Energetic rupture, coseismic and post-seismic response of the 2008 MW 6.4 Achaia-Elia Earthquake in northwestern Peloponnese, Greece: an indicator of an immature transform fault zone

Abstract

SUMMARY The 2008 June 8, moment magnitude MW 6.4 crustal earthquake in northwestern Peloponnese, Greece, was a strong-shaking dextral strike-slip event with teleseismic broad-band and high-frequency energy magnitudes Me of 6.8 and 7.2, respectively. A high stress drop 5–10 times the global average is associated with excessive high-frequency energy. The NE–SW trending fault plane shown by the aftershock distribution and focal mechanism is not associated with previously mapped faults, and no obvious coseismic surface rupture was discovered. Contrasting the enhanced rupture energy, the event created no substantial coseismic or post-seismic surface deformation, likely due to a fault buried below a detached thick and compositionally weak flysch layer. Comparative spatial analysis including over 30 regional strike-slip events between 1965 and 2009 reveals a NE–SW striking diffuse transform fault zone subparallel to the Cephalonia Transform Fault. The dextral sense of motion along the transform zone is consistent with the ongoing Global Positioning System (GPS)-derived deformation along the West Hellenic Arc and the motion on the Cephalonia Transform Fault. Characterizing this system is important to constraining the seismic hazard near Patras, a major port city immediately NE of the 2008 event.