FINAL SCIENTIFIC REPORT - TOPOMED PROJECT TopoMed

FINAL SCIENTIFIC REPORT - TOPOMED PROJECT
TopoMed
Plate re-organization in the western Mediterranean:
lithospheric causes and topographic consequences
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A Collaborative Research Project for the ESF-EUROCORE Programme
4-D Topography Evolution in Europe:
Uplift, Subsidence and Sealevel Change (TOPO-EUROPE)
INDIVIDUAL PROJECT 3-IT (Italy):
Topographic evolution and subduction around the
Calabria Arc (PI: Claudio Faccenna)
RESEARCH UNIT: Università Roma TRE
PI:
Claudio Faccenna
RESEARCH UNIT: CNR-ISMAR Bologna
PI:
Alina Polonia
Title: The accretionary complex of the Calabrian Arc subduction
system: study of active deformation and seismic hazard assessment
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RESEARCH UNIT: Università Roma TRE
PI:
Claudio Faccenna
The Research Unit of Roma TRE did not receive fundings for the project.
Title: Recent tectonic and deformation in Calabria.
The general aim of the Roma TRe project consists in defining the geometry, kinematics and
seismology of the potentially active faults on the Tyrrhenian side of Calabria.
To do so, the project was splitting in the following steps:
1. Realization of a data base including, among other products, results from the following three
phases;
2. Definition of geometry, kinematics and seismological characteristics of the active faults of
Calabria, including where possible, estimates of recent displacement;
3. Analysis and interpretation of off-shore seismic reflection profiles (Tyrrhenian region and
Catanzaro basin);
4. Definition of seismic parameters of main faults.
Following the project plan, this first year of activity was mainly devoted to 2, 3 and 4.
2. Definition of geometry, kinematics and seismological characteristics of the active faults of
Calabria, including where possible, estimates of recent displacement;
We carried out Morphotectonic analysis using DEM and aerophotograph of the study region. This
study was performed using DEM map (at 10 meter confidence) and aerophotograph interpretation
(Volo Italia at scale 1:75.000 and 33.000). From this analysis, we extract river profile and
parameters (concavity, stream-gradient indices) location of knickpoints. This analysis has been
particularly efficient in the area around the Sila massif. There, we found the presence of elevated
knickpoints and the geometry of river down-cutting indicates two phase of erosion, the latter
probably faster. If the detailed description of our result is probably not pertinent for our analysis,
this analysis is a fundamental step towards understanding large scale uplift rate of calabria and it
seismo-tectonic frame. Morphotectonic analysis was mainly concentrated also in the faulted area,
where the relationships between river down-cutting, fan deposits and fault scarps and other
geomorphic feature (triangular facets and wine valley cup) gives first order indications on fault
activity.
We performed structural analysis over Calabria (Tyrrhenian side) from the Crati Valley to Gioia
Tauro Valley. The collected data can be integrated with previous work, where fault kinematics has
been investigated. We carried out structural analysis over the main recent faults to extract their
main recent slip direction. We measure kinematic indicators, as slickensides, striae, grooves and,
only locally fibers, along the main and along subsidiary fault planes along the main fault zones. To
obtain a significant statistical orientation, we collected several measurements for each fault zones.
Overall, we collected more than 250 fault kinematics. Data are implemented and compared with
previous studies carried out using the same criteria (Tortorici et al. (1996) over Calabria; Tondi et
al., (2008) on the Sila massif; Spina et al. (2008) in the Crati Valley. The result of this analysis is
summarized in Figure 1. Here, we will illustrate our main result from the Crati Valley, Catanzaro
basin, Serre and Aspromonte and Tindari region. In the Crati Valley of northen Calabria, a set of
left-lateral arranged en-echelon normal faults is nicely exposed. Cello et al., (1992) and Tortorici et
al. (1996) describe the morphological features along this fault system, along with structural data
indicating an overall oblique dextral kinematics. These faults are active from the Upper Miocene,
as denounced by growth deposits, but they show two sets of triangular facets and cross cut, in one
site, an Upper Pleistocene cones and fluvial terraces. Kinematics analysis on fault planes at four
stations (stop 10, 8. 7, and 5) confirm Tortorici et al. (1996) and Spina et al (2008) analysis. The
main faults show a normal to oblique dextral kinematics. However, at two locations (stop 5, 10) we
found evidence of a second set of striae, superimposed on the previous one, indicating a normal
to oblique sinistral motion. The Sila massif shows well-exposed fault planes along its northern and
southern side, and within the plateau itself. To the north, near Corigliano (stop 3), the northern side
of the Sila massif is bordered to the north by a well exposed fault planes marking the contact
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between basement units and Middle Pleistocene deposits. Slickensides along the main fault show
a normal to oblique-dextral motion. On the Sila massif plateau, Galli and Bosi (2003) describe a
NNE –SSW striking fault zone (the Lake fault system). Paleoseismological trenching permit to
define the recentmost Holocene slip along the fault. Tondi et al. (2008) performed a kinematic
analaysis along the main fault zone showing an overall oblique-sinistral kinematics. North of
Lamezia Terme, the Catanzaro basin is bordered by an E-W fault, marking the contact between
basement units and the recent deposits. Kinematic analysis along the main fault near (stop 13, 15)
show a main normal down-dip motion. Moving towards the south, the Serre range is flanked
towards the west by normal faults, namely the Serre-Cittanova system stepping down and
bounding the Mesima and Gioia Tauro basin (Tortorici et al., 1995; Monaco et al., 2000; Jacques
et al., 2002; Galli and Bosi, 2002). The main fault zone, well marked by triangular facets, outcrop
only in few sites. The Cittanova fault, at stop 21, 22 and 24 are measured also nearby the
trenching site, shows a main normal dip-slip motion. Towards the southwest, the prosecution of the
Cittanova fault splays into several horsetail segments prosecuting inside the Messina trough. One
of this segment (S. Eufemia fault) shows a normal to oblique-sinistral motion (stop 23) in
agreement with Tortorici et al.’s, (1996) data set. To the west, the Capo Vaticano promontory is
bordered by the main EW Coccorino fault (Monaco et al., 2001), showing normal kinematics (stop
19). Summing up, from the Catanzaro basin towards the north, in fact, a system of EW fault is also
present. Galli et al. (2006) emphasize the role of this fault set and of the sinistral NNW fault set in
the Sila massif, indicating that in this area a NNE-SSW extensional field is at work. Our data
confirm this hypothesis also for the Crati Valley fault system where a more recent slip event could
be in agreement with this strain pattern. In the Le Serre massif, conversely, the extensional trend
change and appear dominated by a well-defined NW-SE stretching direction. The Capo Vaticano
E-W fault system could be related to some local features or to an accommodation zone. West of
the Messina through, in northern Sicily, the most recent fault system slightly turns again into a
more EW stretching direction.
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Fig. 1-Structural map of the recent/active faults examined in this project. The arrow near the fault
mark the sense of slip derived from statistical analysis on the kinematic indicators along the fault
planes. Stereonets (Schmid net, lower emisphere) show the trace of fault planes and the arrow
indicates the kinematic of the fault. (further description of the result in the text).
3. Analysis and interpretation of off-shore seismic reflection profiles (Tyrrhenian region and
Catanzaro basin);
1. Analysis and interpretation of seismic lines. The analysis is focused on two main region,
following the disponibility of seimic lines. The first one is located on the Ionian region offCatanzaro. The second one on the Tyrrhenian side. Here, seismic campaigns are however
quite old (Barone et al., 1982) and difficult to obtain. More recently, a new seismic campaign
SISTER 99 was acquired (Bertotti et al., 1999), improving the previous set of single-channell
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low resolution multichannell. The Sister 99 campaigns acquired 24 to 48 channels seismic data
over 2400 km along the Tyrrhenian margin. The analysis of tectonic structure off-Calabria will
be carried out in collaboration with the University of Palermo (Dott. F. Pepe). Despite the net of
lines are large, we hope that the good quality but the net of the Sister 99 seismic line will help
to detect tectonic structure over this “poorly explored” region. In particular we analyzed fault
pattern off-shore Calabria using the unpublished Sister-D1 multi-channel seismic line (Bertotti
et al., 1999) that runs parallel to the W Calabrian coast. This profile is particularly relevant to
analyze the possible source of the September, 8, 1905 earthquakes that is probably localized
between Capo Vaticano and the Eolian Island (e.g., Michelini et al., 1995; Galli et al., 2009).
We reconstructed the seismo-stratigraphy of the Tyrrhenian margin accordingly to the previous
works (Pepe et al., 2010) and to the poor dredges and oil-wells available for this area. In
particular we distinguished Plio-Quaternary unit, Messinian unit, Oligocene-Tortonian clastic
and terrigenous deposits, and Kabilian-Calabrian basement unit. After that we depth-converted
the time seismic reflection profiles, using interval velocity typical for the hypothesised
lithologies.
Figure 2. Position of the Sister 99 seismic lines that are under investigation for this study.
4. Seismotectonic of Calabria:
We analyzed earthquake focal mechanisms are reconsidered from the Calabrian Arc, southern
Italy, where heterogeneous seismotectonic domains occur and where the causative faults of
several destructive earthquakes are still unknown. An up-to-date database of earthquake focal
mechanisms as reliable as possible is compiled by reviewing the quality metadata of existing
mechanisms. A total of 128 mechanisms are selected and included in the database: 118
mechanisms elaborated after waveform analyses and 10 mechanisms elaborated after P-wave first
motions of earthquakes with good network coverage and no less than 14 records. The database
includes focal mechanisms from earthquakes up to a minimum of magnitude 3. Mechanisms from
low magnitude earthquakes, in particular, are elaborated with the Cut and Paste (CAP) method and
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are the main methodological issue addressed in this paper. Mechanisms in the database are grouped
into five subsets and inverted to obtain the seismic stress of major seismotectonic domains in the
study area. Results are compatible with three major domains subject to markedly different regional
stresses along the arc. Two further domains are also found separating the three main domains.
These two transitional domains are likely forced in their transfer kinematics by the different
dynamic regimes occurring in the adjacent main domains rather than by the regional stress. The
focal mechanisms from low magnitude earthquakes are kinematically well consistent with the
seismotectonic regimes of the domains where they fall. The presented database responds to the
need of qualitatively selected data not much for experts who may have easy access to focal
mechanism metadata, rather for a broader audience of Earth scientists and government agencies
involved in neotectonic and seismic hazard studies.
Figure - Selected earthquake focal mechanisms for the Calabrian Arc (Table 1). Following the
classification adopted in the World Stress Map (Zoback, 1992; http://dc-app3-14.gfz-potsdam.de/),
different colors identify different types of mechanisms: red = normal faulting (NF) or normal faulting
with a minor strike-slip component (NS); green = strike-slip faulting (SS); blue = thrust faulting (TF)
or thrust faulting with a minor strike-slip component (TS); black = unknown stress regime (U).
Beach ball dimensions are proportional to earthquake magnitude. White background of beach balls
is for mechanisms from waveform analysis, whereas grey background is for mechanisms from Pwave first motions.
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RESEARCH UNIT: CNR-ISMAR Bologna
PI:
Alina Polonia
Title:
The accretionary complex of the Calabrian Arc subduction system:
study of active deformation and seismic hazard assessment
State of the art
The Calabrian Arc (CA) is part of the most active seismic belt in Italy, and the Ionian Sea has
been described as the last remaining segment of oceanic crust subduction in the central
Mediterranean [DeVoodg et al., 1992; Faccenna et al., 2001; Faccenna et al., 2004]. Southern Italy
and in particular the regions facing the Ionian Sea, such as Sicily and Calabria, are characterized
by a high seismic hazard, and have been struck repeatedly by strong and destructive earthquakes
in the past (1169, 1542, 1624, 1693, 1783, 1905, 1908) [Bottari et al., 1989; Piatanesi and Tinti,
1998; Jacques et al., 2001; Galli and Bosi, 2003; Gutscher et al., 2006; Jenny et al., 2006] often
associated with tsunamis [Tinti and Piatanesi, 1996; Piatanesi and Tinti, 1998; Tinti et al., 2004].
At the toe of the CA (Figure 1), the thick sedimentary section of the African plate has been
scraped off from the descending plate, and piled up along thrust faults. This has resulted in the
emplacement of a thick (up to 10 km) and about 200-300 km wide accretionary complex.
The CA accretionary wedge developed due to the SE-NW Africa/Eurasia convergence,
presently occurring at a very slow rate (<5 mm/y), as reported by recent GPS studies [Calais et al.,
2003; Reilinger et al., 2006; Serpelloni et al., 2007; D’Agostino et al., 2008; Devoti et al., 2008].
Despite the very slow modern-day plate convergence rates observed by GPS, subduction may
locally still be active in the CA, and subduction rate is the result of the convergence rate and the
velocity of the subduction hinge [Doglioni et al., 2006].
The regional geometry of the subduction complex has been described through the analysis of
seismic data in different regions of the Ionian Sea [Rossi and Sartori, 1981; Finetti, 1982;
Cernobori et al., 1996; Doglioni et al., 1999; Catalano et al., 2001; Finetti, 2005; Minelli and
Faccenna, 2010], but the fine-scale structure of the accretionary wedge (i.e., location of the plate
boundary, depth of the basal detachment, geometry and structural style), the overall structural
model of the subduction complex and the activity of subduction processes were still poorly
constrained. The lack of seismicity along the subduction fault plane showing a characteristic
shallow dipping thrust-type focal mechanism can be interpreted in three ways: 1) subduction has
ceased [Wortel and Spakman, 2000; Goes et al., 2004]; 2) subduction is active but aseismic; 3)
subduction is active but with a large locked fault plane [Chiarabba et al., 2005; Gutscher et al.,
2006]. There is little consensus regarding the location and geometry of the major faults absorbing
plate motion, as well as the exact position of the outer deformation front of the accretionary wedge.
This front represents the African/Eurasian plate boundary in the Ionian Sea but has been mapped
by previous authors in widely varying locations, even in positions not corresponding to the
subduction foredeep/trench [Rossi and Sartori, 1981; Frepoli et al., 1996; Catalano et al., 2001;
Bigi et al., 2003; Faccenna et al., 2001; Goes et al., 2004; Chiarabba et al., 2005; Govers and
Wortel, 2005; Lucente et al., 2006]. Part of the problem is, however, that only few studies
[DeVoodg et al., 1992; Chamot-Rooke et al., 2005a; Gutscher et al., 2006] have focused on the
fine structure of the outermost part of the CA system. In fact, high-resolution geophysical data were
lacking in this key region where transition between the accretionary wedge and the Ionian abyssal
plain occurs. This hampered efforts to understand whether the Calabria subduction zone is still
active or not, to determine if the wedge is still growing, and which structures may accommodate
present-day plate convergence.
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Fig. 1 - Geodynamic setting of the study area. The Eurasia/Africa plate converge rate is indicated by the red
arrow. The geological model is modified from Morelli A., and Barrier E., 2004, Commission for the geological
Map of the World, coord. by Cadet J.-P. and Funiciello R. The NW ward dipping subducting slab of the
African plate is represented by the yellow isodepth lines in the Tyrrenian Sea.
Objectives and work strategies of the RU within TOPOMED project
The CNR ISMAR-Bo research planned activity was mainly devoted to reconstructing the regional
architecture of the submerged portion of the subduction complex, location and geometry of active
faults absorbing plate motion and relationships between tectonics and sedimentation.
More specific objectives addressed though the proposed activity are:
• structure and evolution of the accretionary complex and slope basins;
• volume/mass balancing estimate in the accretionary complex;
• outward and vertical growth rates of the accretionary complex;
• STEP fault geometry and its role in segmentation of the subduction complex;
• Identification of sedimentary deposits in the subsurface related to catastrophic events in the
area.
In order to address these issues we have analysed in detail the structure and the evolution of the
external CA, through a multi-scale approach addressing tectonics, kinematics and mass balancing
in the accretionary complexes as well as submarine earthquake geology.
The activity has been focused in three working areas selected through the preliminary
interpretation of existing data:
- Outermost CA subduction complex (area 1 in Fig.2);
- western lateral boundary of the subduction complex at the toe of the Malta
escarpment (area 2 in Fig. 2).
- Inner CA subduction complex offshore Calabria (area 3 in Fig. 2).
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Available data
All the existing geophysical data in the working area (Fig. 2) have been recovered and
organized in a digital form. Existing data may be listed as follows:
- Multichannel Seimsic (MCS) data: CROP-Mare, Ministeriali, MS datasets;
- Sparker profiles: dataset J collected by ISMAR during 70’s.
- CHIRP profiles collected during two expeditions with R/V OGS Explora in 2007 and 2009.
- Morphobathymetric data acquired with R/V OGS Explora (2007 and 2009) in the outermost
accretionary wedge at the transition with the abyssal plain.
- Geophysical (MCS, CHIRP and gravity) data acquired with R/V CNR-Urania in March 2008
in the frame of CNR and MIUR projects.
- Sub-bottom data collected by University of Munchen across the outer deformation front
have been kindly provided by Prof. Werner Hieke for cruise planning purposes.
- Sediment samples (gravity cores) collected in tectonically controlled sedimentary basins.
Fig. 2 – Shaded relief bathymetric map (GEBCO data) with the location of the geological and geophysical
data available in the working area. The three key areas studiedduring the second year of the TopoMed
project are represented by the black boxes. Newly acquired data (MCS and CHIRP seismic data) are
represented by the red and green lines.
Activity
The activity developed during the third year may be summarized as follows.
1) Porcessing of one MCS profile belonging to the CROP-Mare dataset and crossing
longitudinally the subduction complex close to the Messina Straits region.
2) Interpretation of selected MCS profiles belonging to the CROP-Mare datasets crossing
regions of the subduction complex not studied during the previous two years of the project.
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3) Interpretation of selected MCS profiles collected during the CALAMARE cruise (R/V CNR
Urania, 2008).
4) Integrated interpretation of geophysical data at different scales (morphobathymetric, CHIRP
and MCS data).
5) Synthesis of the results
6) Integrated study of selected sediment cores to verify the interplay between tectonics,
seismic activity and sedimentation in the Western Calabrian Arc.
Results
The ISMAR-BO Research Unit has addressed structure and evolution of the submerged
portion of the CA, through an integrated approach involving analysis of old geophysical data (deep
MCS and sparker data) and newly acquired geophysical data in key areas of the subduction
complex (Figure 2). Pre-stack depth migrated crustal-scale seismic profiles have been used to
reconstruct the overall geometry of the subduction complex, i.e., depth of the basal detachment,
geometry and structural style of different tectonic domains, and location and geometry of major
faults. High-resolution multi-channel seismic (MCS) and sub-bottom CHIRP profiles acquired in key
areas during a recent cruise, as well as multibeam data, integrate deep data and constrain the fine
structure of the accretionary wedge, the activity of individual fault strands and the interplay
between morphotectonic setting and deeply rooted processes (Polonia et al. 2011).
The multi-scale integrated approach allow us to obtain the necessary geological constraints
of the Calabrian Arc subduction complex to: 1) define the overall structure of the subduction
complex; 2) reconstruct post-Messinian evolution of the accretionary wedge; 3) quantify the recent
deformation in the outer subduction complex; 4) reveal whether the accretionary wedge is still
growing; 5) define location and geometry of active faults in the subduction complex; 6) define
relationships between topography of the subduction complex and deeply rooted tectonic processes
and slab dynamics; 7) reveal relationships between tectonics, seismicity and sedimentation in the
Ionian Sea.
•
Structure of the accretionary complex and slope basins;
Pre-stacked depth migrated seismic sections have been used to reconstruct the overall
architecture of the subduction complex, wedge geometry (width, thcinless and taper) and
dècollement depth (Fig. 3). Structural style has been described in the different portions of the
subduction complex and its variations related to the structure of the incoming African plate, to
different rates of deformation and the presence of lithosperic faults that produce a segmentation of
the subduction complex.
Fig. 3 – Line drawing of the pre-stacked seismic profile CROP M-2B across the subduction complex. The
salt bearing complex lies above the basal detachment represented by the base of the Messinian
evaporites, while the well layered Tertiary and Mesozoic African plate sediments are attached to
the lower plate and moves towards NW (modified from Polonia et al., 2011).
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We identified four main structural domains in the subduction complex (Fig. 4): 1) the postMessinian accretionary wedge; 2) a slope terrace; 3) the pre-Messinian accretionary wedge and 4)
the inner plateau. Variation of structural style and seafloor morphology in these domains are strictly
related to different tectonic processes, such as frontal accretion, out-of-sequence thrusting,
underplating or subcration and complex faulting.
The CA subduction complex is segmented longitudinally into two different lobes delimited by
a NW/SE deformation zone that accomodates differential movements of the Calabrian and the
Peloritan portions of CA. This can explain the NW-SE extension observed in the straits of Messina
as well as why Calabria has advanced further SE relative to NE Sicily. The formation of the two
lobes and their evolution may be driven by additional factors, such as tectonic rotations related to
different rates of collision with the Mediterranean Ridge along the irregular Africa/Eurasia plate
boundary and generally by plate fragmentation during the terminal stages of subduction. Structural
style variations, such as taper angles, uplift rates and seafloor morphologies within the two lobes,
suggest different rates of plate coupling on the subduction thrust with those in the Eastern lobe
facing Calabria being higher. We propose these two lobes represent two distinct domains of the
subduction complex, characterized by different stages of subduction and/or plate fragmentation in
the Ionian Sea. In particular, the WL corresponds to areas where the slab is already detached,
while the EL corresponds to the region of the CA where local earthquake tomographic maps image
a in depth continuous slab penetrating into the mantle.
Fig. 4 - Structural map of the CA region derived from integrated interpretation of available seismic
data and multibeam bathimetry provided by the CIESM/Ifremer Medimap group [Loubrieu B.,
Mascle J. et al., 2008] superposed over a gray levels bathymetric slope map. Major structural
boundaries, active faults and the extent of the structural domains (i.e. pre and post-Messinian
wedges and inner plateau) are indicated (Modified from Polonia et al., 2011).
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• Post-Messinian evolution of the accretionary complex;
The emplacement of the Messinian evaporites in the sedimentary section produced an abrupt
change in wedge building processes marked by variations in topographic slope angles, basal
detachment depths, as well as variations in structural style and deformation rates. The very low
tapered post-Messinian accretionary wedge in the western region of the CA, is a salt bearing
accretionary complex where frontal accretion of the Messinian and Plio-Quaternary units do
actually occur along a basal detachment located at the base of the Messinian evaporites. The preMessinian accretionary wedge is constituted by Tertiary and Mesozoic sediments; here the basal
detachment is located at the top of the Mesozoic carbonates or oceanic basement. Underplating
processes and duplex formation are active in this region. The transition between the post and preMessinian accretionary wedges is the locus of complex faulting that enhances fluid flow and mud
diapirism.
The post-Messinian CA subduction complex has structural style, width and geometries similar
to the recent Western Mediterranean Ridge, suggesting it is growing at a similar rate despite the
very different convergence velocities reported by GPS data. Simple cross sectional area balancing
made on the depth seismic section imply that the CA long-term subduction velocity, averaged over
the last 5 Ma, is in the order of 3.5 cm/yr, about 10 times higher than GPS current motion. This
suggests that convergence rate has slowed down significantly in recent times (1 Ma) or that the
outward wedge velocity changed through time, being much faster than the subduction rate during
the emplacement of the evaporites. The Messinian times may thus be seen as a new cycle in the
accretion, possibly characterised by high growth rates of the accretionary wedge.
Fig. 5 - a: pre-stack depth migrated MCS line CROP M-2B with colour-code seismic velocities derived from
seismic data migration. b: simplified line drawing of the time migrated seismic line CROP M-2B. The postMessinian wedge has been highlighted with a grey pattern. c: simplified line drawing of a time migrated
seismic section across the Mediterranean Ridge (modified from Reston et al., 2002). The two accretionary
wedges have similar size despite the Mediterranean Ridge is growing ten times faster than the Calabrian Arc
(modified from Polonia et al., 2011).
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•
Outward and vertical growth rates of the accretionary complex;
Seismic imaging reveals active deformation at the wedge toe that produces sediment uplift,
shortening and offscraping.
Kinematic reconstructions made on the seismic sections, suggest that the outer deformation
front has migrated towards SE at a rate of about 2 cm/yr in the last 5Ma. This value is comparable
to that proposed for the Mediterranean Ridge by Kastens [1991] through analysis of sediment
facies within the wedge. The rapid rate of outward growth is reflected in the very low taper angle,
which is about 1-1,.5°, that might be explained by the strong evaporites and the very weak basal
detachment favouring the outward growth rather than vertical stacking of accreted units.
Uplift rates on single folds in the outermost accretionary wedge has beene stimated through
the analysis of the deformation of known stratigraphic levels such as the Augias megaturbidite bed
emplaced after the Santorini eruption and related tsunami occurred 3500 yr b.p. (Kastens and
Cita, 1982). This megaturbidite bed is uplifted and deformed along the outer deformation front and
its uplift relative to the abyssal plain level has been used to calculate the uplift rate along the outer
deformation front that is about 1 mm/yr.
•
Location and geometry of active faults absorbing plate motion
Outermost accretionary wedge: although shallow thrust-type seismicity along the CA is
lacking, we identified several active tectonic features at the wedge front that produce shortening
and uplift of the shallowest sedimentary units. This implies that subduction could be either aseismic
or active but with a locked fault plane. In this latter case, plate motion could be accommodated by
relatively large earthquakes with long recurrence intervals.
Out-of-sequence thrusting in the inner wedge: shortening is active also at the transition
between the salt-bearing post-Messinian accretionary wedge and the pre-Messinian complex at
about 100-120 km northwest of the deformation front. Here a flat slope terrace (i.e. wedge-top
Messinian basin) develops where the basal detachment cuts from the base of the Messinian
evaporites to deeper levels, and the subduction thrust changes its dip from a rather flat geometry
to a 4° steep subduction thrust. In this region main tectonic processes are related to out-ofsequence thrusts and duplex structures. We believe that three of these out of sequence thrusts, in
particular, represent major splay faults that are likely to have caused large earthquakes in the past
and may be the source regions for future events.
STEP fault: at about 70 Km East of the toe of the Malta escarpment, a lithospheric subvertical fault system and a listric fault outcropping at the seafloor offset the accretionary wedge as
well as deeper reflectors and controls the formation of a fan-shaped basin whose geometry
suggests syn-tectonic sedimentation above an East dipping transtensive fault. We interpret this
fault system as a major lithospheric structure that segments the subduction complex close to a
continental corner and thus may be described as a “STEP” fault [Govers and Wortel, 2005]
accommodating different rates of slab roll back. We suggest that this structure plays a fundamental
role in controlling subduction processes and margin segmentation, and this area is a key-region to
understand connections between shallow processes, deeply rooted structures and seismic risk
assessment.
Seismic data reveal the existence of both compressive and transtensive active faults in the
subduction complex. In our interpretation, the Malta STEP fault system, together with the boundary
between the two lobes and a set of out-of-sequence thrust faults (SPLAYS) at the transition
between the pre- and post-Messinian wedges, represent seismogenic features likely to have
generated major earthquakes in the past. In fact, these structures are active, are large (100 km),
are deeply rooted, and bounds sectors of the margin characterized by different deformation rates.
In particular, the observed out-of-sequence thrust faults reflect the structural contrast between a
shallow décollement (Messinian evaporites) in the frontal wedge and a deeper basal detachment
within the pre-Messinian sediments, primarily due to differences in rheology. The out-of-sequence
thrust faults in the Eastern lobe (offshore Calabria) should be taken into account for any reliable
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seismic risk assessment because this subduction lobe is characterized by higher deformation rates
and steeper structures in depth.
•
Relationships between tectonics and sedimentation in the Ionian Sea.
Sediment cores from the Ionian abyssal plain (3800-4000 m water depth) as well as other
deep marine basins developed on the flanks of the Calabrian accretionary wedge have sampled
turbidite sequences which likely contain a record of the great earthquakes in the region. Including
the Augias turbidite, we were able to sample a number (more than 10) turbiditic cycles in the
gravity cores. Radiocarbon ages have been obtained from planktonic foraminiferal samples above
and beneath suspected seismic related deposits events and are being analyzed in conjunction with
Pb210 and Cs137 radiocarbon datings to resolve mass flow sedimentary processes associated
with some recent (19th and 20th century) or older anomalous geological events.
14
References
Argnani A. and Bonazzi C. (2005), Malta Escarpment fault zone offshore eastern Sicily: Plio-Quaternary
tectonic evolution based on new multi-channel seismic data, Tectonics, 24, TC4009,
doi:4010.1029/2004TC001656.
Bigi S. ., et al. (2003), Décollement depth versus accretionary prism dimension in the Apennines and the
Barbados, Tectonics, 22, 1010, doi:1010.1029/2002TC001410.
Bottari A. et al. (1989), Source parameters of earthquakes in the Strait of Messina, Italy, during this century,
Tectonophysics, 166, 221-234.
Calais E., et al. (2003), Evidence for a post-3.16 Ma change in Nubia-Eurasia-North America plate motions?
Earth and Planetary Science Letters, 216, 81-92.
Catalano S., et al. (2001), On the Mesozoic Ionian Basin, Geophysical Journal International, 144, 49-64.
Cernobori L., et al. (1996), Crustal image of the Ionian basin and its Calabrian margins, Tectonophysics,
264, 175-189.
Chamot-Rooke N., et al. (2005a), Western Mediterranean Ridge mud belt correlates with active shear strain
at the prism backstop geological contact, Geology, 33, 861-864, doi:810.1130/G21469.21461.
Chamot-Rooke N., et al. (2005b), DOTMED – Deep Offshore Tectonics of the Mediterranean: A synthesis of
deep marine data in eastern Mediterranean, Mémoire de la Société géologique de France &
American Association of Petroleum Geologists, special number, 177, 64 pp, 69 maps with cd-rom.
Chiarabba C., et al. (2005), A new view of Italian seismicity using 20 years of instrumental recording,
Tectonophysics, 395, 251-268.
D'Agostino N., et al. (2008), Active tectonics of the Adriatic region from GPS and earthquake slip vectors,
Journal of Geophysical Research, 113, B12413, doi:12410.11029/12008JB005860.
De Voogd B., et al. (1992), Two-ship deep seismic soundings in the basins of the Eastern Mediterranean
Sea (Pasiphae cruise), Geophysical Journal International, 109, 536-552.
Devoti R., et al. (2008), New GPS constraints on the kinematics of the Apennines subduction, Earth and
Planetary Science Letters, 273, 163-174.
Doglioni C., et al. (2007), Subduction kinematics and dynamic constraints, Earth-Science Reviews, 83, 125175.
Doglioni C., et al. (1999), Foredeep geometries at the front of the Apennines in the Ionian Sea (central
Mediterranean), Earth and Planetary Science Letters, 168, 243–254.
Doglioni C., et al. (2006), Simple kinematics of subduction zones. Int. Geol. Rev. 48, 479–493.
Faccenna C., et al. (2001), History of subduction and back-arc extension in the Central Mediterranean,
Geophysical Journal International, 145, 809-820.
Faccenna C., et al. (2004), Lateral slab deformation and the origin of the western Mediterranean arcs,
Tectonics, 23, TC1012, doi:1010.1029/2002TC001488.
Finetti I. (1982), Structure, stratigraphy and evolution of Central Mediterranean, Bolletino di Geofisica
Teorica ed Applicata, XXIV, 247-312.
Frepoli A., et al. (1996), State of stress in the southern Tyrrhenian subduction zone from fault-plane
solutions, Geophysical Journal International, 125, 879-891.
Kastens K.A. (1991), Rate of outward growth of the Mediterranean Ridge accretionary complex,
Tectonophysics, 199, 25-50.
Kastens, K. A., and M. B. Cita (1981), Tsunami induced sediment transport in the abyssal Mediterranean
Sea, Geol. Soc. Am. Bull., 89, 591–604.
Galli P., and Bosi V. (2003), Catastrophic 1638 earthquakes in Calabria (southern Italy): New insights from
paleoseismological investigation, Journal of Geophysical Research, 108, B1, 2004,
doi:2010.1029/2001JB001713.
Goes S., et al. (2004), A recent tectonic reorganization in the south-central Mediterranean, Earth and
Planetary Science Letters, 226, 335-345.
Govers R., and Wortel M.J.R. (2005), Lithosphere tearing at STEP faults: Reponse to edges of subduction
zones, Earth and Planetary Science Letters, 236, 505-523.
Gueguen E., et al. (1998), On the post-25 Ma geodynamic evolution of the western Mediterranean,
Tectonophysics, 298, 259-269.
Gutscher M.A., et al. (2006), Source of the 1963 Catania earthquake and tsunami (southern Italy): New
evidence from tsunami modeling of a locked subduction fault plane, Geophysical Research Letters,
33, L08309, doi:08310.01029/02005GL025442.
Jacques E., et al. (2001), Faulting and earthquake triggering during the 1783 Calabria seismic sequence,
Geophysical Journal International, 147, 1-25.
Jenny S., et al. (2006), Seismic potential of Southern Italy, Tectonophysics, 415, 81-101.
15
Loubrieu B., J. Mascle, and MediMap Group, 2008. Morpho-Bathymetry of the Mediterranean Sea.
In
Special Publication, 1/3.000000 scale map., CIESM, 2008, pp. 1-2.
Lucente F.P., et al. (2006), Seismic anisotropy reveals the long route of the slab through the western-central
Mediterranean mantle, Earth and Planetary Science Letters, 241, 517-529.
McHugh C.M.G., et al. (2006), Submarine earthquake geology along the North Anatolia Fault in the Marmara
Sea, Turkey: A model for transform basin sedimentation, Earth and Planetary Science Letters, 248,
3-4, 661-684.
Minelli L., and Faccenna C. (2010), Evolution of the Calabrian Accretionary wedge (Central Mediterranean),
Tectonics, In Press.
Morelli A., and Barrier E., 2004, Commission for the geological Map of the World, coord. by Cadet
J.-P. and Funiciello
Piatanesi A., and Tinti S. (1998), A revision of the 1693 eastern Sicily earthquake and tsunami, Journal of
Geophysical Research, 103, 2749-2758.
Polonia A., et al. (2008), Rapporto sulle indagini di sismica a riflessione, gravimetriche, magnetometriche,
morfobatimetriche e campionamento fondo mare nell' Arco Calabro (Mar Ionio). Campagna
CALAMARE-08
–
N/R
CNR
URANIA
Napoli
2008-04-15
Bari
2008-05-12,
URL:http://projects.bo.ismar.cnr.it/CRUISE_REPORTS/2008/CALAMARE2008_ITA_REP/.
Polonia, A., L. Torelli, P. Mussoni, L. Gasperini, A. Artoni, and D. Klaeschen, 2011, The Calabrian Arc
subduction complex in the Ionian Sea: Regional architecture, active deformation, and seismic
hazard, Tectonics, 30, TC5018, doi:10.1029/2010TC002821.
Reilinger R., et al. (2006), GPS constraints on continental deformation in the Africa-Arabia-Eurasia
continental collision zone and implications for the dynamics of plate interactions, Journal of
Geophysical Research, 111, B05411, doi:05410.01029/02005JB004051.
Reston T.J., J. Fruehn, von R. Huene, and IMERSE Working Group (2002), Frontal accretion along the
western Mediterranean Ridge: the effect of the Messinian evaporites on wedge mechanics and
structural style, Marine Geology, 186, 59-82.
Rossi S., and Sartoni R. (1981), A seismic reflection study of the external Calabrian arc in the northern
Ionian Sea (Eastern Mediterranean), Marine Geophysical Researches, 4, 403-426.
Serpelloni E., et al. (2007), Kinematics of the Western Africa-Eurasia plate boundary from focal mechanisms
and GPS data, Geophysical Journal International, 169, 1180-1200.
Tinti S., et al. (2004), The new catalogue of the Italian tsunamis, Natural Hazards, 33, 439-465.
Tinti S., and Piatanesi A. (1996), Finite-element Simulations of the 5 February 1783 Calabrian Tsunami,
Physics and Chemistry of the Earth, 21, 39-43.
Wortel M.J.R., and Spakman W. (2000), Subduction and Slab Detachment in the Mediterranean-Carpathian
Region, Science, 290, 1910-1917.
16
Preliminary results of this study has been published in the following works/presentations.
Billi, A., Faccenna, C., Bellier, O., Minelli, L., Neri, G., Piromallo, C., Presti, D., Scrocca, D., and
Serpelloni, E. (2011) Recent tectonic reorganization of the Nubia-Eurasia convergent
boundary heading for the closure of the western Mediterranean, Bull. Soc. géol. France,
2011, t. 182, no 4, pp. 279-303.
Billi, A., Presti, D., Orecchio, B., Faccenna, C. and Neri G. (2010), Incipient extension along the
active convergent margin of Nubia in Sicily, Italy: the Cefalu-Etna seismic zone, Tectonics,
Vol. 29, No. 4, TC4026, doi:10.1029/2009TC002559.
Billi, A., Presti, D., Orecchio, B., Faccenna, C. and Neri G. (2010), Incipient extension along the
active convergent margin of Nubia in Sicily, Italy: the Cefalu-Etna seismic zone, Tectonics,
Vol. 29, No. 4, TC4026, doi:10.1029/2009TC002559.
Faccenna et al. (2010) Topography of the Calabrian subduction zone: clues for the origin of Mount
Etna, Tectonics, in press.
Faccenna et al. (2010) Topography of the Calabrian subduction zone: clues for the origin of Mount
Etna, Tectonics, in press.
Faccenna, C., and Becker, T.W. (2010) Shaping mobile belt from small scale convection, Nature,
Vol 465, doi:10.1038/nature09064.
Faccenna, C., and Becker, T.W. (2010) Shaping mobile belt from small scale convection, Nature,
Vol 465, doi:10.1038/nature09064.
Faccenna, C., and Becker, T.W. (2010) Shaping mobile belt from small scale convection, Nature,
Vol 465, doi:10.1038/nature09064.
Faccenna, C., Molin, P., Orecchio, B., Olivetti, V., Bellier, O., Funiciello, F., Minelli, L. Piromallo, C.,
Billi, A.. (2010) Topography of the Calabrian subduction zone: clues for the origin of Mount
Etna, Tectonics, on line.
Guillaume, B., F. Funiciello, C. Faccenna, J. Martinod, and V. Olivetti (2010), Spreading pulses of
the Tyrrhenian Sea during the narrowing of the Calabrian slab, Geology 38; no. 9; p. 819–
822; doi: 10.1130/G31038.1.
Guillaume, B., F. Funiciello, C. Faccenna, J. Martinod, and V. Olivetti (2010), Spreading pulses of
the Tyrrhenian Sea during the narrowing of the Calabrian slab, Geology 38; no. 9; p. 819–
822; doi: 10.1130/G31038.1.
Guillaume, B., F. Funiciello, C. Faccenna, J. Martinod, and V. Olivetti (2010), Spreading pulses of
the Tyrrhenian Sea during the narrowing of the Calabrian slab, Geology 38; no. 9; p. 819–
822; doi: 10.1130/G31038.1.
Minelli, L., and Faccenna, C. (2010), Evolution of the Calabrian accretionary wedge, central
Mediterranean, Tectonics, doi:10.1029/2009TC002562.
Minelli, L., and Faccenna, C. (2010), Evolution of the Calabrian accretionary wedge, central
Mediterranean, Tectonics, doi:10.1029/2009TC002562.
Minelli, L., and Faccenna, C. (2010), Evolution of the Calabrian accretionary wedge, central
Mediterranean, Tectonics, doi:10.1029/2009TC002562.
Olivetti, V., M. L. Balestrieri, C. Faccenna, F. M. Stuart, and G. Vignaroli (2010), Middle Miocene
out-of-sequence thrusting and successive exhumation in the Peloritani Mountains, Sicily:
Late stage evolution of an orogen unraveled by apatite fission track and (U-Th)/He
thermochronometry, Tectonics, doi:10.1029/2009TC002659, in press.
Olivetti, V., M. L. Balestrieri, C. Faccenna, F. M. Stuart, and G. Vignaroli (2010), Middle Miocene
out-of-sequence thrusting and successive exhumation in the Peloritani Mountains, Sicily:
Late stage evolution of an orogen unraveled by apatite fission track and (U-Th)/He
thermochronometry, Tectonics, doi:10.1029/2009TC002659, in press. .
Olivetti, V., M. L. Balestrieri, C. Faccenna, F. M. Stuart, and G. Vignaroli (2010), Middle Miocene
out-of-sequence thrusting and successive exhumation in the Peloritani Mountains, Sicily:
Late stage evolution of an orogen unraveled by apatite fission track and (U-Th)/He
thermochronometry, Tectonics, doi:10.1029/2009TC002659, in press.
Polonia A., /The Calabrian Arc subduction complex: active deformation and the geological record of
earthquakes in the Ionian Sea. Invited talk, ESF Conference: Submarine Paleoseismology, The
Offshore Search of Large Holocene Earthquakes*. 11-16 September 2010.
17
Polonia A., Bortoluzzi G., Gasperini L., Ligi M. et al., 2008. Rapporto sulle indagini di sismica a riflessione,
gravimetriche, magnetometriche, morfobatimetriche e campionamento fondo mare nell' Arco Calabro
(Mar Ionio). Campagna CALAMARE-08 – N/R CNR URANIA Napoli 2008-04-15 Bari 2008-05-12
URL:http://projects.bo.ismar.cnr.it/CRUISE_REPORTS/2008/CALAMARE2008_ITA_REP/.
Polonia A., L. Torelli, F. Riminucci, L. Gasperini, M.-A. Gutscher, P. F. Gallais, Mussoni, L.G. Bellucci, L.
Capotondi, 2010. The Calabrian Arc subduction system: active faults, mud diapirism and the geological
record of catastrophyc events in the subsurface. 39th CIESM Congress, Venice, 10-14 May 2010.
Polonia A., L. Torelli, F. Riminucci, P. Mussoni, D. Kläschen, M.-A- Gutscher, F. Gallais, 2010. The Calabrian
Arc subduction complex in the Ionian Sea. European Geosciences Union, General Assembly 2010,
Vienna, Austria.
Polonia A., Torelli L., Capozzi R., Riminucci F., Artoni A., Ramella R., and the CALARC group.
African/Eurasian plate boundary in the ionian sea: shortening and strike slip deformation in the outer
calabrian arc accretionary wedge. November, 2008 GNGTS meeting.
Presti D, Andrea Billi, A. Orecchio, B., Totaro, C. Faccenna , C and Neri, G. Earthquake focal
mechanisms, seismic stress, and seismotectonics of the Calabrian Arc, Italy, sottomesso.
Riminucci F., A. Polonia, L. Torelli, P. Mussoni, 2010. Seafloor morphology in the different domains of the
Calabrian Arc subduction complex– Ionian Sea. European Geosciences Union, General Assembly
2010, Vienna, Austria.
18