Seismicity and Fault system

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					                                     ANALYSIS OF THE DEFORMATIONS OF WESTERN CORINTH RIFT
                                                      BY SATELLITE GEODESY
                                                        Maya ILIEVA1,2,3, Rana CHARARA1,3, Pierre BRIOLE3
                                                                        1 University “Pierre and Marie Curie” Paris – 6, France
                                                               2 Bulgarian Academy of sciences, Laboratory of geodesy, Sofia, Bulgaria
                                                                  3 École Normale Supérieure, Laboratory of geology, Paris, France

 Introduction                                                                            Seismicity and Fault system
In the area of Eastern Mediterranean the African plate goes under the                 Studied areas are characterized by high seismicity and natural hazard potential. There is serious seismic risk not
Eurasia plate and the latter collides with the Apulian plate. The                     only for the city of Patras, which is one of the biggest cities in Greece, but also for the neighbouring towns and
studied zone is also determined as a complex junction of several                      villages.
more tectonics blocks which drift in different directions and with
different velocities.

                      Fig.1. Sachpazi et al. (2000)
The investigation covers the Gulf of Patras and Central Ionian
Islands. The area of Patras is a transition zone between the Corinth
rift and the northwestern end of the Hellenic arc, while in the area of                                                            Fig.2                                                                                        Fig.3
the Central Ionian Islands the transition zone between the West                       KFZ and the northwestern part of the WHA are the seismically most active region of Greece. One of the most
Hellenic arc and the Apulian plate is recognized as Kephalonia Fault                  significant recent events (M = 6.3) in the studied area occurred on August 14, 2003 northwest of the Lefkada island.
Zone (KFZ) with strike-slip faulting.                                                 The maximum intensity has been evaluated as Io = VII+ to VIII in the town of Lefkada (Pavlides et al., 2004).

 GPS measurements                                                  InSAR
Two GPS campaigns were carried out in 2003 and 2006,              For the study of the Lefkada earthquake, from the available 13 ascending (Asc) and 20 descending (Desc) ENVISAT images, 7
All data were processed using GAMIT software Version              Asc and 9 Desc, respectively, were used. There is one image before the earthquake for both groups in this set. 21 Asc and 36
10.7 and the same processing strategies. We used precise          Desc interferograms were processed with ROI_PAC software Version 3. This data set was used to generate Maps of coherence.
orbits and GPS data from ten surrounding IGS stations to          On the base of the known fault parameters, synthetic models for expected interferograms were created.
tie our network to ITRF2000.

                                                                                                                                                                                             Fig.8                                                                      Fig.9


                                                                      Fig.6. The 14 August 2008 Lefkada
Only the horizontal solutions are presented here and also              earthquake and the aftershocks
some vectors from others grouped by Nyst (Nyst et al.
2003) that show that the average uncertainties of the
velocity vectors are in the order of ± 30 mm/yr.

                                                                                                                                  Fig.10. Differential Asc Interferogram Fig.11. Map of coherence from 21                                       Fig.12. Synthetic Asc
                                                                                                                                             030321-041105                       Asc interferograms                                                 Interferogram

                                                                      Fig.7. Coulomb stress distribution after
                                                                              the Lefkada earthquake
The residual of the velocity field after a block rotation of
5+0.5˚/Myr till zero velocity for PRSL is presented. In
“Europe fixed”, the Rotation Pole is located at 21.12˚E,                                                                       Fig.13. Differential Desc Interferogram Fig.14. Map of coherence from 36                                        Fig.15. Synthetic Desc
39.09˚N (Avallone et al. 2004).                                                                                                            030625-040714                      Desc interferograms                                                  Interferogram

The difference between the velocity of point PRSL and
the other points define the Western Block of Central
Greece, in which they show that the northern limit of the            References
block is located to the north of Trichonis Lake.                  Avallone A., P. Briole, A.M. Agatza-Balodimou, H. Billiris, O. Charade, C. Mitsakaki, A. Nercessian, K. Papazissi, D. Paradissis, G. Veis (2004). Analysis of eleven years of deformation
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                                                                  Nyst, M., and W. Thatcher (2004), New constraints on the active tectonic deformation of the Aegean, J. Geophys. Res., 109, B11406
                                                                  Hollenstein C, A. Geiger, H.G. Kahle, G. Veis ( 2006). CGPS time-series and trajectories of crustal motion along the West Hellenic Arc, Geophys. J. Int., 164, 182-191.
   Acknowledgements                                               Hollenstein Ch., M.D. Müller, A.Geiger, H.-G. Kahle (2008). GPS-Derived Coseismic Displacements Associated with the 2001 Skyros and 2003 Lefkada Earthquakes in Greece. Bulletin of the
                                                                                 Seismological Society of America, Vol. 98, No. 1, pp. 149-161.
                                                                  Sachpazi M., A. Hirn, C. Clément, F. Haslinger, M. Laigle, E. Kissling, P. Charvis, Y. Hello, J.-C. Lépine, M. Sapin, J. Ansorge (2000). Western Hellenic subduction and Cephalonia Transorm: local
We would like to thank Panagiotis Elias, Aurore Franco,                          earthquakes and plate transport and strain. Tectonophysics, 319, 301-319.
                                                                  Pavlides S.B., G.A. Papadopoulos, A. Ganas, G. Papathanassiou, V. Karastathis, D. Keramydas, A. Fokaefs (2004). The 14 August 2003 Lefkada (Ionian sea) earthquake. 5th International Symposium
Antonios Mouratidis for their invaluable help.                    on Eastern Mediterranean Geology, Tessaloniki, Greece, 14-20 April 2004.

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