Geophysical Research Journal
Supporting Information for
Segmented Hellenic slab rollback driving Aegean deformation and seismicity
M. Sachpazi1*, M. Laigle2, M. Charalampakis1, J. Diaz3, E. Kissling4, A. Gesret5, A.
Becel6, E. Flueh7, P. Miles8, and A. Hirn9
1Institute
of Geodynamics, National Observatory of Athens, Lofos Nymfon, 11810, Thissio, Athens, Greece.
2Univ.
Nice Sophia Antipolis, CNRS, IRD, Observatoire de la Cote d Azur, Geoazur UMR-7329, 250 rue
Albert Einstein, Sophia Antipolis 06560 Valbonne, France.
3Instituto
de Ciencias de la Tierra Jaume Almera, ICTJA-CSIC, 08028, Barcelona, Spain.
4Institute
of Geophysics, ETH Zurich, Sonneggstrasse 5, 8092 Zürich, Switzerland.
5
Mines Paris Tech, PSL Research University, Centre de Geosciences, 77 Fontainebleau, France.
6Lamont-Doherty
Earth Observatory, Columbia University, P.O. Box 1000, 61 Route 9W, Palisades, NY
10964.
7GEOMAR
Helmholtz Centre for Ocean Research, Kiel, Wischhofstr. 1-3, 24148, Kiel, Germany.
8Commission
for the Geological Map of the World, 77, rue Claude-Bernard 75005 Paris, France.
9
Institut de Physique du Globe, Sorbonne Paris Cite, Univ Paris Diderot, UMR 7154, CNRS, F-75005 Paris,
France.
Contents of this file
Text S1
Figures S1 to S3
Introduction
The files contained in the supporting material give information on the seismological data.
We also show 3 supplementary figures that highlight the methodology we use:
Text S1: Description of the earthquake data and mechanisms.
Supplementary figure S1: Distribution of teleseismic events used in RF imaging.
1
Supplementary figure S2: RF Methodology illustration.
Supplementary figure S3: Example of synthetic RFs showing that the time difference of
the negative-positive Ps signals marking the top and bottom of subducting crust (LVL) is
sensitive on the signal filtering frequencies.
Text S1. Earthquake Locations and Mechanisms
Location and focal mechanism determination of the Leonidio Mw 6.4 and Argos Mw 5.0
earthquakes by TWR seismological array
In 2008 two intermediate-depth earthquakes (Mw 6.4 6 January at Leonidio and Mw 5.0
18 June at Argos, in Figure 3) occurred below eastern Peloponnesus 50 km apart. Over
50 seismological stations from the TWR network including permanent NOA (National
Observatory of Athens) seismographs with clear data (minimum epicentral distance 2
km) provided 50 P-readings (31P for Argos) and 44 S-readings for Leonidio (24 Sreadings for Argos). These yielded an excellent constraint on both epicentral coordinates
and hypocentral depths and allowed these two earthquakes to be discussed in relation
to the structural elements we imaged. Focal mechanisms for both events have been
computed using first-arrival polarities and the FPFIT code [Reasenberg and
Oppenheimer, 1985] and are plotted in Figure 3. On the same figure we plotted CMT
Harvard mechanism of the 8 January 2006 intermediate depth earthquake (Mw 6.7)
which occurred east of the small island of Kythira a few months before the TWR
deployment (hypocenter from www.gein.noa.gr 36.20°N 23.40°E depth 69 km). To
discuss the deformation within the subducting crust, we project the three mechanisms
onto a dipping plane which has the same strike and dip angle as the subducting slab.
The strike and dip angles are chosen as N310°E and 18° [Gesret et al., 2011].
Location of the shallow subduction 2008 Methoni Mw 6.8 earthquake
On 14 February 2008 an Mw 6.8 large earthquake occurred about 80 km offshore
Southwest Messinia, the westernmost peninsula of Peloponnesus. This was the largest
instrumental interplate event recorded in this part of the subduction. Its epicenter has
been located using the closest stations of TWR network leading to up to 26 P-readings
and 4 S-readings. Its location, as well as those of the larger aftershocks, in a period
spanning 4-5 months from the main event, are displayed on the same map (Figure 3).
Focal mechanism of the main event has been computed using first-arrival polarities and
the FPFIT code [Reasenberg and Oppenheimer, 1985] and is also displayed in Figure 3
as a flat thrust mechanism on a north-easterly dipping plane consistently with sourcemodeling from various agencies (Harvard CMT, NOA CMT bbnet.gein.noa.gr).
Local earthquakes location with TWR and NOA arrays
High–resolution observation of intermediate depth seismic activity could be achieved by
our TWR dense deployment. Over 40 earthquakes (Ml <3.5) were processed for the
period of 2006-2008. A mean of 30 P-readings and 15 S-readings arrivals provided well
resolved hypocentres at depths of 60-80 km with vertical errors less than 3-4 km. A
significant improvement-densification of the NOA array at the end of TWR project
allowed extending in time (2009-2014) the obtained seismic image. In order to discuss
the spatial distribution of hypocenters with respect to the resolved slab Moho from these
two datasets we plotted those located from 0-10 km below the slab Moho (in blue) and
above it (in purple) (Figure 3). Same colors are adopted for the three intermediate depth
earthquakes which occurred in the slab crust.
2
Figure S1. Distribution of teleseismic events (blue circles) used in RF imaging. Map is
centered in the study area with concentric circles denoting 30° increments.
3
Figure S2. Receiver Function Methodology.
Figure S3. Example of synthetic RFs computed for a model of an oceanic crust 7 km
thick LVL at 50 km depth, between an upper plate mantle and a slab mantle. Note that
the negative Ps phase (blue line) is imaged earlier and the positive one (red line) is
imaged later with commonly used filtering frequencies (wave periods longer than 2
seconds) of Ps imaging (black arrow) [Gesret et al., 2010]. This leads to an
overestimated thickness of the LVL and an underestimated depth of the top of the LVL.
The only stable part of the signal which remains insensitive to filtering frequencies is the
null amplitude between these opposite polarities Ps phases (grey line).
References
Reasenberg, P., and D. Oppenheimer (1985), U.S. Geological Survey Open-File Report
85–739, 109 p.
4