio >> 1, then the heterogeneity is much larger than the
spatial mean. After testing different fracture criteria, we decided to primarily use
a plastic yield criteria for its simplicity. Coupling our fractal heterogeneous stress
and spatial mean background stress with a stressing rate that brings points to failure
under our failure criteria, we produce synthetic focal mechanism catalogues. We
find that when Heterogeneity Ratio << 1, there is little to no variation in the focal
mechanism orientations. Additionally, the P-T plots align with the spatial mean
background stress. When Heterogeneity Ratio >> 1, there is great variation in the
focal mechanism orientations and the P-T plots are on average aligned with the
stressing rate. Focal mechanism inversions of our data also show similar trends, i.e.,
when Heterogeneity Ratio >> 1, the inverted stress tensor is approximately aligned
with the stressing rate. If in some regions of the real Earth the stressing rate orientation does not align with the background stress orientation and Heterogeneity Ratio
≥ 1, this could require reinterpretations of stress studies that utilize focal mechanism data. Using our simulations, we estimate for two regions, the Southern San
Andreas and the San Gabriel Mountains, the orientation bias towards the stressing
rate, as a function of Heterogeneity Ratio. We also compare simulated results with
Jeanne Hardebeck’s focal mechanism data to estimate the parameters Alpha and
Heterogeneity Ratio for Northern California, East Bay and Southern California.
Last, we model apparent stress rotations after mainshocks and propose a new interpretation. Namely, if the stress is spatially heterogeneous in 3D, the rotation is due
to the perturbation in stress not the pertubation + mean stress; therefore, one can
achieve the observed rotations in seismicity with a non-zero spatial-mean background stress.
Fault Mechanisms of Recent Earthquakes in the Aegean Region Inferred
from Regional Moment Tensor Inversions.
N. Meral Ozel, Bogazici University Kandilli Observatory and ERI, [email protected]
boun.edu.tr; M. Yilmazer, Bogazici University Kandilli Observatory and ERI,
[email protected]
The recent sequence of earthquakes in the Sıgacik-Aegean region (Ml=5.7, Ml=
5.8, Ml= 5.9 and their aftershocks occurring within the period 17 October to 30
November, 2005 were recorded by broad band seismic stations in Aegean Region
and enabled the analysis of their fault mechanisms. The analysis of these regional
earthquakes provides useful information to better characterise the geology and seismotectonics of the region. It should be noted that most of the moderate-size earthquakes recorded in this region did not rupture the surface, thus, their source mechanisms solutions provide essential information for the association of the activity with
mapped faults and possibly help identification of unknown faults. The Regional
Moment Tensor (RMT) inversion method has been applied to analyse the SıgacikAegean region earthquake activity. The moment tensor inversion was performed
in three frequency bands, which depend on the magnitude of the event; ranging
from periods 10-30 sec for 3.6<M<4.5, through 20-50 sec for 4.5<M<5 and 20100 sec for M>5, up to the window 50-200 sec for the largest events occurring in
the region. RMT solutions are determined for about 38 events recorded by the BB
stations of Kandilli Observatory and some BB stations of the Greeks seismic network. Majority of the events (32) show strike slip with an oblique component. One
of the nodal planes is striking NE-SW and the other shows northwest strike with
normal mechanisms. This earthquake activity was observed in the southern margin
of the Gulbahce fault, around Sıgacık bay in a region concidered to be under N-S
extension as a response to the westward motion of Anatolian block. The observed
solutions, showing NE-SW oriented strike-slip faulting, are in agreement with
the bathymetric and the multi-channel seismic surveys conducted in this region.
The aftershocks occurring in the region also align in the east-norteast directions in
accordance with the computed mechanisms.
Twelve Years and Counting: Regional Moment Tensors in and around
Northern California
M. Hellweg, Berkeley Seismological Laboratory, [email protected]; L. Gee, Albuquerque Seismic Lab, USGS, [email protected]; D.
Dolenc, Berkeley Seismological Laboratory, [email protected]; D.
Templeton, Berkeley Seismological Laboratory, dennise[email protected]
edu; M. Xue, Berkeley Seismological Laboratory, [email protected];
D. Dreger, Berkeley Seismological Laboratory, [email protected]; B.
Romanowicz, Berkeley Seismological Laboratory, [email protected]
edu.
As part of the Rapid Earthquake Data Integration (REDI) system, moment tensor
(MT) solutions have been automatically calculated for Northern California earthquakes with ML > 3.5 since 1994, using both a complete waveform (CW) and a
surface wave (SW) algorithm. In general, these preliminary solutions, calculated
using broadband data from the stations of the Berkeley Digital Seismic Network
(BDSN), are completed 9 to 15 minutes after the earthquake occurs. Before publishing, the solution is reviewed by an analyst, often one of Berkeley Seismological
Laboratory’s (BSL) graduate students. The BSL MT catalog is available on the web
at http://seismo.berkeley.edu/ ~dreger/mtindex.html. In addition to Northern
Seismological Research Letters Volume 77, Number 2 March/April 2006 221
California events, the catalog contains mechanisms for several earthquakes from
western Nevada, and southern and off-shore Oregon. Both MT methods have
been adapted to determining solutions for local and regional earthquakes with
Greens functions and mode files calculated specifically for California. If the event
is located in the California Coast Ranges, gil7 is used, mend1 for events offshore
of Cape Mendocino and socal for all other areas of Northern California. This level
of regionalization appears sufficient for moment tensor recovery in the 20 to 100
second passband. Overall, the mean difference (m.d.) between Mw and ML is small
(m.d. = 0.06). However Mw is signficantly greater than ML in two regions—the
North Bay/Geysers (m.d. = 0.26) and the Cape Mendocino/Gorda plate areas
(m.d. = 0.19). In both these regions, discrepancies may be as much as one magnitude unit. There is evidence that this is due to source processes. This is balanced
by ML > Mw (m.d. = 0.28) in eastern California, which may be a path effect. We
present MT analysis from several interesting cases, such as small, recent events in
Long Valley with significant non-double-couple components, and an assessment of
the Crest stations in northwestern California. We review the MT for the Mw 4.8
off-shore Oregon event on July 12, 2004, in light of data from the Oregon Array for
Teleseismic Study (OATS).
The Real-time SCSN Moment Tensor Solution: Robustness of Mw, and Style
of Faulting.
J. Clinton, UPRM / ETH Hoenggerberg, [email protected]; E.
Hauksson, Caltech, [email protected]
We have automatically generated moment tensor solutions and moment magnitudes (Mw) for >1700 earthquakes of local magnitude (ML) >3.0 that occurred
from September 1999 to November 2005 in Southern California. The method
is running as a realtime component of the Southern California Seismic Network
(SCSN), with solutions available within 12 mins of event nucleation. For local
events, the method can reliably obtain good quality solutions for Mw with
ML>3.5, and for the moment tensor for events with ML>4.0. The method uses
the 1-D Time-Domain INVerse Code (TDMT_INVC) software package by
Doug Dreger. The Green’s Functions have been predetermined for various velocity
profiles in Southern California, which are used in the inversion of observed three
component broadband waveforms (10 s-100 s), using data from at least 4 stations.
Automatic solutions have an assigned quality factor dependent on the number of
stations in the inversion, and the goodness of fit between synthetic and observed
data. If a minimum quality factor is attained, the ML or Mw is 5.0 or greater, and if
the event is in the Southern California reporting regions, the Mw will be the official
SCSN/CISN magnitude.
The Mw from the high quality solutions determined from our method generally correlate very well with ML, except in regions at the perimeter of the network.
The Mw reported here indicate the SCSN ML systematically underestimates the
magnitude in Baja, Mono Lakes area, Coso region and the Brawley seismic zone,
and overestimates the magnitude in the Coastal Ranges.
Comparisons of the moment tensors determined using this model are made
with Harvard Centroid Moment Tensors generated for larger earthquakes in the
California region, and recent 3-D models for events in the LA region, with excellent correlation.
Most of the earthquakes with good quality solutions exhibit strike-slip faulting, in particular along the major late Quaternary strike-slip faults. Thrust faulting
on east-west striking planes is observed along the southern edge of the Transverse
Ranges, while northwest striking thrust faulting is observed in the Coast Ranges.
Normal faulting is most common in Baja California and southern Sierra Nevada
including the western Basin and Range region.
The Mw values can be unreliable due to excessive background noise in the
waveforms, which can originate from ambient noise, a very recent mainshock, or
distant teleseisms.
Local and Moment Magnitude Scales in the Iranian Plateau Based on
Strong Motion Records
J. Shoja-Taheri, Ferdowsi Univ. of Mashad, Earthquake Research Center,
[email protected]; S. Naserieh, Ferdowsi Univ. of Mashad, Earthquake
Research Center, [email protected]; H. Ghofrani, Ferdowsi Univ. of
Mashad, Earthquake Research Center, [email protected]
Availability of large number of recorded strong motion data by the Iranian strong
motion Network has motivated this study to develop relations for routine determination of ML and MW from digital horizontal components of the strong motion
records. The datasets is comprised of about 800 accelerograms recorded by 82
earthquakes of magnitude 4.5 and larger. For MW scale the objective technique was
employed. Testing variety of time windows shows that the estimated MW values are
best correlated with the corresponding values reported by teleseismic data when S
window durations are chosen. The regression has the form of Mwo= (0.92 ±0.08)
Mwt + (0.45±0.22). Mwo and Mwt are respectively the estimated and reported
moment magnitudes. The ML scale is based on the horizontal synthesized WoodAnderson seismograms. We have employed the Monte Carlo technique to evaluate
-logA0 as a function of distance. Results indicate that the attenuation curve has
three distinct sections. At distances less than 65 km amplitudes decay slightly less
rapid than 1/R (R0.94). Between 65 and 106 km, amplitudes are approximately
constant. Between 130 and 200 km, amplitudes decay at a rate that is consistent
with R-0.5. Finally, the relationship between the local and moment magnitudes in
Iran using strong motion data is: ML= (0.59± 0.06) MW + (2.60±0.15)
Size Scaling of Signals in the Early Portion of P Waveforms
m. Lewis, University of Southern California, [email protected]; Y. Ben-Zion,
University of Southern California, [email protected]>.
The process of earthquake rupture is normally described by a cascade model in
which the eventual event size is determined by the stress on the fault and not the
nucleation process. Some studies however reported scaling with magnitude of signals, which may be related to the nucleation process, early in the P waveforms. In
this study we use a large data set to investigate if any scaling can be observed with
a variety of proposed techniques. Umeda (1990) and Ellsworth and Berzoa (1995)
suggested that P waveforms are characterized by an initial phase of low amplitude
followed by strong motion of the main event, and that the time between these two
scaled with the final magnitude. Iio (1995) measured the time difference between
the very first onset and the projected onset if the P wave was a ramp function, and
suggested that this scaled with final event size. A second set of methods, following Nakamura (1988), Allen and Kanamori (2003) and Kanamori (2004), look at
how the frequency content of the waveform in the first few seconds changes with
final event magnitude. Using data generated by clusters of similar earthquakes on
the Karadere-Duzce branch of the North Anatolian fault, we search systematically
for the Ellsworth/Berzoa-type nucleation, Iio-type nucleation, and Nakamura-type
period in the early P waveforms. The cross correlation coefficient of the waveforms
in each cluster is >0.95, giving sets of data generated by events with very similar
source locations. The great reduction of variations in site and path effects allows us
to focus more accurately on scaling that might exist in source properties. However,
the available magnitude range of events in each cluster is limited to about 3 units or
less. From an initial study of about 700 waveforms, we find that Ellsworth/Berzoatype initial low amplitude phase exists only 10% of the time. This phase and the
Iio-type phase do not appear to scale with the final events size. In contrast, measurements of the Nakamura-type period in the first few seconds show a scaling with the
final event magnitude, although with large scatter.
Energy Partition and Scaling Relations during Earthquake Rupture
Processes
Z. Shi, University of Southern California, [email protected]; A. Needleman,
Brown Unviersity, [email protected]; Y. Ben-Zion, University of
Southern California, [email protected]; D. Coker, Oklahoma State Unviersity,
[email protected]
We perform 2D finite element simulations to study the evolution of energy quantities during dynamic ruptures in a model that incorporates geologically-relevant
aspects of fault zone structure and laboratory-based rheology. The main goal is to
improve the understanding of the energy partition between dissipative mechanisms
(e.g., heat, creation of new surface areas, plastic strain) and seismic radiation in
structures at different evolutionary stages. We also attempt to clarify properties of
dynamic ruptures in different model realizations (e.g., nucleation and arrest processes, crack vs. pulse modes, possible generation of opening modes) and study
the scaling relations between various source parameters (e.g., apparent stress, rapture velocity, radiation efficiency). Immature fault zones are represented by model
realizations consisting of a homogeneous solid with geometrically complex initial
structures. On the other hand, mature fault zones are represented by realizations
with geometrically simple initial structures and/or incorporation of material contrast. Initial results will be presented in the meeting.
Can Seismic Energy Radiation be Estimated From Near-Fault Ground Motion
and Mapped Over Earthquake Fault Zones?
A. McGarr, usgs, [email protected]; J. Fletcher, usgs, [email protected]
Rivera and Kanamori (2005) claim that the method developed by McGarr and
Fletcher (2002) for estimating seismic energy ES by analyzing near-fault energy flux
is flawed because it does not take into account interactions between slips within different portions of the fault plane. To address the question of how these interactions
might affect estimates of ES based on near-fault energy flux, we used kinematic
slip models developed for the M7.3 Landers and M6.7 Northridge earthquakes to
calculate ES directly by integrating the energy flux, at distances of about 200 km,
over the focalsphere. First, we found that estimates of radiated energy in the farfield from individual subfaults agree with estimates reported previously using near-
222 Seismological Research Letters Volume 77, Number 2 March/April 2006
fault energy flux. Second, to test for the effects of interactions between different
fault patches, we calculated ES for the whole earthquake by averaging the energies
calculated for 172 different directions in a homogeneous whole-space. Although
the energy flux for a particular direction shows the effects of the interactions, either
constructive or destructive, if averaged over many directions, then these interference effects cancel. For both the Landers and Northridge earthquakes, the far-field
energy estimates agree closely with the near-fault estimates published before. Thus,
interactions due to slip on different portions of an earthquake fault appear to have
no significant effect on the total seismic energy radiated into the far field. This
implies that the near-fault energy flux, measured from slip models, can be used to
map seismic energy radiation over the fault zone of an earthquake.
Aftershock Abundance: Forecasting Aftershock Rates When Catalog
Completeness Is High
A. Christophersen, Victoria University of Wellington, Annemarie.
[email protected]; M. Gerstenberger, Institute of Geological
and Nuclear Sciences, [email protected]
In May 2005, the United States Geological Survey began publishing daily online
maps of short term earthquake probabilities (STEP) for California (http://pasadena.wr.usgs.gov/step/). The input to the probability model are earthquake rates
which are calculated from two empirical laws for earthquake clustering: The modified Omori’s law for the decay of aftershock activity with time and the GutenbergRichter relation for the distribution of earthquake magnitudes.
Immediately following a large earthquake, the completeness magnitude is
high as smaller earthquakes are not detected. Thus, in the initial time after a mainshock, the STEP model relies on generic aftershock behavior when calculating
forecasts.
We present an alternative formulation of aftershock rates which can be
adjusted for an on-going sequence, even if the amount of data is limited. The rate is
based on the abundance, i.e. the average number of aftershocks per mainshock in a
time interval which in retrospective analysis is deemed to be complete. The modified Omori’s law can be applied to relate the number of earthquakes in the model
time interval to the expected number of earthquakes in any other time interval. The
Gutenberg-Richter relation is used to distribute the expected rate of aftershocks in
magnitude. In real time, the observed number above an estimated completeness is
compared to the model expectation and used to up-date the model parameters.
Using the ANSS catalog, we defined earthquake clusters via a two step process. First the catalog was searched for sequences containing at least one earthquake
above a minimum magnitude. We trialled different search radii and decided on a
window size in space derived from a declustering method for the Californian catalogue. Each sequence with at least 3 earthquakes was fitted by an ellipse using the
scatter of the epicentres. A time window of up to 10 days from the most recent event
associated with the sequence was used to determine the duration of the sequence.
Events within the ellipse were further analyzed to derive aftershock parameters. We
used the time interval 0.1 to 10 days for mainshocks between magnitude 3.0 and
6.5 to determine the model abundance.
Earthquake CORE: Culture, Outreach, Resources and
Education
Poster Session
the current tendency of almost all local agencies to focus their efforts on rapid dissemination of earthquake information, it is the ISC that becomes the source for
the most complete earthquake information. We wait more that a year for all possible earthquake data to be collected before we can start analyzing it and editing the
bulletin. The time required to complete the data collection is determined by the
many agencies that send the data. As soon as the data are parsed and inserted into
the database, contributed hypocenters are grouped and phase readings are associated with the automatically selected primary hypocenters. This automatic process
is repeated every few days and the information is available, on-line, from the ISC
website. Many of these events will be relocated by ISC seismologists who manually
review every event that complies with one of the following conditions: .
The reported magnitude is higher than 3.5.
The event was reported by at least 2 agencies.
The event was recorded at a distance greater than ~1000 km. An /ISC solution/ is provided when: There are more than 4 phase readings (P or S) and when
the solution converges successfully. On the average, about 3500 events with more
than 150,000 associated readings are reviewed each month. Other services of ISC
involve maintenance of the International Registry of seismic stations (jointly with
USGS/NEIC), Links to web-sites with additional seismological information,
Information about seismologists and seismological institutions (national points
of contact), Bibliography lists, reports and documentation of ISC’s software. Visit
www.isc.ac.uk <http://www.isc.ac.uk/> for move details.
The COSMOS VDC (http://db.cosmos-eq.org/): a Search Engine for
World-wide Strong-motion Data
R. Archuleta, UCSB, [email protected]; J. Steidl, UCSB, [email protected]
crustal.ucsb.edu; M. Squibb, UCSB, [email protected]
The COSMOS Virtual Data Center (VDC) continues to expand its metadata database and to add services for the web user. As of Jan 1, 2006, the VDC provides access
to 513 earthquakes, 3,103 stations, and 26,579 acceleration traces. The database has
grown rapidly with the inclusion of large data sets, including several earthquakes
off Honshu, Japan and the 2005 Anza and Northern California earthquakes. The
VDC continues to add all current available data from its data providers, including
CGS and the USGS, as well as historical data of interest, including the NGDC
dataset. The VDC is dedicated to the inclusion of all stations for all earthquakes
that meet its criteria: magnitude of 5.0 or greater in active tectonic regions (e.g.
Southern California, and Japan), and 4.5 in less active tectonic regions (e.g. Eastern
United States). The COSMOS VDC offers a variety of search mechanisms: mapbased, earthquake and station lists, and by range or keyword on database fields;
and has the capacity to zip data files at the time of download. The VDC also sends
new event notices to previous users of the database. In the last year, the VDC has
expanded and refined its configurable design spectra overlay for response spectra
and improved search options. Direct access from the VDC Station pages to the
COSMOS Geotechnical VDC, which contains borehole information, is currently
under development, as is an improved map interface. In 2006, the VDC expects
to provide records in standard COSMOS formats, in addition to their native
format. Under concurrent development is a downloadable tool for conversion of
COSMOS format files to a variety of file types, including html files, legacy formats,
browser viewable plots, and files compatible with spreadsheet and mathematical
analysis applications. The COSMOS VDC is currently supported by the USGS,
CGS, NSF and COSMOS.
USGS Earthquake Hazards Program Unveils Redesigned Website
L. Wald, USGS, Golden, [email protected]
International Seismological Centre—an Update
M. Aspinwall, ISC, [email protected]; M. Botlon, ISC, [email protected]
ac.uk; P. Dawson, ISC, [email protected]; J. Harris, ISC, [email protected]; A.
Shapira, ISC, [email protected]; D. Storchak, ISC, [email protected]
The /International Seismological Centre/ is a non-governmental, non-profit making organization, charged with the final collection, analysis and publication of
earthquake source information from all over the world. Earthquake data is received
from more than 100 seismological agencies representing every part of the globe.
This data comprises readings from almost 3,000 seismograph stations. The Center’s
main tasks are to re-determine earthquake locations and magnitudes, making use of
all available information and to search for new earthquakes, previously unidentified
by individual agencies and distribute this information to the global seismological
community. The International Seismological Centre, ISC, is widely recognized as
the source of the most comprehensive reliable listing of global seismicity data. This
information is made available by the ISC through CD-ROMs and on-line Bulletins
and Catalogues from the ISC website. The ISC international team, of only 7
people, is integrating the efforts of seismologists who run stations and networks
around the world and provide readings of phase arrivals and amplitudes. The ISC
builds on those efforts to locate tens of thousands of earthquakes each year. With
On January 31, 2006 the U.S. Geological Survey Earthquake Hazards Program
(EHP) unveiled a completely redesigned website. The new website uses a database
backend for content management, and the most current web techniques for easy
maintenance of the overall appearance of the website. Additionally, new bureau
recommendations for USGS websites have been incorporated into the new design.
Other websites in the EHP are being incorporated onto the same webserver and
into the overall EHP website structure, with the goal of making earthquake information easier to find for Internet users. The website is divided into five sections:
Earthquake Center, Regional Information, Learning & Education, Research &
Monitoring, and Additional Resources. 1) The Earthquake Center section offers
real-time earthquake information, including Latest Earthquake maps and lists,
ShakeMaps, moment tensors, real-time feeds, and the new Earthquake Notification
Service (ENS), along with historic earthquake information and access to scientific
data. 2) The Regional Information section contains links to Advanced National
Seismic System (ANSS) regions, National Seismic Hazard Maps, Quaternary
Faults, regional offices, and earthquake information by State or Country. 3) The
Learning & Education section has resources for learning about earthquakes, including Earthquakes for Kids, FAQ, Preparedness & Response information, glossary,
USGS earthquake-related publications, photo collections, and a new Earthquake
Seismological Research Letters Volume 77, Number 2 March/April 2006 223
Topics area. Each topic is associated with a list of USGS and non-USGS webpages
for learning about that particular topic. 4) The Research & Monitoring section contains links to research projects and products organized by topic, ANSS and other
seismic monitoring network information, and scientific data links. 5) Finally, the
Additional Resources section has links to USGS Products & Publications, other
USGS organizations and related non-USGS organizations. As with any good
website, the EHP website will continue evolving, growing, and improving with
time with the incorporation of other EHP websites and additional products and
resources. Future plans include an upgrade of the Latest Earthquakes maps, and the
addition of PAGER (Prompt Assessment of Global Earthquakes for Response, see
related abstract on ANSS products). The EHP website URL is http://earthquake.
usgs.gov/.
The Station Information System (SIS) at the Southern California Earthquake
Data Center (SCEDC)
V. Appel, California Institute of Technology, [email protected]; R.
Clayton, California Institute of Technology, [email protected]
The Southern California Earthquake Data Center (SCEDC) has developed the
Station Information System (SIS) to manage station metadata for the Southern
California Seismic Network (SCSN). The goal of this project was to develop a system that could interact with a single database source to enter, update and retrieve
station metadata easily and efficiently.
The system provides the SCSN real-time processing system with accurate
response information for all active stations in the network, as well providing
research users with quality station/channel information for stations that have parametric and waveform data archived at the SCEDC. The SIS stores all information
required to generate dataless SEED and COSMOS V0 volumes on the fly and provides users with an interface into complete and accurate station metadata for all
modern and currently-operating stations, as well as complete-as-possible information for historic stations. The SIS allows stations to be added to the system with a
minimum, but incomplete set of information, using predefined defaults that can
be easily updated if more information on the station becomes available. As a direct
result of our SIS efforts, the SCEDC is in a position where we can effectively manage our station data and easily exchange and integrate our metadata with our CISN
partners and other organizations
Summary of the ISC Bulletin of Events of 2003
D. Storchak, International Seismological Centre, Thatcham, UK., [email protected]
isc.ac.uk; M. Bolton, International Seismological Centre, Thatcham, UK.,
[email protected]
The ISC Bulletin for the year 2003 is now available on the Internet and the ISC
CD Volume 14. In our presentation, we give an overview of the data published
in the Bulletin. We describe the major sources of parametric data contributed to
the ISC and compare the data sets from other global data centres with that of the
ISC. We evaluate the importance of re-analysis on a global scale from the distribution of events for which the ISC associates independently reported phase readings
or hypocentres. We discuss the overall and regional completeness of the Bulletin
as well as completeness in the oceanic and continental areas. We exhibit and give
explanation for the differences between locations and magnitudes computed by the
ISC, IDC and NEIC. We also give a summary of “new” events discovered by the
ISC from previously unassociated phase readings, and other events of special interest in the Bulletin. We discuss the magnitude threshold policy, which was applied
to select events for manual review at the ISC and show the difference between the
Collected, Reviewed and Comprehensive ISC bulletins available on-line.
Updating Default Depths in the ISC Bulletin
M. Bolton, International Seismological Centre, Thatcham, UK., [email protected]
ac.uk; D. Storchak, International Seismological Centre, Thatcham, UK., [email protected]; J. Harris, International Seismological Centre, Thatcham, UK.,
[email protected]
The International Seismological Centre (ISC) publishes the definitive global bulletin of earthquake locations. In the ISC Bulletin, we aim to obtain a solution with
a free depth, but often this is not possible. Subsequently, the first option is to then
obtain a depth derived from depth phases (3.2% of ISC hypocentres). If sufficient
depth phases are not available, we then use the reported depth from a reputable
local agency (17%). Finally, as a last resort, we set a default depth (29%).
In the past, common fixed depths of 10 km, 33 km, or multiples of 50 km
have been assigned. Assigning a more meaningful default depth, specific to a seismic region will increase the consistency of earthquake locations within the ISC
Bulletin and allow the ISC to publish improved positions and magnitude estimates.
Additionally, we hope to acquire a better association of reported secondary arrivals
to corresponding seismic events.
We aim to produce a global set of default depths, based on a typical depth for
each area, from well-constrained events in the ISC Bulletin or where depth could
be constrained using a consistent set of depth phase arrivals provided by a number
of different reporters.
In certain areas, we must resort to using other assumptions. For these cases,
we use a global crustal model, Crust2.0 [Bassin et al., 2000], to set default depths to
half the thickness of the crust.
Public Education—Disaster Preparedeness Education Program in Turkey
O. Cakin, Bogazici University, Kandilli Observatory & ERI, [email protected]
tr; M. Petal, Bogazici University, Kandilli Observatory & ERI, [email protected]
com; S. Sezan, Bogazici University, Kandilli Observatory & ERI, [email protected]
edu.tr; Z. Turkmen, Bogazici University, Kandilli Observatory & ERI, [email protected]
Following the devastating 1999 Kocaeli earthquake in Turkey USAID Office of
Foreign Disaster Assistance provided support to Bogazici University, Kandilli
Observatory and Earthquake Research Institute (BU KOERI) to undertake
the Istanbul Community Impact Project, in 2000. Within three years this led to
establishment of the Disaster Preparedness Education Program with national
impact and then a department called Disaster Preparedeness Education Unit at
BU KOERI. The program faces the challenge of devising strategies to reach out
to large urban populations, to empower people at the individual, family, school,
workplace, agency, organization and neighborhood level to participate in disaster mitigation and consists of four education programs which are Basic Disaster
Awareness(BDA), Community Disaster Volunteers(CDV), Structural Awareness
for Seismic Safety(SASS), Non-Structural Mitigation(NSM) and outreach to hospitals, people with disabilities and schools.
BDA program was delivered by seminars and a “cascading” model of instructor training developed in cooperation with the Ministry of Education, several
non-governmental and neighborhood organizations and one large municipality in
Istanbul. The success of these efforts led to a follow-on project with the Republic
of Turkey Ministry of Education to expand the program to 50 provinces and five
million children in high-risk areas throughout the country, and the development
of a distance-learning curriculum to reach out through cyberspace to all corners
of Turkey. Besides, instructor training of teachers from Technical High Schools
for SASS and NSM programs were implemented as a pilot study in Istanbul. The
development of a curriculum for CDV involved two CERT/USAR experts from
California. Later, college instructors from the Republic of Turkey Civil Defense
Directorate collaborated to produce a jointly logoed curriculum to disseminate it
throughout the country.. With support from American Red Cross, a curriculum for
NSM was developed based on a research on effective methods of anchoring building contents At the community level, all programs are disseminating by volunteer
instructors of Turkish Red Crescent Society and several NGOs.
What’s Shaking? Teaching about the Hazard of Earthquakes in Public High
Schools
E. Iversen, NCPACE, [email protected]
Communicating the hazards of earthquakes to teenagers is challenging. Most of the
students currently in secondary school have not experienced a significant temblor
since the last one occurred in the San Francisco Bay Area seventeen years ago. The
problem is that the event is viewed as part of the past and not as prologue. This
attitude is not limited to teenagers by any means!
In my paper I will present an interdisciplinary curriculum I developed using
equipment and publications that are available to teachers everywhere. My objective
was to incorporate theoretical and empirical activities into a course that was both
educational and fun. Materials and equipment were borrowed from the Governor’s
Office of Emergency Services and the US Geological Survey and some items were
purchased or donated by commercial firms. The course concluded with the students
working in teams to build model towers that were then destructively tested on a
shake table. At the end of this project my students had a better understanding of
what it means to have the earth move under their feet and are more inclined to take
precautions.
Evolution of the Catfish (Namazu) as an Earthquake Symbol in Japan
G. Smits, The Pennsylvania State University, [email protected]; R. Ludwin,
University of Washington, [email protected]
Namazu, the earthquake-causing subterranean catfish of Japanese folklore, is a wellknown icon of earthquake folklore. Following the Ansei Edo Earthquake in late
1855, anonymous entrepreneurs produced and sold hundreds of varieties of catfish
picture prints (namazu-e). Many of these 1855 prints were sophisticated expressions of thinly-veiled political views, using the earthquake-catfish and other symbols as cover to avoid censure by the military government.
224 Seismological Research Letters Volume 77, Number 2 March/April 2006
Geology textbooks and works dealing with the social or historical ramifications of earthquakes commonly suggest an ancient origin for the earthquake catfish
(Bolt, 1993; Zeilinga de Boer & Sanders, 2005; Hanada Kiyoteru, 1972). However,
primary sources indicate that the earthquake-catfish only began to manifest itself in
Japanese culture in the seventeenth century, and was not well known until at least
a century later. Throughout the early nineteenth century, images of giant catfish
occasionally appeared in the popular press in connection with stories about earthquakes, and the Namazu came to full prominence following the Ansei-Edo earthquake of 1855, when the overturning moment of the earthquake coincided with
social unrest, advances in printing technology and the need for discretion.
Earthquake Catfish (Jishin Namazu): Alive and Well in Japan
W. Berglof, University of Maryland University College, [email protected]
edu.
Earthquake Catfish ( Jishin Namazu): Alive and Well in Japan The earthquake catfish (jishin namazu) of Japanese folklore is instantly recognizable to most Japanese
people, but of course believed in literally by few (rather like Santa Claus). In Japanese
folk tradition earthquakes are caused by a giant namazu, an enormous catfish that
lives in muddy water below the surface of the earth. Earthquakes occur when the
namazu thrashes about. The movement of the namazu is normally restricted by a
deity, the best known of which is the Kashima deity associated with Kashima Jingu
(Grand Shrine) in Ibaraki Prefecture northeast of Tokyo. The deity restricts the
movement of the catfish by means of a kaname-ishi rock (keystone or pivot stone).
If the deity relaxes for a moment earthquakes may then occur. The best-known
extant kaname-ishi is at Kashima Jingu (rather unimpressive when one actually
views it), and there are several others throughout Japan, such as one at the nearby
Katori Jingu and another near Ipponmatsu in Shizuoka Prefecture. As a well-known
aspect of Japanese folklore, the namazu appears in Japan in numerous informational
signs, brochures, and other items directly or indirectly related to earthquakes, and
has been featured in the logos for international scientific meetings. Catfish are
believed by some Japanese to be one of the animals that are especially sensitive to
earthquake precursors and thus might help in predicting earthquakes. The namazu
is also well known because of namazu-e (literally, catfish pictures), which appeared
in abundance shortly after the destructive Edo-Ansei earthquake of 1855. Although
many pictures were created during a brief period they are usually not discussed in
formal histories of Japanese art. Nevertheless the prints are avidly sought by collectors having an interest in Japanese earthquakes and earthquake culture, and a
full-length book discusses them (Ouwehand, 1964). A special exhibit at Tokyo’s
Edo-Tokyo museum in September and October 2005 marking the 150th anniversary of the 1855 earthquake featured an exhibition of namazu-e. One of the earliest
references in English to the jishin-namazu was in The Bulletin of the Seismological
Society of America, v. 13, 1923, shortly after the disastrous great Kanto earthquake
of 1 September 1923. However, the accompanying illustration in BSSA has distinctly human arms and legs while most other illustrations of catfish have simply
looked like fish. The earthquake catfish remains one of the better known features
of Japanese folk tradition.
Wednesday, 19 April—Oral Sessions
Plenary Session: Learning from the Past
Lessons Learned From Ground Rupture and Strong Ground Motion
N. Abrahamson, Pacific Gas and Electric, [email protected]
The recent large magnitude earthquakes (1999 Koceali, 1999 Chi-Chi, and 2002
Denali) have lead to a dramatic increase in the number of available strong ground
motion data close to large magnitude shallow crustal earthquakes providing an
opportunity to test the extrapolation of the existing ground motion attenuation
relations to large magnitudes at short distances. Overall, at short distances and
spectral periods less than 1 sec, the median ground motion from these new data
is smaller than predicted by standard ground motion models and the variability is
larger; at longer periods, the median values of the ground motions are similar to
existing models. Part of this reduction is due to the improved site classifications
that resulted from a significant effort to measure Vs30 at strong motion sites that
recorded these large earthquakes as well as other smaller earthquakes.
The near fault effects of directivity (large velocity pulse due to constructive
interference from rupture between the site and epicenter) and fling (large velocity pulse due to the permanent tectonic deformation) were observed in these large
earthquakes. The directivity effects observed for the Kocaeli earthquake are consistent with existing models. The Chi-Chi earthquake did not show strong directivity
effects due to the shallow hypocenter. The near fault ground motions from all three
earthquakes showed strong fling effects. The duration of the fling pulse, of about 5
seconds was approximately constant for all three events,
Estimates of the median and variability of ground motions from a future M8
earthquake on the Northern San Andreas fault based on the new earthquake data
are compared to estimates based on standard ground motion models currently in
use.
The Giant Sumatran Earthquakes of 2004 and 2005 (Joint
with EERI)
Presiding: Kerry Sieh and Aron Meltzner
Teleseismic Relocation and Assessment of Seismicity (1918-2005) in the
Region of the 2004 Mw 9.0 Sumatra-Andaman and 2005 Mw 8.6 Nias Island
Great Earthquakes
E. Engdahl, University of Colorado, [email protected]; A.
Villasenor, Institute of Earth Sciences “Jaume Almera”—CSIC, [email protected]
ija.csic.es; H. DeShon, University of Wisconsin, [email protected]
The Mw 9.0 2004 Sumatra-Andaman Islands and Mw 8.6 Nias Island great earthquake sequences have already generated over 5000 catalog-reported earthquakes
along ~1700 km of the Sumatra-Andaman and western Sunda regions. Studies of
prior regional seismicity have been primarily limited to global catalog locations
that often have poorly constrained locations and depths. Approximately 3650 teleseismically well-recorded earthquakes occurring in this region during the period
1918-2005 are relocated with special attention to focal depth. Uncertainties in
the epicenters and reviewed focal depths in this region are on the order of 15 and
10 km, respectively. Improved accuracy of locations and depths in the region fosters interpretation of focal mechanism data and provides additional details about
the subducting Indo-Australian slab. The revised earthquake dataset reveals a sharp
delineation between aftershocks of the 2004 and 2005 earthquakes near Simeulue
Island and a steepening in plate dip from south to north. The downdip width of the
aftershock zone of the 2004 Mw 9.0 earthquake varies from ~200 km at its northern end to ~275 km at its southern end, and events located between 35-70 km focal
depth occur more frequently in the southernmost section of this aftershock zone.
Outer-rise and near-trench normal and strike-slip faulting aftershocks also increase
in frequency following the 2004 and 2005 earthquakes. Earthquake swarms triggered along the Andaman back-arc spreading center north of Sumatra and near
Siberut Island 100 km south of the Nias Island aftershock sequence illustrate the
complex and variable nature of seismicity following these great earthquakes.
Reverse-time Migration of Teleseismic P Waves: Imaging the 28 March 2005
Sumatra Earthquake
K. Walker, IGPP/SIO/UCSD, [email protected]; P. Shearer, IGPP/SIO/
UCSD, [email protected]; M. Ishii, IGPP/SIO/UCSD, [email protected]
We apply reverse-time migration to image the rupture of the 28 March 2005
Sumatra Mw 8.6 earthquake with teleseismic P waves recorded by the Global
Seismic Network and the Japanese Hi-net. We estimate and deconvolve the resolution image kernel from the P-wave image to improve the resolution. Tests using station corrections obtained by aftershocks indicate that global 3D velocity heterogeneity does not significantly degrade our GSN image. Our final image suggests that
the rupture started slowly, had a total duration of about 120 s, and propagated at 2.9
to 3.3 km/s from the hypocenter in two different directions: first toward the north
and then, after a ~40 s delay, toward the southeast. Our images are consistent with
a rupture area of ~40,000 km2, the locations of the first day of aftershocks, and the
Harvard CMT Mw of 8.6, which implies an average slip of ~6 m. The earthquake is
similar in its location, size, and geometry to a Mw ~8.5 event in 1861. The average
slip is consistent with a partially coupled subduction interface, GPS forearc velocities, and the ~59 mm/yr convergence rate if the 2005 earthquake released elastic
strain that accumulated over many hundreds of years rather than just since the last
1861 event. Alternatively, the measured GPS forearc velocities may not represent
the average since the 1861 event, and the 6-m average slip may indicate that the
slab-plate coupling is strong on average.
Rupture Kinematics and Strong Ground Motion Estimates of the 2005, Mw
8.6, Nias- Simeulue Earthquake from the Joint Inversion of Seismic and
Geodetic Data
A. Konca, Tectonic Observatory, California Institute of Technology, [email protected]
gps.caltech.edu; V. Hjorleifsdottir, Tectonic Observatory, California
Institute of Technology, [email protected]; A. Song, Tectonic Observatory,
California Institute of Technology, [email protected]; D. Helmberger,
Seismological Research Letters Volume 77, Number 2 March/April 2006 225
Tectonic Observatory, California Institute of Technology, [email protected]
edu; K. Sieh, Tectonic Observatory, California Institute of Technology, [email protected]
gps.caltech.edu; J. Avouac, Tectonic Observatory, California Institute of
Technology, [email protected]
We have analyzed the source of the 2005, Mw 8.6, Nias-Simeulue earthquake using
geodetic data along with teleseismic, surface wave and normal mode data. The
Mw8.6 Nias event occurred within an array of continuous GPS stations and produced measurable vertical displacement of the fringing coral reefs above the fault
rupture. Using normal mode data amplitudes together with geodetic misfits we
could place tight constrains on the moment and the fault dip, where dip is determined to be 80 to100 with corresponding moments of 1.24x1029 to 1x1029 dyne-cm,
respectively. The geodetic constraints on slip distribution helped to eliminate the
trade-off between the slip and rise time inherent to purely seismic inversions. These
rupture kinematics are validated by successfully predicting the very long period
seismic waveforms (100 s to 500 s). Our results show that the Nias-Simeulue earthquake had relatively slow rupture velocities of ~1.5-2.5 km/s and long rise times of
up to 20 seconds. The earthquake nucleated between two separate slip patches, one
beneath Nias and one beneath Simeulue Island. The gap between the two patches
and the hypocentral location may be coincident with a local geological disruption
of the forearc. This study emphasizes the importance of using multiple datasets in
understanding seismic ruptures. The long period seismic data along with the geodetic data is used to determine fault dip and seismic moment. Using this geometry
and seismic moment constraint, joint modeling of coseismic GPS measurements
along with teleseismic waveforms place tight constraints on finite source models,
which can be used to estimate near-field ground motions and to give rapid assessments of damage or tsunami warnings. Using the models from joint inversions, we
estimate the peak ground velocity on Nias Island to be about 30 cm/s, an order of
magnitude slower than for thrust events in continental areas. These slow ground
velocities are due to several factors, including (1) the large distance between the
surface and the rupture; (2) the relatively low stress drops (long rise times) and slow
rupture velocities.
The “Simeulue Saddle” and Rupture Overlap in the 2002, 2004, and 2005
Sunda Megathrust Earthquakes
A. Meltzner, Tectonics Observatory, Div. of Geological and Planetary
Sciences, California Institute of Technology, [email protected]; R.
Briggs, Tectonics Observatory, Div. of Geological and Planetary Sciences,
California Institute of Technology, [email protected]; K. Sieh, Tectonics
Observatory, Div. of Geological and Planetary Sciences, California Institute of
Technology, [email protected]; A. Konca, Tectonics Observatory, Div. of
Geological and Planetary Sciences, California Institute of Technology, [email protected]
gps.caltech.edu; Y. Hsu, Tectonics Observatory, Div. of Geological and Planetary
Sciences, California Institute of Technology, [email protected]
The December 2004 and March 2005 Sunda megathrust earthquakes nucleated
northwest and southeast of Simeulue island, respectively, and each ruptured bilaterally into the 100-km-long island. Uplift at the northwestern tip of Simeulue was
1.5 m during the 2004 earthquake, and uplift at the southeastern tip in 2005 was
1.5 m or more. Uplift associated with each earthquake diminished toward the
center of the island, as did slip on the underlying megathrust, according to slip
inversions. Cumulative uplift was as little as 0.5 m along the west coast of central
Simeulue. Hence, although the 2004 and 2005 uplifted regions overlap, there is an
uplift deficit, or saddle, on central Simeulue. Rupture during an M 7.3 earthquake
in 2002 produced up to ~20 cm of uplift in central Simeulue, near the sites of lowest uplift in 2004-2005, but even including that uplift, the saddle persists. No events
similar to 2002 can be found in the historical record for at least the previous 94
years. The occurrence of the 2002, 2004, and 2005 earthquakes, their relative locations and timing, and their associated patterns of uplift raise important questions
about rupture boundaries and earthquake triggering. Why didn’t the 2004 earthquake continue southward to encompass the future 2005 rupture? Why didn’t the
2002 earthquake continue farther onto the 2004 or 2005 rupture planes? It does
not appear that the 2002 and 2004 ruptures extended into regions of recent high
slip. Could the rupture terminations have been controlled by permanent structural
boundaries? Along the west coast of Simeulue, the 2004 and 2005 tsunami run-up
heights did not exceed several meters, but an M ~7.6 earthquake in 1907 is associated with a tsunami that was significantly larger there. This, coupled with high
1907 intensities on Nias island, may indicate that the 1907 earthquake involved
substantial slip on a portion of the megathrust updip of the 2005 rupture, west of
Simeulue and Nias. Future work is required to determine whether the 1907 rupture
transgressed the 2002, 2004, and 2005 rupture boundaries. We will discuss these
questions and share preliminary findings, including a slip inversion for the 2002
earthquake.
Seismic Activity in the Sumatra-Java Region Prior to the December 26, 2004
(Mw=9.0-9.3) and March 28, 2005 (Mw=8.7) Earthquakes
A. Mignan, IPG Paris, [email protected]; G. King, IPG Paris, [email protected]
ipgp.jussieu.fr; D. Bowman, Cal State Fullerton, [email protected];
R. Lacassin, IPG Paris, [email protected]; R. Dmowska, Harvard
University, [email protected]
A promising approach to assessing seismic hazards has been to combine the concept of seismic gaps with Coulomb stress change modeling to refine short-term
earthquake probability estimates. However, in practice the large uncertainties in
the seismic histories of most tectonically active regions limits this approach since a
stress increase is only important when a fault is already close to failure. In contrast,
recent work has suggested that Accelerated Moment Release (AMR) can help to
identify when a stretch of fault is approaching failure without any knowledge of
the seismic history of a region. AMR can be identified in the regions around the
Sumatra Subduction system that must have been stressed before the 26 December
2004 and 28 March 2005 earthquakes. The effect is clearest for the epicentral
regions with less than a 2% probability that it could occur in a random catalogue.
Less clear AMR is associated with the regions north of Sumatra around the Nicobar
and Adaman islands where rupture in the December 2004 earthquake was less vigorous. No AMR is found for the region of the 1833 Sumatran earthquake suggesting that an event in this region in the near future is unlikely. AMR similar to that
before the December 2004 and March 2005 events is found for a 750 km stretch of
the southeastern Sumatra and western Java subduction system with the implication
that a very large earthquake may occur in this region, possibly in the next few years
to decades.
Interseismic Strain Accumulation and Future Giant Earthquakes Scenarios
in the Mentawai, Central Sumatra, Subduction Zone
M. Chlieh, Tectonics Observatory, California Institute of Technology,
Pasadena CA, [email protected]; J. Avouac, Tectonics Observatory,
California Institute of Technology, Pasadena CA, [email protected]; K.
Sieh, Tectonics Observatory, California Institute of Technology, Pasadena CA,
[email protected]; D. Natawidjaja, Research Center for Geotechnology,
Indonesian Institute of Sciences, Bandung, Indonesia, [email protected];
J. Galetzka, Tectonics Observatory, California Institute of Technology,
Pasadena CA, [email protected]
The south equatorial segment of the sumatra subduction zone (the Mentawai segment) is known to have produced giant earthquakes in 1797 and 1833 (Mw >
8.5). The northern adjacent segment (Nias) that broke in 1861 and again in March
2005 (Mw=8.7) highlight the occurence of a future giant in the Mentawai segment. Paleogeodetic and GPS data from the Sumatran subduction zone provide
an unusual opportunity to understand the physical parameters that control the
behavior of a subduction interface. Interseismic strain measurements recorded over
the last several decades by coral growth rings and GPS instruments are fit well by a
simple model that assumes lateral variations in the depth of the updip and downdip
limits of the locked fault zone (LFZ). The minimum width of the LFZ is about
100 km near the Equator and increases to about 200 km farther south. Near the
Equator, where the width of the LFZ is about 100km, smaller earthquakes occurred
(Mw = 7.7 in 1935 7.2 in 1984) than the area farther south where giant earthquakes happened in 1797 and 1833. The background seismicity also fit very well
with the downdip end of the LFZ. This difference in both the seismic behavior and
width of the LFZ is related to lateral variations in both the age of the subducting
plate and the normal plate convergence rate and so to the thermal structure of the
plate interface. We find that the downdip end of the LFZ is everywhere between
the 300C and 400C isotherms, corresponding to the stable sliding activation of
quartzo-feldspathic rocks.
Near Fault Ground Motions from Large Earthquakes (Joint
with EERI)
Presiding: Paul Spudich and David M. Boore
Near-fault Strong-motion from the M6.0 Parkfield, California Earthquake of
September 28, 2004
A. Shakal, California Geological Survey, [email protected]; H.
Haddadi, California Geological Survey, [email protected];
M. Huang, California Geological Survey, [email protected]
The 2004 Parkfield, California earthquake yielded the first extensive set of nearfault strong-motion recordings. The strong motion measurements are highly varied, with significant variations over only a few kilometers. Peak accelerations ranged
226 Seismological Research Letters Volume 77, Number 2 March/April 2006
from 0.13 g to over 2.5 g (perhaps the highest acceleration recorded to date). The
largest accelerations occurred near the north and south ends of the inferred rupture
zone. The town of Parkfield itself had relatively low ground acceleration, a fraction
of that at stations only 2 km away. The displacement at Parkfield was not small,
however, and was dominated by simple long-period motion, like other stations near
the fault. A total of 56 three-component recordings of ground acceleration were
obtained within 20 km of the fault, with 49 of these being from within 10 km of the
fault. Records were also obtained from a few instrumented structures.
Variation of Recorded and Simulated Near-fault Ground Motion Considering
Fault Rupture Processes
A. Pitarka, URS Corporation, [email protected]; P. Somerville,
URS Corporation, [email protected]; N. Collins, URS
Corporation, [email protected]; R. Graves, URS Corporation, robert_
[email protected]; H. Thio, URS Corporation, [email protected]
Analyses of differences between surface/subsurface earthquake rupture dynamics and their effect on near-fault ground motion suggest that a possible cause for
the relatively low near-fault ground motion observed from large surface rupturing
earthquakes could be the high fracture energy consumption in the top 4-5 km of
the earth crust. The distinct weakening of the rupture as it crosses the shallow crust
during large earthquakes is caused by substantial changes in porosity and frictional
behavior of the earth materials. We will present a brief overview of such analyses
considering both recorded motions and dynamic rupture simulations. In a specific application of this approach, we have investigated the variation of near-fault
ground motion from the 2004 Parkfield earthquake relative to an existing attenuation model. The same analyses were performed on recorded motions and synthetic
broadband time histories simulated using both kinematic and dynamic rupture
models, which were derived from inversions of strong motion velocity waveforms.
The spatial variability of near-fault ground motion simulated on a dense network
of stations is not greater than that of the observations, suggesting that the existing
strong motion network has captured most of the spatial variation of the ground
motion due to the source process and site response effects. We will present analyses of relations between key dynamic rupture parameters and their variation with
depth derived for the Parkfield earthquake. Their comparison with relations derived
for other earthquakes and surface/subsurface dynamic rupture models will also be
shown.
High Frequency Earthquake Radiation Inferred from Near-fault Ground
Motions: Contraints from a Dynamic Rupture Model and Empirical Green’s
Tensor Derivatives
N. Pulido, National Research Institute for Earth Science and Disaster
Prevention (NIED), [email protected]; L. Dalguer, Department of
Geological Sciences, San Diego State University, California, [email protected]
edu.
Simple dynamic crack models have theoretically demonstrated that strong variations of the rupture velocity at the crack boundaries (stopping phases) play a very
important role in the radiation of high frequency (HF) from the source. In the
case of large earthquakes the dynamic process is much more complex than for a
simple crack model. For large earthquakes strong variations in rupture velocity during the fault rupture progression may have a strong influence on the HF generation
across the fault plane. To address this problem we have investigated a spontaneous
dynamic fault rupture process of the 2000 Western Tottori prefecture earthquake
( Japan), by using a 3D-FDM scheme coupled with a slip weakening fault-friction
law. The dynamic model parameters are constrained by the final slip and stress
time histories obtained from a kinematic model. In order to infer the HF from
our dynamic model we calculate the gradient of local rupture velocity across the
fault plane and multiply by the dynamic stress drop distribution obtained from the
dynamic model. This product gives an indication of the HF radiation as it represents the flat level of far-field radiated acceleration Fourier spectra (FFS) for a crack
model. Calculation of this product across the fault plane for the Tottori earthquake
suggest that HF is radiated from regions where a large rupture velocity gradient is
overlapped with a strong dynamic stress drop. Regions in the fault with an uniform
rupture do not radiate HF, even when accompanied by an important stress drop. In
this paper we try to infer the source HF radiation directly from near-fault strong
ground motion recordings. For this purpose we calculate HF ground motions as
an incoherent rupture of cracks covering a finite fault plane. Rupture times of every
crack are constrained by results of the dynamic model. HF ground motion contribution from each crack to every site are obtained by convolving an Empirical
Green’s Tensor Derivatives (EGTD), to accurately account for propagation path,
with the slip function at each crack. For this purpose we use the slip functions from
the dynamic model at each crack location by modifying their acceleration Fourier
spectra amplitude to allow for a variable spectral flat level and fmax. Model parameters to describe the HF radiation are the FFS and fmax values. These parameters
are obtained by a GA inversion scheme by comparing HF acceleration envelopes as
well as the FFS of simulations and observation at all available K-Net and Kik-net
near-fault recordings. EGTD are obtained from a set of clustered weak events with
known focal mechanism by solving a system of linear equations in the frequency
domain. EGTD accurately describe an average propagation path between each station and a focal zone corresponding to large slip regions across the mainshock fault
plane.
Influence of Fault Dip and Near-fault Crustal Heterogeneity on Normalfaulting Rupture Dynamics and Ground Motions
D. O’Connell, Seismotectonics and Geophysics Group, USBR, Denver, CO
80225, [email protected]; S. Ma, Institute for Crustal Studies, University of
California, Santa Barbara, CA 93106, [email protected]; R. Archuleta,
Institute for Crustal Studies, University of California, Santa Barbara, CA 93106,
[email protected]
We used a 3D elastic finite-element approach with split nodes to investigate the
influence of fault dip (30°to 60°), fault lengths of 30-48 km, and typical velocity contrasts across the top several km of normal faults on rupture dynamics and
near-fault ground motions to maximum frequencies of 1-3 Hz. In a homogenous
half-space and for dips < ≈50° hangingwall fault-normal peak horizontal velocities
were larger than on the footwall because of constructive interference of direct Swaves and Rayleigh waves. However, for dips of > 50°, maximum peak horizontal
fault-normal velocities occurred on the footwall because the region of constructive
interference between S-waves and Rayleigh waves kinematically shifts to the footwall. Introducing a several-km-thick low-velocity basin typical of normal faults in
the hangingwall eliminates the constructive interference between Rayleigh waves
and S-waves on the footwall and confines maximum fault-normal peak horizontal
velocities to the hangingwall. The surface S-wave velocity in the hangingwall basin
was set to 1 km/s and to 3 km/s on the footwall. Peak horizontal velocities on the
footwall within 100 m of the fault never exceeded 1 m/s and where usually < 0.5
m/s even when extreme shear stresses were used in the top several km of the fault
that produced peak horizontal velocities of > 4 m/s on the hangingwall. Most of
the differences result from > 70% of the slip occurring on the hangingwall sides of
the faults. Low footwall fault-normal peak horizontal velocities persist even when
the fault is moved > 100 m into either the footwall or hangingwall side of the lateral
velocity discontinuity. Normal- and reverse-faulting initial shear stresses with the
same amplitudes (except for sign) and all other initial conditions the same produce
not only substantially different peak slip velocities on the faults, but distinctly different dominant periods of peak slip acceleration. Normal-faulting peak slip accelerations often occurred between 1 and 3 Hz, while all reverse-faulting peak slip
accelerations occurred at frequencies > 3 Hz. Normal-faulting is not only associated
with lower peak slip velocities relative to reverse-faulting but has a distinctly lowerfrequency spectrum of slip accelerations.
Site Effects for Near-fault Forward-directivity Motions
A. Rodriguez-Marek, Washington State University, [email protected]; J.
Bray, University of California, Berkeley, [email protected];
Empirical studies of recorded near-fault forward-directivity motions have shown
systematic effects on the characteristics of the recorded velocity pulses due to site
effects. These studies, however, are limited by the lack of availability of forwarddirectivity motions recorded across a wide range of site conditions. This shortcoming is addressed by performing numerical simulations of seismic site response to forward-directivity ground motions using a fully nonlinear soil model that responds to
bi-directional shaking. Near-fault recordings are represented using simplified sinepulse time histories that can be characterized by its peak ground velocity (PGV)
and pulse period (Tv). The results of the analyses showed that site effects generally
result in a lengthening of the period of velocity pulses. The amplification of PGV
depends on soil properties, but amplification is generally observed even for large
input rock PGVs. At soft soil sites, seismic site response is largely a function of the
yield strength of the soil, because strength limits the intensity of motions at the
ground surface. A critique is made of the manner in which near-fault site effects are
handled in current building codes.
Constraints on Near-fault Motions from Unstable Landform Features in New
Zealand
M. Stirling, GNS Science, [email protected]; R. Anooshehpoor,
Nevada Seismological Lab, [email protected]
We have recently undertaken the first New Zealand-based pilot study to investigate
the use of ancient precariously-balanced rocks (rocks that are unstably balanced
on top of a pedestal) as a criteria for testing estimates of earthquake shaking from
probabilistic seismic hazard models for long return periods. Our pilot survey of
sites in the South Island of New Zealand has used precariously-balanced rocks to
Seismological Research Letters Volume 77, Number 2 March/April 2006 227
provide estimates of the maximum ground motions that could have occurred at the
sites since the rocks became precarious. Age estimates for the precariously-balanced
rocks (generally 40,000 to 80,000 years) are made from a limited number of cosmogenic dates of bedrock removed from the pedestals of the rocks. Comparisons of
the maximum peak ground accelerations and ages of the precarious rocks to seismic
hazard curves derived from the New Zealand national seismic hazard model show
that the rocks indicate considerably lower hazard than the seismic hazard model at
sites located within 5 km of active faults, whereas the agreement is more favourable
for sites located away from active faults. The variability about the median estimates
of peak ground acceleration for the fault sources, and/or the median accelerations
for the fault sources assumed in the seismic hazard model may therefore be overestimated for the sites near active faults. Our findings are consistent with those of
parallel efforts to test PSH models from historical data, and key findings from the
next generation attenuation modelling (NGA) project.
Beyond the San Andreas, the Other Active Faults of
Northern California
Presiding: Jim Lienkaemper and John Baldwin
The Earthquake Cycle on a Plate Boundary Fault System: San Francisco Bay
Area 1600-2006
D. Schwartz, USGS, [email protected]; W. Lettis, William Lettis and
Associates, [email protected]; J. Lienkaemper, USGS, [email protected]; S.
Hecker, USGS, [email protected]; K. Kelson, William Lettis and Associates,
[email protected]; T. Fumal, USGS, [email protected]; J. Baldwin, William
Lettis and Associates, [email protected]; G. Seitz, San Diego State University,
[email protected]; T. Niemi, U. of Missouri, [email protected]
The historical record of Bay Area earthquakes is considered complete at magnitude
5.5 back to 1850. The striking contrast between the large number (29) of moderate
magnitude earthquakes (M 5.6-6.4) from1850 to 1906 and their absence after is a
primary observation leading to the concepts of the earthquake cycle and the acceleration of seismicity prior to a great earthquake. However, the historical record is
incomplete with no accurate quantification of either the number or magnitude of
moderate events prior to 1850 for comparison. Paleoseismic studies cannot easily
identify moderate earthquakes, but they do extend the record of large events (M6.7
and larger). Recent investigations of the region’s major strike-slip faults now provide a longer view of the Bay Area earthquake cycle
We have developed a preliminary paleoearthquake chronology for the major
faults; these have durations of 1000 to 3000 years. Although the completeness of
individual fault chronologies is variable, the paleoearthquake history across the
entire fault system since 1600 is essentially complete. We find evidence of surface faulting for large events on the northern San Andreas (SAN), Santa Cruz
Mountains San Andreas (SAS), northern Hayward (NH), southern Hayward
(SH), Rodgers Creek (RC), northern Calaveras (NC), San Gregorio (SG), and
Green Valley (GVY) faults that is post-1600 and pre-1776 (founding of Mission
Dolores). The timing of these, listed in order of their mean radiocarbon age (with
age-range uncertainties in parentheses), is: SH 1620 (1605-1645): SAS 1640
(1600-1670): GVY 1700 (1685-1776); NH 1705 (1670-1776); SG 1720 (16951776); SH 1730 (1685-1776); RC 1740 (1690-1776); SAN 1750 (1720-1776);
and NC 1760 (1670-1830). (Given dating uncertainties, the actual ordering of
earthquakes may have been different). Offset data, which reflect magnitude, are
limited. However, measured point-specific slip (RC, 1.8-2.3m; SG, 3.5-5.0m; SAN
3.0m) and modeled average slip (SH, 1.9m) indicate large magnitude earthquakes
on the regional faults.
Major observations of the Bay Area earthquake cycle are: 1) between 1600
and 1906 the San Andreas fault failed in a series of large earthquakes rather than
as a multi-segment 1906-type rupture; 2) a regional cluster of large earthquakes
occurred between 1670-1776, and likely during a shorter interval in the 18th century; 3) the estimated moment release of the cluster (irrespective of the order of
events) is comparable to the moment release of 1906; and 4) the cluster was followed by a regional quiescence of large earthquakes, with only two (1838, 1868)
until 1906. The Bay Area paleoseismic record has the potential to extend these
types of observations through multiple earthquake cycles.
The Relationship of the 1911 Calveras Earthquake to Static Shear Stress
Changes Following the 1906 San Francisco Mainshock
D. Doser, Univ. Texas at El Paso, [email protected]; R. Stein, U. S.
Geological Survey, [email protected]; S. Toda, AIST, [email protected]; E.
Grunewald, Stanford University, [email protected]
The 1906 M=7.8 San Francisco earthquake was among the largest known events
to subject creeping faults to a sudden and large stress change. The 470-km-long
fault rupture is calculated to have produced broad areas of static stress drop along
the San Andreas’s neighboring right-lateral strike-slip faults, including the creeping Hayward and Calaveras faults (Harris & Simpson, 1998). Sudden creep-rate
changes lasting a few months to several years have been observed following the
much smaller 1983 M=6.5 Coalinga (Mavko et al., 1985; Simpson et al., 1989;
Toda & Stein, 2002), 1989 M=7.1 Loma Prieta (Simpson & Reasenberg, 1994;
Lienkaemper & Simpson, 1996), and 2003 M=6.2 San Simeon (Hardebeck et al.,
2004) shocks. These creep changes have been explained by static shear stress changes.
Such changes can be opposite in sign to the secular creep. The 1911 Calaveras earthquake near Morgan Hill struck on or near the Calaveras fault. Although disputed
by Felzer & Brodsky (2005), the 1906 stress shadow has been invoked to explain
why there was there was just one M≥6 shock in the succeeding 75 years, in contrast
to the 14 such shocks in the preceding 75 years (Stein, 1999;). Many studies have
considered why the enigmatic 1911 shock struck in the calculated stress shadow
of the 1906 earthquake ( Jaumé & Sykes, 1996; Harris & Simpson, 1998; Hori &
Kameda, 2001), but because the sign and magnitude of the 1906 static stress change
depends on the geometry of the receiver fault, such analyses are speculative without
a 1911 focal mechanism. From global waveform analysis, we attempt to determine
a mechanism and an improved estimate of magnitude for the 1911 event. A preliminary comparison of seismograms of the 1911 Calaveras and the 1984 Morgan
Hill events recorded at Gottingen, Germany suggests the earthquakes have similar
mechanisms, with the 1911 event having 2 to 3 times the amplitude of Morgan
Hill. We will further verify these observations through additional analysis of body
and surface waveforms.
New Quaternary Fault Map Database for the San Francisco Bay Region,
California
R. Graymer, U.S. Geological Survey, [email protected]
A team of USGS, CGS, academic, and private geologists, who make up the
Northern California Quaternary Fault Map Database Task, have prepared: 1)
New detailed fault map databases of the northern Calaveras Fault (Kelson and
others), the Gualala reach of the San Andreas Fault (Prentice and others), the
Rodgers Creek Fault (Hecker and Randolph-Loar), the Concord-Green Valley
Fault (Bryant and Wills), and the West Napa Fault (Hanson and others) 2) New
regional fault map databases of the Foothills Fault system of the southern Santa
Cruz Mountains (Kennedy), faults in northern Monterey and Santa Cruz Counties
(Rosenberg), and Quaternary folds and thrust faults in the northeast San Francisco
Bay region (Unruh and others). These new fault maps have been combined with
recently completed digital versions of the peninsula San Andreas Fault (Prentice
and others) and the Hayward Fault (Lienkaemper), into the existing Quaternary
Fault map database (Bryant) to produce a preliminary revised Quaternary fault
map database for the region. The database records a variety of observations associated with interpretations of fault location and activity. The database also includes
3-dimensional surfaces for the primary Holocene-active faults derived from hypocenter locations, geophysical expression, and extrapolation of surface observations.
Although still preliminary, the new work provides significant improvement to the
understanding of Quaternary faults in the region, including the following observations: A) There are considerably more Quaternary faults in the region than previously mapped, including blind reverse and thrust faults. Many have potential,
although not proven, Holocene activity. These potentially Holocene-active faults
should be targets for future paleoseismic and tectonic geomorphic studies. B) Some
faults previously thought to be Quaternary-active are now known not to be, and
have been removed from the fault map database. C) Surface fault complexity associated with bends and stepovers is thought to overlie simple though-going faults
at depth in some cases. D) Fault activity data suggest that some fraction of the slip
from the Northern Calaveras Fault is transferred to the West Napa Fault through a
series of left stepovers in northern East Bay hills and by the Southhampton Fault.
New Coastal Strike-Slip Faults with Relatively High Rates of Slip and
Deformation between the Offshore San Andreas and Onshore Maacama
Faults, Northern Coastal California, Mendocino County
D. Merritts, Franklin and Marshall College, [email protected]; D.
Springer, College of the Redwoods, [email protected]; R. Walter, Franklin
and Marshall College, [email protected]; C. Lippincott, San Diego
228 Seismological Research Letters Volume 77, Number 2 March/April 2006
State University, [email protected]; J. Muller, NASA-Goddard, [email protected]
core2.gsfc.nasa.gov.
In the San Francisco Bay area, the San Andreas fault (SAF) splits into several major
strands that have been mapped northward as right-stepping en echelon faults (e.g.,
the Hayward, Rodgers Creek, and Maacama faults). The SAF itself continues north
of San Francisco at a strike of ~N34W for 270 km before going offshore at Point
Arena, where the fault begins to bend markedly ~30° clockwise before returning to
shore at Point Delgada another ~100 km to the north. Few active faults have been
mapped in the crustal region between the offshore SAF and the onshore Maacama
fault north of Point Arena. The coastline along this part of the SAF is marked by
a prominent flight of marine terraces that can be traced nearly continuously for
~35 km in the vicinity of the town of Mendocino. Our analysis of 10-m digital elevation models, combined with GPS ground surveying of the marine terraces (~2-m
vertical resolution), mapping from large-scale air photos, and field work, reveals at
least three previously unmapped strike-slip faults with 1) lengths of at least 5-10 km
each, 2) relatively high slip rates (4-6 mm/yr estimated on one fault), 3) significant amounts of cumulative right-lateral strike-slip fault offset, and 4) shear zones
ranging from 1-5 m in width. As with the better-known faults to the east, these
faults appear to be right-stepping en echelon fault segments. One of the faults, here
named the Pacific Star fault, strikes parallel to the SAF; the other two strike ~N1020W and bound an ~3-km long coastal zone of transtensional subsidence in which
the 125-ka marine terrace (U-Th date from solitary coral Balanophyllia elegans)
is warped downward to the west and buried beneath a repeated sequence of peats
and beach sands with radiocarbon dates spanning the late Pleistocene to Holocene.
Locally, the strike-slip and associated conjugate normal and reverse faults cause the
marine terraces to change altitude up to several tens of meters. Regionally, however,
the four major terrace “steps” have generally consistent altitudes, which we interpret
to be the result of the slight component of normal convergence along the SAF.
Structure of the Hayward Fault, California, from Relocated Seismicity and
Focal Mechanisms
J. Hardebeck, USGS, [email protected]; A. Michael, USGS, [email protected]
usgs.gov; T. Brocher, USGS, [email protected]
Relocated hypocenters and recomputed focal mechanisms for ~20,000 small earthquakes, 1967-2004, obtained using a 3D seismic velocity model from travel-time
tomography, reveal the structure of the Hayward Fault at depth. While 3D relocations do not image fine-scale structure as sharply as cross-correlation relative relocations, they are more accurate on average in an absolute sense. First-motion focal
mechanisms computed using a 3D velocity model are also more accurate than those
from a 1D model, as unmodeled lateral velocity contrasts can systematically bias the
computed azimuths and take-off angles of the rays to each station.
The focal mechanisms found using the 3D velocity model are uniformly consistent with the strike of the Hayward Fault and nearly pure right-lateral slip. Prior
studies using a 1D velocity model found heterogeneous focal mechanisms along the
Hayward Fault near San Leandro, suggesting complex faulting and a possible segment
boundary. Although the earthquake locations near San Leandro are somewhat diffuse, the similarity in mechanisms suggests a through-going main fault and subparallel smaller faults, which may not pose a significant barrier to rupture propagation.
North of San Leandro, the relocated seismicity defines a single sharp vertical to steeply east-dipping plane that projects upward to the surface trace of the
Hayward Fault. South of San Leandro, sparse seismicity above ~4 km dips shallowly
to the east, projecting upwards towards the surface trace of the Hayward Fault and
downwards to a steeply east-dipping plane beneath the surface trace of the Mission
Fault. At >4 km depth, the seismicity along this trend merges smoothly to the
south with the seismicity of the central Calaveras Fault. This geometry suggests that
earthquake scenarios that include ruptures that span both the Hayward and central
Calaveras Faults should be considered in future earthquake hazard assessments.
A 1650-Year Record of Large Earthquakes on the Southern Hayward Fault
J. Lienkaemper, US Geological Survey, [email protected]; P. Williams,
Williams Assoc., [email protected]link.net.
The Hayward fault, a major branch of the right-lateral San Andreas fault system,
traverses the densely populated eastern San Francisco Bay region, California. We
conducted a six-year paleoseismic investigation to better understand the Hayward
fault’s past earthquake behavior. Our site is in Fremont near the south end of
Tyson’s Lagoon, which is a sag pond formed in a right step of the fault. Because
the Hayward fault creeps at the surface, we identified paleoearthquakes primarily
using features that we judge to be unique to ground ruptures or the result of strongground motion, such as fault-scarp colluvial deposits, fissure fills and evidence of
liquefaction. We correlate the most recent event evidence to the historical 1868 m
6.9 earthquake, which caused liquefaction in the pond. We recognize ten additional
paleoruptures since about AD 350 (+200/-160 yr). Event ages were estimated by
Bayesian chronological modeling using the program Oxcal, which incorporates historical and stratigraphic information as well as radiocarbon and pollen data. The
mean recurrence interval (RI) for these 11 events is 151 ± 23 yr (2 s.d. of mean
RI). The sample standard deviation of the RI is ±72 yr (2 s.d.). This long-term (AD
350-1868) RI is similar to a previously determined RI of 130 ± 40 yr for the period
AD 1470-1868. Our event sequence supported by redundant event evidence from
several trenches across fault traces on both sides of the pond, correlated by tracing key stratigraphic units across the pond. Our preliminary estimate of aperiodicity or coefficient of variation (COV) in the recurrence interval for the southern
Hayward fault is approximately 0.24. The current regional earthquake probability
model, Working Group 2002, assumes much larger COV values for the Hayward
and other major faults, so future models are likely to significantly increase the earthquake probabilities for the Hayward fault and for the region as a whole.
How Seismologists, Engineers and Emergency Planners
can Work with Policymakers to Improve Disaster Planning
and Mitigation (Joint with SSA and DRC)
Presiding: Linda Rowan, Brian Pallasch and Ray Willeman
Global Natural Hazard Risk Identification and International Development:
Linking Mitigation to Regional Economic Development
A. Lerner-Lam, Lamont-Doherty Eearth Observatory, [email protected]
edu; R. Chen, Center for International Earth Science Information Network,
[email protected]
Two recent reports by the World Bank and the United Nations quantify the global
exposure of populations and economic activity to natural hazards. For example, the
World Bank’s disaster risk “Hotspots “study estimates risk levels by combining hazard exposure with historical vulnerability for two indicators of elements at risk-gridded population and Gross Domestic Product (GDP) per unit area—for six major
natural hazards: earthquakes, volcanoes, landslides, floods, drought, and cyclones.
(Earthquake risks are incorporated using a formulation based on the GSHAP studies.) Calculating relative risks for each grid cell rather than for countries as a whole
provides estimates of risk levels at sub-national scales. These can then be used to
estimate aggregate relative multiple hazard risk at regional and national scales. The
UN’s Disaster Risk Index study achieves essentially the same result. By casting mortality and economic loss in geographic terms, both studies have provided baseline
arguments for linking disaster losses to other factors inhibiting economic growth,
and for linking hazard mitigation to strategies for sustainable development.
However, the global analysis undertaken in these projects is clearly limited
by issues of scale as well as by the availability and quality of data. For some hazards,
there exist only 15- to 25-year global records with relatively crude spatial information. Data on historical disaster losses, and particularly on economic losses, are also
limited. On one hand the data are adequate for general identification of areas of the
globe that are at relatively higher single- or multiple-hazard risk than other areas.
On the other hand they are inadequate for understanding the absolute levels of risk
posed by any specific hazard or combination of hazards. Nevertheless it is possible
to assess in general terms the exposure and potential magnitude of losses to people
and their assets in these areas. Such information, although not ideal, can still be
very useful for informing a range of disaster prevention and preparedness measures,
including prioritization of resources, targeting of more localized and detailed risk
assessments, implementation of risk-based disaster management and emergency
response strategies, and development of long-term plans for poverty reduction and
economic development.
The challenge within international development institutions and organizations is to use the top-level momentum generated by these global studies to develop
country- or region-appropriate programs in natural hazard risk reduction based
on scientific evidence, technical capacity, and political will. Thus the global methodologies must be “downscaled”, not only to achieve better spatial and temporal
resolution, but also to customize particular approaches to risk-conscious economic
development. A new effort by the United Nations Development Program and the
ProVention Consortium, the Global Risk Identification Program, is now being
designed. “GRIP” will provide the evidence base and standards-driven framework
for national approaches to hazard mitigation in the context of sustainable development programs.
CISN Display: Enhanced Delivery of Real-time Earthquake Hazards
Information for Critical Users
N. Scheckel, California Institute of Technology, [email protected];
M. Vinci, California Institute of Technology, [email protected]; E.
Hauksson, California Institute of Technology, [email protected]; D.
Seismological Research Letters Volume 77, Number 2 March/April 2006 229
Oppenheimer, U.S. Geological Survey, Menlo Park, [email protected]; P.
Friberg, Instrumental Software Technologies, Inc., [email protected]
The California Integrated Seismic Network (CISN) has developed an easy to use, realtime earthquake notification system called the CISN Display that has been designed
to offer critical users a quick, comprehensive picture of local, regional, and global seismicity as well as areas of potential damage following a significant earthquake.
The display provides a GIS map of all earthquakes recorded by partners of
the Advanced National Seismic System with information on magnitude, epicentral
location, and time of occurrence.
For significant earthquakes, additional links may include tsunami information bulletins or warnings from the NOAA tsunami warning centers, ShakeMaps,
special reports from seismic network operators, aftershock probabilities, and related
information.
Since the CISN Display’s official release over a year ago it has successfully
served emergency managers, utility and lifeline operators, news media, critical facility operators and others with immediate and inclusive key decision-making earthquake hazards information, which helps fulfill a CISN mandate: to disseminate
earthquake information in support of public safety, emergency response, and loss
mitigation.
The latest release, in February 2006, brings to the CISN Display integrated
features such as QWEmailer (a package that allows users to configure personalized
earthquake notification), greater display options such as Map or Kiosk mode, the
development of an “Incident-Reporting tool” for better bug reporting, as well as
enhanced messaging from the Tsunami Warning Centers.
CAPSS: Involving the San Francisco Community in the Community Action
Plan for Seismic Safety
M. COmerio, University of California, Berkeley, [email protected]
In San Francisco, the Community Action Plan for Seismic Safety (CAPSS) began
when building officials asked the Structural Engineers Association of Northern
California for help with seismic repair building codes. The mayor suggested that
something more was needed, and with the help of the Applied Technology Council
(ATC) the multi-part CAPSS program was begun. Consultants were hired develop
loss estimates to understand the impact of a variety of earthquake scenarios on the
city’s private building stock. At the same time, a citizen’s advisory board composed
of distinguished structural engineers, architects, seismologists, planners, housing
advocates, and other community representatives met with consultants to shape how
the findings from the loss estimate would be used to develop mitigation and community education policies. The relationship between the citizen’s advisory committee and the consultant team demonstrated the importance of community input.
The unique physical and social character of the housing stock required special procedures for evaluating damage and estimating economic impacts. The old wooden
soft-story apartment buildings make up 75% of San Francisco’s housing stock and a
high percentage are rent-controlled. Thus the most vulnerable buildings house the
most vulnerable populations. While the first phase of the loss estimate was completed in 2002, much of the work on building codes and preparedness policies has
been delayed. The second phase of CAPSS will establish strengthening procedures
for pre- and post-earthquake situations. The third phase will develop a long term
mitigation plan, including voluntary and mandatory measures and education programs.
Geography of Earthquake Risk in the South of Market District of San
Francisco: People, Place and Policy
J. Wilson, Oregon Emergency Management, [email protected]
The South of Market area experienced violent ground shaking and severe liquefaction during the 1906 San Francisco earthquake and significant damage during the
1989 Loma Prieta earthquake. Conditions that contribute to San Francisco’s seismic risk—such as older buildings lacking seismic reinforcement, vulnerable populations including recent immigrants, the poor, elderly, and the disabled, and soft
soils—are concentrated in this area of the city.
Historic maps and photographs dated from the 1850’s relates environmental
change to seismic risk. Videotaped conversations with study area residents, local
officials, and regional seismic experts document earthquake risk perception and
present efforts to address seismic risk. The South of Market Redevelopment Project
Area, originally created as the South of Market Earthquake Recovery Area following the Loma Prieta earthquake, represents the same general area that experienced
San Francisco’s worst damage and loss of life in the 1906 earthquake (Hansen and
Condon, 1989). Results suggest a need for more culturally specific earthquake
information, as well as risk reduction programs that address low-income and affordable housing problems.
Following Hurricane Katrina the plight of urban poor, exacerbated by their
dislocation and reliance on state and federal emergency aid, was brought to the
attention of the nation and the world. In the United States, urban disasters will
increasingly affect the inner city poor, recent immigrants, the elderly and disabled.
Like the Ninth Ward of New Orleans, the South of Market neighborhood in San
Francisco is representative of the type of poor conditions in many metropolitan
cities that have a systemic vulnerability to natural disasters.
The scope of this geographical study is a broad examination and representation of seismic risk in the South of Market. The presentation of material frames the
complexities of the problems in this neighborhood that compound the potential
risk of a large nearby earthquake. This project presents the perspective of a vulnerable population that has little or no voice in public safety decision-making. It is also
meant to provide a reference for decision makers to better understand how socioeconomic, physical and political elements combine to create vulnerability.
A Hint for Improving Disaster Plans and Developing Better Earthquake
Mitigation Strategies: Partnership.
C. Weaver, U S Geological Survey, Seattle, WA, [email protected]
Raw earth science information is almost useless in helping policymakers establish
mitigation strategies and improve disaster response plans. Too often, earth scientists
finish research papers with words to the effect that “this amazing result must now
be included in earthquake hazard assessments”. How wrong and naïve! It is unfortunate that most seismologists fail to understand that no matter how much praise
their last paper received from their peers, the public policy arena is about timing,
context and connections. In most local and state situations, that means establishing
a strong partnership with emergency managers. This simple step establishes connections to policymakers and helps put scientific results in context.
Partnership is not built quickly. For seismologists to make a difference with
policymakers, they need to commit to continuing discussions with emergency managers, engineers, and others concerned with developing mitigation strategies and
improved earthquake response. To build these partnerships, seismologists must participate in a variety of forums and activities with emergency managers. A second key
point is to let others carry the news forward. Once emergency managers understand
a scientific result, they almost universally become very empowered to push those
results into the hands of policymakers. And finally, seismologists need to appreciate
that policymakers sometimes will only accept small changes that may seem insignificant given the scientific results. Because this is a likely outcome, this reinforces
the need for a long-term partnership with emergency managers.
Two examples from the Pacific Northwest illustrate the role of partnership.
The National Tsunami Hazard Mitigation Program is a State-Federal partnership
designed to build public awareness of tsunami issues. Nearly all aspects of this program are driven by the needs of the emergency management community, including the science to improve tsunami evacuation plans. A second example is the
Cascadia Region Earthquake Workgroup (CREW), a private-public partnership
that supports regional earthquake mitigation. CREW, using state-of-the art ground
motions developed by the USGS published the first scenario for a Cascadia magnitude 9 earthquake that is now being used by regional organizations to develop
strategies to improve the resiliency of lifeline and transportation systems in the
Pacific Northwest.
Reduced Earthquake Risk and Losses as Consequences of Improved
Seismic Monitoring
P. Somerville, URS Corporation, Pasadena, CA, [email protected]
com; W. Leith, U S Geological Survey, [email protected]
The combination of the earthquake hazard and the vulnerability of the built human
environment creates earthquake risk. Earthquake risk is growing at an alarming rate,
despite advances in earthquake science and engineering. This is the result of unprecedented growth and the lack of focused and applied public policy that would cause
the available design and rehabilitation techniques to be properly and universally
applied. Earthquakes thus continue to cause an unacceptable level of damage in
terms of lives lost, property destroyed and services interrupted (annual earthquake
losses in the U.S. are $5.6B, with a single-event loss potentially over $100B).
To better understand the role that effective monitoring plays in risk and loss
reduction, the USGS asked the National Research Council in 2003 to study the
economic benefits of improved seismic monitoring. The NRC report, released in
June, 2005, concluded that a fundamental role of monitoring is to reduce uncertainty, leading to increased accuracy of damage predictions and loss estimation,
as the basis for more effective loss avoidance regulations, as well as enabling more
effective emergency preparedness and response activities and improved earthquake
forecasting capabilities. The funding required for significantly improving monitoring was found to be small when compared with the benefits of reducing the cost of
constructing new facilities, strengthening existing structures to achieve acceptable
performance, and losses that will be avoided after major damaging events. Costs
were considered in the context of the more than $800B invested annually in build-
230 Seismological Research Letters Volume 77, Number 2 March/April 2006
ing construction, the $17.5 trillion value of existing buildings, and estimates of massive earthquake losses from large urban quakes.
Monitoring benefits also come from improved loss-estimation model outputs, which increase public knowledge, confidence, and understanding of seismic
risk; better correlation between seismic risk and building-code and land-use regulations; more efficient use of insurance to offset losses; and more accurate determination of the nature and growth of seismic risk. Benefits in emergency response and
recovery include expediting hazard identification, promoting rapid mobilization,
and facilitating the rapid identification of buildings that are safe for occupation and
those that must be evacuated. Although difficult to quantify in many cases, the ultimate benefits are lives saved, property spared, and reduced human suffering.
near-normal rupture propagation speeds. Past studies have indicated that increasing the rise time from 10 to 100 s reduces the tsunami generation efficiency in the
source region by approximately 30%. For greater rise times, tsunami waves leave
the source region prior to completion of seafloor deformation. A sensitivity test is
performed in which tsunami amplitudes outside the source region are calculated as
a function of an exponential slip time function with constant t (Kanamori, 1972).
Results indicate that tsunami amplitudes outside the source region are reduced to
approximate one third for t = 1000 s and to approximately 10% for t = 1 hour. It is
likely that a combination of anomalous source and propagation effects are needed
to explain the regional tsunami observations related to tsunami generation (or lack
thereof ) from the Andaman segment.
The Giant Sumatran Earthquakes of 2004 and 2005 (Joint
with EERI)
Presiding: Lori Dengler and Emile Okal
The Cataclysmic 2004 Tsunami on NW Sumatra—Preliminary Evidence for a
Near-Field Secondary Source Along the Western Aceh Basin
G. Plafker, Plafker Geohazard Consultants, [email protected]; S.
Nishenko, Pacific Gas and Electric Company, [email protected]; L. Cluff,
Pacific Gas and Electric Company, [email protected]; M. Syahrial, iyal.com,
[email protected]
Two Earthquakes and Tsunamis that Changed the Perspective of Indonesian
People
G. Prasetya, BPPT, Indonesia for the Institution, [email protected]
The December 26th, 2004 Sumatra-Andaman earthquake and tsunami followed
by the 28 March 2005 event tragically demonstrated the global need for tsunamihazard assessment, tsunami education, and community preparedness. Field surveys
in the coastal area of Sumatra Island and other islands in Indian Ocean soon after
the events brought new insights on tsunamis dynamics and characteristics through
erosional and deposition patterns (sand and mud), run-up height and inundation,
wave front and bore formation, wave-structure interactions and flow depth, coastal
protection and management of the coastal low-lying areas and the importance of
consistent education and local wisdom on natural hazards (earthquake and tsunamis) to save the people who lived in the coastal area.
These events changed perspectives and brought all stakeholders in this region
together to work on recovery, reconstruction and mitigating future events. The
Early Warning System is in progress and during the one-year remembrance of the
events, a successful full-scale evacuation exercise was carried out in the Padang area,
which is considered at high risk based on return period of 1833-type events. The scientific community such as Indonesian Association of Geologists and Geophysicists
led the dissemination of the earthquake and tsunami information to the people
across the country through formal and informal meetings and workshops. These
Associations submitted a proposal to the central government to establish a National
Geology Agency. The local government of Semeulue Island off the Aceh coast has
offered their island as a Natural Laboratory for the Earthquake and Tsunami for
the scientific community. Semeulue Islanders demonstrated the effectiveness of oral
tradition in saving lives during both major events.
The December and March earthquakes and tsunamis not only caused many
deaths and extensive damages but also caused psychological and social impacts.
These great earthquakes have provided much scientific evidence, new insights on
hazard assessment and have fundamentally changed Indonesian hazard mitigation
priorities and programs for future events.
Tsunami Generation from the Andaman Segment of the M>9.0 December 26,
2004 Sumatra-andaman Earthquake
E. Geist, U.S. Geological Survey, [email protected]
One year after the M>9.0 2004 Sumatra-Andaman earthquake, there is still uncertainty regarding the rupture process and tsunami generation capacity of the northernmost Andaman segment (~10°-14°N). Aftershock distributions, rupture imaging, GPS measurements, and vertical displacement of coral reefs all suggest that
rupture continued into the Andaman segment from the south and that there was
enough coseismic slip on the interplate thrust to generation significant tsunami
energy. Contrary to this, however, inverse travel-time modeling from regional tidegauge stations and tsunami runup heights in Myanmar suggest that the effective
rupture length for tsunami generation was much shorter (700-800 km). Both tsunami source and propagation effects are examined in testing different hypotheses
for tsunami generation at the Andaman segment. One hypothesis is that slip on the
interplate thrust occurred at normal slip rates. In this case, the lower than expected
tsunami runup heights in Myanmar may have been caused by accelerated dissipation of tsunami energy during propagation across the broad and shallow shelf in
the Andaman Sea. Propagation effects may include dissipation by turbulent breaking far offshore, indicated by the seaward breaking limit of the modeled leading
wave, and amplitude dispersion (fission) modeled using a 1D non-linear, dispersive form of the shallow-water wave equations. Another hypothesis is that slip rates
were anomalously slow along the Andaman segment, following the initial break at
The tsunami generated by the great Sumatra earthquake of 12/26/2004 devastated
~200 km of Sumatra coast from the Banda Aceh area on the north end of the island
to Meulaboh on the west coast. Of the ~223,000 lives lost during this event, 72%
of the casualties (~160,000) were caused by the near-field tsunami in northern
Sumatra; the remaining deaths resulted from the far-field tsunami throughout
the Indian Ocean. Post-tsunami reconnaissance surveys of the northwest coast of
Sumatra indicate tsunami flow depths of 5 to 12 m along the north coast and 7 to
20 m along the west coast; peak runup is ~39 m west of Banda Aceh near Lhoknga.
Flow depths and runup heights are significantly larger than tectonically-generated
tsunamis documented for earthquakes of comparable magnitude. The data suggest
that alternate sources may have contributed to the tsunami, in addition to slip on
the Sumatra megathrust. Maximum Vertical displacement on the megathrust totals
only 2.8 m, assuming 20 m horizontal slip, 8° fault dip, and dip-slip displacement.
To investigate alternative tsunami sources, interviews were conducted with
more than 110 eyewitnesses, located both on land and offshore during the tsunami.
We compiled systematic data on wave arrival times, precursory sea withdrawal,
number of waves, wave train characteristics, wave heights, and wave periods. Our
data along the west coast indicate that tsunami arrival time from start of the earthquake ranged from ~22 minutes near Lhoknga to ~32 minutes near Meulaboh,
where the continental shelf is widest. Back tracing these arrival times, using a simple
linear wave model, indicates a candidate source along the western Aceh Basin, coincident with the steep eastern margin of the forearc high and the West Andaman
fault of Sieh & Natawidjaja (2000). Our working hypothesis is that the fault is a
steeply-dipping backthrust that splays off the Sumatra megathrust, and that large
coseismic uplift along it in 2004 generated the devastating near-field tsunami.
The Impact of the December 26, 2004 Mw 9.2 Sumatra Earthquake and
Tsunami on Utility, Bridge, and Highway Systems in Aceh Province, Sumatra
L. Cluff, PG&E, [email protected]; S. Nishenko, PG&E, [email protected];
G. Plafker, USGS, [email protected]
The MW 9.2 Sumatra earthquake struck Banda Aceh at 7:59 local time. Strong to
violent shaking reportedly lasted five to six minutes. Buildings greater than three
stories were seriously damaged or collapsed due to long-period ground motions.
The one- to two-story, traditional, unreinforced masonry buildings were undamaged.
About 250 km of the west coast of Aceh Province experienced tsunami waves
ranging from 10 m to 39 m high. Unreinforced masonry construction could not
resist the tsunami forces and most were obliterated. Well-designed and constructed
buildings were able to withstand the waves, except for those impacted by waves carrying large boats or debris. Tectonic subsidence occurred along most of the Aceh
coast, ranging from 20 cm to 1 m, causing submergence that will hinder restoration
of roads, bridges, and utility distribution systems. Hundreds of bridges were picked
up and swept inland, some more than a kilometer. Extensive liquefaction occurred
in near-shore beach deposits for about 100 km along the coast from Meulaboh to
Calang. A 12-MW power plant, mounted on a barge, was swept inland from the
harbor in Banda Aceh more than 3 km. The power plant was undamaged. Most
power plants in the Aceh Province were not damaged by the earthquake or tsunami.
Petroleum storage tanks survived the earthquake and tsunami, except for tanks that
were not full. Most aboveground distribution systems for utilities were seriously
damaged or destroyed by the tsunami. Electric power was restored within a few
days.
Seismological Research Letters Volume 77, Number 2 March/April 2006 231
Port and Harbor Damage from December 26, 2004 Tsunami and Earthquake—
South India and the Andaman Islands
M. Eskijian, California State Lands Commission, [email protected];
As part of a team sponsored by the American Society of Civil Engineers, I surveyed
damage from the December 26, 2004 tsunami and earthquake, as it affected the
port of Chennai, India and also the port of Port Blair, South Andaman Island. There
was a combination of earthquake and tsunami damage to these two ports. The Port
of Chennai in South India had no prior warning, no action plan and was totally
unprepared. As the first wave hit the port, three vessels broke off their moorings,
due to buoyancy forces. Structural damage to wharves resulted from vessel impact.
Two dolphins were totally destroyed, and as the vessels struck one wharf, cranes and
other equipment were destroyed. One container vessel remained moored indicating that the tsunami current was not sufficient to break its mooring lines. On one
of the moving vessels, crew members jumped to a crane, and then onto a wharf.
The Port of Port Blair, South Andaman Island had a different scenario. In this port,
the protocol was that if an earthquake occurred, all vessels were required to leave
the port, as soon as possible. Most vessels were able to depart, and there was little
damage to the port infrastructure, as a direct result of the tsunami. However, there
were numerous wharves and piers that failed, due to the earthquake. This paper will
document the types of damage experienced by the two ports, and possible mitigation measures.
Ancillary Records of the 2004 Sumatra Tsunami: New Challenges and
Opportunities for Geophysicists
E. Okal, Northwestern University, [email protected]
The 2004 Sumatra tsunami was recorded not only by tidal gauge stations, but also
by a number of instruments which had not been designed for that purpose, and
which were often operating under extremely unfavorable response characteristics.
This includes hydrophones and infrasound sensors of the IMS/CTBTO, satellite
altimeters, GPS receivers used to map perturbations in the ionosphere, and seismometers reacting to the arrival of the tsunami on shorelines, as well as on large icebergs part of, or detached from, the Antarctic ice shelves. While some such observations had been previously recognized (altimetry; GPS), the Sumatra data is of high
enough quality to allow quantitative estimations. In addition, these records often
emphasize the shorter periods of the tsunami wavetrain (down to 60 s) which have
been observed systematically for the first time in the far field during the Sumatra
tsunami (hydrophone, seismic records); their systematic study and modeling are
unparalleled opportunities for the understanding of singular and delayed effects
of tsunamis in distant harbors. In several fields (infrasound; seismic low-frequency
recording), the interpretation of the mechanism of physical transfer of energy
between the tsunami and the receiver remains a challenge warranting significant
further investigation.
Extending ANSS: Next Generation Earthquake
Monitoring I (Joint with EERI)
Presiding: William Leith and Robert Nigbor
Future Seismic Instrumentation for ANSS
J. Evans, U.S. Geological Survey, [email protected]; W. Savage, U.S. Geological
Survey, [email protected]; C. Hutt, U.S. Geological Survey, [email protected]
gov; D. Oppenheimer, U.S. Geological Survey, [email protected]
Envisioned in 2000 as a five-year capital investment program, the Advanced
National Seismic System (ANSS) has proceeded with incremental funding significantly below anticipated levels for the last four years. Planning for and procuring
instrumentation for ANSS is challenged by such funding. Low annual capital budgets encourage purchasing low-cost instrumentation to get more stations on the
ground, yet evolution of seismic data analysis needs generally calls for the wider
bandwidths and dynamic ranges of relatively expensive systems. Near-source and
urban ground-response monitoring both need high spatial density of sensors, perhaps not to unaliased density but certainly depending on the shortest wavelengths
sought and the complexity of the observing environment. In free-field strong
motion, for example, complexity in the source and in the path result in the spatial
variance of most derived parameters rising very rapidly with interstation distance
(within 1-2 km) to a multiplicative factor of ~2 in the far field and ~3 close to the
rupture (with one in 20 sites more extreme). This high spatial variance implies station spacing <1 km. In structural monitoring, wavefield complexity generally scales
with structural complexity, thus station spacing even <10 m. At the other extreme,
Regional- to global-scale monitoring requires longer-period data at very-low-noise
sites with sensitive, low-noise, broadband seismographs, although site-to-site varia-
tion in ambient noise levels offers an option for somewhat lower costs in certain
applications. These factors drive instrument and array design beyond the concepts
established at the start of ANSS, toward: separable (modular) sensors, recorders,
telemetry, power, and timing; integrated systems so inexpensive that maintenance
sensibly may be done by wholesale replacement; low-cost and more ubiquitous
telemetry links; using devices originally developed for larger markets; and mixed
arrays of high-amplitude-resolution systems combined with lesser systems to
improve spatial resolution. Operational matters may continue moving toward: siting and maintenance using mass permitting; deployment in volunteers’ homes and
corporate facilities; and remote health monitoring as well as most corrections of
instrument health. This presentation will describe efforts to address these issues and
their impact on specification and procurement of future ANSS instrumentation.
The “GeoNet” Monitoring System of New Zealand
H. Cowan, New Zealand Earthquake Commission, [email protected]; K.
Gledhill, GNS Science, [email protected]
GeoNet is a facility to monitor and collect data on geological hazards in New
Zealand. The design, construction and operation of GeoNet are funded by the New
Zealand Government to provide national coverage for hazard detection, emergency
response and to increase the quality, applicability and confidence limits of hazards
research. GeoNet consists of a national seismograph network for uniform earthquake location and data collection capability; regional seismograph networks to differentiate shallow and deep earthquakes and to enhance monitoring of volcanoes; a
strong motion accelerograph network to record near-fault ground motion, regional
attenuation, microzone effects, and the response of built structures; a national network of continuously-recording GPS stations and more dense regional networks to
monitor earth deformation; and, a national landslide emergency response capability. Four years into its ten year rollout, the GeoNet Project has reached an important milestone with core network coverage in place. Data from these networks are
telemetered continuously to two independent centers providing redundancy in the
event of system failure at either node. GeoNet incorporates a modern data management centre (www.geonet.org.nz), allowing efficient data archiving and monitoring of all stations. The installation program now shifts to regional enhancements
to monitoring of the actively-deforming plate boundary zone and urban centers.
Continuous-recording GPS stations have already recorded motions attributed to
slow slip events on the subduction interface beneath the North Island. Other interesting measurements include a swarm of earthquakes recorded near the capital city,
Wellington during 2003-2004, which may be related to changes in motion detected
at CGPS stations. The socio-political environment in which GeoNet operates has
been rapidly evolving as central and local government, along with the business sector, focus increasingly on the economic and social impacts of disasters and how
these can be mitigated. A strategic review has identified opportunities to develop
an integrated approach to risk management within which to effectively situate the
GeoNet investment.
ANSS Accelerometer Data—Not Just for “The Big One” (Anymore)
K. Pankow, Univ. of Utah Seismograph Stations, [email protected]; J.
Pechmann, Univ. of Utah Seismograph Stations, [email protected]; W.
Arabasz, Univ. of Utah Seismograph Stations, [email protected];
Traditionally, accelerometers have been used for recording triggered strong-ground
motions from earthquakes with M > 4. The data from these instruments have been
primarily used by engineers for building design and by seismologists modeling
fault rupture histories. Although older generation strong-motion instruments were
“incapable of recording small or distant earthquakes” (p.12, USGS Circular 1188,
1999), advances in accelerometer and digital recording technology have greatly
reduced this limitation. Following the 2002 Denali Fault earthquake (DFE), we
learned that modern continuously telemetered strong-motion instruments provide
valuable recordings of some teleseismic earthquakes (Pankow et al., BSSA, v.94,
2004). Since the DFE, we have learned that these instruments also provide valuable recordings of small (0.5 < M < 4) local earthquakes. In this paper, we show
examples from both teleseismic and small local earthquakes recorded on accelerometers located in Utah. The majority of these instruments are located on soil, in
valley settings generally devoid of weak-motion instruments. Using a dataset of 31
earthquakes (M 0.5 to M 3.2) located in the Salt Lake Valley, Utah we determined
the magnitude and distance ranges over which first arrivals could be successfully
picked from accelerometers located on both rock and soil. Somewhat surprisingly,
earthquakes as small as M 2 are well-recorded on accelerometers to epicentral distances of 20 km, even at soft soil sites. In fact, digital telemetry recordings from
accelerometers are superior to analog telemetry recordings from short-period seismometers located on soil in the same distance range. ANSS accelerometers are collecting a rich new dataset. This dataset is important not just for recording “the big
one” and for strong-motion seismology, but also for studies of teleseisms, structure,
and local seismicity.
232 Seismological Research Letters Volume 77, Number 2 March/April 2006
IRIS Collaborations with the ANSS Backbone Network
R. Butler, IRIS, [email protected]; K. Anderson, IRIS, [email protected]
The Incorporated Research Institutions for Seismology (IRIS) cooperates closely
with the USGS in establishing the Advanced National Seismic System Backbone
Network of permanent stations in the United States. More than 50% of the ANSS
Backbone sites in the lower 48 States have benefited from joint IRIS-USGS collaboration. This cooperation extends from hosting ANSS sites to establishing and
upgrading infrastructure. The USArray component of EARTHSCOPE managed
by IRIS is funding 35 new and upgraded ANSS sites in the lower 48 States and
Alaska through the USGS Albuquerque Seismological Laboratory. Progress in the
USArray component of the Backbone continues with all facilities scheduled to be
in place by September 2006. In addition to seismometers, USArray is also installing
magnetotelluric sensors and real-time GPS at many Backbone sites. ANSS telemetry being provided by USGS provides the real-time link for data transmission, and
ANSS has helped USArray integrate its new data acquisition systems with the satellite telemetry system. As part of its Global Seismographic Network (GSN) program
cooperation with ANSS, IRIS has funded the site preparations at 11 ANSS stations
through IRIS member Universities, and continues to fund new site preparations for
the ANSS in cooperation with USGS and IRIS Members. As Affiliate stations and
arrays of the GSN, IRIS has incorporated 4 US Atomic Energy Detection Systems
(AEDS) and International Monitoring System (IMS) sites as part of the USArray
component of the ANSS Backbone. In cooperation between NSF, USGS, and
IRIS, 20 stations of the GSN form a core component of the ANSS Backbone in
the conterminous US, Alaska, Hawaii, and Puerto Rico. The mixture of VBB and
BB instruments of the GSN enhances the ability of the ANSS to record the full
spectrum of global teleseismic signals as well as national and regional events. All
data from the ANSS Backbone are archived and available in real-time through the
IRIS Data Management System.
Probabilistic Estimates of Monitoring Completeness of Seismic Networks
D. Schorlemmer, ETH Zurich, [email protected]; J. Woessner,
California Institute of Technology, [email protected]; C. Bachmann,
ETH Zurich, [email protected]
The monitoring completeness of seismic networks varies in space and time. It
strongly depends on station distribution and recording quality per station. We
introduce a new method to estimate spatial and temporal monitoring completeness
of seismic networks from phase data.
For each station, we extract a probability distribution of having detected an
earthquake of magnitude M at a distance D. Given the network’s minimum number
of detected phases for triggering and locating events, we compute either completeness maps for a particular probability level or probability maps for the detectability
of events with a particular magnitude. This approach has several advantages over
alternative ways in completeness estimates: Contrary to estimating completeness
based on the Gutenberg-Richter distribution, our approach does not assume any
event-size distribution and is based solely on empirical data. Because the method
does not work on earthquake samples, no averaging over space and time occurs.
It also offers the possibility of estimating the completeness in low-seismicity areas
where methods based on parametric earthquake catalogs fail due to sparse data.
Additionally, each station’s probability distribution allows for inspections of its performance, intrinsically including site effects.
We present case studies from Switzerland and southern California and compare them with estimated completeness levels of other methods. Because the only
ingredients to the probabilistic estimates of monitoring completeness are the phase
data and a station list, this approach is easy to adopt to other seismic networks. We
envision this method to become a viable additional tool for the design and management of seismic networks from local to global scales.
How to Install More Strong Motion Stations for Less Money More Quickly
D. Oppenheimer, United States Geological Survey, [email protected]; J.
Evans, United States Geological Survey, [email protected]; W. Savage, United
States Geological Survey, [email protected]; C. Hutt, United States
Geological Survey, [email protected]
Earthquake strong motion (SM) data recorded in urban areas provide considerable benefit to society. “ShakeMaps” can guide emergency response activities.
Recordings can be used by engineers to improve building codes. Near real-time
data from instrumented structures can indicate if the design criteria are exceeded.
However, the seismological community is making very slow progress installing
SM instruments in regions with high seismic hazard. Consequently, we continue
to record data that are very spatially aliased. In 2005 there were ~1465 SM stations operating in California, whereas Vision 2005 (Borcherdt et. al, 1997) recommended 4400 stations be installed. At the current rate of SM station installation, it
will likely take decades to achieve this vision. Part of the problem is limited funding.
However, a related, but addressable problem is that the type of SM instrumentation and telemetry that seismic networks now use is too expensive to purchase,
install, and operate, and instrument capabilities far exceed the requirements for
operation in noisy urban locations. Advances in technology provide an alternate
approach. COTS computer hardware coupled with16-bit MEMS accelerometers
can be assembled into a small SM “appliance” with wireless capabilities. The widespread adoption of always-on wireless routers in the home and office environment
provides nearly unlimited locations to install appliances. A public solicitation for
volunteers to host these appliances would eliminate complex permitting processes
and offer free telemetry. Inexpensive non-volatile storage provides nearly unlimited
event waveform storage to survive long Internet outages or hosts who inadvertently
interrupt Internet access. Appliance software could automatically register with
seismic networks, send state-of-health messages, synchronize time, upload triggers,
and download software and configuration updates. To foster participation, hosts
of these appliances could be granted access to websites that show the triggered
waveforms from their appliances. Simple maintenance like battery replacements
could be performed by the hosts, and malfunctioning appliances similarly could
be exchanged by mail. Installations of several hundred appliances per year are easily achievable for modest investments and could revolutionize the level of seismic
monitoring of strong motion.
The M7.6 Kashmir Earthquake of 8 October 2005 (Joint
with EERI)
Presiding: Roger Bilham and Saif Hussain
Geology of the Kashmir Earthquake and its Geomorphic Consequences
M. Khan, National Centre of Excellence in Geology, University of Peshawar,
[email protected]; G. Khattak, National Centre of Excellence in Geology,
University of Peshawar, [email protected]; M. Shafique, National Centre of
Excellence in Geology, University of Peshawar, [email protected]; L. Owen,
University of Cinnanti, Oh, [email protected]
Kashmir Earthquake 2005 has been the latest and most devastating Himalayan
earthquakes. Well known geological attributes of the Himalayan tectonics played a
role in causing this earthquake. Geological processes have also played a great role in
enhancing the associated damage to life and property.
What caused the Kashmir Earthquake 2005? The earthquake was epicentred
in the Hazara Kashmir Syntaxis, a narrow NNW trending antiformal fold structure that marks transition between NW-SE Himalayan trend in the east and E-W
Hazara trend in the west. The Main Boundary Thrust that warp around the syntaxis
apparently was not responsible. Instead a fault line that traverses oblique to the syntaxial trend, more or less NW-SE from Bagh, through Hattain Bala, Muzafarabad
and Balakot was activated. This fault is referred to as Bagh Fault or the Kashmir
Boundary Thrust. All the mapped versions of this fault show its termination at
Balakot. However, damage did not cease at Balakot but continued NW into Jabori,
and Allai Kohistan area. This region is underlain by a seismically well defined structure called the Indus Kohistan Seismic Zone. Pattan Earthquake, 1974 (6.9M), and
Hazara Earthquake, 2004 (5.8M) were associated with this seismic zone. The interplay between the Bagh Fault, the Hazara Kashmir Syntaxis and the Indus-Kohistan
Seismic Zone suggests that the Himalayan trend does not terminate at the syntaxis
but continues north-westward into Allai Kohistan area as a subsurface structure.
The E-W Hazara trend is therefore a surface expression in response to gypsum-bearing Hazara Formation at basement levels.
We use field studies to assess the geomorphic response and its relation with
the damage in the earthquake-hit region. More than a thousand landslides were
triggered by the earthquake, including the mega-slide at Hatian Bala. Knowing that
slopes are mostly steep in the region, it is not only the fault line and its vicinity that
caused sliding but the lithologies played a major role in causing the slides. Traverses
between Bagh in the south-east and Allai, Kohistan in the north-west showed that
whereas landsliding was a dominant consequence of the earthquake, liquefaction
did play a role in damage to several relatively colluvium-rich, water saturated terraces.
The Blinding of the Himalayan Arc at the Western Syntaxis
L. Seeber, Lamont-Doherty Earth Observatory, [email protected]; J.
Armbruster, Lamont-Doherty Earth Observatory, [email protected];
K. Jacob, Lamont-Doherty Earth Observatory, [email protected]
A prominent topographic front and a belt of thrust earthquakes mark current continental convergence along the 2500km long Himalayan arc. Surface structure is
generally more complex because it displays deformation accumulated since collision
and may also be decoupled by upper crustal detachments. The Western Syntaxis is
Seismological Research Letters Volume 77, Number 2 March/April 2006 233
a sharp NW-plunging anticline that separates the Himalayan arc from the much
smaller Hazara arc to the west and is traced for over 300km across the India-vergent
thrust belt from the deformation front to Nanga Parbat. The syntaxis-anticline is
asymmetric, despite structural and lithologic continuity around it. It is overturned
toward W-NW and the western limb, the Hazara arc, is a far-traveled thin-skin
feature decoupled from its roots. A local seismic network revealed 30y ago that
the Himalayan belt of thrust earthquakes continues for at least 80km beyond the
syntaxis, where it was named the Indus-Kohistan seismic zone (IKSZ). This NWstriking seismogenic thrust fault accommodates N-E convergence and is parallel to
a prominent topographic front, but is discordant with NE-striking surface structures and is blind. The 1974 M6.0 Pattan earthquake hinted at the disastrous-earthquake potential of the IKSZ. The 2005 M7.6 thrust earthquake ruptured across the
syntaxis and only part of the IKSZ. As a result, this blind structure could now be
primed for another destructive event. The detachment capping the IKSZ is likely
to extend up dip across the Hazara arc to the Salt Range. This huge active shallow-crustal fault underlies much of densely populated northern Pakistan. Paucity
of regional historic earthquakes prompted the suggestion that the evaporite associated with the detachment at the Salt Range made this fault particularly weak and
aseismic, but this hypothesis may be overly optimistic. Evaporite is not prominent
at either the syntaxis or the Indus re-entrant where the basal (Salkhala) formation
outcrops and its weakening effects may be localized. Furthermore, large ruptures
tend to accommodate large and rare displacements and may thus miss the historic
window. The large seismic gap along the Himalayan front SE of the 2005 rupture is
another likely source of large earthquakes brought closer to failure by that rupture.
Surface Faulting during the October 8th, 2005, Muzaffarabad Earthquake and
Coulomb Stress Increase on the Jhelum Fault
P. TAPPONNIER, Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252
Paris Cedex 05, France, and LGIT, Gr, [email protected]; G. King,
Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris Cedex 05,
France, and LGIT, Gr, [email protected]; L. Bollinger, Institut de
Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris Cedex 05, France, and
LGIT, Gr, [email protected]; J. Grasso, Institut de Physique du Globe
de Paris, 4 Place Jussieu, 75252 Paris Cedex 05, France, and LGIT, Gr, [email protected]
ujf-grenoble.fr.
As mapped prior to the earthquake, the Jhelum Thrust follows the northeast banks
of the Jhelum and Kunhar rivers, where it is marked by clear slope-breaks at the
base of prominent triangular facets. SW of Garhi Dopatta, it cuts the river, keeping
a SSE-strike across the mountains towards Bagh. Just north of Muzaffarabad, the
thrust steps leftwards by a few kilometers after crossing the Neelum. It dips eastwards under a large hanging-wall anticlinorium, whose core exhumes schistosed
Murree red-beds and locally their substratum. At depth, it coincides with a segment
of the well-known “Indus Kohistan Seismic Zone (IKSZ).
The 8th October earthquake produced complex, but clear surface breaks,
which can be mapped from the giant Hattian landslide in the south to Balakot in
the north. The main thrust rupture is visible as a flexural scarp at the base of cumulative scarp-slopes in most places. Prominent hinge scarps and open cracks have
formed in the folded hanging wall. The orientation of such cracks is usually guided
by the steep Murree beds underneath. Near Muzaffarabad, both the coseismic hanging-wall cracking and flexural slope increase must have played an important role
in triggering large rockslides, particularly in the brittle infra-Cambrian dolomites.
Large cumulative offsets and spectacular flexural folding of five fluvial strath terraces is observed where the Jhelum thrust crosses the Neelum-Kishanganga river,
at Nissar camp. About 5 meters of coseismic offset have raised the youngest terrace
adjacent to the present river channel.
Facing the Jhelum thrust, another clearly active fault, the Jhelum fault, follows the Jhelum river from Muzaffarabad to Murree. This NS-trending fault, marks
the base of the steep, up to 2 km-high range-front that has forced the 160°-southward hairpin turn of the river. Its ≥ 60 km-long trace cuts and offsets left-laterally
nine west-bank tributaries of the river. Locally, this second fault coincides with the
well-mapped MBT (Murree Thrust). The present-day kinematics suggests that it
still acts as a lateral ramp of the Murree-Abottabad imbricated thrust wedge. We
interpret the left-step of the Jhelum Thrust north of Muzaffarabad to result from
current motion on the Jhelum Fault, a rare example of interaction between two
intersecting active faults. At the same time, motion on the Jhelum thrust appears
to be responsible for offsetting and folding the MBT, thus accounting for its 180°
bend northwest of Pir Panjal. Coulomb stress increases due to the 8 October 2005
earthquake on the Jhelum fault reach about 20 bars in the north, which implies
that it has been brought closer to rupture. The possible occurrence of a second,
triggered, M ≥ 7 earthquake between Muzaffarabad and Murree on this latter fault
is possible.
The October 2005 Kashmir Earthquake—EERI Reconnaissance Report
S. Hussain, Coffman Engineers, Inc., Encino, CA, [email protected];
B. Khazai, The Earth Institute at Columbia University, New York, [email protected]
ldeo.columbia.edu; A. Nisar, MMI Engineering, Oakland, CA, [email protected]
MMIEngineering.com.
An EERI reconnaissance team visited Pakistan between the 13th through 20th
of November, 2005. The trip included a helicopter survey of the area affected by
the October 8 earthquake and a meeting with the Prime Minister of Pakistan.
This report summarizes some of the salient portions of the information obtained
by the EERI team. The official death toll as of November 2005 stands at 87,350
with approximately 138,000 injured and over 3.5 million rendered homeless. The
earthquake severely affected over 500,000 families and killed about 19,000 children, most of them in widespread collapses of school buildings. It is estimated that
over 780,000 buildings have been either destroyed or damaged beyond repair and
many more rendered unusable for extended periods of time. Lifelines were adversely
affected, especially roads and highways of which hundreds of kilometers were made
unusable mainly due to landslides and bridge failures. Several areas remained cutoff via land routes several months after the main event. Power, water supply and
telecommunication services were down for varying lengths of time. Services in
most areas were restored within a few weeks. Important and pertinent lessons can
be learned from the varied performance of URM (Unreinforced Masonry) bearing wall and wall-infilled concrete frame buildings in response to intense ground
shaking, as well as from the many landslides that occurred due to this earthquake. It
appears that there was no prior policy related to earthquake hazard or code enforcement in the region even though most practicing engineers in major urban areas use
the UBC for building design. However UBC seismic zoning for Pakistan is not
typically followed. The magnitude of the logistical problem of administering aid
and relief efforts was tremendous, and the early days of the disaster were marked
by an uncoordinated effort between a whole host of organizations. A coordinating
structure was later created by the government under the Federal Relief Commission
(FRC) and the ERRA (Earthquake Relief and Rehabilitation Authority). Relief aid
is being disbursed by the many NGO’s working in the area as well as government
authorities, though not without challenges and difficulties.
Performance of Engineered and Non-engineered Structures in Northern
Pakistan and Azad Kashmir during the October 8 Earthquake
A. Syed, NWFP University of Engineering & Technology Peshawar, Pakistan,
[email protected]; A. Naeem, Chairman Department of Civil
Engineering UET Peshawar, [email protected]; Q. Ali, Faculty
Department of Civil Engineering UET Peshawar, [email protected]; A.
Naseer, Faculty Department of Civil Engineering UET Peshawar, [email protected]; M. Javed, Faculty Department of Civil Engineering UET
Peshawar, [email protected]; M. Ashraf, Faculty Department of
Civil Engineering UET Peshawar, [email protected]; Z. Hussain, PhD
scholar Department of Civil Engineering UET Peshawar, [email protected]
The Oct 8, 2005 earthquake of Kashmir resulted in more than 80,000 deaths with
infrastructure loss of more than US$5.2 billion. The Mw=7.6 earthquake left more
than 4 million people homeless/affected. Experts from Earthquake Engineering
Center (UET Peshawar) carried out extensive research in the affected areas since
October 8. The construction in these areas comprised of stone masonry, un-reinforced brick masonry, un-reinforced concrete block masonry and reinforced
concrete structures. In this event of ground shaking that may have resulted in
ground accelerations of 0.5g or more (as published by researchers), stone masonry
experienced the most damage whereas brick masonry performed relatively well.
Engineered structures like bridges performed fairy well. Engineering University
(UET) Peshawar has proposed modular designs to the government for reconstruction of schools & basic health units to be constructed in reinforced concrete with
seismic detailing (even for single storey) in these areas. Since the number of housing
units is enormous, it is proposed to construct housing units in confined concrete
block masonry and solid clay brick masonry whereas fly-ash and other pozzolans
are recommended as partial replacement of cement to reduce the cost because per
capita income of people in these areas is very low therefore indigenous materials are
encouraged for use.
Pakistan Earthquake of October 8, 2005 (Mw7.6): A Preliminary Report on
Source Characteristics and Recorded Ground Motions
S. Singh, Instituto de Geofísica, UNAM, [email protected]; A.
Iglesias, Instituto de Ingeniería, UNAM, [email protected]; R.
Dattatrayam, India Meteorological Department, [email protected]
unam.mx; B. Bansal, Department of Science & Technology, India, [email protected]
ollin.igeofcu.unam.mx; X. Perez-Campos, Instituto de Geofísica, UNAM,
234 Seismological Research Letters Volume 77, Number 2 March/April 2006
[email protected]; G. Suresh, India Meteorological Department, [email protected]
ollin.igeofcu.unam.mx.
We present a preliminary source study of the Pakistan earthquake of October 8,
2005 (Mw7.6) and the far-field ground motions that it generated. Our analysis is
based on regional broadband seismograms recorded at stations operated by the
India Meteorological Department (IMD) which are situated to the south of the
epicentre, and at non-IMD stations which are located to the north. We find that
the source spectrum of the earthquake is reasonably consistent with an (2 model
with a seismic moment, M0, of 2.94x1020 N-m and a corner frequency, fc, of 0.051
Hz (Brune stress drop of 9.5 MPa). The spectrum is similar to that of the Bhuj
earthquake of 2001 (Mw7.6). The radiated seismic energy, ER, estimated from the
empirical Green’s function (EGF) technique is 2.70x1016 J, a value more than 8
times greater than that reported by the U.S. Geological Survey. Based on ER estimated from the EGF technique, we obtain normalized radiated energy, ER/M0, of
9.1x10-5, and an apparent stress, ta, of 2.7 MPa. The rupture area of 100x15 km2
(estimated from slip distribution mapped from the inversion of teleseismic body
waves) gives a static stress drop of about 11.3 MPa. This yields a radiation efficiency
of 0.49, implying a “brittle” rupture typical of interplate events. The peak ground
motions (Amax and Vmax) recorded at regional distances (800<R<2500 km) are
some what smaller (especially at northern stations) than those observed during the
Bhuj earthquake. Stochastic method requires a stress drop of (10 MPa to explain
the observed peak ground motions and predicts Amax and Vmax exceeding 1g and
100 cm/s, respectively at hard sites in the epicentral region.
Next Generation of Ground Motion Attenuation Models
(EERI session joint with SSA)
Presiding: Yusef Bozorgnia and Norm Abrahamson
The “Next Generation of Ground Motion Attenuation Models” (NGA) Project:
An Overview
M. Power, Geomatrix Consultants, [email protected]; B. Chiou,
California Department of Transportation, [email protected]; N.
Abrahamson, Pacific Gas & Electric Company, [email protected]; C.
Roblee, NEES Consortium, Inc., [email protected]
The “Next Generation of Ground Motion Attenuation Models” (NGA) project
is a partnered research program conducted by Pacific Earthquake Engineering
Research Center-Lifelines Program (PEER-LL), U.S. Geological Survey (USGS),
and Southern California Earthquake Center (SCEC). The project has the objective
of developing updated ground motion attenuation relationships through a comprehensive and highly interactive research program. Five sets of updated attenuation relationships are developed by teams working independently but interacting
throughout the development process. The attenuation relationships development is
supported by other project components that include: development of an updated
and expanded PEER database of recorded ground motions; conduct of supporting research projects to provide constraints on the selected functional forms of the
attenuation relationships; and a program of interactions throughout the development process to provide input and reviews from both the scientific research community and the engineering user community. An overview of the NGA project
components, process, and products developed by the project is presented in this
paper.
Campbell-Bozorgnia Next Generation Attenuation (NGA) Relations for PGA,
PGV and Spectral Acceleration: A Progress Report
K. Campbell, EQECAT, Inc., [email protected]; Y. Bozorgnia,
Pacific Earthquake Engineering Research Center, [email protected]
The authors are one of five teams developing empirical ground motion (attenuation)
relations for active shallow crustal regions as part of the PEER Next Generation
Attenuation (NGA) Project. Each Developer Team was provided with a common
database of worldwide strong-motion recordings and supporting metadata, but was
given the freedom to use separate data selection criteria, parameters, functional
forms, and statistical regression methods. We chose to exclude aftershocks and
poorly recorded earthquakes using criteria that required smaller events to have a
larger number of recordings than larger events. One of the biggest challenges was
to develop a functional form that accounted for the apparent change in magnitude scaling around M 6.5–7.0 as suggested from several recent large earthquakes
in Alaska, California, Turkey, and Taiwan. After extensive exploratory analysis,
we selected a trilinear rather than the more traditional quadratic functional form
to model the magnitude-scaling characteristics of ground motion. Parameters
included in the model are moment magnitude, closest distance to rupture and to
the surface projection of rupture, buried reverse faulting, normal faulting, sediment
depth (both shallow and basin effects), hanging-wall effects, average shear-wave
velocity in the top 30 m, and nonlinear soil behavior as a function of shear-wave
velocity and rock PGA.
PEER-NGA Empirical Ground Motion Model for Horizontal Spectral
Accelerations from Earthquakes in Active Tectonic Regions
B. Chiou, California Department of Transportation, [email protected];
R. Youngs, Geomatrix Consultants, Inc., [email protected]
We present an empirical model for estimating peak spectral accelerations from
earthquakes in active tectonic regions. The model is one of five being developed
as part of the Pacific Earthquake Engineering Research Center’s Next Generation
of Attenuation (NGA) models project. Our model uses an updated version of the
Sadigh et al. (1997) ground motion estimation relationships. The updates include:
a modified form of magnitude scaling at low frequencies; modeling site effects in
terms of VS30, including soil non-linearity; incorporation of hanging wall effects;
and modeling of wave propagation effects such as regional differences in Q and
the change from body wave to surface wave geometric spreading as the distance
from the source increases. Ground motion relationships are presented for spectral
frequencies in the range of 0.1 to 100 Hz (spectral periods from 0.01 seconds to 10
seconds). The estimated ground motions represent the randomly horizontal component of motion. The relationships were developed using a mixed effects regression model that incorporates the effect of data truncation at low ground motion
levels.
Tsunamis
Presiding: Rob Witter and Brian Atwater
Sedimentary Differences in Near-source Deposits of the 2004 South Asia
Tsunami and Hurricane Katrina
A. Moore, Kent State University, [email protected]; B. McAdoo, Vassar
College, [email protected]; H. Fritz, Georgia Tech Savannah, hermann.
[email protected]
Although the 2004 South Asia tsunami and Hurricane Katrina had similar inundation distances in Sumatra and the Gulf Coast, respectively (up to 5 km in Sumatra,
up to 10 km along the Gulf Coast), the sediments left in the wake of these disasters
differed significantly. Characterizing these differences may aid in discerning the
deposits of prehistoric tsunamis from those of prehistoric storms. In Sumatra, the
South Asia tsunami left a thin (~10-15 cm) sheet of sand, to within tens of meters
of the total inundation distance (~1 km). The sand thickened in topographic lows,
and thinned both landward and seaward. The base often showed signs of erosion,
and the sand was typically normally graded and plane laminated. Trees in the inundated area showed abrasion by sand to nearly the total flow depth, suggesting that
sand was well mixed in the water column and that the dominant mode of transport
was suspension. In contrast, sediments from Hurricane Katrina are often relatively
thick (~50-100 cm) sheets that do not extend more than 300 m from shore. The
sand does not appear to thin and thicken with topography, but commonly ends
at even low topographic highs. Like the tsunami deposits, the base often showed
signs of erosion, but the sand was generally ungraded and was dominated by bedload structures, including climbing ripples and cross-stratification up to 40 cm high.
Trees in the sedimented area showed abrasion only at the top of the flow where
floating objects battered away bark. The lack of abrasion lower on the trees suggests
that sediment here was carried as bedload and that suspended load was a relatively
minor component of the sediment load. Different damage to trees in Sumatra and
the Gulf Coast suggests that whereas tsunami deposition is generally from suspension, hurricane deposition is generally from bedload. Because bedload is a less efficient transport mechanism, hurricane sediments do not travel so far inland as do
tsunami sediments, for the same inundation distance.
Evidence of Combined Entrainment and Suspension Deposition As Recorded
in Tsunami Sand Sheets from the Recent SE India Tsunami and the 1700AD
Cascadia Tsunami
C. Peterson, Portland State University, [email protected]; H. Jol,
University of Wisconsin, Eau Claire, [email protected]; H. Yeh, Oregon State
University, [email protected]
An understanding of the mechanisms of tsunami sand transport and deposition are
critical to the potential modeling of tsunami flow from preserved tsunami deposits. Tsunami sand deposition has been assumed to occur from suspension deposition out of turbulent flow. These assumptions were based on evidence of normal
Seismological Research Letters Volume 77, Number 2 March/April 2006 235
grain-size grading, alternating sand and mud laminae, and a lack of internal crossbedding. Wide-spread observations of sand ripples and heavy-mineral sorting in
recent tsunami sand sheets from Kalpakkam, Devanaanpattina, Parongipettai,
and Nagapattinam, in SE India demonstrate deposition by entrainment processes.
Asymmetric sand ripples with 5-20 cm spacing and 1-5 cm amplitude were observed
on the surfaces of undisturbed tsunami sand sheets (2-50 cm thick) at shore-normal
distances of 80-430 m from the shorelines. Heavy-mineral segregation occurred
in foredune crests, broad overwash fans, and distal sites at distances of 30-300 m
(Kalpakkam), 200-300 m (Parongipettai), and 100-430 m (Nagapattinam). Under
normal surfzone resuspension processes the smaller, denser heavy-minerals (ilmenite-magnetite ~5 spg) are in suspension equivalence with larger, lighter quartz and
feldspar (~2.5 spg). The heavy and light minerals were sorted from each other during tsunami bedload entrainment on the basis of their differing critical entrainment
velocities. Normal grading was observed in the light mineral fractions of the sand
sheets at Kalpakkam, Parongipettai, and Nagapattinam. Based on these observations a 1700AD Cascadia sand sheet deposit from Seaside, Oregon was reexamined
for evidence of entrainment deposition. The sand sheet (10-35 cm in thickness)
occurs at a tsunami pour-over locality in the Neawanna wetland, between the 12th
Ave and Broadway Bridges. The sand sheet fan is normally graded, contains mud
and sand laminae, does not show cross-bedding in trenches, and was assumed to
represent suspension deposition. However, high-frequency 500 MHz ground
penetrating radar (GPR) PulseEkko 1000A system, demonstrated clear evidence
of low-amplitude (5-10 cm) very-low angle internal cross-bedding (~1 m wavelength) in the sand sheet. The internal cross-bedding changed direction with fan
radiation geometry over a 100 m distance. These results indicate that tsunami sand
sheets develop from both entrainment and suspension deposition, possibly at the
same time under hyperconcentrated flow conditions.
Numerical Modeling of Submarine Landslide-Generated Tsunamis at
Seward and Valdez, Alaska, with Constraints from Recent Multi-beam and
High-resolution Seismic Surveys
E. Suleimani, Geophysical Institute, University of Alaska Fairbanks,
[email protected]; H. Lee, USGS, Menlo Park, CA, [email protected]; P.
Haeussler, USGS, Alaska Science Center, [email protected]; R. Hansen,
Geophysical Institute, University of Alaska Fairbanks, [email protected]
The Alaska coastal communities of Seward and Valdez suffered extensive damage
and a total of 43 tsunami fatalities during the M9.2 1964 Great Alaska Earthquake.
The earthquake induced submarine landsliding in many places including both
Resurrection Bay (location of Seward) and Port Valdez, and the resulting landslidegenerated tsunamis caused most of the damage and deaths in the two communities.
As a part of the National Tsunami Hazard Mitigation Program, we are evaluating
and mapping potential tsunami inundation of a number of coastal communities
in Alaska, including Seward and Valdez. For these communities, submarine landslide-generated tsunami potential must be evaluated for comprehensive inundation
mapping because this mechanism of tsunami generation is known to be critical for
these communities. Also, numerical modeling of the 1964 underwater slides and
tsunamis will help to validate and improve the models.
Recent multi-beam and high-resolution sub-bottom profile surveys of
Resurrection Bay and Port Valdez provide new information about the morphology
of landslide deposits in both areas. On the submarine slope adjacent to Seward,
the surveys show medium- and large-sized blocks, which we interpret as landslide
debris that slid in the 1964 earthquake. In Port Valdez, there are no blocks near
the old Valdez town site, but rather a broad lobe that extends across the fiord bottom, which we interpret as a relatively fluid debris flow deposit. The surveys provide
information on the geometry of the slides (areas, runout, and volumes). This information is being used in landslide and tsunami modeling.
A three-dimensional numerical model of an incompressible 3-D viscous slide
with full interaction between the slide and surface waves is used to simulate Seward
and Valdez slope failures and the resulting tsunami waves. The long-wave approximation is used for both water waves and slides. The equations of motion and continuity for the slide and for surface waves are solved simultaneously using an explicit
finite-difference scheme on a grid of 4.5m x 9m resolution. Numerical simulations
yield slide transformations and velocities, and maximum wave amplitude distributions for different slide scenarios.
A Comprehensive Study of Tsunami Risk in New Zealand, Including
Probabilistic Estimates of Wave Heights from All Sources, Damage to
Buildings, Deaths and Injuries
K. Berryman, GNS Science, [email protected]; W. Smith, GNS
Science, [email protected]
tres around the New Zealand coastline. We have treated both epistemic uncertainty
and aleatory variability, in order to establish confidence limits for the wave heights
and loss estimates. Modelled impacts include likely damage to buildings, deaths and
injuries. Where possible, we have used historical and paleotsunami data to validate
source models. We have been able to place formal statistical uncertainties on the
empirical relationships between source models and wave height. Earthquake sources
were modelled as either characteristic earthquake or Gutenberg-Richter sources, as
appropriate. Wave heights were modelled using Abe’s formulae for distant and local
source tsunamis, calibrated by numerical modelling. Inundation modelling and loss
estimation were done using GIS, with detailed elevation models. Three separate
inundation models were used to address the epistemic uncertainty in onshore water
depths. The study shows that the ongoing risk from tsunamis in New Zealand is
significant. The most likely sources of damaging tsunamis are South America and
the subduction zone to the east of New Zealand. Historical incidents have caused
few casualties and little damage to property and infrastructure, but the fragility is
now much greater because of recent coastal development. On a national basis, the
median estimates of damage to property from tsunamis are about twice what we
expect from earthquakes, and the deaths and injuries are many times more, although
the tsunami loss estimates have large uncertainties. Deaggregation indicates that
while some locations are most prone to tsunamis from distant sources, others are
more exposed to local tsunamis. The second part of the study (not reported here)
examines tsunami preparedness. It is being used by the Ministry of Civil Defence
and Emergency Management in order to develop effective warning systems and
especially to face the challenges presented by tsunamis of local origin.
The paper is presented on behalf of a large collaborative team, representing
GNS and other institutions.
Tsunami Monitoring and Warning in Puerto Rico and the Caribbean
C. von Hillebrandt-Andrade, Puerto Rico Seismic Network, UPR,
[email protected]; V. Huérfano, Puerto Rico Seismic Network, UPR,
[email protected]
In the wake of the December 26, 2004 devastating earthquake and tsunami, attention has been focused worldwide to the establishment of local and regional tsunami
warning systems.
For these systems to be effective four critical areas need to be addressed: tsunami inundation mapping, tsunami monitoring and warning, communications
and dissemination and education. The Puerto Rico Seismic Network (PRSN) has
actively been involved in all areas, but this presentation will focus on tsunami monitoring and warning efforts.
The objective of the tsunamis warning and monitoring component of the
tsunami warning system is to detect and inform as rapidly and accurately as possible potential tsunamigenic events and then confirm whether or not a tsunami has
indeed been generated. For the Northeastern Caribbean the sources of the tsunamis
are local, regional and teleseismic earthquakes as well as submarine landslides and
less so volcanic activity.
Given the available technology, the focus of the system has been on the
detection of seismic events. For local earthquakes, a magnitude threshold of 5.0
has been established for which real and near real time data and information are
needed, although it is as of magnitude 6.5 that tsunami warning messages would be
issued. For regional and teleseismic events, the tsunami warning and watch thresholds of 7.5 and 8.0 have been established. To achieve the local detection threshold,
the PRSN has established stations and/or data exchange protocols in Puerto Rico,
the U. S. and British Virgin Islands (VI) and the Dominican Republic. For regional
earthquakes and teleseisms, the PRSN has also incorporated into the Early Bird
automatic earthquake location and dissemination system, GSN seismic stations
and a constantly growing number of broadband stations operated by other seismic
networks in Central America, South America and the Caribbean. The nine joint
broad band and strong motion GSN type stations the USGS will be installing in the
Caribbean for tsunami warning purposes in 2006 will also be incorporated into the
system. For data exchange Earthworm and SeisComp utilities are used. For the confirmation of whether or not a tsunami has been generated, sea level gauges, as well
as DART buoys, are needed. The PRSN has received funding from FEMA to install
a six station tide gauge network which will complement ten NOAA tsunami ready
tide gauges operating in PR and the VI. As DART buoys are installed, the data
from these will also have to be incorporated into the system. All of these activities
are being coordinated together with other local, regional and international institutions, including the Pacific Tsunami Warning Center and the IOC International
Co-ordination Group for the Tsunami and other Coastal Hazards Warning System
for the Caribbean Sean and Adjacent Regions.
We have examined all the likely sources of tsunamis that can affect New Zealand,
and developed a probabilistic methodology to evaluate their potential to generate
tsunamis, the likely waves produced, and their impact on the principal urban cen-
236 Seismological Research Letters Volume 77, Number 2 March/April 2006
Seaside Tsunami Awareness Program
J. Wilson, Oregon Emergency Management, [email protected]
Oregon Emergency Management (OEM) partnered with the Oregon Department
of Geology and Mineral Industries (DOGAMI on a pilot Tsunami Awareness
Program for the City of Seaside, Oregon. The program was funded by the National
Tsunami Hazard Mitigation Program (NTHMP) to determine the most effective
means of educating the public on tsunami hazards and preparedness practices.
The Seaside Tsunami Awareness Program began in September of 2004 and
concluded in June 2005. A Tsunami Outreach Coordinator was hired to manage
the program and was chiefly responsible for developing and implementing the
outreach strategies and evaluating the program’s feasibility and success. Volunteerdriven outreach efforts were used to create an educational outreach program that
would not rely on long-term funding. Program volunteers were recruited throughout the community; with significant support provided by high school students,
retired residents, and City representatives.
Outreach efforts targeted local residents, businesses, visitors, and children.
Because a portion of the residential community is Hispanic, outreach information
was provided in Spanish to ensure all local residents were informed about tsunami
hazards. Five outreach strategies were implemented to reach target audiences:
Neighborhood Educator Project Business Workshop School Outreach Program
Public Workshop Tsunami Evacuation Drill
Public opinion surveys before and after the Tsunami Awareness Program
were used to gauge how outreach strategies influenced the public’s comprehension
of tsunami risk. Post-outreach surveys indicated that approximately 68% of the
local households received information from a Neighborhood Educator and 2,200
people participated in the outreach events. From the program’s findings, it is clear
that outreach efforts should continue and should include a variety of outreach strategies that target businesses, students, and the general public.
The information from this pilot program provides a comprehensive overview
of complimentary outreach strategies. These strategies will assist coastal communities in Oregon and other Pacific states in establishing a framework for their own
outreach programs. A newly published report by DOGAMI describes Seaside’s
Tsunami Awareness Program, the program’s findings, and the best approach to
implement future outreach efforts.
Extending ANSS: Next Generation Earthquake
Monitoring II (Joint with EERI)
Presiding: William Leith and Robert Nigbor
A New Low Complexity Real-time Ground Motion Reporting Network
A. Rosenberger, Geological Survey of Canada, [email protected]; G.
Rogers, Geological Survey of Canada, [email protected]; J. Cassidy,
Geological Survey of Canada, [email protected]
A new low complexity real-time ground motion reporting network. Rapid earthquake information systems which display ground shaking levels on a map generally
require the analysis of full waveform data from several hundred seismic sensor channels. In a conventional seismic network, this involves the retrieval of digital waveform data over telemetry links or dial-up connections; data are then processed in a
data centre where peak ground motion and spectral parameters are determined as
input to the mapping program. Operations in such a system are, in general, complex
and involve large sophisticated real-time data acquisition systems. The Geological
Survey of Canada operates a new 300 channel strong motion network in southwest British Columbia which avoids this level of complexity. All our low cost strong
motion instruments have embedded processors which compute ground motion
parameters such as PGA, PGV and spectral intensity (SI), locally and in real time.
Every instrument is connected to the Internet and standard Internet protocols are
used to communicate parametric data from an event to a list of recipients. Real-time
ground motion peak values are reported immediately after a post-trigger observation time interval and can be used to generate the first snap-shot map of the severity
and spatial distribution of ground shaking before source parameters of the earthquake become available. A significant advantage of this network is its decentralized
structure and its response time due to true distributed computing. The transmission
of large amounts of digital waveform data from the instruments to a central facility is no longer time-critical. Data are automatically downloaded over the Internet
about ten minutes after the initial trigger to ensure that all activity was captured.
The integrated data logger keeps a continuous 36 hour record of digital data in a
ring-buffer and also stores triggered data in non-volatile memory. We present some
details of the instruments employed, the structure of this new network and a prototype client system which was developed for the British Columbia Ministry of
Transportation. This client system receives ground motion data from the network
and displays PGA and SI on a thematic GIS generated map in real time.
DamageMap Prototype Using Real-time GPS Point Positioning
K. Hudnut, USGS, [email protected]; E. Safak, USGS, [email protected]
gov; A. Borsa, UCSD, [email protected]; J. Langbein, USGS, [email protected]; K. Stark, Stark Consulting, [email protected]; D.
Barseghian, Stark Consulting, [email protected]; A. Aspiotes,
Honeywell, [email protected]; A. Acosta, USGS, [email protected];
I. Stubailo, UCLA, [email protected]; M. Kohler, UCLA,
[email protected]; P. Davis, UCLA, [email protected]
We have developed and tested the prototype for a system that can determine
whether or not large buildings have remained structurally sound in the immediate
aftermath of a significant earthquake. Assessment of damage after a large earthquake
must be made both rapidly and accurately. For this application, it is most important
to robustly and reliably measure the large (10’s to 100’s of cm’s) displacements associated with structural damage in real-time with low latency. The data fades, gaps,
and outliers that are common with other real-time GPS systems are not acceptable
here. System performance must hold over the many years of inaction, then prove to
be extremely reliable and robust by performing flawlessly for a short burst of activity
when an earthquake occurs. Major urban areas with numerous high-rise buildings
are vulnerable to both the immediate damage, and to the damaging longer-term
economic downturn associated with business disruption. Even for a non-damaging
earthquake, occupants of high-rise buildings can suffer business disruption associated with uncertainties about structural integrity following strongly felt shaking.
For those buildings rapidly judged to be structurally sound, business disruption
is minimized. Given the wide range of possible earthquake shaking effects, it is
important to have intelligent infrastructure in place to provide accurate information automatically and rapidly to inform human decision-making. At UCLA we
have instrumented the roof of the Factor Building with three GPS units. Two are
constantly reporting position using the point positioning method. A third operates
as an RTK rover on a baseline to a nearby base station, also outputting its position
in real-time independently. Test results on reliability, as well as system noise and
accuracy of displacement measurements are compared for both types of systems.
For the DamageMap application, both theory and initial test results indicate that
the point positioning system is superior to RTK in terms of overall system robustness. RTK also typically has several negative aspects for logistical implementation,
some of which we have eliminated through developing and implementing internetbased streaming of RTK correction messages.
Monitoring Civil Structures Using a Network of Wireless Sensors
R. Govindan, University of Southern California, [email protected]; J.
Caffrey, USC, [email protected]; E. Johnson, USC, [email protected]; S.
Masri, USC, [email protected]
Monitoring Civil Structures Using a Network of Wireless Sensors J. Caffrey, R.
Govindan, E. Johnson, S. Masri Large civil structures form the backbone of our
industrialized society, and are critical to its day-to-day operations. Structural health
monitoring (SHM) is a highly active area of research devoted to developing tools
and techniques for automatic assessment of structural integrity. SHM systems often
automatically acquire and process data from hundreds (if not thousands) of sensors.
The high cost of cabling required acquire sensor data is a serious impediment to the
development of large-scale SHM systems. Tiny wireless sensors are an easily deployable low-cost alternative that will bring SHM systems within the realm of practicality. Today, it is possible to build battery-powered coin-sized devices containing a
processor, significant flash memory, and a low-power radio, together with MEMS
sensors capable of measuring vibration. These wireless sensor nodes can be relatively
easily mounted onto the structure, each device within a few meters of another. This
dense placement can greatly increase the spatial resolution of data collection, and
improve the quality of damage assessment. Our research group at the University
of Southern California has been examining the development of wireless systems
for SHM. We have prototyped two software systems, and have experimented with
them on realistic structures. Wisden is a wireless sensor network based data acquisition system that can deliver time-synchronized structural response data reliably
from several locations in the structure over multiple hops to a base-station. Wisden
supports flexible self-organizing sensor network deployments of up to several tens
of un-tethered wireless nodes and avoids the high cabling, installation and maintenance costs incurred by traditional wired data acquisition systems. Netshm provides a programmable sensor-actuator network system that can be used by SHM
engineers to implement SHM algorithms in a higher level language such as Matlab
or C. Netshm uses a two-tier hierarchy comprising of resource constrained sensor
nodes in the lower tier and more endowed gateway nodes in the upper tier and can
theoretically scale to hundreds of nodes.
Seismological Research Letters Volume 77, Number 2 March/April 2006 237
Using Networked Wireless Structural Arrays for Urban Damage Detection
M. Kohler, UCLA, [email protected]; P. Davis, UCLA, [email protected]
edu; R. Govindan, USC, [email protected]
Studies, University of California, Santa Barbara, CA, [email protected]; C.
Strepp, COSMOS, Pacific Earthquake Engineering Research Center, University
of California, Berkeley, CA, [email protected]
The 72-sensor embedded seismic array in the UCLA Factor building is a testbed for
structural health monitoring, recording continuous waveforms at 500 Hz. Dense
networks such as this present a unique opportunity to develop distributed embedded network systems that will enable large-scale earthquake monitoring applications
with a focus on continuous recording in real time and wireless communications.
The building’s dynamic characteristics can be observed for long time scales and for
different sources of excitation such as wind gusts and mechanical devices. For example, temporary decreases in frequencies of modes of vibration can be correlated with
moderate-to-strong shaking, and spectral amplitudes of ambient vibrations have
clear daily and weekly patterns that correlate with working hours, wind velocities,
and non-seismic vibrations. Stacking further enhances the signal and enables computations for source characterization. Wireless untethered devices capable of measuring structural vibrations represent an emerging technology that can significantly
increase the spatial resolution of structural response to earthquakes. A network of
these wireless sensors can be used to instrument structures relatively cheaply and
quickly. These sensors have onboard processing capabilities making it possible to
intelligently process sensor data within the network. In the absence of this capability, the high sampling rates required for structural monitoring can overwhelm
the radio bandwidths of existing sensor platforms. Designing networks of wireless
sensors that can reliably deliver data, or process data in-network, is not without its
challenges: wireless communication is notoriously unpredictable and time-varying,
and the sensor nodes have limited battery life. We have developed a software system
that addresses some of these challenges, yet allows structural data acquisition from
a relatively large (about 30 nodes) network of wireless sensors. We describe here
this system, discuss results from our experiments, and propose a large-scale urban
experiment using the system that would fully characterize building responses before
and after a future damaging earthquake.
We propose to establish interoperability between the COSMOS/PEER-LL
GVDC, and the COSMOS (strong motion) VDC, by writing and implementing
new web services. The COSMOS/PEER-LL GVDC is currently developed and
maintained at the University of Southern California (USC) under the direction
of Carl Stepp, and the COSMOS VDC search engine for strong motion data is
housed at the University of California Santa Barbara (UCSB), under the direction
of Ralph Archuleta and Jamison Steidl. The linking of the two data centers is to provide end users access to information on strong motion maintained at the COSMOS
VDC in close proximity to geotechnical and geophysical data maintained at the
GVDC, and vice versa. A two-way link can be developed that permits users of
either data center to search both centers from one access point. For example a user
could enter the COSMOS VDC and after having identified recordings that satisfy
a set of search criteria, would be linked to the GVDC and could obtain geotechnical and or geophysical data from borings with a specified radius of the recording
station sites. Benefits of this GVDC—COSMOS VDC interoperability include
1) more detail on site conditions for strong-motion data users (geotechnical and
geophysical data tends to be more current on the GVDC than in the COSMOS
VDC); 2) increased efficiency through a reduction in duplication of data at the
two centers; 3) COSMOS VDC access to the GVDC’s better search tools for site
specific conditions and 4) finding usable event data associated with a given area
from the GVDC. In terms of accessing the GVDC from the COSMOS VDC, the
primary advantage is that the presence of any geotechnical and or geophysical data
in proximity to the strong ground motion site of interest would be indicated on
the COSMOS VDC’s corresponding webpage. In the reverse case, accessing the
COSMOS VDC from the GVDC, the COSMOS VDC strong motion stations
could be dynamically displayed as a layer on the GVDC map, subject to operational
efficiency considerations. Funding to create this linkage is currently being sought.
Real-time Structural Health Monitoring Incorporating Soil Structure
Interaction Effects
S. Soyoz, university of california irvine, [email protected]; M. Q. Feng, university of california irvine, [email protected]; E. Safak, US geological Survey, [email protected]
usgs.gov.
Modal parameters are often used for the purpose of structural health monitoring
(SHM) and damage detection. However, environmental conditions and, more
importantly, soil structural interaction (SSI) can also cause changes in modal
parameters. So a rational way is to construct a database of the modal parameters
under different environmental conditions and earthquake excitations, so that their
effect can be excluded when evaluating structural damage.
Also structural damage might happen such that it wouldn’t be possible to
track it just using the earthquake motion itself and even from modal values obtained
before and after the event. So a permanent change like story drift should be tracked
and incorporated to natural frequency signature for complete SHM purposes.
The authors have instrumented the CalIT2 building, a four-story reinforced
concrete structure, located on the UC Irvine Campus with 43 accelerometers.
What makes this building special is that these sensors are not only installed on the
super-structure, but also in the free-field, and deep onto the rock layer of the soil
foundation, making it possible to examine the soil structure interaction.
Starting from November 2004 when this building was new and unoccupied,
ambient vibration of the building has been regularly measured and the dynamic
characteristics of the structure identified to develop a database. Within one year,
two moderate earthquakes were also recorded. It was observed that the modal
parameters obtained during the earthquake excitations differ from those obtained
under ambient vibrations. The change was found to be mainly due to the SSI. Also
the effect of SSI on story drift was observed to be considerable. So far, SSI has not
been taken into consideration in the current SHM research, which may result in
erroneous results. The discovery made in this research will contribute to the development of a realistic framework for health monitoring of real-life civil engineering
structures by incorporating SSI with monitoring.
Real time data and current status regarding the SHM of Cal-IT2 can be found
on: http://mfeng.eng.uci.edu/Maria_Feng/Research_activities/health_monitoring/waveform2.html
Establishing Connectivity between the COSMOS Geotechnical Virtual Data
Center and the COSMOS Virtual (Strong Ground Motion) Data Center
J. Swift, Dept of Civil and Environmental Engineering, KAP, University of
Southern California, Los Angeles, CA, [email protected]; M. Squibb, Institute for
Crustal Studies, University of California, Santa Barbara, CA, [email protected]
edu; R. Archuleta, Institute for Crustal Studies, University of California,
Santa Barbara, CA, [email protected]; M. Steidl, Institute for Crustal
Advances in Volcano Seismology: Enhanced Monitoring
Capability through Application of Complementary
Methods
Presiding: Charlotte Rowe and Heather DeShon
Using Tiltmeters, GPS Receivers, Time-lapse Photography, and
Photogrammetry as Aides for Interpreting Volcanic Seismicity during the
Ongoing Eruption of Mount St. Helens
S. Moran, USGS-CVO, [email protected]; D. Dzurisin, USGS-CVO, [email protected]; R. LaHusen, USGS-CVO, [email protected]; M. Lisowski,
USGS-CVO, [email protected]; J. Major, USGS-CVO, [email protected];
S. Schilling, USGS-CVO, [email protected]; D. Sherrod, USGS-CVO,
[email protected]
It is often difficult to uniquely interpret seismic signals in the absence of visual
observations and data from other geophysical instruments. The ongoing eruption
of Mount St. Helens is a case in point. It has been highly seismogenic, with roughly
one million earthquakes recorded to date. All earthquakes have been shallow (<
2 km), with many occurring in the upper 500 meters of the conduit. Earthquakes
have consisted of hybrid and low-frequency events and have occurred either as very
regularly spaced events (so regular that they have been dubbed “drumbeats”) or as
distinctly larger events that are at least one full magnitude unit above the average
drumbeat magnitude. The drumbeats have accompanied continuous extrusion
of a series of fault gouge-covered dacite spines. We have attempted to correlate
earthquakes with spine extrusion through use of time-lapse photography and GPS
receivers to estimate extrusion rate for periods of minutes to weeks. These efforts
included colocating a seismometer and GPS unit on an active spine and using a
telescopic time-lapse camera system deployed within 400 m of the vent to measure
hypothesized mm- to cm-scale jerks of the erupting spine. We also installed tiltmeters near the vent to look for correlations between discrete tilt events and earthquakes. However, these methods were not precise enough to measure such small
motions. At larger spatial scales, time-lapse photography from cameras on the crater
rim has proven successful in tracking long-term spine motion. In particular, several spine motion changes have correlated visually with changes in the character of
drumbeat seismicity. The cameras have also captured substantial slumps of parts of
a spine in direct association with larger (M 2.5—3.5) earthquakes. Digital elevation
models, single- and dual-frequency GPS receivers, and visual observations have also
established a link between periods of spine breakup and the occurrence of larger
earthquakes, suggesting a causal relation.
238 Seismological Research Letters Volume 77, Number 2 March/April 2006
Improvements to Absolute Locations from an Updated Velocity Model at
Mount St. Helens, Washington
W. Thelen, University of Washington, [email protected]
edu; S. Malone, University of Washington, [email protected]
edu; A. Qamar, University of Washington, [email protected]; S.
Pullammanappallil, Optim LLC, [email protected]
Over 1,000,000 earthquakes have been detected at Mount St. Helens, Washington
since it reawakened in Fall 2005. While less than 1% of these earthquakes have been
formally located, these absolute locations are important to the understanding of
the ongoing dacitic eruption. Picks of well-recorded P-waves on 10 to 15 permanent seismic stations are used with an improved 1-D velocity model and station
corrections to generate new catalog locations for a recent subset of earthquakes.
Formal errors in earthquake location are 100-500 meters; however, because of the
large station corrections needed to minimize average residuals, the systematic errors
due to unknown and variable velocity structure are likely to be larger than this.
Using relative relocations of event families, we find hundreds of events that cluster
into very small volumes. These clusters have little constraint on the actual location
of the cluster in space, since only the relative lag time between similar earthquakes
is kept. This highlights the need for a realistic shallow velocity model to achieve
improved absolute locations that may supplement high-resolution relative locations. To improve the shallow portion of the existing velocity model, we deployed a
4-km long refraction line that extended from the 1986 Dome north to the Pumice
Plain. Our transect consisted of 39 vertical component stations at 100 m spacing,
which alternated between 1 Hz and 4.5 Hz sensors to enhance the recording of
low frequencies across the array. During our 3-day deployment, we recorded 11
earthquakes above magnitude 2.0, as well as coherent energy from rockfall sources
across the entire line. The often emergent character of the earthquakes allows only
the identification of first arrivals. To determine the S-wave velocity structure, we
use the Refraction Microtremor (ReMi) method on earthquakes with extended
codas and rockfall signals. In our new model, shallow P-wave velocities are as low
as 2000 m/s while our deepest P-wave velocities are above 4 km/s. S-wave velocities
vary from approximately 200 m/s at the surface to 1.9 km/s at 2 km depth. This
improved velocity model combined with the existing deeper velocity model, allows
us to recalculate station corrections for all permanent stations within 20 km of the
active vent. The result is a decrease in station corrections an average of 14% for all
stations and 33% for stations on the volcanic edifice. When applied to a subset of
recent volcanic earthquakes, we find improved depth resolution within the shallow
edifice. This study shows the practicality of small-scale refraction experiments on
active volcanoes to improve shallow 1-D P-wave and S-wave velocity models. An
accurate shallow velocity model is vital for improved depth resolution and a greater
understanding of the role of earthquakes in dome morphology, lava extrusion and
volcanic eruption.
Small Scale Shallow Attenuation Structure at Mt. Vesuvius, Italy
E. Del Pezzo, INGV—Osservatorio Vesuviano Napoli, Italy, [email protected]
it; F. Bianco, INGV—Osservatorio Vesuviano Napoli, Italy, [email protected];
L. De Siena, INGV—Osservatorio Vesuviano Napoli, Italy, [email protected]
We present a high resolution 3-D model of S-wave attenuation (Qs-1) for the volcanic structure of Mt. Vesuvius. Data from 959 waveforms relative to 332 volcanotectonic earthquakes located close to the crater axis in a depth range between 1 and
4km (below the sea level) recorded at 5 3-component seismic stations were used
for the inversion. We obtained the estimate of Qs-1 for each source-station pair
using a single-station method based on the normalization of the S-wave spectrum
for the coda spectrum at 12s lapse time. This is a modification of the well known
coda-normalization method to estimate the average Qs-1 for a given area. We adopt
a parabolic ray-tracing in the high resolution 3-D velocity model which was previously estimated using almost the same data set; then we solve a linear inversion
scheme using the L-squared norm with positive constraints in 900m-side cubic
blocks, obtaining the estimate of Qs-1 for each block. Robustness and stability of
the results are tested changing in turn the input data set and the inversion technique. Resolution is tested with both checkerboard and spike tests. A further test is
carried out comparing the coda-normalization method with the ordinary spectral
decay method, which furnishes comparable results. Results show that attenuation
structure resembles the velocity structure, well reproducing the interface between
the carbonates and the overlying volcanic rocks which form the volcano. Analysis
is well resolved till to a depth of 4-5 km. Higher Q contrast is found for the block
overlying the carbonate basement and close to the crater axis, almost coincident
with a positive P-wave velocity contrast located in the same volume and previously
interpreted as the residual high density body related to to the last eruptions of Mt.
Vesuvius. We interpret this high-Q zone as the upper part of carbonate basement
in which most of the high energy seismicity take place. The low-Q values found at
shallow depth are interpreted as due to the high heterogeneity due to the mixing of
lava layers and pyroclastic materials extruded during the last eruptions.
Anomalous Thin Crust and High Attenuation beneath the Taupo Volcanic
Region of North Island, New Zealand from 3-D Tomographic Inversion of
Short-period and Broadband Data
J. Chiu, CERI, University of Memphis, [email protected]; M. Reyners,
Institute of Geological and Nuclear Sciences, New Zealand, [email protected];
J. Pujol, Department of Earth Sciences, University of Memphis, [email protected]
Abundant crustal and subduction zone earthquakes were recorded by a temporary
seismic array of mixed short-period and broadband stations around the Taupo
Volcanic Region of North Island, New Zealand. Spatial distribution of earthquakes
provides an excellent opportunity to explore seismogenic structure associated with
volcanic activities and subduction zones. The S-waveforms for shallow earthquakes
are, in general, very complicated due to the very significant lateral velocity and
structural variations of shallow crust which is mostly lava and volcanic deposits.
Significant lateral velocity variations from a JHD analysis can be correlated with
the topographic and surface geological features indicating very inhomogeneous
shallow crust. Crustal thickness beneath the Taupo Volcanic Region is relatively
thin (~15 km) in contrast to the typical continental crust (~30 km) beneath the
surrounding region. Three low velocity zones can be traced along three distinct geothermal active regions from near surface dipping toward east to depth 15~20 km
where these three zones seem to merge and connect together. This low velocity eastward dipping zone reveal the path and origin of the magmatic sources related to
the volcanic activities and is probably responsible for 2~4 sec of P-wave travel time
delay observed in a land-ocean seismic profile across the Taupo Volcanic Region.
Crustal earthquakes are mostly clustered as swarm at depth shallower than 10 km
associated with subsurface volcanic activities. Results from waveform modeling
reveal that intermediate depth earthquakes must be located near the upper surface
of the subducting slab in order to develop two distinguished P-arrivals. The seismogenic zone at intermediate depth is most probably less than 10 km of thickness and
is located near the uppermost surface of the slab.
Infrasound from Strombolian Eruptions at Mount Erebus Volcano
K. Jones, New Mexico Institute of Mining and Technology, [email protected]; R.
Aster, New Mexico Institute of Mining and Technology, [email protected]; J.
Johnson, University of New Hampshire, [email protected]; P. Kyle, New
Mexico Institute of Mining and Technology, [email protected]; W. McIntosh,
New Mexico Institute of Mining and Technology, [email protected]
During the 2005-2006 field season, the Mount Erebus Volcano Observatory
installed an upgraded network of seven infrasound sensors and a digital, triggered
time-stamped camera surveillance system. The infrasound network is designed
to precisely locate degassing/explosion events and estimate impulsive gas volume
fluxes. These and other data are telemetered to McMurdo station on a year-round
basis and thence exported to New Mexico Tech via the Internet. Following an
unusual eruptive quietus during 2002-2003, the volcano entered a new period of
energetic Strombolian activity in early 2004 that continued through the entirety
of 2005 and on into at least early 2006. Infrasound observations are a particularly
straightforward, largely weather-indifferent, and robust mechanism for assessing
the sizes of these impulsive events and for investigating near-surface eruptive processes and their seismoacoustic signatures.
We will discuss new infrasound observations in the context of Strombolian
eruption dynamics and associated physical parameters. In particular, clear video
recording of emerging gas bubbles from the remarkably exposed vent (occupied by
a persistent phonolitic lava lake) coupled with infrasonic data offer the possibility
of robustly constraining bubble parameters. The wide size range and large number
of recent well-recorded events (several hundred) will be exploited to explore scaling
relationships and possible variability in the volcano acoustic-seismic ratio with time
and/or event size.
Large Scale Ground Deformation of Etna Observed by GPS between 1994 and
2001
N. Houlie, Berkeley Seismological Laboratory, [email protected]
We have processed thirty Global Positioning System (GPS) campaigns carried out
at Etna from 1994 to early 2001 between the last two main flank eruptions of the
Mt. Etna (Sicily, Italy). This rest period allowed us to investigate the deep magma
plumbing system of the Mt. Etna. The temporal dynamics of twenty-three points
observed three times or more were analyzed. All the time series show a first-order
linear trend during the five years period. It suggests that the volcano was continuously deformed by the action of a deep source while a discrete activity of the volcano
was observed at the summit. We have interpreted the residual deformation field
as the result of an major eastward motion of the eastern flank of the volcano. The
results will be discussed by using seismological and tectonic settings.
Seismological Research Letters Volume 77, Number 2 March/April 2006 239
Wednesday, 19 April Poster Sessions
Advances in Volcano Seismology: Enhanced Monitoring
Capability through Application of Complementary
Methods
Poster Session
Separation of Qi and Qs from Passive Data at Mt. Vesuvius: A Reappraisal of
Seismic Attenuation
E. Del Pezzo, INGV—Osservatorio Vesuviano Napoli, Italy, [email protected]
it; F. Bianco, INGV—Osservatorio Vesuviano Napoli, Italy, [email protected]
it; L. Zaccarelli, INGV—Osservatorio Vesuviano Napoli, Italy, [email protected]
ov.ingv.it.
Seismic attenuation in the area of Mt. Vesuvius is reappraised by studying more than
400 S-coda envelopes of small local VT earthquakes recorded at Mt. Vesuvius from
1996 to 2002 at the 3-D stations of OVO and BKE. The purpose is to obtain a
stable separate estimate of intrinsic and scattering quality factors for shear waves.
We investigate 4 frequency bands, centred respectively at fc=3,6,12 and 18Hz with
a bandwidth of 0.6fc. Then, we stack the normalized (at 12s lapse time) filtered
coda envelopes obtaining a single stacked trace for each component and station.
Stacked envelopes are fit to the multiple scattering model of Zeng in the hypothesis
of constant velocity half space. Results show that the scattering attenuation (proportional to Qs-1, the inverse scattering-quality factor) is much stronger than the
intrinsic dissipation (proportional to Qi-1) and that Qs-1 decreases with frequency.
Intrinsic attenuation is much less frequency-dependent. We also fit the data with
the diffusion model in the assumption of half-space, finding the same values for
the estimates of Qs-1 and Qi-1 obtained using the multiple scattering model. We
assume this evidence as an indirect indication of the presence of diffusive processes
in the shallow crust underlying Mt. Vesuvius. In order to test the consequences of
the half space assumption we fit the stacked coda envelopes at BKE to the diffusion
equation solved with the boundary condition of a diffusive layer over a homogeneous half space. We test both a fully absorbing and a reflecting boundary condition, setting the half space at a depth of 2 km below the sea level, representing the
carbonate basement at Mt. Vesuvius. Results show that the diffusivity, D, estimated
in the assumption of reflecting boundary condition is greater than that estimated
in the assumption of uniform half space, whereas the diffusivity estimated with the
absorbing boundary condition is close to the estimate done in the assumption of
half space. OVO station shows results different from those obtained at BKE for
the frequency bands centered at 12 and 18Hz. We interpret this anomaly as due
to an effect of strong lateral heterogeneity which modifies the redistribution of the
seismic energy into the coda at OVO.
3-D Scattering Image of Mt. Vesuvius, Preliminary Results.
A. Tramelli, INGV Napoli—Osservatorio Vesuviano, [email protected]; M.
Fehler, Los Alamos National Laboratory, [email protected]; E. Del Pezzo,
INGV Napoli—Osservatorio Vesuviano, [email protected]; F. Bianco, INGV
Napoli—Osservatorio Vesuviano, [email protected]
Since the last 1944 eruption Mt. Vesuvius is in a quiescent stage. The scientific interest for this volcano comes from its story of plinian and subpliniam eruptions and
from the fact that this behavior is justified [Civetta and Santacroce, 1992] by a continuous magma filling from a reservoir located in the shallow crust. Simulations of
its pyroclastic flows show that a possible activity resume would create a dramatic
scenario due to the presence of hundred thousand of people living on Vesuvius
flanks. Recently some experiments were done to define the geological structures
beneath Mt. Vesuvius [Zollo et al., 1996; Auger et al., 2001]. In particular Scapra
et al., 2002, showed a shallow high-velocity bodies located beneath and Southward
to the crater. The knowledge of the Vesuvius geological structures is essential for a
precise identification of possible precursors of future eruptions; this work grows up
in this context.
We show the preliminary results of a three-dimensional scattering image. We
analyzed earthquakes collected by the national seismic network during the period
1996-2000 using Nishigami’s method (1991) to estimate the three-dimensional
distribution of scattering coefficient in the lithosphere below Mt. Vesuvius. The single scattering approximation (Sato, 1977) was used to fit the seismic coda envelope
and to get the ratio between the real and theoretical envelope. This ratios are related
to the spatial variations of the scattering coefficient and we used three-dimensional
velocity model (Scapra et al., 2002) to locate these relative scattering coefficients
values in a grid placed below the volcanic edifice.
Multiple Denoising and Classification Methods for Improving Seismic
Surveillance: Applications at Guagua Pichincha, Soufriere Hills and
Redoubt Volcano
C. Rowe, Los Alamos National Laboratory, [email protected]; A. GarciaAristizabal, Escuela Politecnica Nacional—Instituto Geofisical, [email protected]
igepn.edu.ec; R. White, U. S. Geological Survey, [email protected]
Large swarms of long-period seismic events have been repeatedly observed at andesitic volcanoes during episodes of dome extrusion; the ability to recognize these
families of stationary, nearly identical sources may provide important contributions
to real-time hazard assessment during eruption crises. In previous work, application
of cross-coherency filtering in retroactive waveform cross-correlation demonstrated
improved ability to detect event similarity compared to other techniques. Here,
we explore the relative benefits of combined methods including cross-coherency
filtering, neural network auto-associative filtering and wavelet as applied to domerelated swarm events at active volcanoes. Both scanning detection and retroactive
pick-centered correlation methods will be applied to triggered and continuous
waveform data. Hierarchical dendrogram-based clustering will be compared to a
neural network classifier for the derived parameters. Our example data sets include
pre- and syn-eruptive waveforms from the 1999 eruption of Guagua Pichincha
Volcano, Ecuador, the 1995-1996 early eruption sequence at Soufriere Hills
Volcano, Montserrat, the 1989 pre-eruption swarm at Redoubt Volcano, Alaska.
Can 4D Seismic Tomography Forecast Volatile-rich Magma Intrusions and
Explosive Activity at Mt. Etna?
D. Patanè, Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania,
[email protected]; G. Barberi, Istituto Nazionale di Geofisica e Vulcanologia,
Sezione di Catania, [email protected]; O. Cocina, Istituto Nazionale di
Geofisica e Vulcanologia, Sezione di Catania, [email protected]; P. De Gori,
Istituto Nazionale di Geofisica e Vulcanologia, Centro Nazionale Terremoti,
[email protected]; C. Chiarabba, Istituto Nazionale di Geofisica e Vulcanologia,
Centro Nazionale Terremoti, [email protected]
Forecasting volcanic eruptions is a primary target for geophysics. The continuous
and paramounting volcanic and seismic activity at Mt Etna makes this volcano an
almost unique laboratory where verify the potential of seismological studies. We
used repeated three-dimensional tomography (4D) to recover variation of elastic
parameters during different volcanic cycles. Here we show that an anomalous low
Vp/Vs volume is revealed by seismic tomography, during the 2002-2003 eruptive
period, in correspondence with the eruptive fracture system. This anomaly was
absent during the pre-eruptive period and rose up only a few months before the
onset of the eruption. We interpret the low Vp/Vs volume as caused by a shallow
intrusion of volatile-rich (≥ 4 wt%) basaltic magma. The gas topping the intrusion
was responsible for the October 2002-January 2003 this high explosive flank eruptions, activity rather unusual for a basaltic volcano. The observed time changes of
velocity anomalies suggest that 4D tomography provides the basis for a more efficient volcano monitoring and short and midterm eruption forecasting of explosive
activity.
Volcano-tectonic Earthquake Sequences near Active Volcanoes and Their
Use in Eruption Forecasting
R. White, U S Geological Survey, Menlo Park, CA, [email protected]; C.
Rowe, Los Alamos National Laboratory, [email protected]
We summarize data from over 40 Volcano-Tectonic (VT) earthquake sequences
that have occurred in association with eruptions and intrusions and compare them
with more than 40 shallow tectonic earthquake sequences along volcanic arcs. A
few examples demonstrate the manner in which VT seismicity relates to eventual
phreatic and magmatic activity, i.e., to the relative openness of a volcanic system. We
present depth and distance distributions for VT sequences at a variety of volcanoes.
Observations confirm that the preponderance of VT earthquake energy is released
in distal regions a kilometer or more laterally from the active crater and generally
prior to the onset of significant phreatic activity, as well as long-period and very
long-period seismicity. Just prior to the onset of magmatic activity, distal VT seismicity may be replaced by smaller-scale proximal VT activity directly beneath the
active crater. Distal VT earthquake sequences are shown to relate to deformation,
long-period and very-long-period seismicity. We present an example of how VT
seismicity may be used to forecast eruptive activity.
240 Seismological Research Letters Volume 77, Number 2 March/April 2006
Broadband Characteristics of Volcanic Earthquakes Recorded during
2004—2005 at Mount Saint Helens, Washington
S. Horton, CERI, Univeristy of Memphis, [email protected]
From October 2004 to May 2005, CERI operated four to six broadband seismometers within 5 to 20 km of Mount Saint Helens (MSH) to help monitor recent seismic and volcanic activity. Thousands of shallow volcanic earthquakes were recorded,
and here I focus on the larger events having magnitude between 2.5 and 3.3. These
volcanic earthquakes have significantly higher spectral amplitudes between about
0.l to 2 Hz compared to tectonic earthquakes of similar depth and magnitude while
spectral amplitudes between 3 and 10 Hz are comparable. Although broad-band
waveforms of the volcanic events have several times longer duration than tectonic
events, 5 Hz high passed signals show similar duration. Very-long-period (VLP)
band passed (0.1 to 0.3 Hz) waveforms show remarkably consistent signals for
multiple earthquakes at any given station concurrent with the higher frequencies.
This systematic VLP signal that underlies the volcanic earthquakes can be observed
to at least 20 km distance. The CERI network was deployed in cooperation with
the Pacific Northwest Seismic Network at the University of Washington, and the
Cascades Volcano Observatory of the US Geological Survey.
Seismo-acoustic Monitoring at Tungurahua Volcano
M. Ruiz, University of North Carolina, [email protected]; J. Lees, University
of North Carolina, [email protected]; J. Johnson, University of New
Hampshire, [email protected]
An eruptive activity cycle was recorded on summer 2004 at Tungurahua volcano,
with more than 2,000 degassing signals. These events were classified as short-duration explosions, long-duration jetting tremors, and chugging sequences. Pressure
amplitudes of explosion events cover three orders of magnitude with a power-law
distribution (0.1 to 180 Pa) at the closet infrasonic station at 3.5 km from the vent.
Using a fuzzy-logic method and a dendogram tree, we found four waveform clusters
characterized by different pressure-built times and a variable compression-rarefaction ratio. These event families did show no distinctive amplitude or temporal correlation. Travel time analysis of seismic first arrivals and infrasonic waves and estimations of total acoustic power indicates that explosions start with a seismic event
at a shallow depth followed by an out-flux of gas, ash and solid material through
the vent. Particle motion analysis shows that explosions initiate with a compression
signal at vertical seismic components, which is followed by a larger radial motion in
horizontal components. This pattern is invariable on different azimuths suggesting
that it is related to a source process.
Seismicity Related to the 2005 Explosive Events at Volcán De Fuego, México
F. Nunez-Cornu, Universidad de Guadalajara, Puerta Vallarta, MEXICO,
[email protected]; D. Vargas-Bracamontes, Centro de Investigation
en Matematicas, [email protected]; C. Suarez Placenzia, Universidad
de Guadalajara, Puerta Vallarta, MEXICO, [email protected]
The current eruptive process of Volcan de Fuego (also known as Colima Volcano),
which began in August 1998, has presented several intermittent effusive and explosive phases. Since early 2005 a sequence of explosive events with VEI less than or
equal to 3 occurred. This activity increased gradually. On May 30 the most intense
explosion since 1999 occurred, which generated a plume that reached heights over
3,500 m above the crater, and also produced pyroclastic flows. In the month of June
the volcano generated four explosive events having characteristics similar to those
of May. These constant explosions caused constant morphological changes on the
top of the volcano, the most significant of which were the collapse of the North
and South walls of the crater in the first week of June, and the creation of a new
crater in July. This explosive activity was similar to that produced by the volcano
in 1903—1904, when its maximum level was reached having more than one explosion daily. Many of the explosive events were recorded by the digital three-component seismic stations operated by the University of Guadalajara and Jalisco Civil
Defense. A study of these signals is presented. These signals were recorded not only
by stations located on the volcanic edifice, but also by the stations BSSJ and MCUJ
at 184 and 182 km on the northern coast of Jalisco and CEBJ (Ceboruco Volcano)
at 200 km distance in Nayarit. These stations recorded the seismic signal and the
infrasonic wave. The origin times of some of the explosions as well as the sound
velocity at the explosion times were calculated using record sections of the sonic
wave. Velocities of the seismic waves between the volcano and the seismic stations
were also evaluated. Finally, the magnitude of the seismic signals and the energy of
the infrasonic waves were calculated and compared with the size of the explosions
reported by other authors.
Cross-correlation Analysis Reveals Waveform Similarity in Long-period
Events Prior to Eruptive Activty at Mt. Spurr Volcano, Alaska
J. Brown, University of Wisconsin-Madison, [email protected]; H. DeShon,
University of Wisconsin-Madison, [email protected]; S. Prejean,
USGS Alaska Volcano Observatory, [email protected]; C. Thurber,
University of Wisconsin-Madison, [email protected]; J. Power, USGS
Alaska Volcano Observatory, [email protected]
Mt. Spurr Volcano, Alaska last erupted during a series of three blasts in 1992, and
understanding the role of seismicity over the eruptive cycle is important for volcano hazard assessment of nearby Cook Inlet and the Anchorage region. Crosscorrelation (CC) techniques can significantly improve the accuracy of pick times
for volcano-related seismic signals, which are often noisy due to the unconsolidated nature of the volcanic edifice and the range of magmatic processes occurring
within the volcano. We apply the bispectrum-verified CC package BCSEIS (Du
et al., 2004) to waveforms recorded at Spurr for the eruption sequence of 1992.
Bispectrum cross-correlation is used to identify high-quality correlations that may
fail traditional time-domain threshold methods. Cross-correlation coefficient values obtained using the CC technique allow us to define and compare families of
similar earthquakes at Spurr. The vast majority of correlating seismic events can be
classified as either volcano-tectonic (VT) earthquakes or long period (LP) events.
The latter are believed to occur in response to in situ fluid or gas activity. Families
of correlated VT events occur throughout 1992 at shallow depths beneath both
the summit and the Crater Peak vent, the site of major eruptive activity in 1992.
Another family of deep VT events (up to 30 km below sea level) occurs beneath the
Crater Peak. Using BCSEIS we have also successfully cross-correlated LP events,
even where the initial catalog time is severely mispicked due to emergent phase
characteristics.
We find a noteworthy temporal pattern during the 1992 eruptive cycles for
one distinct family of LP events. LP events with dissimilar waveform characteristics occur throughout the entire year within the volcanic complex at various depths
(2 km above sea level to as deep as 40 km below sea level). However, the correlated
LP family (CC coefficients greater than 0.70) occurs only within 5 to 25 days prior
to eruption. The LP family, characterized by highly similar waveforms, occurs at a
depth greater than 15 km. We suggest the onset of activity in this LP family serves
as a potential precursory indicator of eruptive activity.
Cross-correlation and Double-difference Techniques Used in Earthquake
Relocations at Shishaldin Volcano, Alaska
N. Meyer, UW-Madison, [email protected]; H. DeShon,
UW-Madison, [email protected]; C. Thurber, UW-Madison, [email protected]
geology.wisc.edu; S. Prejean, USGS-AVO, [email protected]
Shishaldin Volcano, located on Unimak Island, is one of the most active volcanoes
in the Aleutian arc, erupting over twenty times in the last century. Over 3400 earthquakes have been located in the vicinity of the volcano since the installation of a
6-station short-period seismic network by AVO in 1997 and a similar 5-station
network at neighboring Westdahl volcano in 1998. Daily seismicity levels are high
compared to other volcanoes along the arc but are not always associated with eruption-related activity. In order to better understand the spatial and temporal development of seismicity at Shishaldin, we compute high-resolution relative earthquake
locations and identify clusters of similar waveform families using waveform crosscorrelation techniques. We apply the bispectrum waveform alignment method of
Du et al. (2004) (BCSEIS) to calculate cross-correlation coefficients for use in
earthquake cluster identification algorithms and improve the accuracy of differential travel times for earthquake relocation. The bispectrum method correlates waveforms in the third-order spectral domain, significantly decreasing errors due to correlated noise inherent in many signals and increasing the reliability of differential
times. The differential times are used to relocate hypocenters using the double-difference (DD) method of Waldhauser and Ellsworth (2000) (hypoDD). Relocation
results using the BCSEIS-DD approach are robust for events both beneath and
to the west of the volcano. The most recent large eruption at Shishaldin occurred
in April and May, 1999, and prior to this eruption, on March 4, 1999, a ML 5.2
tectonic event occurred 10-15 km west of the volcano. The frequency-magnitude
distribution suggests a tectonic origin for this activity (b value = 1.11), and events
relocated west of the volcano show a well-defined strike in excellent agreement with
a strike-slip focal mechanism determined by Moran et al. (2002). Many volcanotectonic and long-period events occurred beneath the summit during a period of
increased activity in 2002. We are continuing to examine waveform similarity for
these spatially and temporally clustered events. Our preliminary results indicate
that our approach results in improved relative earthquake locations despite noisy
volcanic signals and limited network coverage.
Seismological Research Letters Volume 77, Number 2 March/April 2006 241
High-precision Earthquake Location and Three-dimensional P-wave
Velocity Determination at Redoubt Volcano, Alaska
H. DeShon, University of Wisconsin Madison, [email protected];
C. Rowe, Los Alamos National Laboratory, [email protected]; C. Thurber,
University of Wisconsin Madison, [email protected]
Redoubt, a stratovolcano located along the Cook Inlet approximately 166 km from
Anchorage, Alaska, most recently erupted in 1989/1990, and because of its repeated
historic eruptions, routine monitoring with efficient analysis of its behavior is necessary. The Alaska Volcano Observatory (AVO) has monitored Redoubt using permanent seismic stations since 1988 and currently maintains 5 short-period, vertical and 2 short-period, three-component stations on the volcano. Seismic signals
recorded at Redoubt from 1989-2005 include volcano-tectonic, long-period, and
hybrid events, as reflected in the hypocenter catalog reported by AVO. Over 5000
events have been recorded at Redoubt between Dec. 1989 and Nov. 2005.
Volcano seismic networks typically have few stations and marginal coverage, providing challenges for earthquake location in a complex, three-dimensional
setting. Routine catalog locations are performed using analyst phase picks and
an approximate, 1D velocity model. To improve earthquake location precision at
Redoubt, we compute a three-dimensional P-wave velocity model using doubledifference tomography combined with waveform cross-correlation techniques.
Waveforms recorded at volcanoes are often noisy and/or emergent. We use waveform cross-correlation techniques to improve the pick accuracy of the AVO catalog
data. Differential travel times for well-constrained events are used to simultaneously
invert for hypocenter location and P-wave velocity structure. Shot and earthquake
arrival times recorded by temporary stations deployed on Redoubt in July 1991
supplement the catalog picks. The double-difference tomography method provides
significantly improved absolute and relative earthquake locations. Synthetic models
are used to assess the accuracy of the resulting 3D model.
The 3D velocity model includes a very high velocity (Vp > 6 km/s) core similar to some other volcanoes. All Redoubt events through Nov. 2005 are relocated
through the 3D model. We investigate seismicity associated with the 1989/1990
eruption, and we use cross-correlation results to identify similar earthquakes within
the catalog.
High-precision Earthquake Locations at Great Sitkin Volcano, Alaska using
Waveform Alignment and Double-Difference Techniques
J. Pesicek, Univ. of Wisconsin—Madison, [email protected]; H.
DeShon, Univ. of Wisconsin—Madison, [email protected]; C.
Thurber, Univ. of Wisconsin—Madison, [email protected]; S.
Prejean, USGS-AVO, [email protected]
Great Sitkin volcano, located 1870 km SW of Anchorage, is one of many active volcanoes along the central Aleutian arc. Great Sitkin has had no significant eruptive
activity since 1974. Following the installation of a 6-station short-period seismic
network around the volcano by the Alaska Volcano Observatory (AVO) in 1999,
over 1700 earthquakes have been located in the vicinity of the volcano. In 2002, a
period of increased activity was observed, dominated by two different earthquake
swarms with a combined total of over 750 located events. The first swarm began
March 17 with a mainshock magnitude of ML 4.3 and continued into April. The
second, larger swarm began May 28 and continued into July, again with a mainshock magnitude of ML 4.3. The nature of these swarms may suggest migration
of magma at Great Sitkin (Moran et al., 2002). The frequency-magnitude distribution, however, indicates that the second swarm is tectonic in origin (b value
= 0.95). In contrast, the frequency-magnitude distribution of the first swarm is
inconsistent with a b value around 1, suggesting a volcanic origin. In order to better understand the spatial and temporal development of seismicity at Great Sitkin,
and to explore the nature of these two swarms, we apply the waveform alignment
method of Du et al. (2004) (BCSEIS), which uses the bispectrum method to verify
cross-correlation (CC) derived differential times for groups of similar earthquakes.
The bispectrum method correlates waveforms in the third-order spectral domain,
significantly decreasing errors due to correlated noise inherent in many signals
and therefore increasing the reliability of differential times obtained by CC. The
improved CC data obtained by BCSEIS are then used to relocate hypocenters
using the double-difference (DD) method of Waldhauser and Ellsworth (2000)
(hypoDD). This method effectively minimizes errors due to unmodeled velocity
structure by minimizing residuals between observed and theoretical travel times
between similar events. The small seismic network at Great Sitkin, and the noisy
signals often produced in volcanic areas provide an opportunity to test this method
under difficult conditions. Preliminary results indicate the presence of abundant
similar waveforms, suggesting the BCSEIS-DD analysis approach will result in
improved locations despite the noisy environment and sparse network.
Recent Results from the 28 September 2004, M6.0
Parkfield, California, Earthquake
Poster Session
Comparing the 1966 and 2004 Parkfield Events
M. Hellweg, Berkeley Seismological Laboratory, [email protected];
D. Dreger, Berkeley Seismological Laboratory, [email protected]
After observing similarities in the seismograms of the 1922, 1934 and 1966
Parkfield earthquakes recorded at regional (SBC, TIN, MHC and BRK) and teleseismic distances (DBN) Bakun and McEvilly (1979, 1974) proposed that they
might be “characteristic earthquakes” which rupture the same segment of fault in
the same direction, and begin at the same hypocenter. While the 2004 Parkfield
earthquake occurred on the same fault segment, it started at the southeast end of
the rupture and progressed to the northwest, unlike the previous events. Dost and
Haak (2006) compare records from the station DBN (De Bilt, the Netherlands, ~
8927 km distance) for the Parkfield events. They find for the four Parkfield events,
that the correlation is lowest for the 1966 event (0.81—0.88), while among the
others it is greater than 0.95. The 1966 event was recorded by the stations of the
WWSSN. We have digitized records from the LP channels for stations from a
range of distances and azimuths, and compare them with WWSSN-LP simulated
records for the 2004 event, as well as synthetics calculated from kinematic models
of a northwestward and a southeastward rupture. We explore variation of fit as a
function of azimuth and distance, and whether we can detect differences in rupture
directivity from these data, and how differences change with station distance and
azimuth.
Small Magnitude Source Parameters in the Parkfield Region
B. Allmann, Scripps Institution of Oceanography, UCSD, [email protected]
edu; P. Shearer, Scripps Institution of Oceanography, UCSD, [email protected]
edu; G. Lin, Scripps Institution of Oceanography, UCSD, [email protected]
We investigate source parameters of small earthquakes in the Parkfield segment of
the San Andreas Fault (SAF) with catalog magnitudes between 0 and 5 that have
been recorded by the Northern California Seismic Network. We compute Brunetype stress drops by analyzing P-wave spectra from 50,777 waveforms that occurred
between 1984 and June 2005. By using waveforms of many sources recorded on
many receivers, we are able to isolate source, receiver and path dependent terms
with an iterative least-squares method. Resulting source spectra are corrected for
attenuation using a spatially varying empirical Green’s function (EGF). Stress drops
are estimated from the best-fitting corner frequency of the EGF-corrected spectra
based on a Madariaga source model. Plotting the resulting stress drop estimates at
relocated hypocenter locations and gridding them over the fault plane allows us to
analyze spatial and temporal variations of stress drop along the fault. Our overall
stress drop estimates show no dependence on estimated moment. In addition, the
estimated median stress drops increase with depth within the upper 10 km of the
crust. After applying a seismicity-based median filter to the computed stress drop
estimates, we observe robust lateral variations in stress drop. These variations appear
to correlate with b-value variations that have been observed in the area. We also
investigate temporal changes of stress drop before and after the M6.0 2004 Parkfield
earthquake. We use the bootstrap method to identify areas of statistically significant stress drop change before and after the M6 earthquake. Comparison of waveforms of repeating cluster earthquakes over the same time period suggests that the
observed temporal changes are indeed a source effect rather than caused by attenuation changes in the shallow crust. Finally, we compare the stress drop estimates with
existing slip models for the 2004 M6.0 mainshock.
Detecting Stress-induced Spatiotemporal Variations of Scatterers, Parkfield,
CA
T. Taira, Carnegie Institution of Washington, [email protected]; P. Silver,
Carnegie Institution of Washington, [email protected]; F. Niu, Rice University,
[email protected]; R. Nadeau, Berkeley Seismological Laboratory, [email protected]
berkeley.edu.
Spatial and termporal variations in stress at seismogenic depth constitute a key
property of the source region that affects the earthquake nucleation process. One
promising approach to observing such variations is the use of scattered waves associated with cracks/fractures and produced by deviatoric stress accumulation. We have
developed a scatterer-imaging methodology—not only to retrieve P-P, P-S, S-P, and
S-S scattering intensities simultaneously—but also to enhance the spatial resolution of these scatterers using a probabilistic approach. With this imaging method,
we have analyzed seismic data from two source arrays. The first is an aftershock
sequence of the M=4.7 October 20, 1992 Parkfield earthquake recorded by a dense
242 Seismological Research Letters Volume 77, Number 2 March/April 2006
borehole seismic network (HRSN) around the San Andreas Fault (SAF). We have
detected a well-constrained high-scattering region for the S-S scattering mode that
is located 5 -10 km south-southeast of the epicenter of the 1966 M=6 Parkfield
earthquake at 5 km depth. The strength of the S-S scattering mode, combined with
the relative weakness of the P-P scattering mode, implies that structural heterogeneity is dominated by variations in the shear modulus, suggesting that the S-S scatterers are associated with fluid-filled fractures. The high-scattering region is located in
the transition zone between the creeping and the locked sections of the Parkfield
segment of the SAF. No scatterers were found in the creeping section. We hypothesize that the observed scattering distribution reflects the distribution of deviatoric
stress magnitude, with high deviatoric stresses in the transition zone compared to
the creeping section. We test our hypothesis using a second source array, utilizing
events following the September 28, 2004 M=6.0 Parkfield earthquake. We designed
the source array (from aftershocks of this event) to be as similar as possible to the
1992 source array (location is approximately 300 m east of the 1992 source array).
The coseismic stress change from the 2004 mainshock should reduce stress in the
locked/transition region and increase stress at the edges. If our hypothesis is correct, there should be a corresponding change in scatterer distribution that should
follow the change in deviatoric stress magnitude: namely reduced scattering in the
transition zone (i.e., fractures close) and possibly increased scattering in the creeping section. The preliminary data show that we are able to detect scatterers from the
second source array, and we are presently evaluating the differences in the distribution of scatterers between these two time periods.
Co-seismic and Post-mainshock Variations in Seismic Velocity on the San
Andreas Fault at Depth and Implications from the 2004 M6 Parkfield
Earthquake
Y. Li, Department of Earth Sciences, University of Southern California, [email protected]
edu; J. Vidale, IGGP, UCLA, [email protected]; P. Chen, University
of Southern California, [email protected]; E. Cochran, IGGP, UCSD, [email protected]
ucsd.edu.
The data recorded for explosions and earthquakes at the dense linear seismic
arrays deployed across and along the San Andreas fault near Parkfield in the fall
of 2002 and after the M6 Parkfield earthquake on September 28, 2004 show obvious changes in seismic wave traveltimes within the fault zone during this time
period. Seismic stations and explosions in the two experiments were co-sited. The
array site was located in the middle of a high-slip part of the surface rupture in
the 2004 M6 earthquake. Waveform cross-correlations of recordings at the same
stations for repeated shots and earthquakes at focal depths to 6 km in the 2002
and 2004 experiments illuminate that seismic velocities were decreased by at least
~2.5% within a ~150-m-wide zone along the fault strike at seismogenic depth and
smaller changes (0.2-0.5%) beyond this zone to a distance of ~500 m from the fault
trace, most likely owing to the co-seismic damage of rocks during dynamic rupture
of this M6 event. The width of the damage zone characterized by larger velocity
changes is consistent with the low-velocity waveguide model on the San Andreas
fault, near Parkfield that we derived from fault-zone trapped waves (Li et al., 2004).
The damage zone is not symmetric but extends farther on the southwest side of
the main fault trace. Waveform cross-correlations for repeated aftershocks in 21
clusters, located at different depths and distances from the array site show ~0.71.1% increases in S-wave velocity within the fault zone during 3 months starting a
week after the earthquake, indicating that the damaged rock has been healing and
regaining the strength through rigidity recovery with time, most likely due to the
closure of cracks that had opened during the mainshock. The healing rate was not
constant with time but largest in the earlier stage of post-mainshock healing process. The magnitude of fault healing varies across and along the rupture zone, being
slightly larger healing beneath Middle Mountain, correlating with an area of large
mapped slips. The greater damage was inflicted and thus greater healing is observed,
in regions with larger slip in the mainshock. The fault healing is most prominent at
depths above ~7 km. We also use the same date from repeated earthquakes occurring before and after the 2004 M6 Parkfield for shear-wave splitting (SWS) analysis
to examine if the SWS method is sensitive to detect the small changes in seismic
velocity due to co-seismic damage and post-seismic healing of fault-zone rocks
caused by this M6 earthquake.
Apparent Changes in Repeating Earthquake Depths Associated with the 28
September 2004, M6.0 Parkfield Mainshock
J. Siegel, U.C. Berkeley Seismological Lab., [email protected]; R. Nadeau,
U.C. Berkeley Seismological Lab., [email protected]
Repeating earthquake data are used to address wide ranging issues in the fields of
earthquake physics, earthquake forecasting, fault zone mechanics and active tectonics. In order to accurately interpret and model the repeating quake data, however,
complete and accurate identification of repeating sequence members is required.
To achieve this, high-precision relative re-locations with theoretical resolutions on
the order of a few 10s of meters or less are generally used. High-precision techniques generally assume time-invariant, seismic velocities. However, theoretical
considerations suggest that even small deviations from this assumption can have a
significant impact, and time-dependent seismic velocities have been observed along
earthquake faults in California (Rubin, 2002; Rubenstein and Beroza, submitted;
Schaff and Beroza, 2004). The effect of such velocity changes on high-precision
re-locations and their significance for repeating earthquake studies have yet to be
explored, however. In this presentation we contrast location changes of characteristically repeating micro-earthquakes recorded on the surface by the NCSN with
those recorded down boreholes by the HRSN (sensors at ~ 200 depth). The location changes we investigate are apparently the result of reduced seismic velocities
induced by the the 28 September 2004, M6.0 Parkfield, California earthquake. Our
preliminary results indicate that changes in the repeating event locations (principally an increase in depth) occur using either surface or borehole data. However,
changes observed with surface data are nearly an order of magnitude greater than
those observed using the borehole data. This is consistent with recent findings
that suggest time-dependent velocity changes induced by large events are shallow.
Immediately following the Parkfield M6, location changes using surface data are as
large as 50 to 100 m and only about ~ 10 to 20 m using borehole data. This contrast is significant because it suggests that the rupture patches of repeating events
following the mainshock at Parkfield, including those in the SAFOD zone (with
typical rupture dimensions of ~ 20 to 60m), are not overlapping when viewed with
surface data and are therefore not representative of characteristic event repetition.
However, when viewed using borehole data the events do show predominant overlap indicative of characteristic repetition. In both data sets, an exponential decay in
location changes are also observed through time, suggesting that seismic velocities
are recovering and that healing of the damage caused by the mainshock (giving rise
to the velocity reductions) is taking place.
Parkfield Earthquakes and Micro-repeater Recurrence Times
C. Goltz, UCD, [email protected]
The 2004 Parkfield earthquake brings the number of events observed on the
Parkfield section to seven. This sequence of M ≈ 6 earthquakes is considered to
be a classic example of characteristic earthquakes which are defined to occur quasiperiodically on major faults.
A fundamental question also of great importance to hazard assessment is
whether recurrence time statistics of such events follow a particular statistical distribution and, if so, which one. The answer may not simply be obtained by statistical
fitting as the data is extremely sparse, Parkfield being one of the most extensive data
sets available worldwide.
Recently, however, advances in seismological monitoring and improved
processing methods have unveiled so-called micro-repeaters, micro-earthquakes
which recur exactly in the same location on a fault. It seems plausible to regard
these earthquakes as a miniature version of the classic characteristic earthquakes.
Micro-repeaters are much more frequent than major earthquakes, leading to longer
sequences for analysis.
In this paper I present results for the analysis of recurrence times for several
micro-repeater sequences from Parkfield and adjacent regions and compare them to
the sequence of large events. I find that, once a parametric distribution is at all fittable, the statistics can be well fitted by a Weibull distribution and I give theoretical
reasons for this finding.
Seismicity Precursor Modeling of M6.0 2004 Parkfield Earthquake
V. Korneev, Lawrence Berkeley National Laboratory, Earth Science Division,
[email protected]
The M6.0 2004 Parkfield and M7.0 1989 Loma Prieta strike-slip earthquakes on
the San Andreas Fault (SAF) reveal seismicity peaks in the surrounding crust several months prior to the main events. Earthquakes directly within the SAF zone
were intentionally excluded from the analysis because they manifest stress-release
processes rather than stress accumulation. The observed increase in seismicity is
interpreted as a signature of the increasing stress level in the surrounding crust,
while the peak that occurs several months prior to the main event and the subsequent decrease in seismicity are attributed to damage-induced softening processes.
Explanation of the observed precursors is based on the fact that these earthquakes
occur on existing faults and that fault zone rocks have less strength and elastic
modulii than a surrounding crust. For an increasing strain load the stress-strain
relationships start behaving nonlinear, and after reaching a maximum stress value
enter a softening (or dilatancy) regime, which is characterized by a development of
multiple fractures and reduction of rock stiffness eventually progressing to a rock
failure (earthquake). During this process, the stronger out-of-fault rock experiences
the same stress load, but does not reach a nonlinear regime. This explanation is
suported by results of numerical modeling using finite-element method. Because of
their frequent occurrence, small magnitude events may be ideal for monitoring of
Seismological Research Letters Volume 77, Number 2 March/April 2006 243
stress changes. The development of active seismic monitoring techniques is necessary to investigate changes in the pre-seismic nucleation zone. Due to the absence
of other precursors (Bakun et. al, 2005), the observed pre-event peaks of seismicity
reported here are especially important for use in earthquake prediction. The peak’s
occurrence several months in advance of the main event should allow special observation of future rupture zones to accurately estimate the earthquake striking time.
Low pre-event seismicity levels in these zones require active monitoring that uses
controlled seismic sources in order to observe changes within the fault zone associated with rock softening. These results leave open the possibility that successful
earthquake prediction may yet be possible.
Kinematic Rupture Model for the 1966 Mw6 Parkfield Earthquake with
Assessment of Resolution
S. Custodio, University of California, Santa Barbara, [email protected]
edu; R. Archuleta, University of California, Santa Barbara, [email protected]
ucsb.edu; P. Liu, University of California, Santa Barbara, [email protected]
The Parkfield segment of the San Andreas Fault has ruptured in ~Mw6 earthquakes at least 5 times in the historical period. Based on similarity of waveforms
from the 1922, 1934 and 1966 Parkfield earthquakes, Bakun and McEvilly (BSSA
1984) proposed the idea of characteristic earthquakes: a given fault segment would
rupture repeatedly in earthquakes that would nucleate in the same hypocenter and
generate slip on the same areas of the fault. Unlike previous Parkfield earthquakes,
the 2004 mainshock did not nucleate near Middle Mountain and rupture to the SE,
but rather nucleated near Gold Hill and ruptured NW. Despite these differences,
do the 1966 and 2004 slip distributions look similar? We compute a kinematic rupture model for the 1966 event by inverting the scarce co-seismic dataset. Only five
strong motion instruments were nearby at the time of the 1966 mainshock; all were
located perpendicular to the fault, near its SE end. Because the data coverage of the
fault is poor, the resolution of the rupture model becomes an important question.
To estimate the resolution of the 1966 rupture model, we use 3 different approaches:
1) we use synthetic slip distributions to generate waveforms at the 5 stations, and
then invert the synthetic waveforms to see how well the initial slip distributions can
be recovered; 2) we invert seismograms of the 2004 earthquake recorded at 5 stations coincident or close to the stations that were in place in 1966; we then compare
the obtained rupture model with one obtained by inversion of a more complete
dataset (Custodio et al., GRL 2005; Liu et al., BSSA submitted); 3) we repeat step
2 using five stations located towards the NW end of the Parkfield segment; thus, for
both the 1966 and 2004 mainshocks, the stations used in the inversions are located
towards the end of the fault where directivity has a major effect. The resolution tests
indicate that the 1966 rupture model is poorly resolved. However, the agreement
between the 1966 rupture model and aftershock locations is good.
Kinematic Modeling of the 2004 Parkfield Earthquake
A. Kim, University of California, Berkeley, Seismological Laboratory, [email protected]
seismo.berkeley.edu; D. Dreger, University of California, Berkeley, Seismological
Laboratory, [email protected]
The extensive seismological data set that recorded the 2004 Parkfield earthquake at
regional as well as local distances is unique in terms of the resolution it can provide
on the kinematic rupture process of a moderate earthquake. In addition, in-depth
examination of kinematic rupture models, their resolution, and reconciliation with
peak ground motion distributions is necessary for better understanding earthquake
rupture physics as well as improving application of finite-source models for rapid
ground motion hazard reporting. ShakeMaps of the peak ground acceleration and
velocity show a distribution that is bilateral in nature. In this study we combine
our earlier results using regional distance CISN waveform and near-fault gps data
with the near-fault strong motion recordings from CSMIP. The objective is to find
a kinematic model that adequately fits each of the data sets. The method that we
employ is a linear, multiple time window approach to invert the data for the spatio-temporal distribution of fault slip, the average rupture velocity and its variation and the slip rise time. Preliminary results using near-fault strong motion data
shows a slip distribution that is consistent with what we obtained previously with
the regional seismic waveform and near-fault gps data in that there is a high slip
patch at the hypocenter and 10-20 km north terminating near Middle Mountain.
This model also has some low levels of slip to the south that is needed to explain the
waveforms and the high peak amplitudes at stations located south of the epicenter. Thus there is an indication of a slight bilateral rupture, which is dominated by
northward rupture. In this study we will examine fault geometry complexity south
of the epicenter across the Gold Hill fault-jog to assess the effect it has on the ability
to fit the southern station waveforms. There has also been some suggestion of supershear rupture during the event and our modeling will investigate this possibility
and its resolution. The results of the work will be discussed in terms of implications
for the use of near-realtime finite-source inversion results in rapid strong ground
motion reporting.
The Effect of Lateral Refraction on Estimates of the Rupture Velocity of the
2004 Parkfield Earthquake from Observations at UPSAR
J. Fletcher, U.S. Geological Survey, [email protected]; P. Spudich, U.S.
Geological Survey, [email protected]; L. Baker, U.S. Geological Survey, [email protected]
usgs.gov; R. Sell, U.S. Geological Survey, [email protected]
Using a short-baseline seismic array (UPSAR) situated about 12 km west of Gold
Hill, we observed the rupture propagation of the September 28, 2004 M6 Parkfield,
CA earthquake on the San Andreas fault. We have reconstructed the main-shock
rupture velocity by projecting high-frequency S arrivals recorded at UPSAR onto
their inferred sources on the San Andreas fault. We compute the average correlation for windows of ground acceleration surrounding each arrival between all pairs
of stations to determine apparent velocity and back azimuth for the S arrivals.
Observations of direct S waves from aftershocks with known locations recorded at
UPSAR show that there can be lateral refraction of the ray paths by as much as 20(
from a straight line projection back to the fault. To correct the inferred source locations for this effect we assembled a collection of aftershocks recorded at UPSAR
that sample numerous back azimuths and performed the same analysis to map the
observed back azimuths from the aftershocks onto their known locations on the
fault. Many aftershocks locate in either a shallow or deep horizontal streak. In some
places on the fault, S waves from shallow and deep aftershocks display the same
amount of lateral refraction. Near the town of Parkfield, however, S waves arriving
at UPSAR leave deep aftershocks along a different azimuth than do S waves that
leave shallow aftershocks. Consequently, the inferred main-shock rupture velocity
depends on this depth-dependent lateral refraction. The observed lateral refraction
is consistent with a high velocity ridge on the SW side of the fault and these observations could be used as an additional constraint on the 3D velocity structure of
this region.
Subsurface Structure of the San Andreas Fault Zone near Parkfield,
California, Inferred from High-resolution Reflection and Refraction Profiling
M. Rymer, U.S. Geological Survey, [email protected]; R. Catchings, U.S.
Geological Survey, [email protected]; M. Goldman, U.S. Geological Survey,
[email protected]; C. Steedman, U.S. Geological Survey, [email protected]
In October 2002, we collected high-resolution seismic reflection and refraction data
along three lines in the Parkfield, California area. One of the two lines we discuss
here crossed the main trace of the San Andreas Fault (SAF), the other crossed the
Southwest Fracture Zone (SWFZ). These two seismic lines are near the southeast
end of Middle Mountain, about 1.8 and 2.7 km northwest of Parkfield, respectively.
The line across the SAF was 1.2 km long and had shot and receiver spacings of 10 m.
The line across the SWFZ was 160 m long and had shot and receiver spacings of
5 m. Seismic sources for both lines were generated by a BETSY Seisgun. Data were
recorded for 2 s at a sampling rate of 0.5 ms. Seismic velocities in the SAF line reveal
a laterally asymmetric velocity structure. Velocities near the surface are about 400
m/s; at a depth of 100 m velocities are 2800 m/s northeast of the SAF and 2000 m/
s southwest of the fault. The seismic velocity structure associated with the SWFZ
line likewise is laterally asymmetric, but with the higher velocities on the southwest
side of the fault. Velocities there are about 400 m/s near the surface; at a depth of
15 m velocities are 2500 m/s on the southwest side and 600 m/s on the northeast.
Seismic reflections on the SWFZ line indicate that the fault dips about 80 degrees
to the southwest, away from the SAF. A subparallel buried fault, which also dips to
the southwest, lies about 50 m to the northeast of the SWFZ. Taken together, we
interpret the seismic images across the SAF and SWFZ to indicate an approximately
vertical SAF and a southwest-dipping SWFZ, with a low-velocity zone between
these faults. Similar fault and velocity geometries were revealed about 11 km to the
northwest, near the San Andreas Fault Observatory at Depth (SAFOD) drill site.
Our interpretations indicate there is a strong correlation between structural setting,
lateral low-velocity zones, and recorded strong ground motions, such as those of the
2004 Parkfield earthquake.
On the Strong Ground Shaking at the Fault Zone 16 and Nearby Stations of
Parkfield Array
H. Haddadi, California Geological Survey, [email protected]; A.
Shakal, California Geological Survey, [email protected]; E. Kalkan,
California Geological Survey, [email protected]; P. Roffers, California
Geological Survey, [email protected]
During the 2004 Parkfield earthquake, peak ground acceleration over 2.5 g was
recorded at CSMIP station Fault Zone 16 (FZ16). The nearby stations also
recorded high accelerations, but in general less than 1 g. The high ground motion
at these stations is addressed in some studies by using an asperity model close to
FZ16. However, not all studies agree on the asperity model for the Parkfield earthquake. We have considered wave amplification at FZ16 and its nearby stations during the aftershocks of Parkfield 2004 earthquake and some earlier events. Some of
244 Seismological Research Letters Volume 77, Number 2 March/April 2006
the analog stations of the Parkfield array were upgraded to digital stations after the
Parkfield 2004 earthquake. The aftershocks recorded at the upgraded stations show
significant wave amplification at FZ16 and the nearby stations. Also, some earlier
events including the M6.5 Coalinga earthquake of 1983 and M6.0 San Simeon
earthquake of 2003 are studied. The records of San Simeon and Coalinga earthquakes at FZ16 and nearby stations show different patterns of wave amplification
that could be due to the path effect.
Seismic Input Energy of Ground Motions during the 2004 (M6.0) Parkfield,
California Earthquake
E. Kalkan, California Geological Survey, Strong Motion Instrumentation
Program, CA 95814-3500, [email protected]; H. Haddadi, California
Geological Survey, Strong Motion Instrumentation Program, CA 95814-3500,
[email protected]; A. Shakal, California Geological Survey,
Strong Motion Instrumentation Program, CA 95814-3500, [email protected]
Accurate characterization of near-fault ground motions is an important consideration for performance evaluation of new and existing structural systems. Ground
motions recorded in the vicinity of fault-rupture can be influenced by forwardrupture directivity and fling. These near-fault effects result in coherent-long period
velocity pulses. These pulses can be initiated either due to succession of high frequency acceleration peaks or integration of distinguishable acceleration pulses. In
this study, spectral seismic input energy contents of forward-rupture directivity
and fling records are compared and contrasted using a set of representative nearfault ground motion recordings from the 2004 (M6.0) Parkfield earthquake. The
compiled strong ground motion accelerograms are rotated into fault-normal and
fault-parallel components thereby the spatial variation of absolute and relative seismic input energy with respect to rupture-plane is investigated. This study emphasizes the importance of local distinctive acceleration pulses. Depends on the ratio
of pulse period to oscillation period of structural system, these pulses impose sudden input energy jump being larger than the energy accumulated at the cessation
of motion.
Simulation of Strong Ground Motion from the 2004 Parkfield Earthquake
K. Sesetyan, Bogazici University, Kandilli Observatory and Earthquake
Research Insititute, Istanbul, [email protected]; R. Madariaga, Ecole
Normale Superieure, Paris, [email protected]; E. Durukal, Bogazici
University, Kandilli Observatory and Earthquake Research Insititute, Istanbul,
[email protected]; M. Erdik, Bogazici University, Kandilli Observatory and
Earthquake Research Insititute, Istanbul, [email protected]
Frisenda and Madariaga developped an explicit finite-difference algorithm for
the computation of radiation from complex ruptures on extended faults. We have
used this technique to simulate the near-field strong ground motion generated
by the 2004, Mw=6.0 Parkfield earthquake. This earthquake took place in a very
well instrumented area producing a substantial amount of high-quality near-field
recordings. Taking advantage of the rare luxury of having a large number of near
field ground motion recordings distributed around the fault zone, we used recordings from 40 stations covering a rectangular area of about 55 km by 33 km in fault
parallel and fault normal directions, respectively. Using a grid spacing of 100 m in
our 4th order explicit finite difference code, we could properly resolve frequencies
of up to 2 Hz at a minimum of 8 grids per wavelength. A one dimensional averaged
velocity structure was used in the simulations of wave propagation. The effect of the
strong velocity contrast between the NE and SW sides of the San Andreas fault in
Parkfield region at 5-12 km’s depth has been investigated by using different velocity
models for the two sides. The effects of different slip distributions and source-time
functions have also been studied. We first used a simplified version of the preliminary source model by Ji (2004). A more recent slip distribution model by Ji et al.
(2005) obtained by the inversion of waveforms from both strong motion and GPS
stations has also been considered. Several different kinematic rupture scenarios
were considered with variable rupture speeds and several source-time functions of
different shapes (decreasing exponential and trapezoidal) and durations.
The San Fernando Valley, California High School Seismograph Project: 2004
Parkfield Earthquake
G. Simila, CSU Northridge, [email protected]
Following the 1994 Northridge earthquake, the Los Angeles Physics Teachers
Alliance Group (LAPTAG) began recording aftershock data using the Geosense
PS-1 (now the Kinemetrics Earthscope) PC-based seismograph. Data were utilized by students from the schools in lesson plans and mini-research projects. Over
the past ten years, several geology and physical science teachers are now using the
AS-1 seismograph to record local and teleseismic earthquakes. This project is also
coordinating with the Los Angeles Unified School District (LAUSD) high school
teachers involved in the American Geological Institute’s EARTHCOMM curriculum. The seismograph data are being incorporated with the course materials
and are emphasizing the California Science Content Standards (CSCS). The network schools and seismograms from the 2004 Parkfield (and 2003 San Simeon)
earthquakes are used as an example. In addition, the worldwide events (e.g. Alaska
2002; Sumatra 2004, 2005) are presented. Also, CSUN’s California Science Project
(CSP) and Improving Teacher Quality Project (ITQ) conducted in-service teacher
(6-12) earthquake workshops with the seismograms.
Paleoseismic Characterization of Earthquake Recurrence
and Hazard Assessment
Poster Session
Earthquake Surface Slip Distributions
S. Wesnousky, University of Nevada, Reno, [email protected]
It has become standard practice during the last 35 years to map the geometry of
rupture traces and assess the surface-slip distribution of large earthquakes that break
the ground surface. The resulting observations have been used in development of
seismic hazard methodologies and assessments, engineering design criteria for critical facilities, the development and discussion of dynamic fault models to predict
strong ground motions, and efforts to predict the endpoints of future earthquake
ruptures. There now exist at least 30 historical earthquakes for which investigators
have put forth maps of earthquake rupture traces with data describing the coseismic
slip as a function of fault length. Here I will put forth an initial compilation of that
data set with the aim of exploring issues bearing on seismic hazard analysis and fault
mechanics.
Using Pollen to Constrain the Age of the Youngest Rupture of the San
Andreas Fault at San Gorgonio Pass
D. Yule, California State University Northridge, [email protected]; S.
Maloney, California State University Northridge, [email protected]; L.
Scott Cummings, Paleo Research Institute, [email protected]
Radiocarbon ages from peat layers at the Burro Flats paleoseismic site at San
Gorgonio Pass constrain the youngest rupture of the San Andreas fault there to
have occurred post 1650. However, these age data cannot determine whether this
rupture correlates with the 1812 Wrightwood rupture thought to have ended in
the San Bernardino region, or the ~1700 earthquake that may have ruptured a
large section of the fault from the Coachella Valley to the Mojave Desert. One way
to resolve this apparent paradox is to consider when European pollen species first
appeared in the sediment record of southern California. The establishment of the
Spanish missions in southern California during the mid- to late-1700’s suggests that
sediment deposited after this period should contain significant traces of European
pollen. The occurrence, or lack thereof, of European pollen in pre-earthquake strata
at Burro Flats can therefore help identify 1700 or 1812 as the youngest rupture at
this site. At Burro Flats, the youngest faulting transects a small basin containing
mud, sand, and peat interlayers. Five samples from these layers were submitted for
standard pollen analysis at Paleo Institute in Golden, CO. All pollen types were
identified to the family, genus, and species level, whenever possible. Results indicate that the pollen record for the samples is dominated by Adenostoma (family
Rosaceae) likely representing native Chamise growing in the surrounding chaparral
vegetation. Pollen types like Brassicacea (the mustard or cabbage family), a common
indicator of European settlement, occur only in very small amounts (<<1%) in the
four, stratigraphically lowest samples, but occur in relatively high amounts (>10%)
in the stratigraphically highest sample. Other non-native species like Eucalyptus
and Erodium cicutarium-type pollen show a similar change at the highest sample.
The pre-earthquake mud and peat layers at the Burro Flats site therefore appear to
record the appearance of European-introduced pollen, and suggest that the youngest rupture of the San Andreas fault at Burro Flats occurred after the mid- to late1700’s and is most likely correlative with the 1812 Wrightwood earthquake.
Slip Rates, Recurrence Intervals, and Earthquake Event Magnitudes for the
Southern Black Mountains Fault Zone, Southern Death Valley, California
Using Optically Stimulated Luminescence
S. Mahan, US Geological Survey—Denver, [email protected]; M. Sohn,
California State University—Fullerton, [email protected]; J. Knott,
California State University—Fullerton, [email protected]; D. Bowman,
California State University—Fullerton, [email protected]
The normal-slip Black Mountain Fault zone (BMFZ) is part of the Death Valley
fault system. Strong ground-motion generated by earthquakes on the BMFZ poses
Seismological Research Letters Volume 77, Number 2 March/April 2006 245
a serious threat to the Las Vegas, NV, Death Valley National Park and Pahrump,
NV. Fault scarps offset late Pleistocene to Holocene alluvial-fan deposits along
most of the 80-km long fault. However, slip rates, recurrence intervals, and event
magnitudes for the BMFZ are poorly constrained due to poor age control. Along
the southernmost section, the BMFZ steps basinward preserving three post-late
Pleistocene fault scarps. Interbedded alluvial and eolian sediments offset by the
BMFZ were dated using Optically Stimulated Luminescence (OSL). The alluvialfan deposits with well-developed desert pavement (Q2) have an age of 24, 312 to
24,713 ± 2,155 years and are offset by three separate scarps. The alluvial-fan surface
with remnant bar and swale topography (Q3a) has an age of 7,032 to 12,908 ± 1,250
years and is offset by two separate scarps. A younger alluvial-fan deposit (Q3b) is
3,739 to 6,354 ± 1,978 years. Surveyed scarp heights on progressively basinward
scarps are 5.5, 5.0 and 2.0 m, respectively, with no horizontal offset. Vertical offsets
and OSL ages indicate a slip rate of 0.2 mm/yr and a recurrence interval of ~8800
years over the last 26,670 years. Vertical displacement and geomorphically constrained rupture lengths suggest estimated moment magnitudes (Mw) between 6.5
and 7.2 for the BMFZ events. The Q2 deposits also overlie a tephra layer postulated
to have erupted from a cinder cone (Cinder Hill) offset 213 m by the right-lateral
Southern Death Valley Fault Zone (SDVFZ). The OSL ages and horizontal offset
suggest a maximum post-late Pleistocene slip rate of 2mm/yr for the SDVFZ. This
slip rate is consistent with late Pleistocene slip rates along the SDVFZ and suggests
a minimum age for the tephra of 26,670 yrs.
The Study and Revision of Probabilistic Seismic Hazard Map of Taiwan
C. Cheng, Geotechnical Engineering Research Center, Sinotech Engineering
Consultants, INC. Taiwan (R.O.C), [email protected]; C. Lee, Institute
of Applied Geology, National Central University, Taiwan (R.O.C), [email protected]
ncu.edu.tw; P. Lin, Institute of Geophysics, National Central University, Taiwan
(R.O.C), [email protected]; B. Chiou, Caltrans’ Geo-Research Group,
Division of Research and Innovation, Sacramento, [email protected];
J. Chern, Geotechnical Engineering Research Center, Sinotech Engineering
Consultants, INC. Taiwan (R.O.C), [email protected]
Taiwan is situated on the boundary between the Eurasian Plate (EP) and the
Philippine Sea Plate (PSP) where active oblique collisions and subduction are taking
place. Therefore, Taiwan’s orogenic belt has high rates of seismicity and high faultslip rates. We adopted available information of geology and seismology to revise the
probabilistic of Taiwan. New Seismic hazard maps were done for 10% and 2% probability of exceedance in a 50 year period individually. In order to construct the maps
we defined three seismic sources which were: (1) regional zones, (2) active faults,
and (3) subduction zones (intraslab and interface). We used the mainshocks from
the earthquake catalog of 1900 to 1999 to evaluate the earthquake recurrence rate
for the regional zones and subduction-intraslab sources by Truncated-Exponential
model. We also used the fault-slip rate to estimate the earthquake recurrence rate
of faults and subduction-interface sources by Characteristic-Earthquake model. For
the first time in Taiwan our revised PSHA took into consideration the fact that
subduction plate sources induce higher ground-motion levels than crustal sources,
and active faults induce the hanging-wall effect in attenuation relationships. We
also used the logic tree method to deal with the uncertainties of each parameter
in the PSHA. The two highest hazard levels in Taiwan were shown in the areas
of eastern longitudinal valley and from the western foothills to the coastal plain.
These two areas are separated by the central mountain range which has a decidedly lower hazard level. After considering the fault activity in our revised PSHA,
we found that the PGA level of near-fields in Taiwan always exceeds 0.4g in 475year return period. However, in previous studies the proper hazard could not be
obtained because fault sources were not considered in the PSHA, especially in long
return period. This situation was very obvious in the central part of Taiwan (ChiChi earthquake disaster region) and in the HsinChu-MiaLi region. It has now been
realized that Northern Taiwan also has a much higher hazard level than previously
estimated. This is due to the discovery of active faults in the vicinity and also due to
the current realization that subduction plate sources induce higher ground-motion
levels than crustal sources.
An Example of Time-dependent Seismic Hazard Analysis from West Central
Taiwan
P. Lin, Institute of Geophysics, National Central University, Taiwan, [email protected]
geo.ncu.edu.tw; C. Lee, Institute of Applied Geology, National Central University,
Taiwan, [email protected]; C. Cheng, Geotechnical Engineering Research
Center, Sinotech Engineering Consultants, INC., Taiwan, [email protected]
tw.
The traditional probabilistic seismic hazard analysis (PSHA) only presents average
hazard through a time period. However, the actual hazard of a region should be
time-dependent. An example in West Central Taiwan can demonstrate this very
well. We introduce our recent results from a review of fault parameters, the model-
ing of active faults and a time-dependent PSHA of the West Central Taiwan region.
New relationships for strong-motion spectral attenuation, which include the effects
of the site conditions and the hangingwall, have also been modeled. Based on these
results, the PSHA can be performed in a more updated and realistic way. The
important active faults in West Central Taiwan are the Changhua fault and the
Chelungpu fault, of which the later moved in September 21, 1999, during the ChiChi earthquake. In this study, we performed the traditional PSHA at first, so as it
can form a basis for comparison. Second, we considered a time-dependent characteristic earthquake model for the Changhua fault and for the Chelungpu fault to
perform another PSHA. Finally, we compared these two results and concluded that
the use of a time-dependent model for the faults is a must in assessing the seismic
hazard of a region. The result also indicates that the Changhua fault is presently
controlling the seismic hazard level of the Metropolitan Taichung area, and the hazard level would be more severe than that during the Chi-Chi earthquake.
A Preliminary Seismicity Model for Southwest Western Australia Based on
Neotectonic Data
D. Clark, Geoscience Australia, [email protected]; J. Schneider,
Geoscience Australia, [email protected]
Examination of two regionally extensive DEMs has resulted in the delineation of 33
new northerly-trending linear fault scarps of probable Quaternary age in southwest
Western Australia, bringing the total number of Quaternary tectonic features to 60
for this area. The features range in length from ~15 km to over 45 km, and from
~1.5 m to 20 m in height. Their distribution is remarkably uniform (ie. strain is
uniformly distributed), and most scarps where a displacement sense could be determined from the DEM data suggest reverse displacement on the underlying fault
(ie. the easterly-trending compressive contemporary stress field is likely to have pertained for tens of thousands of years or more). In the few instances where high-resolution aeromagnetic data is coincident with a scarp location, the ruptures are seen to
exploit pre-existing crustal weaknesses. Nineteen of the features have been verified
by ground-truthing, and range in apparent age from perhaps less than a thousand
years to many tens of thousands of years. A comparison of scarp distribution and
the distribution of earthquake epicentres shows that while some scarps are associated with contemporary seismicity, most are not. This predominance of scarps
not associated with contemporary seismicity suggests that earthquake activity is
migratory and that significant periods of quiescence might separate large events.
Palaeoseismic studies further suggest activity is episodic and interseismic intervals
might range from 20—100 kyr or more. The geometric, recurrence and spatial attributes are consistent with a seismicity model whereby the lower, ductile part of the
lithosphere is uniformly strong and deforms uniformly, and the upper (seismogenic)
layer accommodates this large-scale flow by localized, transient and recurrent brittle
deformation in zones of pre-existing crustal weakness. Furthermore, each scarp represents at least one earthquake event of magnitude larger than 6.0, and in some
cases exceeding magnitude 7.0. There is good evidence from palaeoseismological
studies, and from the height of many of the scarps, that recurrence of large events on
individual faults is characteristic. Hence, the distribution of scarps also provides an
indication of earthquake prone regions within southwest Western Australia.
Geomorphic Evolution of the Cadell Fault, Southeastern Australia:
Implications for Intraplate Fault Behaviour and Seismic Hazard Assessment
A. Prendergast, Geoscience Australia, [email protected]; D.
Clark, Geoscience Australia, [email protected]; C. Collins, Geoscience
Australia, [email protected]; J. Schneider, Geoscience Australia, john.
[email protected]
The 55 km long, 13 m high Cadell fault scarp in southern New South Wales is
the most prominent example of a multiple-event Quaternary fault scarp in eastern Australia. Reverse displacement across the Cadell Fault uplifted Quaternary
sediments and diverted the course of Australia’s largest river, the Murray River. The
scarp has been modified by tens of thousands of years of fluvial landscape evolution,
making seismic hazard assessment challenging. However, this complexity also provides a multitude of erosional and depositional surfaces that may be tied to faulting
events.
We present a new study of the region involving examination of a new 1m
resolution LIDAR DEM, a shallow seismic reflection survey, and optically stimulated luminescence dating of fault-related surfaces. Preliminary dating results suggest that initial uplift occurred between 50-60 ka. This equates to a slip rate of ~0.3
mm/year, which is the highest estimate for an Australian intraplate fault to date.
At least two earthquake events are recorded in fluvial landscape features on the
uplifted hanging wall. In terms of earthquake recurrence, two ruptures along the
entire length of the scarp (~M7.1) could produce the observed relief. However,
the identification of a relay ramp near the centre of the scarp suggests that more
frequent smaller events are responsible for relief generation. The segment lengths
(~20 km and 35 km) suggest events in the range of ~M6.6-6.9 every 5-15 ka. Two
246 Seismological Research Letters Volume 77, Number 2 March/April 2006
shallow seismic reflection profiles over the scarp reveal that the displacement of the
Permian bedrock surface at 200 m depth (below Quaternary cover), is commensurate with the surface expression. The somewhat disturbing implication is that the
Cadell fault, which originally formed in the Palaeozoic, “switched-on” in the late
Pleistocene after a very long quiescence.
Precariously Balanced Rock Methodology and Shake Table Calibration
M. Purvance, University of Nevada, Reno, [email protected]; R.
Anooshehpoor, University of Nevada, Reno, [email protected]; J.
Brune, University of Nevada, Reno, [email protected]
Precariously balanced rocks act as earthquake strong motion seismoscopes that
have been operating on solid rock outcrops for thousands of years, constraining
the maximum unexceeded ground motion amplitude throughout their lifespans.
Numerous field investigations along with laboratory and computer modeling studies have been conducted in order to provide a firm observational and theoretical
basis for the application of this methodology to constrain seismic hazard estimates.
A series of shake table experiments have recently been completed at the University
of Nevada, Reno Large Scale Laboratory. These experiments delineated the overturning responses of a variety of objects ranging in height from ~ 20 cm to ~
120 cm and in height/width ratio from ~ 10 to ~ 2. The bulk of the experiments
involved scaling acceleration time histories (uniaxial forcing) from 0.1g to the point
where each object overturned a specified number of times. In addition, one biaxial
experiment was performed for comparative purposes with the uniaxial overturning
responses. The acceleration time histories utilized include strong motion recordings
of 1979 Imperil Valley, 1985 Michoacan, 1999 Izmit, 1999 Chi-Chi, 2002 Denali,
and 2003 Hokkaido earthquakes along with synthetic acceleration time histories
(full sine pulse and random vibration records). The level of agreement between
the laboratory derived overturning responses and numerically based overturning
predictions of Purvance (2005) is quite high for objects with simple basal contact
conditions (e.g., rocking occurs primarily about two axes). The formulation of
Purvance (2005) overestimates the level of ground shaking required for overturning systematically for the three boulders tested. This is a result of the complex basal
contact conditions between the boulders and the shake table (e.g., rough boulder
undersides resulting in rocking about many axes). A methodology has been developed to measure the degree of basal irregularity via simple measurements that can
be applied in the field. In particular, tilting tests provide the restoring force as a
function of angle of tilt. This information is utilized to adjust the numerical simulations for objects with complex basal contact conditions. The resulting numerical
models predict overturning at lower ground motion amplitudes when compared
to those utilized by Purvance (2005). This initiative marks a further refinement in
the constraints on strong ground motions and seismic hazard estimates provided by
precariously balanced rocks.
Geologic Constraints on Extreme Ground Motions
J. Brune, University of Nevada, Reno, [email protected]
HD
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Probabilistic seismic hazard analysis (PSHA) makes certain statistical assumptions
that are very questionable when extended to low probability maximum ground
motions. The short historical database for instrumental recordings is not sufficient
to resolve the uncertainties. Efforts to remedy this by massive computing efforts
are handicapped by large uncertainties in the important physical input parameters,
uncertainties that can only be reduced by again referring back to the very limited
data base. This situation suggests that we look for geomorphic and geologic evidence constraining ground motions over long periods of time. Since extrapolated
ground motions are extremely large, we might expect to find field evidence for them
if they have occurred in recent geologic time. Such evidence might include lack of
precariously balanced rocks (10 ka to 100 ka), evidence for rock avalanches from
unstable cliffs (a few hundred ka), and strain-shattered rock (up to tens of millions
of years). It is suggested that in some cases the lack of any or all of these indicators
can be used as reliable evidence that such high ground motions have not occurred
over periods from tens of thousands to tens of millions of years. Specific examples
of all these types of data (precarious rocks, un-shattered sandstone cliffs, and unfractured massive sandstones) associated with the San Andreas fault are presented
and discussed. The type of geologic information presented can provide important
information about seismic hazard at low annual probabilities, and can help constrain the uncertainties in statistical and physical modeling.
IT
Earthquakes and Archaeology: Neocatastrophism or Science?
a. nur, stanford university, [email protected]; r. kovach, stanford university, [email protected]
W
From time to time it is argued that archaeological evidence to deduce past earthquake catastrophes are too inconclusive and ambiguous and only enable ‘philocatastrophic’ geophysicists to recklessly promote a dogma of neo-catastrophism.
This is detrimental to scientific progress in both archaeology and seismology/tectonics. Catastrophic events in both disciplines are fact—not a made up dogma:
earthquakes up to magnitude 9 do occur in earth, and major ancient physical collapses have been reliably inferred from archaeological excavations. This real catastrophism poses a series of important questions in both archaeology and tectonics
that cannot be dealt with by simply making lists of past earthquakes based on written pre instrumental documents.
In seismology there is a pressing need for information about past earthquakes
to understand: 1.The general irregularities of the time-space patterns of large earthquakes; 2.The common discrepancy between the long-term plate boundary slip
rates vs. rates inferred from seismicity ; 3.Archaeological evidence for clustering of
destructive earthquakes. This behavior is counter to the common notion of earthquake repeat time.
Archaeology has uncovered several catastrophic collapses that remain unexplained for many decades: 1.The highland and lowland Mayas ; 2.Teotihuacán in
central Mexico ca. 800AD; 3.The Harrapan civilization of the Indus valley in the
second millennium BC; 4.The catastrophic end of the Bronze Age in the eastern
Mediterranean ca. 1200BC .
Archaeological evidence must not be rejected but included—just like textual
evidence and paleo-seismological studies are—in our efforts to establish long-term
seismicity rates and fault system behavior. At the same time archaeologist could
gain a much better understanding of the types of earthquake damage and what their
potential consequences could have been at their respective sites.
Estimating Historical Earthquakes Parameters Using Archeology and
Geology in Um-El-Kanatir, Dead Sea Transform
N. Wechsler, Department of Geophysics and Planetary Sciences, Tel Aviv
University, [email protected]; O. Katz, Geological Survey of Israel, Division of
Engineering Geology and Geological Hazards, [email protected]; S. Marco,
Department of Geophysics and Planetary Sciences, Tel Aviv University, [email protected]
post.tau.ac.il.
Historical records of strong earthquakes on the Dead-Sea Transform (DST) significantly contribute to understanding active faulting and seismic hazard along the
transform. However, historical accounts are often incomplete and inaccurate, referring primarily to damage to settlements and neglecting natural phenomena. It is
thus important to assemble field observations in order to complete and expand the
record. We analyze a special case of a recently-excavated archaeological site 10km
east of the DST eastern boundary fault, which was apparently damaged by a seismogenic landslide. We use the landslide mechanical character to constrain historical
seismic-acceleration along the DST. Um el Kanatir is a Byzantine (6th century)
archeological site in the southwestern part of the Golan Heights (N. Israel). The
location on the slope of a canyon and the outcropped marly formations make the site
susceptible to land slides. Recent excavations revealed typical earthquake induced
damage in the archeological structures, including a displaced and unaligned water
system. We notice typical landslide topography near the damaged water system but
no significant geological fault. We therefore interpret this damage to have been
caused by an earthquake-induced landslide. We calculate the static factor of safety
FS for the water system landslide, from which the critical acceleration ac for landslide triggering can be inferred. The resulting high values of FS (> 2) require strong
seismic-horizontal acceleration to induce slope-instability, indicating that the slope
is generally stable and that a strong earthquake is needed in order to cause failure.
We use the Newmark displacement (DN) method following the empirical equation
of Jibson et al. (2000): Assuming that DN=10cm is the failure criterion, and given
that the Aries intensity Ia in the region (Zion et al. 2004) is: we can calculate the
magnitude MW as a function of distance from the source R. The results show that
the earthquake that triggered the landslide must have been strong (MW > 6.8) and
within 50 km radius from the site. Since archeological findings suggest that the site
has been abandoned in the 8th century, the candidate earthquakes along the DST
are the 746-7, 1202 and 1749 AD earthquakes.
The Northern San Andreas Fault: 100 Years of Scientific
Study/The Impact of the Lawson Report on Earthquake
Science
Poster Session
Timing of Late Holocene Paleoearthquakes on the Northern San Andreas
Fault at the Fort Ross Orchard Site, Sonoma County, California
K. Kelson, William Lettis & Associates, Inc., [email protected]; A. Streig,
William Lettis & Associates, Inc., [email protected]; R. Koehler,
Seismological Research Letters Volume 77, Number 2 March/April 2006 247
University of Nevada, Reno, [email protected]; K. Kang, Sun Pro
Engineering Consultants Co., Inc., [email protected]
Paleoseismic trenching within Fort Ross State Historic Park provides data on the late
Holocene rupture history of the North Coast segment of the northern San Andreas
fault. The 1906 earthquake ruptured through the Fort Ross Orchard site, which
is characterized by a narrow shutter ridge and associated linear trough containing
latest Holocene sediments. Trenches across the northeast-facing fault scarp exposed
sediments interpreted as scarp-derived colluvium and possible fissure-fill deposits,
and tentative upward fault truncations that provide evidence of three possible surface ruptures prior to 1906. Several packages of coarse-grained scarp-derived colluvial sediments were deposited after individual surface-rupturing earthquakes that
pre-date the 1906 rupture. Radiocarbon analyses of 31 detrital radiocarbon samples
collected from the colluvial deposits constrain the timing of earthquakes over the
past approximately 1,000 years. Based on stratigraphic ordering and a statistical
comparison of radiocarbon dates using the OxCal program, we estimate (at a 95%
confidence level) that three pre-1906 surface ruptures at the Orchard site occurred
at AD 1660 to 1812, AD 1220 to 1380, and AD 1040 to 1190. Previous trenches at
the nearby Fort Ross Archae Camp site are consistent with these dates, and further
suggest the occurrence of an earlier event between AD 555 and 950. Collectively,
the Fort Ross Orchard and Archae Camp sites suggest pre-1906 ruptures at AD
1660 to 1812, AD 1220 to 1380, AD 1040 to 1190, and AD 555 to 950. The time
windows for these ruptures are consistent with results from other sites on the North
Coast segment of the fault. However, additional information on the late Holocene
history of rupture events on adjacent fault segments is needed to evaluate whether
or not the long-term behavior of the San Andreas fault involves a mix of large,
1906-type ruptures and shorter, segment-specific ruptures.
A 3000-year Record of Earthquakes on the Northern San Andreas Fault at the
Vedanta Marsh Site, Olema, California
H. Zhang, University of Missouri—Kansas City, [email protected]; T.
Niemi, University of Missouri—Kansas City, [email protected]; T. Fumal,
U.S. Geological Survey, [email protected]
Late Holocene sediment deposited at the Vedanta marsh, Olema, California preserves a continuous earthquake record of the past 3,000 years on the northern San
Andreas fault (SAF). Excavations into the marsh provided exposures of the sediment across the SAF zone. Well-defined, marsh stratigraphy and abundant in situ
organic material allow the determination of the first long, high-resolution, eventby-event record of earthquakes for the northern SAF. Evidence for twelve earthquakes since the deposition of a 3000-years-old unit was identified from the main
fault zone based on fault outward splays, fault upward terminations, fissures, colluvial wedges, and soft-sediment deformation.
The age of the pre-1906 seismic events are well-bracketed by radiocarbon
dates and age modeling using the OxCal radiocarbon analysis program. A constant
sedimentation rate of 1.7 mm/yr was used for undated, fine-grained units. Based on
these data, the timing of pre-1906 earthquakes at the Vedanta site are: AD 1670—
1740; AD 1350—1440; AD 1290—1380; AD 1140—1230; AD 1100—1165;
AD 820—885; AD 650—710; AD 220—BC 70; BC 120—350; BC 240—630;
and BC 660—990. The average recurrence interval at the Vedanta site is ~ 250
years. However, individual recurrence intervals are quite irregular, ranging from as
short as 53 years to as long as 605 years.
Three-dimensional hand excavations were used to expose a buried paleochannel. Both margins of the channel were traced to the SAF and a cumulative rightlateral offset of 7.8—8.3 m was measured for the 1906 and the penultimate
earthquakes. If we assume 5 m of 1906 coseismic slip at Vedanta based on historical records of offsets near the site, then coseismic slip in the penultimate event is
between 2.8—3.3 m. The timing and coseismic slip of the penultimate event suggest that this SAF segment may rupture in earthquakes smaller than 1906. The
Vedanta paleoseismic data does not support the assumption that the fault has failed
as a single, long rupture similar to 1906 in the mid-1600s, and indicates that the
North Coast segment has a higher probability of rupturing in a moderate earthquake than previously estimated.
Stratigraphic Evidence for Major Earthquakes at Bolinas Lagoon, Marin
County, California.
R. Byrne, UC Berkeley, [email protected]; L. Reidy, UC Berkeley, [email protected]
berkeley.edu.
Bolinas Lagoon is located at the southern end of the Point Reyes Peninsula
where the San Andreas Rift Zone crosses the Marin County coast line. During
the winter of 1906/1907 Gilbert visited the lagoon several times and made careful observations regarding vertical and horizontal movement following the 1906
event. Gilbert’s observations form an important part of the California Earthquake
Commission Report (Lawson, 1908). More recently, Berquist (1978) and Knudsen
and colleagues (1999) have used stratigraphic evidence from the lagoon in their
attempts to reconstruct its tectonic history. During 2004 and 2005 we recovered
20+ piston cores from Bolinas Lagoon as part of an investigation designed to determine to what extent recent (i.e., post AD 1850) changes in land use had affected
sedimentation rates. Most of the cores were short cores covering the last 200 years
or so, but two longer cores have estimated basal dates of AD 1000 and AD 400.
We dated our short cores with non-native pollen and lead 210 and several of them
show evidence of the 1906 event in the form of changes in grain size (more silt and
clay and less sand) and magnetic susceptibility. In the longest core, which is dated
by 4 AMS radiocarbon dates on shell, grain size peaks similar to the 1906 peak date
to ca. AD 420, ca. AD 1090, ca. 1220, and ca. 1540. These dates are close to dates
reported for large earthquake turbidites at Noyo Canyon (Goldfinger et al., 2003)
and broadly equivalent to paleoearthquakes identified at Vedanta Marsh, ca. 20 km
north of the lagoon (Niemi, 2002). Geochemical data (XRF) indicate that silt and
clay is derived from the Monterey Formation which is exposed at the Bolinas Bluffs.
Possibly mechanisms for the increased input of silt and clay into the lagoon together
will be discussed, as also will be the potential for a longer record.
Preliminary Earthquake Record of the Peninsula Section of the San Andreas
Fault, Portola Valley, California
J. Baldwin, William Lettis & Associates, Inc., [email protected]; C.
Prentice, U.S. Geological Survey, [email protected]; J.
Wetenkamp, San Jose State University, [email protected]; S.
Sundermann, William Lettis & Associates, Inc., [email protected]
Event timing data for prehistoric earthquakes on the Peninsula section of the San
Andreas fault (SAF) are needed to better understand the behavior of the northern SAF. The Portola Valley Town Center site, in Portola Valley, southwest of San
Francisco, provides a potentially excellent location for collecting event chronology
information on this section of the SAF. The site is characterized by a well-documented location of the 1906 rupture, a buried west-facing monocline, and nearly
continuous deposition of late Holocene fine-grained stratified marsh and fluvial
overbank deposits. The deposits contain abundant peat and detrital charcoal that
can be used for radiocarbon dating. In preliminary trenches at the Town Center
site, we found evidence that we interpret as indicating at least two, and possibly
three surface-rupturing events, including the 1906 earthquake. Evidence includes
warped marsh and fluvial deposits, possible fissure fills and scarp-derived colluvial
units. Charcoal and peaty samples collected from the colluvial and marsh deposits
have been submitted for radiocarbon dating at the Lawrence Livermore Laboratory.
We anticipate these radiocarbon analyses will allow us to begin developing estimates
of the timing of pre-1906 earthquakes on the Peninsula SAF. Such estimates can be
compared to similar event chronologies developed for the North Coast and Santa
Cruz Mountains sections of the SAF, and potentially provide new insight on the
long-term rupture behavior of the northern San Andreas fault.
Tectonic Deformation and Coastal Change Associated with the Offshore San
Andreas Fault Zone West of the Golden Gate
H. Ryan, USGS, [email protected]; T. Parsons, USGS, [email protected]
We have developed a new fault model for the shelf off of the Golden Gate between
Half Moon Bay and Point Reyes based on previously acquired high resolution
multichannel seismic reflection data combined with high resolution chirp profiler
and industry multichannel reflection data, which have recently become available
for analysis. The new fault map shows a series of en echelon strike-slip faults that
deform the shelf between the western trace of the San Gregorio fault zone and the
main trace of the San Andreas Fault. These faults merge and trend onshore near
Bolinas. A 3-D finite element model of the San Francisco Bay area incorporating
the new fault map is used to determine long-term rates of relative uplift and subsidence for the Golden Gate shelf during the Holocene; short-term vertical displacements associated with the 1906 earthquake are also calculated.
The results of the finite element modeling have implications for understanding the dynamics of coastal change related to faulting. Long-term, localized uplifts
of coastal marine terraces are associated with left bends in both the San Gregorio
Fault at Pillar Point near Half Moon Bay, and the San Andreas Fault as it trends offshore near Thornton Beach. In general, the area west of the Golden Gate is modeled
as subsiding at a long-term rate of about 0.2-0.3 mm/yr. The area of calculated maximum subsidence occurs northwest of the Golden Gate where an inferred Holocene
basin is located. The calculated low long-term rates of subsidence, however, suggest
that the 1750 m-thick Pleistocene Merced Formation (of Pliocene and Pleistocene
age) was not deposited in a simple pull-apart basin related to right-stepping faults
on the shelf as has been previously proposed. In contrast to the longer-term subsidence of the Golden Gate shelf, the 1906 earthquake resulted in coseismic uplift that
is calculated to be on the order of 10-15 cm. The 100-year tide gauge record at Fort
Point was analyzed to determine whether this uplift is resolvable in the sea level
248 Seismological Research Letters Volume 77, Number 2 March/April 2006
signal. Since 1906, interseismic deformation is calculated to have caused 5-6 cm of
subsidence across the platform.
Utilization of LiDAR / ALSM Point Cloud Data for Earthquake Geology and
Tectonic Geomorphic Mapping, Analysis, and Visualization
C. Crosby, Arizona State University, [email protected]; J. Arrowsmith,
Arizona State University, [email protected]
The growing availability of LiDAR (Light Distance And Ranging (a.k.a. ALSM—
Airborne Laser Swath Mapping)) data in the earthquake geology and tectonic
geomorphology communities means that these powerful data are being utilized in
an increasing number of research projects. LiDAR point cloud data (x, y, z, return
classification) are challenging to manipulate, so users typically only take advantage
of interpolated surfaces (digital terrain models; DTMs) generated by the LiDAR
data vendor for their analysis. However, by not returning to the LiDAR point cloud
data, users may fail to fully explore the richness of these data sets.
Initiating geomorphic analyses and visualizations with the point cloud gives
users more understanding of the data and control over how those data characterize
the landscape. Details such as the interpolation algorithm and grid resolution can
significantly affect the manner in which the resulting DTM represents the landscape. In addition, beginning with the LiDAR point cloud data allows the user to
assess the point density of the data in the area of interest. By understanding the
variation in ground-return density (which can vary due to topography and canopy
characteristics), the user has a better understanding of potential artifacts that may
be introduced into their DTMs by this variation. Finally, working with LiDAR
point cloud data, both by themselves and in tandem with DTMs, opens a new range
of possibilities for the visualization of these data.
Using LiDAR point cloud data from the Northern San Andreas Fault and
Western Rainier Seismic Zone recently made available via the GEON LiDAR
Workflow (GLW) (http://www.geongrid.org/science/lidar.html), we focus on
optimization of the spline interpolation algorithm, available in the GLW. By tuning
the smoothing and tension parameters in the spline algorithm as well as the grid
resolution we demonstrate how landform representation in areas of low-density
ground returns can be enhanced. Examples of mapping and visualization of faults
and tectonic landforms in these data demonstrate the utility of interactive interpolation of LiDAR point cloud data. Through interactive interpolation, tectonic
landforms may be delineated more efficiently and with greater detail than by working with the vendor generated DTMs.
Simulation- and Statistics-based Analysis of the 1906 Earthquake and
Northern California Faults
M. Glasscoe, Jet Propulsion Laboratory, [email protected]
gov; A. Donnellan, Jet Propulsion Laboratory, [email protected]
nasa.gov; R. Granat, Jet Propulsion Laboratory, [email protected]
gov; G. Lyzenga, Jet Propulsion Laboratory, [email protected]
gov; C. Norton, Jet Propulsion Laboratory, [email protected]; J.
Parker, Jet Propulsion Laboratory, [email protected]
The combination of advanced computer simulation tools and statistical analysis
methods has yielded promising improvements in our understanding of the earthquake process and earthquake forecasts. We are using two computer simulation
tools to study earthquakes in California. In particular, we are studying the long-term
effects in the strain field generated by the great 1906 San Francisco earthquake and
comparing model results with observed data. The first of these tools is the 3D finite
element code, GeoFEST (Geophysical Finite Element Simulation Tool), which
offers a flexible modeling environment to study the long-term stress relaxation of
the region following the 1906 event. The second is the Virtual California simulation tool; this can be used to study fault and stress interaction scenarios for realistic
California earthquakes. We are using statistical methods to analyze the interaction
between Virtual California fault segments and thereby determine whether events
on faults show any correlated behavior. These tools, combined with analysis of
observed GPS and seismic data, will allow us to study the effects of large earthquakes in the region. The result will be a better understanding of the earthquake
cycle for not only the San Andreas, but also for related faults within the region.
Preliminary results from the GeoFEST modeling indicate viscoelastic response in
the lower crust that could be measured at the surface even decades after the 1906
event, depending on the rheology chosen for the subsurface layers. Model results
will be compared to deformation measured by GPS in the region. Preliminary statistical analysis of the Virtual California data indicate some promising insights into
the interactions between fault segments, but further analysis will be necessary to
determine the extent of correlations between fault events.
Significance of Damaging San Francisco Bay Region Earthquakes Before
and after the Major 1906 Earthquake
T. Toppozada, California Geological Survey, [email protected]; D.
Branum, California Geological Survey, [email protected]
We review the history of damaging earthquakes in San Francisco Bay region since
1800. Earthquakes of M~6 to 7 between San Juan Bautista and Fort Bragg, and
inland to Vacaville, were more common before than after the major 1906 earthquake. The more frequent pre-1906 seismicity reflects the high stress build-up that
led to the 1906 earthquake of M 7.8. This earthquake released most of the stress
in the region and was followed by relatively low seismicity until the 1980s. In the
century before 1906, earthquakes of M~7 occurred in 1838 on the San Andreas
fault and 1868 on the Hayward fault. Earthquakes of M~6.5 occurred in 1865 SW
of San Jose, 1892 near Vacaville, 1898 near Mare Island, and 1898 near Fort Bragg.
Twenty earthquakes of M~6 occurred between San Juan Bautista and Winters
between 1800 and 1903 [Toppozada and Branum 2002]. Damage to buildings
from the larger pre-1906 earthquakes led to improving some construction practices, mainly in San Francisco [Tobriner, 2006]. These improvements to vulnerable
buildings mitigated somewhat the damage in the 1906 earthquake. After 1906,
damaging earthquakes have been relatively rare until 1980. An earthquake of M~7
occurred in 1989 near Loma Prieta. Earthquakes of M~6 occurred in 1911, 1926,
1980, 1984 between Monterey and Livermore. As the stress released in the 1906
earthquake continues to rebuild with time, seismicity could increase to be more like
the frequent pre-1906 damaging events. This seismicity could damage vulnerable
structures, and serve to stimulate earthquake preparedness and response. Such activities could mitigate the damage from subsequent strong to major earthquakes. To
estimate the approximate effects of future earthquakes that might precede the next
major 1906-type earthquake, we review the areas damaged by Modified Mercalli
Intensity ~VII or stronger shaking in the pre-1906 earthquakes of M~6 to 7.
Using the Lawson Report and Other Historical Documents to Investigate
Fault Morphology and Coseismic Slip of the 1906 Earthquake in Marin
County
A. Daehne, University of Missouri—Kansas City, [email protected]; T. Niemi,
University of Missouri—Kansas City, [email protected]
As members of the Earthquake Investigation Commission, G.K. Gilbert, J.C.
Branner, and others gathered multitudinous invaluable information of the effects
of the 1906 San Francisco earthquake. Some of these data were published in the
Carnegie Institution Publication 87, commonly referred to as the Lawson Report.
We utilize archival documents and relocate published and unpublished photographs along the San Andreas fault in Marin County to reveal the remains of
original fence lines, as well as the morphologic changes of the landscape over the
past century. The earthquake rupture left significant traces between Bolinas and
Tomales Bay. Famous examples such as the Sir Francis Drake Boulevard (SFDB)
offset, the fence offset at the Strain Ranch, or the displaced paths and bushes at
the former Skinner Ranch characterize the tremendous motion represented by the
strain release. In the Lawson Report and in his field notebooks and letters, G.K.
Gilbert described damage and documented offsets in Marin County starting one
week after the earthquake. Most noteworthy is the often-cited maximum offset of
20 feet (6.1 m) of SFDB built across the head of Tomales Bay, 0.8 km west of Point
Reyes Station. Analyses of archival materials indicate that Gilbert himself did not
trust the measurement. He wrote “As the horizontal throw here is greater than at
any other point, I am disposed to ascribe it in part to the flow of the soft alluvial
formation” and writes that the offset measurement may be 1 or 2 feet less. If the
uncertainty in the original measurement on the SRDB is accounted for, then the
maximum measured coseismic displacement for the 1906 earthquake should more
accurately be considered to be 18 feet (5.5 m). Furthermore, the locations of less
famous documented imagery were utilized to uncover obstructed or demolished
fence lines and to measure offset, to describe the evolution of morphology of fault,
and update the geological mapping for that segment of the rift zone. The results
not only show the change in vegetation that has completely altered the landscape,
but also how processes of erosion and landslides greatly imprint on today’s fault
characteristics.
High-resolution Analysis of 1906 Earthquake Intensities in the City of San
José, California
N. Shostak, San Jose State University, [email protected]
The goal of this study is to determine key factors controlling distribution of seismic
intensities in San José, California during the April 18, 1906 earthquake. The study
was conducted using a high-resolution map of shaking in the city developed specifically for this purpose. The city of San José, located 20 km east of the San Andreas
fault on a sedimentary basin south of San Francisco Bay, lies on alluvium approximately 200 to 300 m deep. Over 450 official damage inspection reports completed
Seismological Research Letters Volume 77, Number 2 March/April 2006 249
by a group of architects and building contractors by April 26, 1906, together with
photographs, sites from the 1908 Lawson report, and contemporary media and personal accounts, form the data set from which nearly 600 structures—commercial,
residential, municipal and church—have been geolocated and assigned Modified
Mercalli intensities (MMI). Contemporary Sanborn fire insurance maps of San José
at a scale of 1” to 50’ provide construction details and precise locations of buildings.
Knowledge of building detail and comments in the inspection reports eliminate
most construction-related variability. The high density of data enables assignment
of MMI values to areas several blocks in extent; in the center of the city, intensities
can be assigned to single city blocks. With this high resolution, it is possible to correlate variations in intensity with mapped Quaternary geologic units. The resulting
patterns of damage in San José indicate that shaking was not uniform throughout
the city, that damage appears to be more intense in a linear band running from
south to north in the central part of the city, and that areas of higher seismic intensity appear to correlate with mapped areas of Quaternary alluvial levee deposits.
Effects and Response of Nevada to the Great 1906 San Francisco, California
Earthquake
C. dePolo, Nevada Bureau of Mines and Geology, [email protected]; P. Earl,
Nevada Historical Society, [email protected]
The Great 1906 San Francisco Earthquake caused long-period ground motion in
western and central Nevada and triggered a significant earthquake sequence, but
the catastrophe generated a much larger social and political response of Nevada to
its sister city’s plight. Long-period ground motion in Nevada is indicated by a seismoscope record in Carson City, light sloshing of canals and ponds, and descriptions
from those who felt it. Several people in westernmost Nevada were awakened by
the waves. Many who were up observed effects, such as rattling windows and swaying lamps, but had a harder time feeling the movement. The only damage reported
in Nevada was to a metal conduit for the lights of the Virginia Street Bridge in
Reno. At least two local, felt earthquakes appear to have been triggered by the great
earthquake and occurred on 19th (PST), possibly along the Pyramid Lake fault
system. In 1906 most families in western Nevada had friends or relatives in the
San Francisco area, and the headquarters of many Nevada mining companies were
located there. With heavy hearts, many Nevadans crowded around telegraph and
train stations to gain word of friends and loved ones. Nevadans responded to the
disaster with generous cash donations and relief supplies, using the rail system as a
primary conduit. Western Nevada received and cared for refugees working their
way east, and gave many men who had lost their livelihood in San Francisco work in
the railroads and mines. Nevada managed the financial impact well and minimized
it to about a month’s duration. The Lieutenant Governor declared public holidays
for six days, April 23rd through April 28th; most banks closed, and no run on
money occurred. Some miners were laid off immediately following the earthquake
because of headquarter damage, but were rehired locally and in the booming mines
of Tonopah and Goldfield.
Integrating Geology and Geodesy in Studies of Active
Faults
Poster Session
Earthquake Cycle Models and Interseismic Strain: a test of effective friction
evolution and transient mantle rheology
E. Hearn, UBC, [email protected]; S. Ergintav, TUBITAK Marmara
Research Centre, Turkey, [email protected]; R. Reilinger, MIT, [email protected]; S. McClusky, MIT, [email protected]
The architecture and rheology of continental lithosphere around faults is often probed
by modeling surface deformation following large earthquakes. In many models, rapid
afterslip on and below the rupture is followed by relaxation of viscoelastic mantle
and/or lower crust with a nonlinear or transient rheology. In the case of the North
Anatolian Fault Zone (NAFZ), the lithosphere model must also produce highly
localized interseismic deformation that is fairly constant (and consistent with the
long-term geologic slip rate) throughout the earthquake cycle. Models of postseismic
deformation following the 1999 Izmit earthquake suggest that stable frictional slip
with a very small velocity-strengthening parameter (A-B = 0.5 MPa) occurs along the
NAFZ in the middle crust, and that the mantle (and/ or lower crust) has a transient
rheology. The effective viscosity of the mantle appears to be 2 to 5 times 1019 Pa s
within a few years of the earthquake, but must increase interseismically.
Deformation around strike-slip faults between earthquakes can be highly
localized and insensitive to time in the earthquake cycle if differential stresses below
the BDT are large compared with coseismic stress changes. However, regional geodynamic models suggest that for the NAFZ, this assumption may not be valid. I
will use finite-element models to investigate how a crustal fault zone creeping at
low shear stress can maintain a near-constant slip rate between earthquakes. One
hypothesis is that pore pressure evolution along the fault zone in the middle crust
causes the effective friction to decrease between earthquakes. I will also test whether
the transient mantle rheology required by the postseismic model is compatible with
the observed interseismic strain.
Variability of Long-term Fault Activity along the North Anatolian Fault,
Turkey
K. Okumura, Hiroshima University, [email protected]; H. Kondo,
Geological Survey of Japan, AIST, [email protected]
The North Anatolian fault is usually regarded as a simple shear zone with a constant
GPS slip rate of 20 to 25 mm/yr. However, geologic data indicate the fault system
is much more complicated. Geologic slip rates are significantly smaller than GPS
slip rates and reucurrence intervals are different among 20th century segments.
The most reliable slip rate estimates come from the 1944 segment. They are 14 m
for 3 earthquake cycles in 910 years, 21 to 23 m for 5 cycles in 1550 years. The
slip rate is about 15 mm/yr. On the 1943 segment 10 to 15 mm/yr is estimated in
Aslancayir. In Erzincan a higher slip rate of 20 mm/yr in past 750 year is estimated.
Recurrence intervals are 150—250 yr (historic) in Marmara, 300±30 yr on 1944
segment, 280—600+ yr on 1943 segment, and 180—220 year in east of Erzincan.
The fault activities are high in 1939 segment and farther east and in Marmara
region, and are evidently low in the 1943 segment. If we consider the bifurcation of
the fault into Bursa, Iznik-Mekece, and Iamit-Marmara strands, the high activity of
the Marmara segment is remarkable. Geometry and tectonic settings may explain
the variability. East of Erzincan is under regional NS compression. Main 1939 segment (Erzincan—Niksar) has almost pure strike slip without extension. There are
no pull-apart basins, which were the result of inaccurate fault mapping. Regional
uplift and rapid lowering of erosional base level prevail along the 1939 segment.
The Amasya branch that ruptured over 100 km in 1939 is a significant strucuture
that takes certain amount of the slip and distributes it into the central Anatolia.
1943 and 1944 segments consist of simple and straight strands without large steps,
discontinuities and bifurcations. The Bolu-Mudrunu duplex is the most complicated with compressional 1999 Duzce segment and short 1957-1967 segments. The
rupture pattern and history differ greatly accross this Bolu-Mudrnu area. 1999 and
Marmara segments consist of WNW transtensional and EW less tensional strands.
Realization of the complexity and varibility will lead us to more realistic understanding of the seismic cycles on the fault.
The Comparison of Long-term and Short-term Slip Rates of a Major Active
Strike-slip Fault System: Mosha Fault, Central Alborz, Iran
M. Shahpasandzadeh, International Institute of Earthquake Engineering
and Seismology, [email protected]
The Alborz mountain range accommodates the overall oblique left-lateral shortening between the southern Caspian basin and central Iran within the broad ArabiaEurasia collision zone. The Alborz range, a roughly 600 km long and 60-120 km
across, involve left-lateral and right-lateral strike-slip faulting on active ENE- and
WNW-trending faults, respectively. The ~150 km long ENE- to NW-trending
Mosha fault show strong historical seismicity in the central Alborz. This fault is
situated at the vicinity of Tehran city and represents an important potential seismic source that threatens the Iranian metropolis. This region has been affected by
destructive earthquakes in AD 958 (X, 7.7), AD 1177 (IX, 7.2), AD 1665 (VIII,
6.5), AD 1830 (IX, 7.1), and 1930 (VI, 5.2). To estimate the long-term and shortterm slip rates along the different segments of the fault, we undertook a combination of tectonic geomorphology and GPS studies. Our preliminary investigations
show a present day left-lateral displacement, which is consistent with the geodetic
and geological slip rates observed along the Mosha fault. The studies indicate a geodetic slip rate of ~ 4±2 mm yr-1 as the left-lateral shear of the overall belt along the
Mosha fault. The preliminary paleoseismological works on the eastern segment of
the fault indicates a minimum left-lateral component of 2.7±0.5 mm yr-1 over a
period of 5 My, although the Holocene offset along the fault corresponds to a slip
rate of ~ 7 mm yr-1.
Preliminary Paleoseismic Observations along US Highway 50, Basin and
Range Province, Central Nevada
R. Koehler, University of Nevada, Reno, Center for Neotectonic Studies,
[email protected]; S. Wesnousky, University of Nevada, Reno, Center
for Neotectonic Studies, [email protected]
A series of active north to northeast trending fault bounded mountain ranges
intersect Hwy 50 in Central Nevada. We have begun a mapping and paleoseismic
study of these faults across a transect extending from the Central Nevada Seismic
Belt to the Utah/Nevada border. The EARTHSCOPE project is installing a dense
250 Seismological Research Letters Volume 77, Number 2 March/April 2006
array of GPS geodetic instruments across Hwy 50, which will contribute to a better
understanding of the modern strain field. Our study will compliment these geodetic efforts by providing geologic information on past earthquake recurrence and
long-term strain distribution across the region. Specifically, our study focuses on
the Toiyabe, Simpson Park,Toquima, Antelope, Monitor, Fish Creek, Egan, Duck
Creek, and Schell Creek Ranges. To date, we have performed air photo and field
mapping across approximately half of the transect. Relative amount of tectonic
deformation is being assessed by comparing scarp heights on offset Quaternary alluvial fans of various ages. These units were differentiated as young (Qfy), intermediate (Qfi), and old (Qfo). Preliminary results show that prominent fault scarps (2 to
16 m) exist along all of the ranges, but the timing of displacements is not uniform
through time. For example, only Qfo surfaces are offset along the Antelope Range,
whereas, Qfi and Qfy surfaces are offset along the Toiyabe, Toquima, and Simpson
Park Ranges. A trench excavated across the East Toiyabe Range Fault (ETRF) at
Tar Creek exposed a downdropped alluvial fan deposit, a narrow package of fissure
fill material adjacent to the fault, and two different packages of scarp derived colluvium. Based on these data, we infer that two earthquakes have occurred on the
ETRF in middle to late Quaternary time. Along the Simpson Park Range, a series
of recessional shorelines of pluvial Lake Gilbert are offset where the fault projects
into Grass Valley. An ash from the highstand shoreline has been submitted for tephrochronology analysis and will place limits on the age of faulting.
Slip Rate of the San Andreas Fault near Littlerock, California
R. Sickler, USGS, [email protected]; R. Weldon, University
of Oregon, [email protected]; T. Fumal, USGS, [email protected]; D.
Schwartz, USGS, [email protected]; L. Mezger, University of Oregon,
[email protected]; J. Alexander, USGS, [email protected]; G. Biasi,
University of Nevada-Reno, [email protected]; R. Burgette, University of
Oregon, [email protected]; M. Goldman, USGS, [email protected]; S.
Saldana, University of Nevada-Las Vegas, [email protected]
Streams offset across the Mojave section of the San Andreas fault yield late
Holocene slip rates of ~36 mm/yr. These data are consistent with the slip rate
inferred at Pallett Creek [8.5 kms to the SE (Salyards et al., 1992)], the local longterm rate [averaged over ~2 Ma, (Weldon et al., 1993) and over ~400 ka (Matmon
et al., 2005)], and kinematic modeling of the San Andreas system (Humphreys and
Weldon, 1994). These results suggest that the rate has been constant at the resolution of geologic offsets, despite the observation that the decadal geodetic rate is
interpreted to be 5-15 mm/yr lower.
Two small streams and a terrace riser at the site are each offset 18 ± 2 m.
Evidence from trenches at one of the 18 m offsets suggests that it was caused by
slip during the past 3 earthquakes, the first of which closed a small depression into
which pond sediments were subsequently deposited. Eight samples of detrital
charcoal from the pond sediments and underlying fluvial deposits were dated. The
youngest C-14 age below the base of the pond is 372 ± 31 yr BP and the oldest
consistent sample in the pond is 292 ± 35 yr BP. These dates are consistent with the
third earthquake back (Event V) at Pallett Creek. Using a time or slip predictable
model to relate dated offsets to slip rate, and the better-constrained ages at Pallett
Creek, yields a slip rate of 36 ± 5 mm/yr.
A 3520 ± 220 yr BP channel deposit offset 130 ±70m may also yield a slip
rate of ~ 36 mm/yr. The range includes 3 different interpretations (~200, ~130,
and ~65 m) that are mutually exclusive. Our preferred interpretation, ~130 m,
requires that the canyon on the NE side of the fault captured the broad valley to the
SW when the gaps in the fault parallel ridges were first juxtaposed by RL slip, not
when the largest drainages on each side were aligned. In order to better constrain
the subsurface bedrock channel morphology, we conducted a hammer-source, 12channel, seismic refraction survey consisting of two fault-parallel and one fault-perpendicular profiles.
Improving the Slip Rate Estimate at Pitman Canyon, Southern San Andreas
Fault
S. Bemis, University of Oregon, [email protected]; R. Weldon, University
of Oregon, [email protected]; R. Burgette, University of Oregon, [email protected]
uoregon.edu.
We have identified several small abandoned debris flow channels and interfluves
at the Pitman Canyon site near Devore, California that might record recent offset
on the San Andreas fault. We have inferred a slip rate of ~23 mm/yr at this location using the recognition of an alluviation event dated several kilometers away at
~2000 years B.P. and the offset of multiple channels incised into this surface. While
the age is currently based on regional correlation and relative soil development, we
are processing radiocarbon and cosmogenic exposure samples for improved age
control. We are focusing efforts on several ~46 meter offsets of small debris flow
channels and lobes, the geometry of which we constrained using data from the B4
LiDAR project. Fieldwork is hindered at Pitman Canyon by thick vegetation due
to the fault acting as a groundwater barrier. Although the LiDAR processing is
ongoing, the currently available 0.5 meter gridded dataset provides valuable partial vegetation removal and geomorphic analysis opportunities. With this dataset,
we approximated the local alluvial surface at the Pitman Canyon site as a planar
surface, and subtracted this plane from the elevation, which removes the regional
gradient and results in a map of residual topography. This highlighted several offset
features that show a match when ~46 meters of right-lateral slip is reconstructed.
The results of this study will contribute to the debate pertaining to the slip rate
of the San Bernardino strand of the San Andreas fault. Preliminary estimates for
this site suggests a slip rate similar to that at Cajon Pass, ~10 km to the northwest.
Ongoing work on the southernmost portion of the San Bernardino strand of the
San Andreas fault suggests a lower slip rate. The location of the Pitman Canyon site
on the northern end of the San Bernardino strand and near the northern termination of the San Jacinto fault where it approaches the San Andreas fault makes this
an important point for constraining the relationship between these fault systems.
Earthquake Science in the 21st Century: Understanding
the Processes that Control Earthquakes
Poster Session
Study of Near-Field Earthquake Processes: Progress of the NELSAM Project
in Tautona Mine, South Africa
Z. Reches, University of Oklahoma, [email protected]; T. Jordan, University
of Southern California, [email protected]; M. Johnston, USGS Menlo Park,
[email protected]; M. Zoback, Stanford Univesity, [email protected];
V. Heesakkers, University of Oklahoma, [email protected]; M.
Zechmeister, University of Oklahoma, [email protected]; S. Murphy,
ISSI, Western Deep, ZA, [email protected]; G. van Aswegen,
ISSI, Western Deep, ZA, [email protected]
The NELSAM project (Natural Earthquakes Laboratory in South African Mines)
focuses on monitoring near-field earthquake processes in deep mines of South
Africa. The NELSAM site is being built with a footprint of about 250 m across
the Pretorius fault at 3.5 km depth in Tautona mine, Western Deep Levels, South
Africa. The practice of deep mines and numerical modeling predict profound
increase of the seismic activity at the site during the next 2-4 years. The work on the
site started in January, 2005, and has been devoted so far to site characterization,
including 3D mapping and in-situ stress measurements, and drilling short holes for
accelerometers-seismometers. Cross-fault drilling initiated in October, 2005, and it
includes five boreholes 40-60 m long each for the installation of creepmeters, strain
meters and temperature sensors, as well as the extraction of microbiological material and monitoring gas composition variations. By January 2006, the NELSAM
site includes eight systems of broadband 3D accelerometers (up to 15 g), out of
the planned 18 accelerometers and velocity systems, and two long boreholes have
been completed. It is anticipated that all installations will be accomplished by May,
2006.
We will report o the internal structure of the Pretorius fault fault-zone, the
structural and seismological characterization of the rupture zone of the M=2.2
earthquake of December 12, 2004, the preliminary near-field seismic observations
of the NELSAM network, and the measured in-situ stress field at the NELSAM
site.
Drilling the Megathrust: The Nankai Trough Seismogenic Zone Drilling
Project
H. Tobin, New Mexico Tech, [email protected]; M. Kinoshita, JAMSTECIFREE, [email protected]
The Integrated Ocean Drilling Program’s Nankai Trough Seismogenic Zone
Experiment (NanTroSEIZE) will, for the first time ever, attempt to drill into, sample, and instrument the seismogenic portion of a subduction zone plate boundary
fault, or megathrust. Access to the interior of active faults in which in situ processes can be monitored and fault zone materials can be sampled is of fundamental
importance to the understanding of earthquake mechanics. Beginning in 2006 with
a 3D seismic survey, and with drilling slated to start in 2007, IODP will undertake an integrated program of geophysical studies, drilling, and instrumentation
designed to investigate the aseismic to seismic transition of the megathrust system
and the processes of earthquake propagation and tsunami generation at the Nankai
Trough subduction zone of SW Japan. The fundamental goal is the creation of a
distributed observatory spanning the up-dip limit of seismogenic and tsunamigenic
behavior. This will involve sampling and instrumenting key elements of the active
plate boundary fault system at several locations off the Kii Peninsula, Japan. Here,
the plate interface and active mega-splay faults are accessible to drilling within the
Seismological Research Letters Volume 77, Number 2 March/April 2006 251
region of coseismic rupture and tsunami source in the 1944 Tonankai M8 great
earthquake. The ultimate objective is to access and instrument the Nankai plate
interface at depths of 3.5 to 6 km to advance our knowledge of aseismic and seismic
faulting processes and controls on the transition between them. NanTroSEIZE will
test models for the frictional behavior of fault rocks across the aseismic—seismogenic transition, the composition of faults and fluids and associated pore pressure
and state of stress, partitioning of strain spatially between basal interface and splays,
temporally between coseismic and interseismic periods, and between infraseismic
and aseismic events vs. seismic events, including recently reported VLF events in
the shallow accretionary wedge. Long-term borehole observations potentially will
ultimately test whether interseismic variations or detectable precursory phenomena exist in the subduction plate interface setting. Eight distinct drilling sites are
targeted, with a comprehensive program of coring, geophysical logging, downhole geophysical and hydrological experiments. Opportunities exist for many new
researchers to become involved in the NanTroSEIZE effort.
Construction of the EarthScope Plate Boundary Observatory: Two Years
Down and Three to Go
M. Jackson, UNAVCO, [email protected]; W. Prescott, UNAVCO,
[email protected]; G. Anderson, UNAVCO, [email protected]; K.
Feaux, UNAVCO, [email protected]; D. Mencin, UNAVCO, [email protected]
unavco.org; F. Blume, UNAVCO, [email protected]
The NSF-funded EarthScope Plate Boundary Observatory is two years into its fiveyear construction phase. By October 2008, PBO will install 875 permanent GPS
stations, upgrade 209 existing (Nucleus) GPS stations to PBO standards, install
103 tensor strainmeter/3-component seismometer borehole packages, install 5
laser strainmeters, and provide campaign GPS, and Geo-EarthScope (satellite
imagery and geochronology) support to the EarthScope Community. At the same
time, PBO will provide rapid and free access to all data and products derived from
PBO instrumentation and services.
As of January 1, 2006, field crews completed 280 of the 875 permanent GPS
stations destined for installation along the Pacific—North American plate boundary. During the same timeframe, 61 of 209 Nucleus stations were upgraded to PBO
standards. PBO installed 10 out of 103 tensor strainmeters/three-component seismometer instrument packages with an initial focus on capturing silent earthquakes
and slip events on the Cascadia subduction zone. Thirty tensor strainmeters/threecomponent seismometer instruments will be installed in 2006. In 2005, the first
long baseline laser strainmeter was installed on the eastern side of the Salton Sea
with units 2 and 3 projected for completion on the western shore in 2006. Overall,
the PBO project is 6% ahead of schedule.
As of January 1, 2006, the combined PBO and Nucleus networks have
returned 59.1 GB of raw GPS data, while the PBO strainmeter network has
returned 9.5 GB of strain and environmental data. All these data, and a range of
derived products including strain time series and GPS station velocities, are available via the PBO web pages at http://pboweb.unavco.org. In addition, seismic data
from five PBO borehole stations are available from the IRIS Data Management
Center in standard SEED format; data from at least five additional stations will be
available within the next two months.
Earthscope Data Management at the IRIS DMC
C. Trabant, IRIS Data Management Center, [email protected]; P.
Johnson, IRIS Data Management Center, [email protected]; M.
Templeton, IRIS Data Management Center, [email protected]; R.
Benson, IRIS Data Management Center, [email protected]; T. Ahern,
IRIS Data Management Center, [email protected]
Over the past 100 years the processes of the Earth’s sub-surface have been increasingly brought into sharper focus. A large part of the improving capability is due to
both the growing number of sensors deployed and the modernization of the instruments themselves. The ongoing EarthScope facility represents a large increase in
scientific capability not only by increasing the number of sensors on the ground
but in generating an interdisciplinary combination of geophysical data. Each component of EarthScope: PBO, SAFOD and USArray are unprecedented facilities
in their own right, but this system of systems is even more extraordinary with its
high-resolution 4-dimensional coverage.
The IRIS Data Management Center (DMC) is the primary archive for all raw
data produced by USArray and will also archive many of the higher-level USArray
data products. Furthermore, the DMC routinely receives PBO strain, (both raw
and processed), seismic data, and some SAFOD seismic data.
In addition to archiving and distributing all of these data, the DMC performs
extensive Quality Control (QC) on all USArray data as it arrives in order to ensure
that the USArray facility reaches its full potential. Limited automated QC is also
done on PBO strain and seismic data. The QC performed at the DMC is a combination of automated processing and hands-on analysis; in this way we are able to
monitor data from many stations with a minimal number of analysts. All aspects
of the data set are scrutinized for accuracy and quality including seismic waveform
data, metadata and instrument response information and monitoring of state-ofhealth channels. All QC measurements generated during this process are communicated back to the network operators and archived for future use. The DMC QC
efforts are done in close coordination with the QC efforts at upstream facilities,
namely at the Array Network Facility at UCSD, USGS NEIC/ASL and cooperating regional network operators.
Diverse Continuous Seismic, Geophysical, and Geodetic Data at the
Northern California Earthquake Data Center (NCEDC)
D. Neuhauser, University of California, Berkeley, [email protected];
F. Klein, US Geological Survey, [email protected]; S. Zuzlewski, University
of California, Berkeley, [email protected]; M. Murray, New
Mexico Tech, [email protected]; L. Dietz, US Geological Survey, [email protected]
usgs.gov; N. Houlie, University of California, Berkeley, [email protected]
berkeley.edu; D. Oppenheimer, US Geological Survey, [email protected]; B.
Romanowicz, University of California, Berkeley, [email protected]
edu.
Today’s seismic, geophysical, and geodetic networks collect a wealth of data for
earthquake monitoring and investigating the fundamentals of plate motion and
earth structure. Seismic, strain, GPS, creep, and electro-magnetic sensors all contribute to our understanding and observation of seismic and aseismic plate motion.
The Northern California Earthquake Data Center (NCEDC) is a long-term
archive and distribution center for geophysical data and their associated metadata
for networks in northern and central California.
Recent discovery of non-volcanic tremors in northern and central California
has sparked user interest in access to a wider range of continuous seismic data in the
region. The NCEDC has responded by expanding its archiving and distribution to
all new available continuous data from northern California seismic networks (the
USGS NCSN, the UC Berkeley BDSN, the Parkfield HRSN borehole network,
and local USArray stations) at all available sample rates, to provide access to all
recent real-time timeseries data, and to restore from tape and archive all NCSN
continuous data from 2001-present. All new continuous timeseries data are also be
available in near-real-time from the NCEDC via the DART (Data Available in Real
Time) system, which allows users to directly download daily Telemetry MiniSEED
files or to extract and retrieve the timeseries of their selection. The NCEDC will
continue to create and distribute event waveform collections for all events detected
by the Northern California Seismic System (NCSS), the northern California component of the California Integrated Seismic Network (CISN). All new continuous
and event timeseries will be archived in daily intervals and are accessible via the
same data request tools (NetDC, BREQ_FAST, EVT_FAST, FISSURES/DHI,
STP) as previously archived waveform data.
The NCEDC also archives and distributes other geophysical timeseries
data such as borehole and laser strain data from the EarthScope Plate Boundary
Observatory (PBO), and long-term strain and creep data from the USGS low frequency network. Continuous and campaign GPS data from northern California
and related campaigns are available from the NCEDC through the GPS Seamless
Archive (GSAC). The NCEDC is a joint project of the UC Berkeley Seismological
Laboratory and USGS Menlo Park, with additional funding from EarthScope.
Accessing SAFOD Data Products: Downhole Measurements, Physical
Samples and Long-term Monitoring
C. Weiland, Department of Geophysics, Stanford University, [email protected]; M. Zoback, Department of Geophysics, Stanford University, [email protected]
pangea.stanford.edu; S. Hickman, U S Geological Survey, Menlo Park, CA,
[email protected]; W. Ellsworth, U S Geological Survey, Menlo Park, CA,
[email protected]
Many different types of data were collected during SAFOD Phases 1 and 2 (20042005) as part of the National Science Foundation’s EarthScope program as well
as from the SAFOD Pilot Hole, drilled in 2002 and funded by the International
Continental Drilling Program (ICDP). Both SAFOD and the SAFOD Pilot Hole
are being conducted as a close collaboration between NSF, the U.S. Geological
Survey and the ICDP. SAFOD data products include cuttings, core and fluid
samples; borehole geophysical measurements; and strain, tilt, and seismic recordings from the multilevel SAFOD borehole monitoring instruments. As with all
elements of EarthScope, these data (including samples) are openly available to
members of the scientific and educational communities. This paper presents the
acquisition, storage and distribution plan for SAFOD data products.
The SAFOD monitoring program includes fiber-optic strain in the Main
hole, and tilt, and seismic recording instruments in both Main and Pilot Holes.
Seismic data from the Pilot Hole array are now available in SEED format from
the Northern California Earthquake Data Center (http://quake.geo.berkeley.
252 Seismological Research Letters Volume 77, Number 2 March/April 2006
edu/safod/). As the instruments and data handling systems develop, all data will
be available through the same web site as soon as possible. Lastly, two terabytes of
unprocessed (SEG-2 format) data from a two-week deployment of an 80-level seismic array during April/May 2005 by Paulsson Geophysical Services, Inc. are now
available via the IRIS data center (http://www.iris.edu/data/data.htm).
All physical samples from all three Phases of SAFOD drilling are being
curated under carefully controlled conditions at the Integrated Ocean Drilling
Program (IODP) Gulf Coast Repository in College Station, Texas. Photos of all
samples and a downloadable sample request form are available on the ICDP website (http://www.icdp-online.de/sites/sanandreas/index/index.html).
A suite of downhole geophysical measurements was conducted during the first
two Phases of SAFOD drilling, as well as during drilling of the SAFOD Pilot Hole.
These data include density, resistivity, porosity, seismic and borehole image logs and
are also available via the ICDP website. Current status reports on SAFOD drilling,
borehole measurements, sampling, and monitoring instrumentation will continue
to be available from the EarthScope web site (http://www.earthscope.org).
Associating Southern California Seismicity with Late Quaternary Faults
J. Woessner, California Institute of Technology, [email protected]; E.
Hauksson, California Institute of Technology, [email protected];
A. Plesch, Harvard University, [email protected]; J. Shaw, Harvard
University, [email protected]; R. Wesson, U.S. Geological Survey, [email protected]
We analyze the southern California seismicity to determine if small, moderate,
or large earthquakes are preferentially caused by slip on the primary fault surface
as described by the geologists, on subsidiary faults, or in the volume surrounding
the primary fault. An improved understanding of the spatial relationship between
hypocenters and late Quaternary faults will contribute to refining earthquake hazard estimates as well as probing the earthquake source and fault zone processes.
Further, this will also allow detailed comparison of the earthquake generation
processes for both small and large earthquakes. In our approach, we use the relocated SCSN/CISN catalog (1981-2005) and associate earthquakes with faults as
defined in the SCEC community fault model (CFM). We use both a deterministic
and a probabilistic approach based on a Bayesian inference. We determine seismicity parameters for on-fault and unassociated seismicity (background seismicity)
and provide an updated frequency-magnitude relation for each individual fault.
From this seismicity-parameter fault-system database, we search for characteristic
regional differences of fault behavior in California. Such mapping of fault behavior
in combination with their seismotectonic characteristics, will improve our understanding of the fault zone process. Mapping of seismicity parameters together with
refined hypocenters pin-points persistent “hot spots” of seismicity, i.,e. areas characterized by high seismicity rates over long periods in contrast to areas of variable
rates influenced by aftershock sequences. As an example, the San Jacinto fault zone
is characterized by variable seismicity patterns, evident in spatially and temporally
clustered seismicity separated by relatively aseismic regions. The San Jacinto fault
has not ruptured in a major earthquake for more than a 100 years along most of its
length, except for the Borrego Mountain segment that ruptured in 1968 and the
Superstition Hill in 1987. We present new insights into the variability of seismicity
parameters that possibly hint to locations along the fault where the physical properties of the fault zone may be highly anomalous.
Relationship of Seismicity to Fault Structure in California
P. Powers, University of Southern California, [email protected]; T.
Jordan, University of Southern California, [email protected]
We constrain seismicity rates perpendicular to strike-slip faults in California using
high-resolution regional and relocated catalogs. In southern California, we use fault
representations of the SCEC Community Fault Model (CFM) to calculate faultrelative distances; in northern California we assume faults coincide with peaks in
seismicity and use the peaks to calculate event distances. When we stack fault-relative earthquake distributions in regions proximal to major, linear fault segments,
we find that the cumulative number of earthquakes a~d–g where d is distance from
a fault and g≈0.8 and g≈1.5 for southern and northern California, respectively. We
attribute the higher value in northern California to the increased localization of
seismicity on faults that may result from the lack of transverse structures common
in southern California. We verified our results by stacking across multiple spatial
and magnitude ranges with various normalization methods. These value holds out
to 7-8km from a fault, beyond which ‘background’ seismicity dominates. Stacking
across increasing lower-magnitude cutoffs indicates that b-value remains constant
away from a fault and that b≈1. On the basis of this result, we hypothesize that
aftershocks of an earthquake away from a fault should be biased towards and along
the fault. To test this hypothesis, we filter our fault segment sub-catalogs for mainshock-aftershock sequences using reasonable time and distance windows and stack
them on the mainshocks in 2km wide bins away from the fault. Stacks of various
mainshock magnitude ranges (within a M2.5—4.5 range) show that aftershocks
are biased towards faults. This result compares well with a model that couples our
seismicity-distance scaling relation with the observation that earthquake aftershock
density d~r-2 where r is distance from a mainshock. These data suggest that we can
improve seismic triggering models by incorporating finer details of the relationship
between seismicity and fault structure.
Seismic Probing of InSAR Anomalies to Understand Fault Zone Compliance
E. Cochran, University of California, San Diego, [email protected]; Y. Li,
University of Southern California, [email protected]; P. Shearer, University of
California, San Diego, [email protected]; J. Vidale, University of California,
Los Angeles, [email protected]; Y. Fialko, University of California, San
Diego, [email protected]
Several recent studies suggest low rigidity, damage, and healing on the network of
faults in the Mojave Desert near the 1992 Landers and 1999 Hector Mine earthquakes. Coseismic InSAR pairs show, for an area within tens of kilometers of the
Hector Mine rupture, amplified shear and normal strain on several faults that did
not rupture during the nearby earthquake. These anomalous deformation zones were
also observed around recently ruptured faults, in particular, the Landers rupture.
In addition, the Landers and Hector Mine fault planes have distinct low-velocity
zones (LVZs) observed in active seismic experiments, most likely extending across
the seismogenic depth range. These LVZs show an increase in velocity and modulus
in the years after fault rupture, presumably due to postseismic healing and recovery.
These data suggest that faults are associated with damage zones with reductions in
seismic velocity by 10-40% and static shear modulus by roughly 50%, which extend
to at least 5 km depth. The geodetically-inferred compliant zones appear to be about
a kilometer wide, whereas LVZs measured from fault-zone-guided waves are only
about 100 m wide. This is likely due to a lateral gradient rather than a sharp step in
velocity and modulus, with the greatest reduction around the primary slip surface.
This spring and summer we will conduct a pilot study to systematically map the
structural cross-section of the Calico fault zone. Observations with InSAR show
localized strain on this fault during the Hector Mine earthquake. A combination
of explosions recorded by closely spaced cross-fault seismic lines, passive monitoring to infer the deeper structure, and further exploration of geodetic observations
will test and extend the current models of active faults. Resolving the quantitative
spatial network of fault compliance as well as its variation over the earthquake cycle
and the possible relation to the effective fault strength are critical ingredients for
our understanding of fault mechanics.
Quantifying Heterogeneities in the Surface Traces of Strike-slip Faults
N. Wechsler, University of Southern California, [email protected];
Y. Ben-Zion, University of Southern California, [email protected]; S.
Christofferson, University of Southern California, [email protected]
com.
Structural heterogeneities play significant roles in the mechanics of faulting. In
general, structural complexities are expected to depend on the following three
variables: 1) The misalignment of the fault zone orientation from the overall plate
motion direction. 2) The total offset accommodated by the fault zone. 3) The ratio
of the time scale for material healing to the time scale of loading. Wesnousky (1994)
and others attempted to quantify surface traces heterogeneities using density of
steps per unit length. In this work we follow Ben-Zion and Rice (1995) and use
the range of size scales (ROSS) to characterize the heterogeneities in a reproducible
and quantitative way. We examine the correlation between the ROSS and related
quantities with the first two variables, assuming that the third is similar for all faults
in a given plate boundary region. We analyze 14 right-lateral strike slip fault zones
in California and 7 fault zones in New-Zealand. Fault zones are defined as 20 km
wide rectangles oriented along the deformation direction. Segments are defined as
continuous lengths of fault bounded by discontinuities (steps or bends > 1°). For
each fault zone we measure on a digitized map the length and orientation of fault
segments relative to the plate motion direction, and calculate the misalignment
(average orientation relative to the plate motion direction), range of misalignment,
range of lengths, and related quantities. Results for both regions show that the
range of misalignment of a fault increases with the misalignment and decreases with
the cumulative offset. Faults with less cumulative offset are poorly aligned with the
plate motion direction and are more complex (have higher range of misalignment).
Rose-diagram analysis shows that faults with higher offset have less unfavorablyoriented long segments than faults with lower offset. While the fault data in the two
examined regions exhibit the same correlations, the measured ranges are not always
comparable. Deviations from correlative trends are compatible with our assumption that the structural complexity depends on both misalignment and cumulative
offset. The range of misalignment appears to be an effective measure of complexity
for faults within a particular plate boundary setting.
Seismological Research Letters Volume 77, Number 2 March/April 2006 253
Fault Geometry and Rupture Dynamics in the Marmara Sea, Turkey
D. Oglesby, University of California, Riverside, [email protected]; P.
Mai, ETH Zurich, [email protected]; K. Atakan, University of Bergen, Kuvvet.
[email protected]; S. Pucci, Istituto Nazionale di Geofisica e Vulcanologia
Sismologia e Tettonofisica Via di Vigna Murata, [email protected]; D. Pantosti,
Istituto Nazionale di Geofisica e Vulcanologia Sismologia e Tettonofisica Via di
Vigna Murata, [email protected]
The mega-city of Istanbul lies very close to the North Anatolian Fault Zone
(NAFZ), which runs south of the city in the Marmara Sea. The fault zone geometry
in this region has been reconstructed from detailed bathymetry studies and recent
images of submarine fault scarps (e.g., Le Pichon et al., 2003; Armijo et al., 2005),
but there remains considerable debate and uncertainty about the lateral extent and
arrangement of individual fault segments and the details of fault linkage between
strike-slip and potentially dipping segments. The size of potential earthquakes in
this region depends very strongly on the details of this fault geometry, and can have
a strong effect on the resulting seismic hazard for Istanbul, depending on the rupture propagation direction and the nucleation location.
In the present work, we use spontaneous dynamic rupture models to investigate the ability of earthquakes to propagate across the entire fault system, leading to
very large events. We experiment with different parameterizations of fault geometry
in the Sea of Marmara by varying fault orientations and offsets, as well as hypocenter
location. Our results imply that while the dip of the linking transtensional Cinarcik
fault near Istanbul does not appear to significantly affect rupture propagation, the
separation between the individual fault segments may have a controlling effect on
earthquake size. We will discuss the implications for the maximum earthquake size
in this region.
Nonuniform Prestress on Branched Fault Systems and the Effects on
Dynamic Fault Branching
B. Duan, University of California, Riverside, [email protected]; D.
Oglesby, University of Califronia, Riverside, [email protected]
A new explicit finite element method (FEM) algorithm, which can handle both
rectangular and triangular elements, is used to study the dynamics of branched fault
systems over multiple earthquake cycles in 2D. The fault stress between earthquakes
is evaluated by a viscoelastic model. Starting from a uniform tectonic stress field, a
highly nonuniform prestress field develops near the branching point and on the
two branch segments after a number of earthquake cycles. The inclination of the
maximum compressive prestress with respect to the fault segments rotates due to
the fault interaction in earthquakes and/or the oblique tectonic loading during
the interseismic period. In particular, this inclination becomes very shallow after a
number of earthquake cycles if the fault segment is in tension by the tectonic shear
loading. The nonuniform prestress field can have large effects on dynamic fault
branching. We find that several distinct fault branching scenarios can occur on a
branched fault, owing to several different prestress patterns developed over multiple
earthquake cycles. We also find two types of “backward branching”, where rupture
propagates around the acute angle between the primary and secondary segments.
In the first case, rupture propagates toward the branching point on the branch segment, and then proceeds onto the “stem” segment of the main fault quickly, while
onto the branch segment of the main fault slowly. The other case is that the slip on
the main fault discontinuously triggers a rupture on the branch segment at a favorable location determined by the nonuniform prestress, then the rupture propagates
bilaterally. These results may have important implication for the 1992 Landers, the
1999 Hector Mine, and the 2002 Denali fault earthquakes. For example, we find
that the branching behavior observed in the 2002 Denali fault earthquake may be
only one of two possibilities, if we take into account the effects of previous earthquake cycles.
Clusters of Earthquakes in the Southern of Iberian Peninsula
A. Posadas, University of Almeria, [email protected]; M. Navarro,
University of Almeria, [email protected]; F. Vidal, University of Granada, [email protected]
The southern part of the Iberian Peninsula forms part of the western border of
Eurasia-Africa plate boundary. This area is characterized by the occurrence of earthquakes of moderate magnitude (the maximum magnitude ranging from 4.5 to 5.5).
From the point of view of seismic activity, this region is the most active one in he
Iberian Peninsula. Until earlier 80, only the National Seismic Network belonging
to the National Geographic Institute monitories the activity in the south of Iberian
Peninsula. From 1983 to the actuality, the Andalusian Seismic Network belonging
to the Andalusian Geophysics Institute and Seismic Disaster Prevention, records
the microseismicity of the area. Nowadays, the earthquakes catalogue used belongs
to the Andalusian Institute of Geophysics and Seismic Disaster Prevention and it
counts on more than 20000 events registered from 1985 to 2001. Today, after 20
years of recording seismic activity, statistics analysis of the catalogue have sense. In
this paper we present a first approach to the clustering properties of the seismicity
in the south of the Iberian Peninsula. The analysis carried out starts with the study
of clustering properties (temporal and spatial properties) in the Southern of Iberian
Peninsula seismicity to demonstrate, by using the Fractal Dimension of the temporal earthquake distribution and the Morishita Index of the spatial distribution of
earthquakes, that this seismicity is characterized by a tendency to form earthquake
clusters, both spatial and temporal clusters. As an example, five seismogenetic areas
of the zone are analyzed (Adra-Berja, Agrón, Alborán, Antequera and Loja). This
particular study of the series find out the b parameter from the Gutenberg-Richter’s
Law (which characterizes the energetic relaxation of events), the p parameter from
Omori’s Law (that characterizes the temporal relaxation of aftershocks) and the
Fractal Dimension of the spatial distribution of earthquakes (to find the characteristic geometry seismogenetic zone).
Locally Induced Seismicity in the Swiss Alps Following the Large Rainfall
Event of August 2005
S. Husen, Swiss Seismological Service, ETH Zurich, [email protected]; N.
Deichmann, Swiss Seismological Service, ETH Zurich, [email protected]
ch; E. Kissling, Institute of Geophysics, ETH Zurich, [email protected]
ch.
The important role of fluids in triggering local earthquakes has been recognized for
several decades. Forced fluid injection at depth or filling of large reservoirs are well
known examples of how artificially induced changes in pore pressures can trigger
local earthquakes. Examples of naturally induced changes in pore pressure that lead
to triggering of local earthquakes are more rare and subtle. Periods of elevated seismicity induced by seasonal groundwater recharge or following intense rainfall are
good examples of the latter. Despite the small magnitudes of these earthquakes, their
study can provide insights into the state of stress and into the hydraulic properties of
the uppermost crust. Here, we present observations on a series of earthquakes that
has been triggered by a large rainfall event in Switzerland. In August 2005, a series
of 47 earthquakes occurred over a 12-hour period in central Switzerland. Given a
background seismicity in all Switzerland of two earthquakes per day, this is equivalent to an increase in seismicity by a factor of 500. Local magnitudes of the earthquakes were between 1.0 and 2.4; some of them were felt locally. The most striking
feature of this earthquake series is a clear correlation with an unusually large rainfall
event in central Switzerland: The earthquakes occurred at the end of this intensive
rainfall period of three days, with more than 300 mm rain. The highest seismicity occurred as two distinct clusters in the region of Muotatal and Riemenstalden,
a well known karst area that also received a particularly large amount of rainfall.
Focal depths of the larger events were mostly shallow, less than two kilometer deep,
in good agreement with reports of local people. Our observations favor a model in
which pore pressure is locally increased due to the large rainfall. The observed time
delay of 74 hours between the onset of the rainfall and the triggered earthquake
activity, as well as the relatively short duration of the earthquake series, suggest a
high permeability of the shallow crust. Earthquakes were mostly triggered in locations with past seismicity. Rather than occurring at new source areas, these earthquakes were clock-advanced. This means that the increase in pore pressure accelerated the occurrence of earthquakes in these areas.
Causes of Intraplate Earthquakes in Greenland, Plate Motion or “Post”
Glacial Uplift
S. Gregersen, GEUS, [email protected]; P. Voss, GEUS, [email protected]; T. Larsen,
GEUS, [email protected]
The Greenland earthquake activity has earlier been described to be concentrated in
the coastal areas around the Greenland ice cap. Updating of the earthquake catalogue still shows this as a fundamental description of the earthquake geography.
Lg wave propagation is as effective as in eastern United States, and in the shield
parts of Canada. The magnitude range calculated from Lg waves has been described
to be from 3 to 5 along the active parts of the coasts, and below 3 under the ice
cap. This is still valid. The improved earthquake geography makes correlations with
geological zones more certain. The causes of the intraplate earthquakes of this lowactivity region were previously interpreted as mainly ridge push. This has been challenged in several papers, giving reason to take up this question with reference to the
updated catalogue.
Direct Test of Static Stress versus Dynamic Triggering of Aftershocks
F. Pollitz, USGS, [email protected]; M. Johnston, USGS, [email protected]
Are aftershocks triggered primarily by the static stress change imparted by the mainshock or dynamic stress changes associated with wave propagation? Many studies
of well-known mainshock-aftershock sequences demonstrate the importance of the
static stress change for controlling the later (post-~1 month) aftershock occurrence.
254 Seismological Research Letters Volume 77, Number 2 March/April 2006
On the other hand, observations of aftershocks occurring during or shortly after
passage of the surface waves demonstrate the strong role of dynamic triggering.
We design a direct test of the competing hypotheses in the San Juan Bautista
area of the San Andreas fault (SAF), where both aseismic and seismic (impulsive)
events of about the same moment release (3 x 1016 Nm), equivalent to about M5
earthquakes, occur often. Since the aseismic events generate no radiated waves,
examination of the aftershock patterns following aseismic and seismic events can
illuminate the relative importance of the static stress change and dynamic stresses.
Within a ~240 km2 area surrounding a 20 km-long part of the SAF near San Juan
Bautista, both aseismic and seismic events of comparable magnitude (5.0 to 5.5)
have occurred, and the local seismicity catalog is complete to M=1.5 since 1975.
We characterize the aftershock sequences of both classes of events using an Omori
law. Comparison between the two classes shows that aftershock rates following
aseismic events are much smaller than those following similar seismic events. This
strongly suggests that at least in the near field, dynamic stresses are the dominant
cause of aftershocks for several weeks following a mainshock. We suggest the underlying cause of this phenomenon to be a change in the state of faults surrounding the
mainshock upon passage of the seismic waves. This may be realized by a reduction
in the net area of contact surfaces across these faults (e.g., Parsons, 2005). This is
consistent with the abrupt increase in acoustic emissions witnessed in pre-faulted
rock samples subject to a transient stress step.
Dynamic Stresses, Coulomb Failure, and Remote Triggering
D. Hill, U.S. Geological Survey, [email protected]
Dynamic stresses associated with crustal Love and Rayleigh waves with 15-30s periods are capable of triggering seismicity at sites remote from the generating mainshock under appropriate conditions. Coulomb failure models based on friction
models best explain those instances when the onset of triggered seismicity coincides
with the Love or Rayleigh wave peak dynamic stresses. The potential for Love or
Rayleigh waves to induce frictional failure on near-critically loaded faults depends
on, among other factors, the angle of incidence on the fault plane. To evaluate this
potential, I 1) calculate stress-perturbation orbits for the tip of the traction vector
acting on a fault surface induced by Love and Rayleigh waves at various angles of
incidence, and 2) examine the form of the stress-perturbation orbits in the σ—τ
space of a Mohr’s diagram with respect to the Coulomb failure criteria, τ = C + μ′σ.
Here, σ and τ are the normal and shear stress components of the traction vector,
respectively, C is the cohesive strength, and μ′ is the effective coefficient of (static)
friction. Angles of incidence with stress-perturbation orbits elongated at a high
angle to the Coulomb failure curve have a greater potential for inducing triggered
seismicity than those with a subparallel orientation. Rayleigh waves have the greatest triggering potential on near-vertical, strike-slip faults with angles of incidence in
the quadrant of the greatest principal stress. The triggering potential for Rayleigh
waves propagating perpendicular to inclined faults is greater for thrust faults than
normal faults, and the triggering potential decreases as the incidence angle becomes
parallel with the fault strike. The rectilinear stress orbits for Love waves produce
maximum shear stress perturbations for incidence either normal or parallel to the
strike of vertical faults. For Love waves incident at 45° on vertical faults, the traction vector becomes an oscillating normal stress. This is consistent with Love waves
propagating as an oscillating pure-shear stress field with the greatest and least principal stress axes at a 45° angle to the propagation direction. Amplitudes of Love
wave stress perturbations on inclined faults vary with the sine of the fault dip.
Dynamic Triggering of Earthquakes Caused by Surface Waves
S. Hernandez, University of Texas at El Paso, [email protected]; A.
Velasco, University of Texas at El Paso, [email protected]; K. Pankow,
University of Utah, [email protected]
A growing collection of remotely triggered earthquakes offers a genuinely exciting
opportunity to address dynamic vs. static earthquake triggering and the physics of
dynamic triggering. The physics of static stress triggering has been thoroughly investigated, but dynamic triggering mechanisms and controlling factors remain speculative. With the vast quantity and quality of broadband digital data, we now have the
opportunity to closely investigate the nature of earthquake rupture processes over
a broad frequency range. Utilizing observations from several networks, we closely
investigate the timing, frequency, amplitude, phase, and particle motion of both
Love and Rayleigh surface waves corresponding to key events with demonstrated
triggering at distances where static stress factors are impossible. We focus on events
with well documented dynamic triggering, such as the 1992 Landers earthquake
and the 2002 Denali Fault earthquakes. We measure surface wave group velocities
and amplitudes to assess the timing, frequency, and stresses caused by the passage
of the surface waves. We will also expand the study to look for possibly triggered
events caused by other large events. Our preliminary results show that both Love
and Rayleigh waves can trigger earthquakes, and that remotely triggered events are
much more common than previously documented.
The June 2005 Southern California Anza Earthquake: An Examination of the
Extended Aftershock Zone and Intermediate Range Triggering of the
Yucaipa Earthquake
K. Felzer, U. S. Geological Survey, [email protected]; D. Kilb,
University of California, San Diego, [email protected]
We examine two apparently unusual events that followed the MW 5.2 earthquake
near the town of Anza, California, on June 12, 2005. (1) Although the mainshock
fault was only several kilometers long, aftershocks stretched for at least 50 km
along the San Jacinto Fault zone; and (2) A MW 4.9 earthquake occurred 4 days
later and 72 km away, near the town of Yucaipa. We test the hypotheses that the
extended Anza aftershocks were triggered by aseismic slip that followed the mainshock (Agnew and Wyatt, 2005) and that the close space/time proximity of the
Anza and Yucaipa earthquakes was a coincidence. To test the aseismic slip triggering hypothesis we measure the density of the Anza aftershocks as a function of distance, r, from the mainshock fault. If a broad region of aseismic slip triggered these
earthquakes we might expect a near constant density, whereas if the earthquakes
are typical aftershocks we expect the density to decay as r-1.4 (Felzer and Brodsky,
2005). We observe the latter. Stochastic models of the Anza aftershock sequence
based on normal aftershock production, local faulting geometry, and excellent local
catalog completeness also look very similar to the observed sequence. This suggests
that the apparently long spatial extent of the Anza sequence resulted merely from
the dense Anza seismic network that provided the unique ability to catalog the
very small aftershocks, which are not usually recorded by regional networks. To test
whether the Anza mainshock triggered the Yucaipa earthquake we extrapolate local
aftershock decay relationships in time and space to estimate the probability of the
mainshock triggering a M(4.9 earthquake near Yucaipa after 4 days. We compare
this to the probability of the Yucaipa earthquake occurring randomly. We find that
the Anza mainshock roughly doubled the probability of a large earthquake occurring at Yucaipa, indicating a 50% chance that the Anza mainshock triggered the
Yucaipa earthquake. We conclude that the extended Anza aftershock sequence is
not out of the norm, and that there is a 50-50 chance that the Anza mainshock
triggered the Yucaipa event. For more information please see http://eqinfo.ucsd.
edu/~dkilb/June2005.html
Anomalous Omori and Inverse Omori’s Law around the Time of Main Shocks
Z. Peng, Department of Earth and Space Sciences, University of California, Los
Angeles, [email protected]; J. Vidale, Department of Earth and Space
Sciences, University of California, Los Angeles, [email protected]
We analyze the seismicity rate immediately after the 2004 Mw6.0 Parkfield earthquake from near-source seismograms. By scrutinizing the high-frequency signals, we
find that a significant fraction of aftershocks are missing in the Northern California
Seismic Network catalog in the first hour after the Parkfield main shock. However,
these newly detected early aftershocks are not enough to match the seismicity rate
extrapolated from large time intervals with the same decay rate (p value). In fact,
we observe a steady or slightly increasing rate of aftershocks for the first 100-200
s, followed by decay of aftershock activity with p = 0.8–0.9 afterward. Thus, there
appears to be a clear early stage of aftershock activity that does not fit the Omori’s
law with a single p value.
In another complementary work, we investigate the foreshock increasing rate
immediately surrounding small main shocks using the Shearer et al. [2005] relocated catalog for the southern California seismicity. Our main shocks are defined as
earthquakes that are not preceded by larger main shocks (m > 3) within 10 km and
100 days. We select as foreshocks events that are within 0.5 km and 100 days before
each potential main shock. The stacked foreshock increasing rate follow the inverse
Omori’s law (1/|t|p), but shows a crossover from a slower value with p = 0.5-0.6 at
times close to the main shock (100-104 s), to a faster value with p = 0.9-1.0 at times
further away from the main shock (104—107 sec).
In summary, we observe that the seismicity rate immediately before and after
the main shock is less than predicted from the Omori’s law with c = 0 and the
long-term p value. Our results can be explained by the epidemic-type aftershock
sequence model, and the rate-and-state model of Dieterich [1994]. Alternatively,
non-seismic stress changes near the source region, such as transient aseismic slip or
pore fluid pressure fluctuations, may share responsibility for the non-Omori behavior immediately before and after the main shock, which was also present in our
recent survey of M3-5 earthquakes in Japan [Peng et al., 2006, submitted].
Source Properties of Earthquakes in the Aftershock Zones of the 1999 Izmit
and Duzce Earthquakes from Iterative Spectral Stacking for Common Source
and Receiver Terms
W. Yang, Department of Earth Science, University of Southern California, Los
Angeles, 90089, CA, [email protected]; Z. Peng, Department of Earth and
Space Sciences, University of California, Los Angeles, 90095, CA, [email protected]
Seismological Research Letters Volume 77, Number 2 March/April 2006 255
ess.ucla.edu; Y. Ben-Zion, Department of Earth Science, University of Southern
California, Los Angeles, 90089, CA , [email protected]
We use an iterative stacking method (Shearer et al., 2005) to study the relative source
spectra of small earthquakes (M<=3.0) in the aftershock sequences of the 1999
Mw7.4 Izmit and Mw7.1 Duzce earthquake sequences. The study employs events
that occurred during the period August 1999 to February 2000 along the KaradereDuzce segment of the north Anatolian fault. A local PASSCAL network consisting
of short period and broadband stations recorded the data. We compute the P-wave
displacement spectra, and separate iteratively from the spectral results stacked source,
receiver and path-dependent terms. We use a simultaneous source spectrum and
single empirical Green’s function fitting method (Shearer et al., 2005) to correct for
attenuation. We then derive the relative source spectra shapes of events in different
potency/moment bins and estimate the Brune-type stress drops. The initial results
from the analysis of two event clusters indicate that the stress drop varies from 0.5 to
6.7 MPa along the fault, and the source spectra are best fitted by the omega-3 decay.
The receiver spectra terms for stations inside or close to the fault zone are found to
be larger than those of other stations. This may be related to the fault-zone trapping
structure and related site effects in the area discussed by Ben-Zion et al. (2003).
Source Properties of Repeating Earthquakes in the Aftershock Zones of the
1999 Izmit and Duzce Earthquakes Based on a Stacked Spectral-ratios and
Moving Time-window
Z. Peng, Department of Earth and Space Sciences, University of California, Los
Angeles, [email protected]; Y. Ben-Zion, Department of Earth Science,
University of Southern California, [email protected]; W. Yang, Department of
Earth Science, University of Southern California, [email protected]
We use a stacked spectra ratio method [Imanishi and Ellsworth, 2006] to study
the relative source spectra of repeating microearthquakes in the aftershock zones
of the 1999 Mw7.4 Izmit and Mw7.1 Duzce earthquake sequences. The analysis
employs 36 sets of highly repeating earthquakes, ranging in size from M 0 to M 3.0,
that occurred from August 1999 to February 2000 along the Karadere-Duzce segment of the north Anatolian fault [Peng and Ben-Zion, 2006]. A local PASSCAL
network consisting of 10 short-period and broadband stations recorded the data.
We use the smallest event in each cluster as the empirical Green’s function (EGF),
and divide the spectra of the other events in that cluster with the spectrum of the
EGF. Stable spectra ratios are obtained by stacking the ratios calculated from moving windows starting from the P waves to the S-coda waves. A multiple empirical
Green’s function (MEGF) method is used to invert for seismic potencies and corner
frequencies of the events. The continuing work will focus on deriving static stress
drops, apparent stresses and radiated energy of these repeating earthquakes. A comparison of the source properties of the repeating small earthquakes with those of
large aftershocks and the Duzce main shock would allow us to examine whether the
dynamics of earthquakes changes with the event size.
How Much Does P-wave Coda Bias S-wave Spectral Estimates?
G. Prieto, UCSD, [email protected]; D. Thomson, Queens University,
[email protected]; F. Vernon, UCSD, [email protected]; P. Shearer,
UCSD, [email protected]
One of the fundamental problems in seismology is the accurate estimation of the
radiated seismic energy of earthquakes. Determining the amount of radiated energy
in a given earthquake can be controversial and uncertainties of around an order of
magnitude are common. Difficulties include accounting for attenuation and path
effects, the very wide frequency band necessary for a reasonable energy estimate,
and the large dynamic range of the earthquake source spectrum. In addition, the
signal may be contaminated by other phases (e.g., coda waves, etc.), which might not
be accounted for. An important question that remains unanswered is to what extent
the P-wave coda contaminates the S-wave spectrum estimate. In other words, what
is the signal-to-noise ratio of the S-wave spectrum to the P-wave coda? To address
this, we use Quadratic Inverse Theory (Thomson 1990, 1994) combined with multitaper spectrum analysis to look at the time evolution of the P-wave spectrum and
estimate a reasonable signal-to-noise ratio for the S-wave spectrum. We apply this
technique to local earthquakes recorded by surface and borehole stations, as well as
small seismic arrays in the Anza region of Southern California.
Variability in Source Parameters, as Measured Downhole at Parkfield, CA
E. Sonley, Carleton University, [email protected]; R. Abercrombie,
Boston University, [email protected]
We calculate the stress drop and radiated energy for small (M1-2) earthquakes
recorded downhole at Parkfield, California. Progress in understanding of the
dynamics of earthquake rupture is currently limited by the large uncertainties in the
observed source parameters. This is particularly a problem for small earthquakes,
the source parameters of which are needed to understand fundamental processes of
earthquake rupture at all scales. Many studies have shown that source parameters of
small earthquakes show extreme variability. We make use of the Parkfield repeating
earthquakes as an example of the variability introduced by using differing methods
of calculating source parameters. Parkfield represents an ideal setting to improve
our knowledge of small earthquakes for a number of reasons: downhole, high
frequency recording by the HRSN began in 1987 providing exception borehole
azimuthal coverage, the instrumentation in the SAFOD pilot hole (PH) began in
2002 greatly increasing the high frequency bandwidth, and the presence of highly
clustered seismicity, including many repeating events, enables the use of empirical
Green’s function (EGF) analysis. Smaller earthquakes in a cluster can be used to
represent the earth’s transfer function between source and observer. The transfer
function can then be removed, in either the time or frequency domain, from a colocated, similar earthquake of larger magnitude. By using methods commonly in
use throughout the literature, in combination with the different source model possibilities, we find that source parameters vary by as much as an order of magnitude
simply by applying different methods. We further conclude that the small repeating
earthquakes that are the target for SAFOD are higher in stress drop and radiated
energy than those observed elsewhere (e.g. Abercrombie, 1995).
Characterization of Co-seismic Strain Release in Southern California Based
on Earthquake Catalog Data
I. Bailey, University of Southern California, [email protected]; T. Becker,
University of Southern California, [email protected]; Y. Ben-Zion, University of
Southern California, [email protected]
We investigate spatial and temporal patterns of inelastic strain associated with
earthquakes recorded in southern California. Using focal mechanism catalogs of
up to 100,000 events, derived from Southern California Seismic Network (SCSN)
data over the period 1982-2004, we generate a catalog of potency (moment divided
by rigidity) tensors for small events (less than M5). A Kostrov-type summation of
the tensors within a region of time and space quantifies the co-seismic strain release
associated with given ranges of magnitudes. Fisher statistics are applied to the
eigenvectors of the tensors within the region, characterizing the distribution and
complexity of the data. Focusing on small events justifies the point source assumption for the tensor analysis, and allows us to analyze detailed small-scale patterns
associated with a large data set. Working directly with data and using strain-based
quantities, rather than performing inversions for stress, allows us to avoid assumptions of homogeneity, minimize possible artifacts and focus on the data patterns
at different scales. Targeting three sub-regions with different dominating faulting
styles (the Los Angeles Basin, Kern County, and the San Jacinto Fault Zone), we
find distinct regional differences in the style of strain release, but do not observe the
equivalent of a Gaussian distribution in the data, as expected for a single dominating structure. We investigate the stability of our method by varying the number of
events and the quality of the employed focal mechanisms, comparing focal mechanisms generated by the programs FPFIT and HASH, and find that the observed
heavy-tailed distributions are not a consequence of poorly constrained data. We
continue our work by analyzing temporal effects and earthquake size effects. We
compare the aftershock dominated strain release from the Landers region with previously studied regions, and investigate the role of different sized earthquakes in the
observed distributions by varying the restriction of the upper and lower magnitude
cutoffs for the regions.
Combing Noisy Waveforms for Signal: Application of Matched Filters to
Identify and Locate Earthquakes in 35-500 s GSN Data
K. Walker, IGPP/SIO/UCSD, [email protected]; P. Shearer, IGPP/SIO/
UCSD, [email protected]
We apply different matched filters to long-period (35 to 500 s) global seismic data
of the GSN network from 1975-2005 in an effort to detect and locate previously
unknown seismic events. These filters are sensitive to longer periods than those routinely used to identify earthquakes, and they detect many events that are visible
only in their surface waves at teleseismic distances. Previously undetected events
are typically very small or radiate most of their energy into surface waves, such as
many oceanic transform earthquakes, mass-wasting events (e.g. landslides, glacial
slip events), and volcanic/magmatic events. The matched filter approach may also
compensate for the difficulty in detecting “normal” earthquakes where gaps exist in
the GSN (e.g., southern oceans). We confirm that our filters are detecting/locating
most shallow events in the standard catalogs down to M 4.5 (and perhaps down to
4.0 with a different data normalization scheme). Our results generally agree with
those of Ekstrom et al. (2005 in press) in that we detect/locate numerous previously
undetected events, many of which are probably related to glacial slip in Greenland
and Antarctica. Our objective is to build on the results of Shearer (1994) by examining a more complete global set of stations and applying filters that are sensitive
to waveform polarity as well as amplitude. Our scientific goal is to use our results
256 Seismological Research Letters Volume 77, Number 2 March/April 2006
to investigate the mechanisms and environmental conditions associated with slow
tectonic and non-tectonic earthquakes. We are currently focusing our attention on
previously undetected events within 15 degrees of the United States.
Marked Co-seismic Fault Weakening in the Presence of Melt Lubrication
S. Nielsen, RISSC, Istituto Nazionnale di Geofisica e Vulcanologia, Roma 1,
Italy, [email protected]; G. Di Toro, Dipartimento di Geologia, Paleontologia
e Geofisica, Universita di Padova, Italy, [email protected]; T. Hirose, Division of
Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto
Japan, [email protected]; T. Shimamoto, Division of Earth and
Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto, Japan,
[email protected]
Fault weakness has been a matter of enlivened debate lately. In theory,several
dynamically-induced weakening processes may be activated during earthquakes but
their physics is complex and their behavior is hard to predict.(e.g., thermal pressurization, frictional melt, elastodynamic lubrication, etc.). As a consequence, direct
observation of faults and experimental data are of crucial importance. Recent estimates of dynamic strength from exhumed ancient faults, combined with laboratory
experiments conducted at high shear rate and intermediate normal stress (up to
1.3 m/s and 20 MPa), suggest surprisingly low coseismic friction in the presence
of melt and weak normal stress dependence. Experimental results are not trivial to
interpret, because the lubrication mechanism depends on an articulate, self-regulating system of many coupled parameters (e.g., temperature, viscosity and thickness of
the melt layer, shear rate and stress, rock melting rate, etc.). However, it is possible to
reproduce the observed behavior reasonably well by treating the thermal diffusion
problem in both the rock and the melt layer as a Stefan boundary problem, coupled
to the fluid dynamic problem of melt shearing and extrusion. The model closely
reproduces the steady-state behavior observed in the experiments: shear resistence,
melt temperature and thickness, normal stress dependence and rate weakening are
reasonably well predicted. Friction in a wide range of parameters can be estimated
with implications for earthquake rupture dynamics.
Thermal Pressurization of Pore Fluids Due to Frictional Heating during
Earthquakes
M. Vredevoogd, UC Riverside, [email protected]; D. Oglesby,
UC Riverside, [email protected]; S. Park, UC Riverside, [email protected]
Thermal fluid pressurization is a possible mechanism for dynamic weakening of fault
friction during an earthquake (Andrews, 2002; Lachenbruch and Sass, 1980; Mase
and Smith, 1987). We calculate the response of a poroelastic material to heat input
to explore thermal pressurization of pore fluids on faults due to frictional heating.
Our solution is calculated on a one dimensional finite element mesh that is perpendicular to a fault, as this is the direction that we assume will have the strongest
temperature and pressure gradients, and thus control the transfer of heat energy.
The fault is located in the middle of our mesh to allow for cases with material heterogeneity across the fault. We use a solution method similar to that of by Mase
and Smith (1987), although our method does not assume material homogeneity
or constant slip rate. We solve the coupled equations for pressure, temperature, and
porosity using the Newton-Raphson iteration technique. We run simulations with
a variety of permeability values and slip time functions to determine what conditions are necessary for thermal pressurization to become a significant factor during
an earthquake.
Structure, Composition and Strain of the San Andreas Fault-zone at Tejon
Pass, California
Z. Reches, School of Geology and Geophysics, University of Oklahoma,
Norman, OK 73019, [email protected]; J. Verrett, School of Geology and
Geophysics, University of Oklahoma, Norman, OK 73019, [email protected]
ou.edu; G. Borges, School of Geology and Geophysics, University of Oklahoma,
Norman, OK 73019, [email protected]; T. Dewers, School of Geology and
Geophysics, University of Oklahoma, Norman, OK 73019, [email protected]; A.
Witten, School of Geology and Geophysics, University of Oklahoma, Norman,
OK 73019, [email protected]; J. Brune, Seismological Laboratory, University of
Nevada, Reno, NV 89557, [email protected]
We study the structure and composition of the San Andreas Fault in Tejon Pass
area, Southern California; this portion of the fault-zone was exhumed to an estimated depth of 4 km or more. The analysis includes field mapping of a region of
~1.5 km by 100-200 m along the San Andreas, grain-size analysis of the fault rocks,
seismic profiles across the fault-zone, as well as meso-structural and micro-structural analyses. The local section across the San Andreas reveals three-four major
fault segments (at least one is currently inactive) in general N60W direction. These
segments bound four distinct zones: (1) A gouge zone that is 50-100 m wide, and
which is composed of pulverized granite with extremely fine-grain (mean grain size
is 0.3 micron); (2) A cataclasite/ultracataclasite zone that is 0-15 m in width, and
which is composed of 5-6 colored, subparallel sheet zones that steeply dip toward
N30E; (3) An elongated pull-apart basin (~ 50 m wide) with young sediments; and
(4) A ~1 m wide zone of dark, organic shale that marked the segment which slipped
during the 1857 earthquake. The dominant meso-structures in the first three zones
are slickensided small faults that indicate transport direction normal to the trend
of the San Andreas Fault. We noted a lack of meso-structures with slip indicators
parallel to the San Andreas Fault. The micro-structural analysis reveals micro shearzones that pervasively penetrate both the pulverized granite (#1 above) and the
cataclasite/ ultracataclasite (#2 above); the closely spaced shear-zones bound apparently non-sheared rock blocks. We think the above fault-rocks formed at different
depth ranges: The pulverized granite (1) formed at depth of 4 km or more, the cataclasite/ ultracataclasite (2) formed at 2-4 km depth, and the dark, organic shale (4)
formed as a surficial sediment that was dragged or collapsed into the active segment.
We will discuss mechanisms that could explain the puzzling phenomena of lack of
distinct structures with shear parallel to the San Andreas Fault.
Earthquake Scaling and Near-source Ground-motions from Multi-cycle
Earthquake Simulation (With Heterogeneity in Rate-and-state Friction)
P. Mai, Institute of Geophysics, ETH Zurich, [email protected]; G. Hillers,
Institute of Geophysics, ETH Zurich, [email protected]; J. Ampuero, Institute
of Geophysics, ETH Zurich, [email protected]; Y. Ben-Zion, Department
of Earth Sciences, University of Southern CA, [email protected]
This study analyzes catalogs of moderate-to-large earthquakes obtained in 3-D
elastic continuous fault modeling governed by rate- and state-dependent friction.
As a proxy for geometrical irregularities of the fault, we parameterize the frictional
response of the system by including spatial distributions of the critical slip distance
L. Fault zones at different evolutionarys stages are then characterized by variable
range-of-size-scales present in the L-distibution.
Our earthquake-cycle simulations return large sets of model quakes whose
source parameters show remarkable similarities when compared against observed
earthquake source parameters. We investigate earthquake scaling relations on bulk
source properties, and examine the characteristics of distributed slip on the fault
plane. In particular, slip of large events (M > 6.5) is highly variable on the fault,
while ruptures tend to start at the edges of asperities (regions of large slip), consistent with imaged finite-source rupture models.
Our investigations also show that the catalog of simulated source models provides a useful resource to generate physically self-consistent scenario earthquakes
for near-source ground-motion prediction. Combined with the pseudo-dynamic
source characterization to model the temporal rupture evolution, we use our event
catalog to calculate near-field seismograms for a suite of scenario earthquakes. For
a given target region, we therefore provide simulation-based ground-shaking maps
that are useful for seismic hazard assessment. The large repository of physics-based
near-source synthetics helps to investigate ground-motion variability for earthquake-engineering purposes.
Scale Seismology. Results. Problems. Possibilities
E. Chesnokov, University of Oklahoma, [email protected]
Results of seismic investigations highly depend on model of interpretation of
observation data. From another side, data of observation dictates the type of interpretation model. For example, the layered media (periodic or random) will have
three different interpretation models in accordance with type of experimental data.
Namely, this medium will be interpreted as a multi-layered medium when wavelength () is less than a thickness (H) of each individual layer; in a case /H ~ 1 we
have inhomogeneous medium and when /H >>1 we can interpret these data in
terms of effectively homogeneous anisotropic (transversely—isotropic) medium.
Thus, one structure (layered medium in our case) has three different models of
interpretation based on various types of data.
The problem is to find the link between these models or finally between different types of measurements. In spite of a number of approaches already in existence
to solve these problems, almost all of them rely on spatial averaging to accomplish
upscaling. A major drawback of such methods is that they neglect fundamental
effects arising from correlations (statistical order) between the microscopic elements. In order to solve this problem, we proposed a mathematical technique partially based on the Feynman diagram. This approach allows us to calculate synthetic
seismograms for various types of media on different frequencies. As shown in a
paper, we did find a 3-D link between sonic ~ 2 kHz—20 kHz and seismic ~ 0
Hz—10 Hz type of measurements.
Full Form Synthetic Seismogram Calculations And Determination of Focal
Mechanism Of Frac Events Based On 3-C Seismic Array Obserbations
A. Vikhorev, Institute of Physics of the Earth Russian Academy of Sciences,
Moscow, Russia, [email protected]; M. Ammerman, Devon Energy Inc.,
Seismological Research Letters Volume 77, Number 2 March/April 2006 257
Oklahoma City, OK,USA, [email protected]; R. Brown, Oklahoma
Geological Survey, Norman,OK, USA, [email protected]; S. Abaseyev,
Sarkeys Energy Center, University of Oklahoma, Norman,OK,USA, [email protected]
ou.edu; E. Chesnokov, Sarkeys Energy Center, University of Oklahoma,
Norman,OK,USA, [email protected]
The general task is to obtain a non-raypath description of waves in a macro- and
micro-inhomogeneous heterogeneous medium. Micro-inhomogeneities are randomly oriented and presented through various fluctuations of properties, through
cracks, pores, inclusions of foreign crystallites, and saturation of pores with liquid.
The wave equation, which needs to be solved, is written for the macro-inhomogeneous medium with the dynamic properties: (1) Coefficients of the generalized
wave equation (1) are grouped into an expanded fourth-rank tensor . They are the
operators, containing time derivatives, they also set the properties of the equivalent medium—the effective properties. For the numerical calculations we used the
general mathematical expression for the source function: (2) Coefficients and orientation of vectors determine the radiation pattern of the source. Comparison of
calculated and real seismograms gives the possibility to determine orientation of
plane of the source and drop stresses in the source area. Statistics of the directions
of horizontal components of drop stresses reflects the orientation of general stress
in studied area.
Teleseismic Receiver Functions Study on the Velocity Structure Beneath
Yanqing-Huailai Basin, Nw Beijing
R. Herrmann, Saint Louis University, [email protected]; Y. Chen, Institute
of Geophysics, China Earthquake Administration, [email protected]; Z. Yang,
Institute of Geophysics, China Earthquake Administration, [email protected]
cn; R. Zhou, Southern Methodist University, [email protected]; B.
Stump, Southern Methodist University, [email protected]
The Southern Methodist University (SMU) and the Institute of Geophysics of the
China Earthquake Administration (IGCEA) operate a broadband seismic network
in the Yanqing-Huailai Basin, 120 km northwest of Beijing. Within the YanqingHuailai Basin, earthquake risk and propagation path assessments are important
because of the basin’s historical seismicity and proximity to Beijing’s large population. The high quality data set recorded by 7 stations around the basin provide us
opportunity to study the detailed velocity structure beneath this region. A mining explosion at near-regional distance produced intermediate period surface wave
that were recorded by this network. The Rayleigh wave dispersion curves from this
explosion covered the period range of 1.5 to 16 sec with the group-velocities range
from 2.36 to 3.05 km/sec. Preliminary analysis of these intermediate period surface waves has provided a baseline to refine the upper crustal velocity structure in
the region. The inverted shear wave velocities at surface range 2.8 to 3.1 km/s and
increases to 3.2 to 3.6 km/s in the upper and middle crust. The inverted models
reflect the path differences and are consistent with the local geology. Our results
support a reduced velocity gradient in the upper crust and are consistent with results
from long range reflectivity study and results from other surface studies conducted
in the region. In order to expand the velocity model through the crust, a couple
dozen teleseismic events in 2003 and 2004 were processed in order to estimate the
receiver functions in the basin. The receiver functions are simple and similar around
the Yanqing-Huailai Basin. A joint inversion of these consistent receiver functions
and phase velocities across the network is under way to further constrain the crustal
structure beneath this region. The crustal structure from jointed inversion will be
compared to the results from previous surface wave study.
Detailed Seismic Velocity Structures in the Focal Areas of Recent Large
Inland Earthquakes in Japan by DD Tomography
T. Okada, Tohoku University, [email protected]; T.
Yaginuma, Tohoku University, [email protected]; J.
Suganomata, Japan Meteorological Agency, [email protected]
ac.jp; A. Hasegawa, Tohoku University, [email protected];
H. Zhang, University of Wisconsin-Madison, [email protected]; C.
Thurber, University of Wisconsin-Madison, [email protected]
Detailed seismic velocity structure in and around the focal area may provide clues
to understanding the generation process of earthquakes. We performed seismic
tomography to obtain the seismic velocity structure in and around the focal areas
of several inland earthquakes in Japan. We applied the double-difference (DD)
tomography method (Zhang and Thurber, 2003), which has the advantage of
obtaining the high-resolution seismic velocity structure in and around the focal
area. The travel time data are from dense temporary seismic networks deployed for
aftershock observation.
We find that the fault zones have specific characteristics in the seismic velocity structure. For the strike-slip type earthquakes (the 1995 southern Hyogo M7.3
and the 2000 western Tottori M7.3), low velocity zones of a few kilometers width
are present along the mainshock fault plane or along the aftershock alignment. This
suggests that the fault planes of these earthquakes are located in or on the edge of
low velocity zones. For the thrust fault earthquakes (the 2004 Mid Niigata M6.8
and the 2003 northern Miyagi M6.4), aftershocks are distributed along a dipping
plane across which the estimated seismic velocities change abruptly. Both P-wave
and S-wave velocities in the hanging wall are lower than those in the footwall. One
possible interpretation is that these two earthquakes occurred on faults that formed
as normal faults (in the Miocene) and are reactivated as reverse faults under the
current compressional stress regime.
Coseismic slip distributions are generally not homogeneous along the fault
plane and large coseismic slip areas are common in recurring large or moderatesized interplate earthquakes in NE Japan. These observations suggest that the large
coseismic slip areas are persistent features that reflect physical properties on the
fault plane. In the earthquakes we have studied, large coseismic slip areas tend to
concentrate in the relatively high velocity areas along the fault plane, consistent
with studies in other areas. These observations suggest a direct correspondence
between high-velocity bodies and asperities.
Detailed Crustal Shear-wave Splitting Observations along the POLARIS-BC
Array
Al-Khoubi, Geological Survey of Canada, Sidney, BC, [email protected];
J. Cassidy, Geological Survey of Canada, Sidney, BC, [email protected]; I.
M. Bostock, Department of Earth and Ocean Sciences, University of British
Columbia, [email protected]
As a part of the POLARIS project, 31 three-component broadband seismic stations
were deployed in an approximately linear array sampling the Cascadia subduction
zone from southern Vancouver Island to northwestern Washington. We utilize
recordings of 67 local earthquakes made during the period April, 2002 to January,
2005 to examine crustal S-wave anisotropy along this dense array (with an average
station spacing of about 10 km). Previous crustal anisotropy studies across the region
have shown: 1) margin-parallel fast directions, in agreement with the direction of
maximum compressive stress obtained from earthquake focal mechanisms; and 2)
some suggestion of a change in fast direction to more margin-perpendicular at stations closest to the coast. The earthquakes used in this study occurred at depths of
10-60 km and therefore sample the North American plate, above the subducting
Juan de Fuca plate. We observe clear crustal shear-wave splitting at most stations.
The fast direction is predominantly NW-SE (margin parallel), however the direction changes to a more E-W direction at the three stations closest to the west coast
of Vancouver Island. This observation may indicate a change in the orientation of the
crustal stress field as one approaches the locked portion of the Cascadia subduction
fault, just to the west of Vancouver Island. Observed delay times ranged from 0.160.32 s, yielding an average anisotropy of 1.9±0.6% for the upper 20-30 km of crust.
Testing the First-Generation RELM Models
D. Schorlemmer, ETH Zurich, [email protected]; E. Field, USGS
Pasadena, [email protected]; T. Jordan, USC Los Angeles, [email protected]
The working group for the development of Regional Earthquake Likelihood
Models (RELM) began in 2001 as a joint effort of the Southern California
Earthquake Center and the U.S. Geological Survey. Given a lack of consensus on
how to develop earthquake rupture forecasts (which quantify the probability of all
large events throughout a region over a specified time span), the goal was to develop
a range of viable models for California. The second step was to evaluate the hazard
and loss implications of each model and formally test each against future seismicity.
A total of 17 5-year forecasts were submitted on January 1st, 2006, representing the
first-generation RELM models. This presentation will give a brief overview of these
models and describe the plan for testing the models comparatively and for consistency with observations. We will also discuss how the RELM project will transition
into the more ambitious Collaboratory for the Study of Earthquake Predictability
(CSEP). In short, CSEP will expand the geographic coverage, introduce other
types of formal tests, and accommodate other types of forecasts (e.g., alarm-based
predictions).
Implementing the Collaboratory for the Study of Earthquake Predictability:
Challenges and Solutions
D. Schorlemmer, ETH Zurich, [email protected]; J. Zechar,
University of Southern California, [email protected]; P. Maechling, Southern
California Earthquake Center, [email protected]; T. Jordan, Southern
California Earthquake Center, [email protected]
The Collaboratory for the Study of Earthquake Predictability (CSEP) aims to
develop the infrastructure for a facility for earthquake forecast experiments. It succeeds the Regional Earthquake Likelihood Model project (RELM), which first
established a testing center for forecasts, currently performing analyses of 5-year
258 Seismological Research Letters Volume 77, Number 2 March/April 2006
models. CSEP will extend the mission of RELM by considering regions outside
of California and considering forecasts that are not grid-based and/or probabilistic. To make testing of different types of models in different regions of the world
possible, technical as well as logistical problems have to be considered. In this presentation, we describe and discuss these aspects. Besides the setup of the testing
center and the software framework envisioned for CSEP, we present the process of
developing testing rules for the different classes of models, the process of establishing a consensus among the participants for testing, and the process of coordinating
multiple testing centers.
Testing Alarm-based Earthquake Prediction Strategies
J. Zechar, University of Southern California, [email protected]; T. Jordan,
University of Southern California, [email protected]
The Regional Earthquake Likelihood Models (RELM) group of the Southern
California Earthquake Center (SCEC) has established a framework for comparative testing of grid-based probabilistic earthquake forecasts (see Schorlemmer et
al., this meeting). The RELM testing procedures, however, are not well suited for
assessing forecasts that are not grid-based or are not stated in probabilistic terms. In
this presentation, we outline approaches to evaluating such alarm-based strategies,
focusing on the use of Molchan’s error diagram (Molchan 1991, 1997, 2003). We
present an addition to this diagram—a plot of miss rate and fraction-of-alarm-spacetime—that allows us to establish statistical significance of a strategy’s performance.
We apply our methodology to strategies that predict intermediate and large earthquakes in California and compare performance of forecasts derived from the USGS
National Seismic Hazard Mapping Project and the Pattern Informatics method of
Rundle et al. (2002). We find that neither of these models has significant predictive skill given a physically naïve null hypothesis. Discussion topics will include the
unique challenges that arise when evaluating alarm-based strategies and plans for
incorporating alarm-based strategy evaluation techniques in the Collaboratory for
the Study of Earthquake Predictability (CSEP).
When the Earth Speaks
F. Freund, SJSU/NASA Ames Research Center, [email protected]; B.
Lau, San Jose State University, [email protected]; A. Takeuchi, Niigata
University, Japan, [email protected]
Earthquake forecasting has been an elusive goal for a long time, not only for seismology. Yet, before major earthquakes, the Earth appears to sends out signals. Most
signals point to transient electric currents in the Earth’s crust. To search for the
cause of such currents attention has focused—for decades, but in vain—on piezoelectricity, a property of quartz, an abundant mineral in certain rocks. The fact
that no generally accepted, physics-based mechanism for the generation of large
currents was available has caused considerable confusion and controversy. During
rock deformation studies we have made an amazing discovery: when we squeeze
one end of a 1.2 m long slab of granite (or quartz-free rocks such as anorthosite
or gabbro) the stressed rock volume generates a voltage which in turn causes two
outflow currents. One, carried by electrons, flows from the stressed rock directly
to ground. The other, carried by defect electrons or holes, flows into and through
the unstressed rock and out the other end. The stressed rock behaves, in fact, as a
battery. The outflow currents can reach 10,000-100,000 amperes per cubic kilometer of stressed rock. The discovery of this previously unknown capacity of igneous
rocks to generate currents offers for the first time a physical basis to re-evaluate a
wide range of reported pre-earthquake signals as potential indicators of impending
earthquake activity.
Ongoing Accelerating Seismicity in California
H. Colella, Cal State Fullerton, [email protected]; D. Bowman, Cal
State Fullerton, [email protected]
Many large earthquakes are preceded by a regional increase in seismic energy release.
This phenomenon, called “accelerating moment release” (AMR), is due primarily
to an increase in the number of intermediate-size events in a region surrounding
the mainshock. We use a backslip elastic dislocation to calculate an approximate
geologically-constrained loading model that can be used to define regions of AMR
before a large earthquake. While this method has been used to search for AMR
before large earthquakes in many locations, most of these observations are “postdictions” in the sense that the time, location, and magnitude of the main event were
known and used as parameters in determining the region of precursory activity.
With sufficient knowledge of the regional tectonics, it should be possible to estimate the likelihood of earthquake rupture scenarios by searching for AMR related
to stress accumulation on specific faults. Here we show a preliminary attempt to use
AMR to evaluate the likelihood of earthquakes on a subset of strike-slip faults in
California. The technique suggests that significant ongoing AMR can be attributed
to loading of the Rogers Creek and Calaveras faults in northern California and the
Cholame and Carrizo segments of the San Andreas fault in southern California.
Because we are unable to constrain the timing of these prospective events, this work
does not constitute a formal earthquake forecast.
Precursory Accelerating Moment Release: Fact Or Data-fitting Fiction
A. Michael, USGS, [email protected]; K. Felzer, USGS, [email protected];
J. Hardebeck, USGS, [email protected]
The high earthquake rate before, compared to after, the 1906 earthquake has long
led seismologists to look for increases in seismicity that could be used to forecast
future mainshocks. This phenomenon has recently been termed Accelerating
Moment Release (AMR) and has been the subject of many studies. We ask whether
the observations of AMR are real and potentially predictive, or if apparent AMR is
simply an artifact due to data-fitting.
The risk of discovering fictitious AMR exists because the time period, area,
and sometimes magnitude range analyzed before each mainshock are often optimized to produce the strongest AMR signal. Optimizing the search criteria may
identify apparent AMR even if no such physical process exists. We explore this possibility by applying the procedure of Bowman et al. ( JGR, 1998) to both the actual
southern California earthquake catalog and simulated catalogs in which no underlying seismicity acceleration actually occurs. The simulated catalogs range from random event locations and times through an ETAS model that includes both realistic
spatial and temporal earthquake clustering and a spatial distribution of seismicity
based on the fault network.
In all of the simulated data sets, we observe apparent AMR before 60-70% of
the mainshocks of M ≥ 5.5, 6.5, or 7.5 despite the fact that no actual AMR is present in these catalogs. Thus, if AMR actually exists in nature it should be found more
than 70% of the time in the observed data. However, using the same approach we
find apparent AMR before only 63% of the M ≥ 5.5 earthquakes in the real southern California data. We also find that if the time period and area are not allowed to
vary, but are fixed to values derived from proposed scaling relationships with respect
to mainshock magnitude, AMR is found for only 13% of the observed M ≥ 6.5
mainshocks. These two results suggest that the AMR observed using this method is
actually the result of data-fitting and does not represent a real, precursory process.
Earthquake Forecasting in Northern California Based on Temporal
Variations in the Strain Field at Seismogenic Depths
S. Sipkin, U.S. Geological Survey, [email protected]
Focal mechanisms produced by the Northern California Seismograph Network for
earthquakes during 1980-2004 are used to study temporal variations in the local
subsurface strain field. Focal mechanisms analyzed in one-half degree grid cells
show changes in the strain field that reflect coseismic or postseismic responses to
earthquakes occurring in the cell. A few changes in the strain field appear to be
preseismic. Preseismic changes in the strain field occurred prior to the 1989 m 6.9
Loma Prieta, the 1992 m 7.2 Petrolia, the 2003 m 6.5 San Simeon, and the 2004 m
6.0 Parkfield earthquakes. The character of these strain anomalies is consistent with
the effects expected from poroelastic strain transients caused by the trapping and
release of fluids along faults in the hypocentral zone.
Nuclear Explosion Monitoring Anniversary Session
Poster Session
The Seismic Networks of the International Monitoring System of the
Comprehensive Nuclear Test Ban Treaty Organization.
S. Barrientos, Comprehensive Nuclear-Test-Ban Treaty Organization, [email protected]; G. Suarez, Comprehensive Nuclear-Test-Ban Treaty
Organization, [email protected]
The International Monitoring System (IMS) of the Comprehensive Nuclear-TestBan Treaty is composed by 337 facilities of four technologies: 16 radionuclide laboratories, 80 radionuclide, 60 infrasound, 11 hydroacoustic and 170 seismic stations.
Of the latter, 50 are primary and 120 are auxiliary stations. After eight years of the
initiation of the build-up phase of the IMS, several important milestones have been
reached in all technologies with nearly 70% of stations installed worldwide. This
note, presents the methodology employed to select new sites together with the
installation of stations and the operational phase of stations which are part of both
the primary and auxiliary seismic networks.
The 50 primary stations, of which 30 are arrays stations, send data on
continuous form to the International Data Centre (IDC) through the Global
Infrastructure of Communications (GCI). The 120 stations of the auxiliary net-
Seismological Research Letters Volume 77, Number 2 March/April 2006 259
work send data upon request, after an event has been detected by the primary seismic and hydroacoustic networks.
The primary seismic together with the hydroacoustic (6 hydrophone and
5 T-phase stations) network are designed to detect and locate world wide events
magnitude 4 and above with enough accuracy to allow possible on site inspections.
(epicentral location errors within 30 km by 30 km). Thus, high signal to noise ratio
in low noise environments are the essential stations in this network. Several examples of this type of stations will be presented, among them results from stations in
Antarctica, Central Asia, Africa, etc   …
More than 70% of the primary seismic network is completed with an additional 12% to be executed by the end of 2006. Data from more than 70 stations of
the auxiliary network are currently requested to generate the various forms of IDC
Bulletins.
In 2005, data from selected stations have been routed, on a test basis and continuous form, to UNESCO recognized Tsunami Warning Systems for emergency
purposes.
assignments are intentionally corrupted, we find that MCMCloc properly corrects
the error in most cases. Ambiguity occurs only in cases where arrivals are not statistically distinct in time (typically when the arrivals are within a few seconds of one
another). Because we can include priors on each aspect of the location problem,
MCMCloc is ideal for combining trusted data with data of unknown quality. This
work was performed under the auspices of the U.S. Department of Energy by the
University of California Lawrence Livermore National Laboratory under contract
No. W-7405-Eng-48, Contribution UCRL-ABS-218118.
On the Detection of Low Magnitude Seismic Events Using Array-based
Waveform Correlation
F. Ringdal, NORSAR, [email protected]; S. Gibbons, NORSAR, [email protected]
norsar.no; T. Kvaerna, NORSAR, [email protected]
The regional coda methodology (Mayeda, 1993; Mayeda and Walter, 1996;
Mayeda et al. 2003) has proven to be a very stable way to obtain source spectra from
sparse regional networks using as few as one station. The availability of these source
spectra provides an opportunity to use them to determine the apparent attenuation of the direct regional phases Pn, Pg, Sn and Lg. We apply a two-step process
to isolate the frequency-dependent Q. First, we correct the observed direct wave
amplitudes for an assumed geometrical spreading. Next, a combined path and site
Q is determined from the difference between the spreading-corrected amplitude
and the independently determined source spectra derived from the coda methodology. Here we develop the technique and apply it to 50 earthquakes with magnitudes greater than 4 in central Italy as recorded by MEDNET stations around
the Mediterranean at local to regional distances. This is an ideal test region due
to its high attenuation, complex propagation, and availability of many moderate
earthquakes. We find that a power law attenuation of the form Q(f )=Qof g fit all
the phases quite well over the 0.5 to 8 Hz band. At most stations the measured Q
values are quite repeatable from event to event. Finding the attenuation function in
this manner guarantees a close match between inferred source spectra from direct
and coda techniques. This is important if coda and direct wave amplitudes are to be
combined in earthquake/explosion discrimination techniques. Knowledge of the
attenuation of the direct phases is necessary to correct for path and site effects in
regional discriminants, such as high frequency P/S ratios. There are many other possible applications for these regional phase Q estimates including hazard analysis and
regional attenuation tomography.
*This research was performed under the auspices of the U.S. Department of
Energy by the University of California Lawrence Livermore National Laboratory
under contract number W-7405-ENG-48. This research has been partially supported by the Dipartimento della Protezione Civile, under contract S4, ProCiv-INGV
(2004-06), project: “STIMA DELLO SCUOTIMENTO IN TEMPO REALE
E QUASI-REALE PER TERREMOTI SIGNIFICATIVI IN TERRITORIO
NAZIONALE”
The matched filter detector is probably the most effective way of detecting a known
signal in a noisy incoming data stream. The application of waveform-correlation
based detectors in seismology has been extremely limited due to the requirement
that the form of the signal needs to be known a priori and this is very rarely the
case for earthquakes or explosions. This limitation restricts the applicability to lowmagnitude events which occur in the immediate vicinity of events for which high
quality signals exist. However, the proportion of seismic events producing similar
waveforms appears to be far higher than initially thought and we present instances
where events, too small to be detected by traditional power detectors, have been
detected easily by the real-time correlation of online data with signal templates from
previous events. We show that even greater improvement in signal detectability can
be achieved using seismic arrays by stacking correlation coefficients from single sensors over an array or network. If two events are co-located, the time separating the
corresponding patterns in the wavetrain as indicated by the cross-correlation function is identical for all seismic stations and this property means that the correlation coefficient traces are coherent even when the waveforms are not. In principle,
the procedure can be applied equally well to large aperture arrays or networks and
small aperture regional arrays. In practice, the use of regional arrays can produce
many more false alarms due to coincidental waveform similarity over short timewindows. We show that many of these false alarms can be filtered out automatically
by performing f-k analysis upon the correlation coefficient traces. It is still unclear as
to how widely applicable such methods will be to general detection seismology but,
for regions for which events with good calibration signals are available, we present
case studies indicating that correlation methods can reduce the detection threshold
by about an order of magnitude.
A Bayesian Hierarchical Approach to Multiple-Event Seismic Location
S. Myers, Lawrence Livermore National Laboratory, [email protected]; G.
Johannesson, Lawrence Livermore National Laboratory, [email protected]
llnl.gov; W. Hanley, Lawrence Livermore National Laboratory, [email protected]
gov.
We develop a new location algorithm by casting the multiple-event forward problem in a Bayesian Hierarchical framework. Event hypocenters, travel-time predictions, phase arrival times, and phase names comprise the forward problem. The
Bayesian hierarchical approach allows us to place statistical constraints on any
aspect of this problem. In general, we have some prior information on each aspect
of the problem—whether it is the travel-time predictions, phase arrival times, or
the location of some events—and we can use all of this information to constrain the
solution. Our statistical model includes error correlations, such as reduced correlation of prediction error as the distance between stations and/or events increases.
Inclusion of error correlation allows us to operate over arbitrarily large geographic
regions. We use the Markov Chain Monte Carlo (MCMC) method to produce a
suite of solutions that are consistent with the Bayesian priors, and we refer to the
procedure as MCMCloc. Posteriori estimates of event locations, travel-time curves,
path corrections, pick errors, and phase assignments are made through analysis of
the posteriori suite of acceptable solutions. We test MCMCloc on a regional data
set of Nevada Test Site nuclear explosions. Locations and origin times are known
for these events, allowing us to assess MCMCloc performance with minimal ambiguity. These tests suggest that MCMCloc provides excellent relative locations—
outperforming traditional multiple-event location algorithms even when location
constraints are not included. Excellent absolute locations are attained when constraints on one or more aspect of the location problem are available. When phase
Regional Body-wave Attenuation Using a Coda Source Normalization
Method: Application to MEDNET Records of Earthquakes in Italy
W. Walter, Lawrence Livermore National Laboratory, [email protected]; K.
Mayeda, Lawrence Livermore National Laboratory, [email protected]; L.
Malagnini, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy,
[email protected]; L. Scognamiglio, Istituto Nazionale di Geofisica e
Vulcanologia, Rome, Italy, [email protected]
Developing Pn Attenuation Models for Eurasia
X. Yang, Los Alamos National Laboratory, [email protected]; S. Taylor,
Los Alamos National Laboratory, [email protected]; W. Phillips, Los Alamos
National Laboratory, [email protected]
In order to improve the effectiveness of the Magnitude and Distance Amplitude
Correction (MDAC) discrimination method, we are developing 1-Hz Pn attenuation models for Eurasia. We have collected 4500 Pn amplitudes from a few thousand
events and 85 stations in Eurasia. We performed careful quality control to ensure
that each amplitude was measured with an analyst phase pick and the signal-tonoise ratio is greater than 2. A declustering algorithm was used in picking the events
so that selected events have a relatively uniform spatial distribution.
The plot of the Pn amplitudes against source-receiver distance shows a complex decay pattern indicating the effects of the upper-mantle velocity structure
and the Earth’s sphericity on Pn geometric spreading. We are currently conducting
numerical simulations to quantify these effects and to develop a realistic 1-D Pn
spreading representation. We have also adopted varible-gridding schemes for the
attenuation inversion. These schemes include equal-surface-area cells, and cells that
meet minimum-number-of-path-hit criterion.
Regional Calibration of Peak Envelope Arrival Time
W. Phillips, Los Alamos National Laboratory, [email protected]; R. Stead, Los
Alamos National Laboratory, [email protected]
Regional coda analysis relies on an estimate of the peak envelope arrival time to set
an origin for purposes of amplitude measurement. Envelope peaks can be associated with one or more phases (Pn, Pg, Sn, Lg, Rg, L or R), depending primarily
260 Seismological Research Letters Volume 77, Number 2 March/April 2006
on frequency band, distance and event depth (in the case of Rg), but dominant
peak types can also vary with path in a two-dimensional sense. The calibration of
these effects over broad areas will improve the measurement of coda amplitudes by
indicating the best regional coda type for a particular path, and by allowing more
accurate prediction of the peak arrival for that phase type. Furthermore, accurate
peak arrival time estimates will enable consistent peak amplitude measurements in
cases where small events produce limited or no coda. These measurements can be
used for magnitude and yield estimation as well as for event identification studies.
Using data from over 41,000 events and 115 Asia stations, we demonstrate that
peak arrival variations can be imaged tomographically for bands from 30 s to 8 Hz.
Long period results match literature results for Raleigh and Love group velocity
studies, and follow continental basin and ocean-continent boundaries. 1 Hz peak
delays are also associated with basin crossing paths, but this may be a modal rather
than a medium velocity effect. Scattering environments such as volcanic regions
have been shown to produce delays in high frequency peaks (4-8 Hz), but, in this
study, high frequency delays are also associated with short distance paths (under
100 km) that cross shallow edges of sedimentary basins.
Joint Inversion for Three-dimensional Velocity Structure of North Africa and
the Middle East
M. Flanagan, Lawrence Livermore National Laboratory, [email protected]
gov; E. Matzel, Lawrence Livermore National Laboratory, [email protected];
M. Pasyanos, Lawrence Livermore National Laboratory, [email protected];
S. van der Lee, Northwestern University, [email protected]; F.
Marone, UC Berkeley, [email protected]; A. Rodgers, Lawrence
Livermore National Laboratory, [email protected]; B. Romanowicz, UC
Berkeley, [email protected]; C. Schmid, ETH, Zurich, Switzerland,
[email protected]
We report on progress towards a new, comprehensive three-dimensional model of
seismic velocity in a broad region extending from the western Mediterranean Sea
to the Hindu Kush and encompassing northern Africa, the Arabian peninsula, and
the Middle East. Our model will be an integration of regional waveform constraints,
surface wave group velocity measurements, teleseismic P and S arrival times, and
receiver functions. These measurements are made from a combination of MIDSEA,
PASSCAL, GeoScope, Geofon, GSN, MedNet, and local deployments throughout
the region. The data offer complementary sensitivity to crust and mantle structures
and are jointly inverted to image the complexity of this tectonically diverse area.
We are in the process of assembling each of these data sets and testing the joint
inversion for subsets of the data. In this phase of the project we focus on computing
group velocity measurements and fitting of regional fundamental and higher mode
Rayleigh waveforms using the PWI (partitioned waveform inversion) technique.
To date we have measured Love and Rayleigh wave group velocities for hundreds of
new paths recorded at the MIDSEA stations and combined them with thousands
of existing paths transecting the region. The new paths have better defined the distribution of anomalies particularly with respect to the boundaries of sedimentary
basins at short periods. In addition we have inverted over 1000 waveforms traversing the Arabian peninsula, Iran, and Afghanistan which extends our original coverage significantly to the east.
We also demonstrate the proposed new data-inversion methodology and discuss results from combining these new measurements in a preliminary joint inversion. The combined data coverage will ensure that our three-dimensional model
comprises the crust, the upper mantle, including the transition zone, and the top of
the lower mantle, with spatially varying, but useful resolution that will allow better calibration of both travel times and waveforms for monitoring throughout the
Middle East and North Africa.
Improving Ms Estimates by Calibrating Variable Period Magnitude Scales at
Regional Distances
M. Pasyanos, LLNL, [email protected]; H. Hooper, Weston Geophysical,
[email protected]; J. Bonner, Weston Geophysical, [email protected]
westongeophysical.com.
The mb:Ms discriminant has proven very successful at discriminating between
earthquakes and nuclear explosions for larger events that can be recorded teleseismically. This discriminant takes advantage of the fact that earthquakes generate
more long period surface wave energy than comparable size explosions. For smaller
events, however, the discriminant has proved more problematic since the signal is
too small to be recorded teleseismically and observable regional surface waves generally occur out of the period band of traditional Ms measurements (18—22 sec).
We seek to improve the mb:Ms discriminant in two ways. First, we incorporate
a variable-period surface wave magnitude technique (Russell, 2005; Bonner et al.,
2005) which is valid for all distance ranges. Secondly, we investigate how a thorough understanding of earth structure can improve the discriminant by isolating
the signal from contaminating noise sources. We then compare the variable-period
results to conventional methods such as the Marshall and Basham (1972) and
Rezapour and Pearce (1998) for variances and magnitude bias. Preliminary results
for Eurasia indicate that variable-period measurements provide a better and more
consistent estimate of the source size. Combined with robust mb measurements,
this should provide a more reliable discriminant for smaller events.
Modeling of the May 21, 1997 Jabalpur Earthquake in Central India: Regional
Path Calibration
C. Saikia, URS Corporation, [email protected]
We modeled seismic phases observed in the regional and far-regional seismograms
recorded at stations in and around the Indian subcontinent from the May 21, 1997
Jabalpur earthquake in central India. By modeling teleseismic P-wave depth phases
(pP, sP), we established its source parameters (dip=65, rake=68, and strike=70,
h=35 km) and source complexity, which consisted of two sources with a total seismic moment of 5.88x1024 dyne-cm and a source 1 to source 2-moment ratio of 1
to 4. The first source had a sharp rise-time of 0.1s and healing time of 0.2s, and is
separated from the second source by only 0.6s. This second source had a total duration of 1s with equal rise and healing times. Source parameters were independently
obtained by modeling regional seismograms of stations BHPL (Bhopal), BLSP
(Bilaspur) and HYB (Hyderabad). Regional waveform modeling was performed
using the multiple-source complexity established in the teleseismic modeling and
station specific wave propagation path models. The Jabalpur event was relocated
using a fixed depth consistent with teleseismic modeling and travel times of teleseismic P, pP and sP phases and travel times of regional P and S phases. The IASPEI
model was used for the location with its crust replaced by the regionalized crustal
model. The relocation parameters were: origin time: 22h51m30.88s±0.75s, latitude 23.063N, longitude 80.073E, h=35 km. Using these revised source parameters and complexity; we analyzed the composition of regional phases to understand
how they were excited, especially how up-going and down-going seismic waves
evolved and interfered as a function of distance. We further modeled amplitude
and travel times of different phases, such as the Pnl, S, SmS, Sm(up)S and surface
waves observed at far regional stations. This required refining path specific structure in the crust and across the crust-mantle transition zone. This study established
far-distance wave propagation models for paths towards CHTO (Chiang Mai,
Thailand), LSA (Lhasa, China), and AAK (Ala-Archa, Kyrgyzstan). We also calibrated a wave propagation model for a path from northwest India to station NIL
(Nilore, Pakistan) using seismograms recorded from an earthquake near Pokhran,
the nuclear test site in India.
A New Approach for Wave Propagation Simulation in Irregular Multilayered
Earth Model with Boundary Element Method
Z. Ge, Peking University, [email protected]; X. Chen, Peking University,
[email protected]
A new approach for wave propagation simulation in irregular multilayered earth
model with boundary element method Zengxi GE and Xiaofei Chen Peking
University, Beijing 100871, People’s Republic of China Local geological conditions
may induce significant amplification of ground motion during earthquakes. The
quantitative assessment of such effects can be made with numerical modeling. The
boundary element methods have gained increasing popularity in seismic wave propagation simulation. Significant advantages over domain approaches are reduction of
dimensionality, the relatively easy fulfillment of radiation conditions at infinity and
the traction free condition at free surfaces. However, the boundary element method
involves in solving of large linear equations. In multilayered media, the dimension
of the equations becomes huge, which limits the application of boundary element
method. In this study we adopted the similar process of the global generalized R/T
matrices introduced by Chen in the boundary element method. Instead of assembling the coefficients matrices in one system, we use a recursive scheme in computing the relationship matrices between the displacements and tractions along the
elements in the interfaces. Using this approach, the memory requirements are only
limited in the number of elements in the boundary of one domain, which can result
in great saving of memory and computing time. The validity of this approach is verified by comparing the numerical results with direct boundary element approaches
and other numerical methods. This method offers an effective mean to compute the
synthetic seismograms in the case of irregular multi-layered media and is applied in
regional seismic wave propagation synthesis. The authors acknowledges the support
of the National Natural Science Foundation of China under grant No. 40444002.
Seismological Research Letters Volume 77, Number 2 March/April 2006 261
Source Phenomenology Experiment in Arizona: Amplitude Ratio Analysis of
Regional Arrivals for Production Mining and Single-fire Sources
C. Zeiler, UTEP, [email protected]; A. Velasco, UTEP, [email protected]
edu; S. Hernandez, UTEP, [email protected]
Explosions recorded at regional distances from production mining have easily been
discriminated against earthquakes by the proximity of the source location to a
mine, their shallow nature, and the accompanying regional surface waves. However,
the discrimination of a production-mining explosion from a shallow single-source
explosion still has not been fully treated. An experiment conducted in Arizona in
2003 was designed to compare these two sources. A coal mine (soft rock) in the
north and a copper mine (hard rock) in the south provided two distinct locations
to record a unique data set of production-mining and single-fired explosions. The
explosions related to production mining represented two distinct mining techniques for moving the two distinct rock types. The single-fired explosions were also
performed as two distinct techniques by containing the explosion or by placing the
explosions near a free-face. The initial comparison of the two types of explosions
showed the single-fired explosions containing higher frequency energy, while the
production explosions excited lower-frequency surface waves. To aid our initial
observations, we calculated the amplitude ratios for P, S, Rg and Lg and plotted it
against magnitude. The P to Rg, P to Lg, P to S and Lg to Rg ratios indicated that
the configuration of the single-fired source was not as important as identifying the
geologic medium in which the explosion occurred. The plot also showed that for
these smaller magnitude events there was no need to discriminate against
Source Features and Scaling of Calibration Explosions in Middle East/
Easterm Mediterranean for CTBT Monitoring
R. Hofstetter, Geophysical Inst. Israel, [email protected]; Y.
Gitterman, Geophysical Inst. Israel, [email protected]; V. Pinsky,
Geophysical Inst. Israel, [email protected]
Large-scale calibration underwater and in-land explosions of different design were
conducted in the last years in Israel, Cyprus and Jordan, under close collaboration
of the national seismological institutions. The experiments were realized in the context of the CTBT monitoring in the Middle East region, and aimed to improve
the velocity models for calculating travel times to regional and IMS stations; to
extend Ground Truth (GT0) database; to observe and quantify dynamic features
of the seismic sources and elaborate scaling laws. Collected data of simultaneous
GT0 explosions were used for analysis of magnitude dependence on charge weight.
The relation for underwater shots was validated, and the equation for land shots
was modified with the scaling factor similar to the estimation of magnitude upper
limit for sources in hard rocks. Obtained network and array observations were used
for joint location analysis of the explosions, based on up-to-date algorithms and
software developed at GII and Ground Truth parameters. In all experiments 3-C
accelerometers with GPS time were deployed in explosion vicinity providing highquality records of seismic radiation for characterization of specific source phenomenology. The experiments contributed to study of explosion source phenomenology
in specific geological settings and understanding main features of seismic energy
generation from point-like sources.
Infrasound Waveguide
E. Herrin, Southern Methodist University, [email protected]; T. Kim, Southern
Methodist University, [email protected]; B. Stump, Southern Methodist University,
[email protected]
On May 30, 2005 eight strongly dispersed infrasound signals were recorded at
one seismo-acoustic array in the Republic of Korea over a period of about 11 minutes. Power spectrum analysis and tools of seismology, such as a forward modeling
technique and the phase-matched filtering (Herrin & Goforth, 1977), were used
to determine the nature of the dispersion. The most likely explanation for these
dispersed infrasound signals are that the dispersion is due to propagation down a
low-velocity waveguide. This can be characterized as an ephemeral “SOFAR” layer
in the atmosphere. To our knowledge, this is the first observation and systematic
analysis of dispersed infrasound signals.
Near Fault Ground Motions from Large Earthquakes (Joint
with EERI)
Poster Session
Effects of Directivity and Supershear Rupture Speed on Near-fault Ground
Motion
A. Bykovtsev, Converse Consultants, [email protected];
H. Quazi, Converse Consultants, [email protected]
Investigation and prediction of near-fault ground motion are one of the most important tasks of the site specific geotechnical investigation for hospitals, schools and
essential buildings. There is no doubt that the peak amplitudes, duration and frequency content of the near-field motion, which are caused by the features of the
earthquake source rupture process, may strongly influence the damage distribution
in the near-faults zones. The recent large earthquakes including the 1999 Chi-Chi,
Taiwan, 1999 Kocaeli, Turkey, 1999 Düzce, Turkey, and 2002 Denali Fault earthquakes reveal the importance of low-frequency (less than 0.7-0.5 Hz) radiation that is
now considered as one of the characteristic properties of the near-field strong ground
motion. It was also found that ground motion for these earthquakes are smaller than
predicted based on empirical ground-motion equations. One of the most important
achievements in understanding the nature of earthquake source is also the evidence
of complex non-planar form of the main fault. Therefore, when analyzing the seismic
radiation from large earthquake source within the broad frequency range, it is necessary to consider both the discrete character of the source properties (heterogeneous
rupture processes and dislocation distribution along the fault), controlling the highfrequency radiation, and the geometrical characteristic (configuration and dimensions of the main fault and subfaults) of the source and effects of directivity and
supershear rupture speed on near-fault ground motion. For rapidly running rupture
the straight path will be unstable. As a rule in rock, we can observe process of bifurcation rupture for mode-I (tensile opening) with generation combine mode condition
on each new parts bifurcated segments. For mode-II (shear sliding) kinking processes of changing rupture trajectory will be presented, which also contained combine mode condition for different segments. For mode III (antiplane shear sliding)
process creating of echelon system of small opening segments oriented at 45o from
the main rupture plain can be observed too. Conditions for determination bifurcation and kinking trajectory for rapidly running rupture were determined based on
exact analytical solutions obtained by Bykovtsev, A.S. (1979,1986). Radiation patterns peculiarities in maximum probable ground motion for different diapasons of
rupture velocities including subsonic, transonic and supersonic rupture propagation
should be taken in consideration for proper seismic hazard analysis in near zones of
active faults. The effects of decreasing ground motion in the near-faults zones for
kinking rupture trajectory will be demonstrated.
The Relationship of Near-fault Velocity Pulse to the Source Parameters
Q. Liu, Institute of Engineering Mechanics, China Earthquake Administration,
[email protected]; Y. Yuan, Institute of Engineering Mechanics, China
Earthquake Administration, [email protected]; X. Jin, Institute of Engineering
Mechanics, China Earthquake Administration, [email protected];
The large velocity pulse is an important characteristic of near-fault ground motions.
Some statistical relationships on the pulse period to the moment magnitude have
been made without considering the variety of rupture velocity, the fault depth, and
the fault distance, etc. Since near fault ground motions are significantly influenced
by the rupture process and source parameters, the relationship on the amplitude and
the period of forward-directivity velocity pulse to the source parameters in half space
are analyzed by finite difference method and kinematic source model in this paper.
The studies show that the rupture velocity, the fault depth, the position of the initial
rupture point and the distribution of asperities are the most important parameters
to the velocity pulse. Generally, the pulse period decreases and the pulse amplitude
increases as the rupture velocity increases for shallow crustal earthquake. In a certain
region beside the fault trace, the pulse period increases as the fault depth increases.
For uniform strike slip fault, rupture initiate from one end and propagate to the other
end of a fault always generate higher pulse amplitude and longer periods than other
cases, while for uniform dip slip fault, rupture initiate from the bottom and propagate to the top of the fault show the same result. For dip slip fault, the pulse spatial
distribution is not symmetric about the fault surface trace. In the same fault distance,
the pulse amplitude on the hanging wall are much higher than that on the foot wall,
and it decrease more slowly on the hanging wall than that on the foot wall.
262 Seismological Research Letters Volume 77, Number 2 March/April 2006
Effects of Directivity on Shaking Scenarios: An Application to the 1980
Irpinia Earthquake, M 6.9, Southern Italy
F. Pacor, Istituto Nazionale di Geofisica e Vulcanologia—Milan—Italy, [email protected]
mi.ingv.it; G. Cultrera, Istituto Nazionale di Geofisica e Vulcanologia—
Rome—Italy, [email protected]; A. Emolo, Università Federico II—Naples—
Italy, [email protected]; F. Gallovic, Charles University—Praha—
Czech Republic, [email protected]; A. Cirella, Istituto Nazionale
di Geofisica e Vulcanologia—Rome—Italy, [email protected]; I. Hunstad, Istituto
Nazionale di Geofisica e Vulcanologia—Rome—Italy, [email protected]; A.
Piatanesi, Istituto Nazionale di Geofisica e Vulcanologia—Rome—Italy, [email protected]; E. Tinti, Istituto Nazionale di Geofisica e Vulcanologia—Rome—
Italy, [email protected]; G. Ameri, Istituto Nazionale di Geofisica e Vulcanologia—
Milan—Italy, [email protected]; G. Franceschina, Istituto Nazionale di
Geofisica e Vulcanologia—Milan—Italy, [email protected]
This work is developed within the framework of the Italian project S3 “Expected
shaking and damage scenarios in strategic and/or priority areas” (Italian
Dipartimento della Protezione Civile in the frame of the 2004-2006 Agreement
with Istituto Nazionale di Geofisica e Vulcanologia). One of the goals is to perform
a sensitivity analysis using various simulation techniques to test the ground motion
variability for different source parameters. We applied deterministic (Compsyn,
Spudich and Xu, 2002; Disp, Okada, 1985; 1992) and hybrid simulation techniques (DSM, Pacor et al., 2005; HIC, Galloviè and Brokešová, 2006) to simulate
an earthquake with complex source characteristic of the 1980 Irpinia earthquake,
M6.9, Southern Italy. The large wave-length characteristics of the adopted source
model were first validated, for the 0s sub-event, comparing the observed and synthetic acceleration envelopes. Then synthetic time series (acceleration, velocity
and displacement) generated with the simulation techniques were compared with
recorded and synthetic data both in time and in frequency domains. The deterministic model fits very well the low frequency content (f<1 Hz) both considering
waveforms and spectra. The DSM method is able to reproduce the observed peak
ground values and spectral content (f >1 Hz) although the simulated waveforms
are more simple than the recorded ones. The HIC model provides broadband seismograms in relatively good agreement with the observed ones. Starting from the
validated model, we fixed the source geometries and varied the kinematic parameters of the rupture scenarios (rupture velocity, nucleation points and asperities).
For each model we generate ground acceleration and velocity at a dense regional
grid of receivers. Peaks ground motions increase as the rupture velocity increases.
The acceleration and velocity distributions around the fault strongly depend on the
position of the nucleation point. On the contrary peak ground displacement are
more sensible to the position of the asperity. Strong peak values are simulated at
directivity sites when the rupture starts near the fault edges. When we compare
the simulation results with the empirical attenuation relationships we observe that
the mean values are similar but the variability obtained from the shaking scenarios
exceeds the empirical standard deviation.
An Efficient Method for Simulating Near-fault Strong Motions at Broadband
Frequencies in Layered Half-spaces
Y. Hisada, Kogekuin University, [email protected]
We developed a hybrid method for simulating broadband strong motions in layered half-spaces. As for the lower frequency range (less than around 1 Hz), we use
the theoretical method by Hisada and Bielak (BSSA, Vol.93, p.1154-1168, 2003),
which can simulate accurate near-fault effects, such as the directivity pulses and the
fling steps from surface faulting, in layered half-spaces. As for the high frequency
range (more than around 1 Hz), we developed a new method for simulating strong
motions in layered half-spaces based on the stochastic source model. In the method,
first, we divide a fault plane into sub-faults, and locate Boore’s point source model
(amplitude spectra; Boore, 1983) on each sub-faults. As for the phase spectra of
the source model, we introduce random and coherent phases at higher and lower
frequencies, respectively. The coherent phases are necessary to reproduce coherent
waves in near sources, such as the directivity pulses and the fling step at lower frequencies. In addition, we use a hybrid radiation pattern, which is homogeneous
and theoretical at higher and lower frequencies, respectively. As for Green’s function, we used the complete Green’s functions in layered half-spaces (Hisada, 1994,
1995), which can generate efficiently strong motions up to very high frequencies.
The simulated waves from all the point sources are superposed to follow the omegasquare rule. We applied the method to observed records, such as the Landers and
Northridge earthquakes, and obtained excellent agreements.
Analysis and “Prediction” of the M=6.2, 1991 and M=7.2, 1992 Cape
Mendocino Earthquakes by Ground Motion Modeling with Empirical Green’s
Functions
L. Hutchings, Lawrence Livermor National Laboratory, [email protected];
D. Kane, UC San Diego, [email protected]; J. O’Boyle, Lawrence Livermore
national Laboratory, [email protected]; L. Scognamiglio, Istituto Nazionale di
Geofisica e Vulcanologia, Rome, Italy, [email protected]; M. Treml, University
of Muenchen, Muenchen, Germany, [email protected]
Two potential Cascadia subduction zone earthquakes occurred in the Mendocino
triple junction area on August 17, 1991 and April 25, 1992, with magnitudes Mw =
6.2 and 7.2, respectively. These have been referred to as the Honeydew and Petrolia
earthquakes, respectively. They have very similar low-angle thrust focal mechanism
solutions and occurred in close proximity in space and time, suggesting that they
may have occurred on the same fault plane. The significance of these earthquakes
to the tectonics of the Mendocino Triple Junction region, the earthquake hazard
to the local population, and the mechanics of their faulting processes is not well
understood. We both test the prediction methodology of Hutchings et al., (2005)
with observed strong motion data and use the best fitting models to identify the
rupture characteristics of these two earthquakes. We generate a suite of 500 rupture
models that span the variability of potential ground motion by spanning the range
of possible rupture parameters. Rupture parameters for each scenario earthquake
are chosen by a Monte Carlo selection using a triangular distribution between
their limits. Rupture parameters include fault geometry and location, hypocenter,
rupture and healing velocities, slip distribution, fault roughness, and asperity location. Rupture models are consistent with the elastodynamic equations of seismology and fracture energy, and they are consistent with a physical understanding of
how earthquakes rupture, laboratory experiments, numerical modeling, and field
observations of earthquake processes. These models are often referred to as quasidynamic models. In several previous validation exercises models that give good fits
to observed accelerograms also have rupture models close to what actually occurred.
This gives rise to the use of the methodology as an inversion tool, which we utilize
and evaluate here.
Do Weak (Strong) Motion Empirical Models Predict Strong (Weak) Ground
Motion? Results from the Kik-net Records in Japan
G. Pousse, Axa-re, [email protected]; F. Cotton, University
Joseph Fourier, [email protected]; F. Scherbaum, University
of Postdam, [email protected]; L. Bonilla, Institut de Radioprotection et
de Surete Nucleaire, [email protected]
The use of ground motion prediction equations to estimate ground shaking is a very
important component in probabilistic seismic hazard assessment (PSHA). However,
when using current published prediction equations in low to moderate seismicity
regions the ground motion is often overpredicted. Equally troublesome is the use
of empirical attenuation equations derived from small magnitude events to predict
the ground motion for large earthquakes. In this study, 3894 borehole records from
the Japanese Kik-net ground motion data (337 events with 4.0(Mw(7.3 and epicentral distance less than 100 km) have been used to derive ground motion empirical
models for different magnitude bin datasets. These records are not affected by nonlinear site response because the downhole sensors are located at 100 m depth inside
rock formations. Our data analysis shows that ground motion predictions obtained
from large earthquakes decay slower than those from small events and the magnitude scaling of ground motion decreases with magnitude. We show that empirical
models computed only from large event records overestimate the predictions with
respect to moderate and small earthquakes. This result explains the overestimation
of weak motion records when using strong motion empirical models in Europe.
This overestimation does not imply regional differences of ground motion attenuation. In addition, we illustrate the pitfalls of deriving empirical equations from
recordings of small magnitude events and applying them for predicting ground
motion of larger events. Our results show that the use of a ground motion empirical model outside the magnitude and distance range of the used dataset strongly
depends on the chosen functional form. We finally point out the magnitude scaling
of the ground motion aleatory variability.
Near-fault Broadband Ground Motions from a Megathrust Earthquake: A
Case of the Great 1923 Kanto Earthquake
H. Miyake, Earthquake Research Institute, University of Tokyo, [email protected]; K. Koketsu, Earthquake Research Institute, University of Tokyo,
[email protected]; R. Kobayashi, Earthquake Research Institute,
University of Tokyo, [email protected]; Y. Tanaka, Earthquake Research
Institute, University of Tokyo, [email protected]; Y. Ikegami,
Seismological Research Letters Volume 77, Number 2 March/April 2006 263
Earthquake Research Institute, University of Tokyo & CRC Solutions Corp., ike-
[email protected]
The Tokyo metropolitan area is under constant threat of strong ground motions
from future megathrust earthquakes along the subducting Philippine-sea slab. The
great 1923 Kanto earthquake (Mw 7.9) is one of the most disastrous earthquakes
in the last century killing about 105,000 people. In addition to the metropolitan
area is located on the sedimentary basin whose deepest point reaches 4 km, distance
between the area and underlying slab is found to be only a few decade kilometers. It
suggest that validation of near-fault ground motions as well as long-period ground
motions from megathrust earthquakes within the basin is highly important for hazard assessment in the Tokyo metropolitan area. We here upgrade the broadband
ground motion simulation of the 1923 event using a physics-based source model
along the new geometry of the Philippine sea slab, and geophysical-based 3D velocity-structure model. We validate the source and 3D velocity-structure models by
comparison of the synthetic and observed waveforms at the University of Tokyo
and detailed distributions of seismic intensities. We first performed low-frequency
ground-motion simulation using these models and the finite element method with
a voxel mesh. The western basin edge complicated the wave propagation and the
excited long-period motions within the basin were found. Since high-frequency
components are essential for seismic intensity measurement, we then simulate highfrequency ground motions using the stochastic Green’s functions and the pseudodynamic source model based on the slip distribution derived. We confirmed the
simulated ground motions are sensitive to the distribution of asperities of the
source model along the shallower plate geometry, where the eastern major asperity
is located closer toward downtown Tokyo than in the previous models.
Inclusion of Stress Distribution on the Fault in Stochastic Finite Fault
Modeling: Application to the M6, 2004 Parkfield Earthquake
K. Assatourians, Carleton University, [email protected]; G.
Atkinson, Carleton University, [email protected]
The stochastic finite-fault model predicts earthquake ground motions from the rupture of an extended fault source. We apply a modification to the stochastic finitefault model of Motazedian and Atkinson (2005 BSSA) to allow for variability of
stress drop on the rupture surface. This is accomplished by modifying the subsource
spectra, under two constraints: (i) we ensure proportionality of the high-frequency
spectral amplitude to stress drop raised to the power 2/3 (this follows from the
Brune source model); and (ii) we ensure independence of the low-frequency spectrum from stress drop. The model is applied to the M6, 2004 Parkfield earthquake.
The effect of non-linear site response (Choi and Stewart, 2005) is considered in the
modeling of observed response spectra. The overall model of this event provides an
average stress drop in the range of 40-60 bars and pulsing area (maximum percentage of the fault slipping at any moment) of >40 percent. We find that model errors
(residuals), measured by the ratio of the observed to the predicted ground motion
parameters, can be reduced by refining the distribution of stress drop along the fault
rupture. Thus the stochastic model has the potential to discern the variability of
source effects along the fault. However, we also conclude that the site effects are
more important, producing a larger influence on model residuals than the effect of
stress distribution at many stations.
Event Location and Source Complexity as Derived from Strong Motion Data
L. Porter, Geocarte International, [email protected]; D. Leeds, David J.
Leeds Associates, [email protected]
Strong motion records can be used to supplement near-regional data in the determination of epicentral and hypocentral locations. In addition, these data can be
applied to an examination of the complexity of the earthquake source itself. For
well-recorded events, there are frequently enough close-in records available to calculate the positions of energy release in greater detail by using the results from the
near-regional data as a starting point. Since most strong motion records are triaxial
the horizontal components are helpful in picking the arrivals of the S-waves and
later phases. Furthermore, the lower gain of such instruments allows the largeamplitude close-in motions to be recorded on scale. This study begins with an initial data set of strong motion records from the 1994 Northridge, California, earthquake as recorded by the eight free field stations in the Van Norman Complex. The
stations in this group are irregularly spaced and lie within a six km square that is
oriented north-south and east-west. The center of this square is about 12 km north
by north-east from the epicenter. For this station cluster the epicentral distances
range from 9 to 15 km and the azimuths (epicenter to station) lie in an angular sector running from 17 to 34 deg. Because the stations are located less than the source
depth (19 km) away from the epicenter, the dip angles from them to the hypocenter
are all greater than 45 deg downwards and lie in the range from -51 to -64 deg.
Recent results have shown that the first arrivals at stations within the Van Norman
Complex all were strongly refracted and thus traveling vertically upwards as they
reached the surface. A velocity profile across this unsynchronized network from
north to south for the tS-tP times gives a value that ranges from 7.7 to 5.2 km/s
with respect to the epicenter. The P-wave arrival (tP) is taken as the start of the
record and that for the S-wave (tS) is picked as the average for the first break of the
longer period waves in the two horizontal records at each station. The procedure is
further refined by rotating the horizontal components to the radial and transverse
directions with respect to the epicenter. The data set has been enlarged to include
stations within a 10 km radius of the epicenter. Of the 61 stations that lie in this
circle, about 30 have records appropriate for this study. This larger group is critical
because it gives more general coverage around the epicenter and can possibly help
resolve the relation between the individual pulses observed during the event and the
permanent horizontal and vertical displacements measured afterwards.
Thermal Pressurization Explains Enhanced Long-period Motion in the
Chi-chi Earthquake
J. Andrews, U.S. Geological Survey, [email protected]
Ground motion recorded in the 1999 m 7.6 Chi-chi, Taiwan, earthquake provides
evidence on the process of thermal pressurization. Spectral response velocity near
the southern portion of the rupture was roughly flat at periods from 1 s to 10 s,
while spectral velocity near the northern portion was about the same at 1 s, but
increased with period to be several times larger than the southern response value at
10 s. The fault is in different lithologic units in the north and south, being within
low-permeability shale in the north. This spatial correlation strongly suggests that
properties of the shale determined the enhanced long-period motion. Shale is both
less permeable and less subject to dilatant damage than other rocks. Thermal pressurization of pore fluid due to frictional heating during fault slip reduces effective
pressure and so reduces shear stress resisting slip. For given heat input, fluid pressure
rise is inversely proportional to the thickness of the pressurized zone. Pressurized
thickness will be larger than the slip zone thickness, due both to fluid diffusion and
to dilatant damage produced by the stress wave at the rupture front. Shear stress will
decay by 1/e at a critical slip value (Dc) about 4 times the pressurized thickness. Slip
zone thickness observed in core samples is 1-2 cm. Laboratory measurements of
permeability in the Chinshui shale imply that fluid pressure will diffuse only 2.5 cm
in 10 s. Therefore, critical slip displacement is expected to be roughly Dc = 0.1 m,
if there is no dilatant damage. Dynamic simulations of the Chi-chi earthquake have
been performed. Average initial stress is constrained by the geometry of the accretionary prism. Self-similar spatial fluctuations in initial stress over the entire fault
produce ground motions that match the southern spectra. Thermal pressurization
at shallow depths in the north produces complete stress drop there and matches
long period amplitudes. In order not to amplify short-period amplitudes, it must
be assumed that the pressurized fluid is promptly spread through a damage zone
1.25 m thick, so that Dc = 5 m, a large fraction of the final slip. Thermal pressurization is a mechanism to increase the magnitude of an event without increasing
short-period motion.
Scaling of High-frequency Ground Motions for the Sumatra, Chi-Chi, and
Kocaeli Earthquake Sequences
A. Frankel, U.S. Geological Survey, [email protected]
Regional and teleseismic P and S-wave spectra from three earthquake sequences
were analyzed to determine the scaling of high-frequency (1-6 Hz) ground motions
for earthquakes with moment magnitudes 5.8 to 9.0. For each of the sequences
studied, I find that the high-frequency Fourier spectral amplitude of ground
motions (above the corner frequency) generally scales as the square root of rupture
area, as determined from aftershock area, empirical relations, or waveform modeling. Therefore, the energy spectral density at high frequencies is proportional to
rupture area. The falloffs of regional and teleseismic P-wave spectra from about
0.5 to 3 Hz are remarkably similar for the Sumatra M9.0 main shock, the subsequent M8.7 earthquake, and their magnitude 6.5 aftershocks. For one station, this
similarity in high-frequency spectral shapes (P and S-waves) is observable up to 6
Hz for M6.5-8.7. Comparable results were found for the Chi-Chi, Taiwan main
shock (M7.6) and its M6 aftershocks, as well as for the Kocaeli, Turkey, earthquake
(M7.5), the adjacent Duzce earthquake (M7.1), and a magnitude 5.8 aftershock.
These observations support a model with constant stress drop with seismic moment
( Joyner, 1984), where the number of sub-events of a given radius is proportional to
overall rupture area (Boatwright, 1982). Thus, there does not appear to be a difference in the average high-frequency excitation per unit rupture area for large earthquakes (M ≥ 7.5) relative to moderate earthquakes (M6). These observations also
indicate that if fault lubrication or supershear rupture velocity occurs during these
large earthquakes, these processes do not have a significant effect on the overall level
of high-frequency energy from the rupture. Using a model of finite faulting with
constant stress drop scaling, I show that saturation of near-source, 5 Hz response
spectral amplitude with increasing magnitude above M6.5 is expected for crustal
earthquakes, since close-in sites only “see” the radiation from nearby portions of the
264 Seismological Research Letters Volume 77, Number 2 March/April 2006
fault. Near-source response spectral values at lower frequencies (≥1 Hz) increase
with increasing magnitude above M6.5, because of the increase of rise time of slip
on the fault.
Ground-motion Scaling in Western Anatolia Region (Turkey)
A. Akinci, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, [email protected]
ingv.it; N. Akyol, Dokuz Eylul University,Izmir, Turkey, [email protected]
edu,tr; S. D’Amico, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy,
[email protected]; L. Malagnini, Istituto Nazionale di Geofisica e Vulcanologia,
Rome, Italy, [email protected]; A. Mercuri, Istituto Nazionale di Geofisica e
Vulcanologia, Rome, Italy, [email protected]
The aim of this work is to provide a complete description of the characteristic of
the ground-motion in the Western Anatolia region (Turkey). In order to do so, we
used about 11.000 waveforms collected from November 2002 to October 2003 at
43 short period station and five broadband station site. The magnitude of events
was ranged from Mw=2.0 to Mw=5.7 and travel path was ranged from a few kilometers to about 200 km. Data provided from a framework of a cooperative project
“Integrated Seismological Studies of Crust Upper Mantle Structure and Anisotropy
in Western Anatolia” (NSF-INT-0217493 and TUBITAK- YDABAG/ 102Y015)
between the Saint Louis University (USA) and Dokuz Eylul University in Izmir
(Turkey). We employed a general form for a predictive relationship including
the source excitation term, an attenuation operator and an operator to account
for the site effect and used an approach described by Malagnini et al. (2000) in
details and that is applied to various regions in the world. Following Boore’s (1996)
implementation of the stochastic ground motion model we predicted the absolute level of ground shaking and compared them with a few strong-motion data
in the region. We also computed the absolute moment rate spectra and the radiated energy applying the method developed by Mayeda et al. (1996, 2003) using
the data registered only by broadband stations. The functional form of the crustal
attenuation term depend principally on the attenuation parameter Q(f ) and on the
geometrical spreading g(r). The regional propagation was modeled in the 0.4 to 10
Hz frequency band using a quality factor Q(f )=130(f/fref )0.62,where fref=1Hz,
to describe the anelastic crustal attenuation in the region and a geometrical spreading function g(r)=r-1.0 for 1<r<20 km, g(r)=r-0.8 for 20<r<40 km, g(r)=r-0.7 for
40<r<100 km and g(r)=r-0.5 for r>100 km . Excitation terms are modeled by using
a Brune spectral model with a stress parameter Δσ = 650 bar and k=0.035 sec. For
magnitude Mw=6.0, the PGA values obtained from the proposed (evaluated) relationship are about 0.1g, 0.02g and 0.01g respectively for 20, 70 and 100 km.
Use of mb vs. Mw in the Search for High-stress Earthquakes
J. Dewey, U.S. Geological Survey, [email protected]; D. Boore, U. S. Geological
Survey, [email protected]
We use comparisons of earthquakes’ teleseismic short-period P-wave magnitudes
(mb) versus their moment magnitude (Mw) to search for earthquakes with abnormally high stress parameters. Our ultimate goal is to estimate the frequency-ofoccurrence of high-stress outliers in the earthquake population. The short-period
magnitude mb is in part a measure of the strength of pulses of high short-period
(about 1 s) energy within the earthquake source-time function. For a suite of moderate and large earthquakes of a given Mw, earthquakes with high-stress asperities
should radiate pulses with higher 1 s energy than earthquakes with low-stress asperities. Influence of asperity-stress on mb may, however, be obscured by the effects
on P-wave amplitudes of scattering, variations in upper-mantle attenuation, source
directivity, and source orientation. A global comparison of mb and Mw from over
13,000 shallow-focus earthquakes of Mw 5 and larger shows over 95% of mb values
within a range of + /- 0.7 magnitude units of median mb for a given Mw, with
larger deviations from median mb being more numerous for anomalously low mb
than anomalously high mb. In the absence of other influences on P-wave amplitudes, and assuming the validity of widely used models relating source-spectrum
to seismic-moment and stress parameter, this could imply that stress-parameters
associated with the vast majority of higher-stress asperities are within an order of
magnitude of the stress parameters associated with asperities in typical earthquakes.
A sample of 103 earthquakes in California and Nevada shows variations in mb for
a given Mw about half those of the global sample. We will use published, independently determined, stress-parameters to evaluate the effectiveness of mb versus Mw
as an indicator of earthquake stress parameter. We will also attempt to determine if
there is a systematic correlation between mb and strong ground motion parameters
for moderate and large earthquakes of similar moment that have been recorded by
strong-motion instruments.
Damage Potential of Near-source Ground Motion Records
P. Bazzurro, AIR Worldwide, [email protected]; N. Luco, AIR
Worldwide (currently at USGS), [email protected];
The assessment of structural response induced by earthquakes for both design and
evaluation is often made using ground motion intensity measures, IMs, as predictors. The most widely used IM is the spectral acceleration, Sa, at the structure’s fundamental period of vibration, T1. Unless the response of the structure is first-mode
dominated and not significantly beyond the onset of structural damage, the response
variability for records with the same value of Sa(T1) is still considerable. We investigate here whether we can identify “non-stationary” features of near-source, forward-directivity accelerograms that, in addition to Sa, improve structural response
estimation. To simplify the search for useful signal characteristics beyond spectral
values, the records are compatibilized to a common spectrum prior to use. We show
that, for the considered structures, velocity pulse characteristics and the duration
of the record do not appreciably improve the accuracy of the response estimates
beyond that achieved by using linear elastic spectral values alone. Furthermore,
this study demonstrates that accelerograms cannot be labeled as “aggressive” or
“benign” without considering a particular structural vibration period and specific
yield strength, Fy. Hence, record characteristics that do not account for T1 and Fy
are not likely to be “good” response predictors. For this reason, inelastic spectral
displacement and the first significant elastic peak displacement of a single-degreeof-freedom (SDOF) oscillator of period T1 are far more effective predictors of
structural response.
Near-fault Ground Motion Destructiveness: The Inadequacy of Some
Popular Intensity Measures
P. Georgarakos, National Technical University of Athens, Greece, [email protected]
yahoo.gr; R. Kourkoulis, National Technical University of Athens, Greece,
[email protected]; G. Gazetas, National Technical University of Athens,
Greece, [email protected]
This study evaluates the validity of different ground motion intensity parameters as
estimators of earthquake destructiveness. Several ground motion parameters have
been proposed over the years, such as peak ground acceleration and velocity, spectral intensity parameters, as well as more elaborate ones incorporating amplitude,
frequency content, and number of cycles or duration of the ground motion. This
study investigates the predictive capability of: (i) peak ground acceleration, A , (ii)
peak ground velocity, V, (iii) maximum velocity step, ∆V, (iv) Arias Intensity, IA, and
(v) average spectral acceleration between T = 0.2 and 0.6 sec, SA,av . We consider as
a simplified damage intensity measure the maximum displacement of a rigid block
supported through Coulomb friction on: (a) horizontal base—symmetric sliding,
(b) sloping base—non-symmetric sliding. We investigate the correlation between
this simplified damage intensity measure, with the above mentioned earthquake
intensity parameters. Symmetric sliding is a representative damage indicator for
elastoplastic systems (e.g. buildings and bridges). Non-symmetric sliding is representative of non-symmetric elastoplastic systems, such as retaining walls, slopes, and
embankments. As excitation we use: (a) the parametric Mavroeidis-Papageorgiou
(truncated Gabor) wavelet—using a variety of its parameters that cover a wide range
of possible near-fault ground motions, (b) 70 near-field accelerogramms recorded
near the fault during well-known major earthquakes, and which bear the effects of
forward-rupture directivity and fling step. The following parameters are examined:
safety factor µg/A for the symmetric, and ay/A for the non-symmetric case (where
ay ≈ tan(f—b), the yield coefficient); dominant frequency of the ground motion (in
parametric wavelet excitation); the form and the details of ground excitation (number of cycles and details of wavelet incorporating “directivity” and “fling” effects);
slope orientation with respect to ground motion direction (non-symmetric case).
The analysis does not reveal a clear correlation between “damage” (maximum sliding displacements) and the examined earthquake intensity measures. Factors that
have a control of sliding and are not included in popular intensity measures, include
the detailed sequence and relative size of long-duration pulses. Slope orientation
also proves significant. All this renders statistical results based on existing earthquake intensity measures unreliable.
Simulated Nonlinear Response of High-rise Buildings for the 2003
Tokachi-oki Earthquake Mw8.3
J. Yang, California Institute of Technology, [email protected]; T. Heaton,
California Institute of Technology, [email protected]; J. Hall, California
Institute of Technology, [email protected]
This research is to investigate how high-rise buildings might perform in ground
motions recorded in the 2003 Tokachi-oki earthquake Mw8.3 which is the largest
well recorded subduction earthquake and provides many near field ground motion
records. We simulate the response of 6- and 20-story steel moment-frame buildings
designed according to both the U.S. 1994 Uniform Building Code and also the
Seismological Research Letters Volume 77, Number 2 March/April 2006 265
Japanese code for 276 recorded ground motions. For each code, we consider buildings with both perfect welds and also with brittle welds similar to those observed
in the 1994 Northridge earthquake. Japanese code buildings with brittle welds have
base yield forces that are 30% and 20 % larger than U.S. code buildings for 6- and
20-story respectively. Although existing short, strong buildings in Japanese towns
performed well in this earthquake, our simulations indicate that flexible buildings would have been strongly excited by this earthquake. Simulated deformations
are large enough in some basin regions that one could expect irreparable damage
at many locations for both the 6- and 20- story buildings. In a few instances, the
20-story building with brittle welds experienced dangerously large deformations
with significant potential for collapse. In this study, we introduce a new parameter
called the “collapse factor”. It is defined to be the scalar multiplier of the recorded
ground motion that is required to cause collapse of the simulated buildings. From
this parameter, we find that although Japanese buildings are stronger , they are also
stiffer which tends to increase the global forces experienced by Japanese buildings
by more than 20% compared with U.S. Buildings, the net effect is that when considering collapse potential, the Japanese buildings can sustain motions about 6%
larger than the U.S. buildings.
Hazard and Risk
Poster Session
Earthquake Risk Estimates for Residential Construction in the U.S. and
Canada
D. Windeler, Risk Management Solutions, [email protected]; M.
Rahnama, Risk Management Solutions, [email protected]; A.
Baca, Risk Management Solutions, [email protected]; L. Hall, Risk
Management Solutions, [email protected]; G. Molas, Risk Management
Solutions, [email protected]; G. Morrow, Risk Management Solutions,
[email protected]; T. Onur, Risk Management Solutions, [email protected]
com; P. Seneviratna, Risk Management Solutions, [email protected]
com; C. Williams, Risk Management Solutions, [email protected]
This study presents results from a seismic risk model developed for the United States
and Canada. We focus on residential construction, considering both economic and
insured exposure. The loss estimation system combines seismic source modeling
from the USGS 2002 and GSC 2005 projects with other studies. Building damage
is estimated via spectral response-based vulnerability functions. This model incorporates variations in site conditions, construction design levels, building inventory,
and insured value.
The risk is presented via relative loss estimates and loss exceedance curves for
residential structures. A gridded map of annualized loss costs is presented for the
two countries. These values are normalized to exposure ($ loss / $1000 value) and,
much like a hazard map, reflect the relative risk at any given point. The highest values, exceeding $5.00 /$K, are found along the length of the San Andreas fault system
as well as the south flank of Kilauea on the Big Island of Hawaii. Regional risk in the
Central and Eastern U.S. is dominated by the New Madrid seismic zone, with loss
costs exceeding $1.50 /$K in the Bootheel area, but repeated moderate events within
the Charlevoix seismic zone imply locally similar values near La Malbaie, Quebec.
Exceedance curves have been created for key cities across the continent that
historically have experienced significant earthquake damage (e.g. San Francisco,
Vancouver, Memphis, Charleston). The relative risk is considered in terms of point
values normalized by exposure and the total annualized losses by metropolitan area.
Loss estimates for these cities have been deaggregated to illustrate the contribution
by magnitude and distance to the risk at each location.
Comparing Site-specific Probabilistic Seismic Hazard in Southern California
with the Usgs National Hazard Maps
F. Terra, URS Corporation, [email protected]; I. Wong, URS
Corporation, [email protected]; J. Zachariasen, URS Corporation,
[email protected]; M. Dober, URS Corporation, [email protected]
urscorp.com; J. Hill, URS Corporation, [email protected]; B. Robb,
Metropolitan Water District of Southern California, [email protected]
We have performed comprehensive site-specific deterministic and probabilistic seismic hazard analyses for 17 sites located throughout southern California including
15 facility sites for the Metropolitan Water District of Southern California. Our
seismic source model is based largely on the southern California model developed
by the California Geological Survey and the USGS (CGS/USGS; Cao et al., 2003)
and used in the 2002 USGS National Hazard Maps for the state. Three important
modifications were made; 1) incorporation of more segment rupture variability
(multi-segment and nonsegmented behavior) in our model as compared to the
CGS/USGS model, 2) weighting the rupture models to reflect the constraints of
our interpretation of the paleoseismic data, 3) addition of offshore faults such as the
San Clemente and San Diego Trough fault zones.
Our model emphasizes modifications to the characterizations of the three
primary faults in southern California: the southern San Andreas, San Jacinto, and
Elsinore fault zones. In the case of the southern San Andreas fault, our rupture
model differs from models developed in previous studies (e.g., WGCEP, 1988;
1995; Cao et al., 2003) in that it includes more rupture scenarios and more evenly
distributed weighting. Our model allows for widely variant rupture scenarios, primarily supported by the paleoseismic analyses, which suggest such variance is as
well supported by paleoseismic data as repetitive “characteristic” ruptures on the
northern and southern sections of the fault zone.
For the San Jacinto and Elsinore fault zones we use short rupture scenarios
(85%) using predetermined segments (70%) in addition to some undefined floating segments. We also allow for longer ruptures, floating two and three segment
ruptures, but do not favor them (15%).
We compare our values to the USGS hazard map values assuming both
uniform firm rock site conditions and the actual site conditions at the sites. Our
results for firm rock site conditions are generally higher than those for the USGS.
On average, our estimates for the actual site conditions compared to the USGS
firm rock at a return period of 2500 years ranges from 11% lower (hard rock) to
44% higher. These differences not only reflect differences due to site conditions
but also our higher computed hazard due to the incorporation of more varied fault
behavior in our seismic source model. State-of-the-practice attenuation relationships were used in the hazard analyses (e.g., Abrahamson and Silva, 1997) although
we intend to revise our estimates with the recently released PEER Next Generation
of Attenuation Project relationships.
New Seismic Hazard Assessment for Guam and the Northern Mariana
Islands
C. Mueller, U. S. Geological Survey, [email protected]; K. Haller, U. S.
Geological Survey, [email protected]; A. Frankel, U. S. Geological Survey, [email protected]; M. Petersen, U. S. Geological Survey, [email protected]
We present probabilistic, time-independent seismic hazard estimates for Guam
and the Northern Mariana Islands. These islands lie along the Mariana volcanic
arc—trench system, where the Pacific plate subducts northwestward beneath the
Philippine Sea plate. Destructive earthquakes with effects of MMI VIII or greater
have occurred at least eight times during the past two centuries in the region.
Earthquakes of M7.5 in 1902 and M7.4 in 1990 are the largest known shallow
events. A M7.8 earthquake on 8 August 1993, located 60 km southeast of central Guam at a depth of about 60 km, is the largest ever recorded in the region. It
caused widespread damage on Guam (MMI IX), especially to longer-period structures. This earthquake may have occurred on the Mariana megathrust, but data and
modeling results are equivocal. No great earthquake has ever been associated with
the weakly coupled Mariana megathrust. To model the hazard we use 1) gridded
and smoothed historical seismicity with M ( 4.7 since 1964 in five depth ranges,
2) faulting on the main megathrust interface with rates estimated from seismicity rather than geologic data (Mmax=8 based on the historic record), and 3) two
crustal faults on Guam that we judge to be active but with very low slip rates based
on geologic evidence. In the absence of region-specific attenuation relations we use
published relations derived from western North America and worldwide datasets
(for a NEHRP B/C boundary site condition). Preliminary pga values with 2%
probability of exceedance in 50 years are about 0.7 g for Guam and 0.5-0.6 g for
the southernmost (populated) Northern Mariana Islands. The hazard estimates at
Guam are dominated by gridded seismicity; due to their assumed low slip rates the
two crustal faults are not significant contributors.
Seismic Hazard Evaluation on the Thai Peninsula, Thailand
M. Dober, URS Corporation, Oakland, CA, [email protected];
I. Wong, URS Corporation, Oakland, CA, [email protected]; J.
Zachariasen, URS Corporation, Oakland, CA, [email protected]
com; C. Fenton, Department of Civil & Environmental Engineering, Imperial
College, London, [email protected]; A. Thongsoi, Panya Consultants
Co. Ltd., [email protected]; C. Sutiwanich, Panya Consultants
Co. Ltd., [email protected]; T. Harnpattanapanich, Royal
Irrigation Department of Thailand, [email protected]
With the recent