The 2011 Oichalia (SW Peloponnese, Greece) seismic swarm: Geological and seismological evidence for E-W extension and reactivation of the NNW-SSE striking Siamo Fault

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Published: Jan 21, 2012
DOI: https://doi.org/10.12681/bgsg.10927
Keywords:
earthquake swarm normal faulting hypoDD Messinia Greece
A. Ganas
Institute of Geodynamics, National Observatory of Athens, Greece
E. Lekkas
Department of Geology, University of Athens
M. Kolligri
Institute of Geodynamics, National Observatory of Athens, Greece
A. Moshou
Institute of Geodynamics, National Observatory of Athens, Greece
K. Makropoulos
Institute of Geodynamics, National Observatory of Athens, Greece Department of Geology, University of Athens
Abstract
The Upper Messinia basin (Peloponnese, Greece) hosted a seismic swarm during the second half of 2011. The geological evidence (surface breaks striking N160°E), the seismological data (distribution of relocated earthquakes and T-axis orientation) and severe damage distribution are aligned along the eastern margin of the basin, so as they are attributed to reactivation of the bordering NNW-SSE normal fault. In particular, the rupture of the 14 August 2011 M=4.8 event is associated to the surface breaks inside the village Siamo. The length of the reactivated fault is estimated as 7 ±1 km based on the longest dimension (NW-SE) of the swarm epicentres (June to October 2011). The mode of rupture of the Siamo fault is probably related to a) the change in stress field orientation from south to north inside the basin (from E-W extension in the Siamo – Katsaro area to N-S extension in the north of Oichalia area) and/or b) to the occurrence of magmatic fluids due to the proximity of Messinia to the Hellenic subduction.
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