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

moment magnitude M W 6.4 crustal earthquake in northwestern Peloponnese, Greece, was a strong-shaking dextral strike-slip event with teleseismic broad-band and highfrequency energy magnitudes M e 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.

Integrating geologic fault data into tsunami hazard studies

“…Strikeslip fault sources B1-B3 are characterized by a steep dip (> 50 • ) and a maximum depth of 20-25 km, as revealed by seismic lines and seismological information on earthquake location and fault plane solutions (e.g. Louvari et al, 1999;Kokinou et al, 2005Kokinou et al, , 2006Feng et al, 2010;Shaw and Jackson, 2010 (Kahle et al, 1996;Hollenstein et al, 2008). These values are consistent with the long-term geological offset of 100-120 km attained by the fault in 6-8 My of activity (Royden and Papanikolau, 2011).…”

“…The largest of them are the M = 7.2 event of 12 August 1953, in Cephalonia ; the 1867, M = 7.2, in Lixouri (Cephalonia Island); and the M = 7.0 transpressive event of 17 January 1983, that occurred on the southwestern part of the Cephalonia Fault source (Louvari et al, 1999). Other significant earthquakes of the instrumental era are the M = 6.4 strike-slip earthquake that occurred on 8 June 2008, on the Achaia Fault source Feng et al, 2010), and two events with M = 6.5 and with M = 6.2 that occurred on the southern part of the Lefkada Fault source, respectively on 22 April 1948 and on 14 August 2003 Benetatos et al, 2007). The earthquakes of 1948 and 1983 also generated tsunamis (NGDC/WDS Global Historical Tsunami Database; Ambraseys and Synolakis, 2010).…”

“…3 for location from east of Crete to Rhodes (East Hellenic Arc). The western lateral termination, in the Ionian Islands, is characterized by a 100-km-wide dextral shear zone, which accommodates the different styles and rates of deformation occurring between the oceanic subduction to the east and the continental collision to the west (Feng et al, 2010;Shaw and Jackson, 2010). The eastern part of the arc is characterized by oblique contraction.…”

Active faulting at the western tip of the Gulf of Corinth, Greece, from high-resolution seismic data

“…The strike-slip system to the southwest is less well defined. It would correspond to the right-lateral NE-SW Achaia-Elia fault that has no surface expression (Feng et al, 2010). The fault activity is mainly attested by the 2008 M W 6.4 Achaia-Elia earthquake (Feng et al, 2010;Margaris et al, 2010).…”

“…The upper 4 km of the crust is characterized by a lack of seismicity, which makes the link between the surface faults and the deep structure quite speculative. One of the reference geodynamic models consists of steeply Flotté et al (2005), and Ferentinos et al (1985); Achaia fault zone from Feng et al (2010); northern blinded faults from Kiratzi et al (2008); Gulf of Corinth faults from this study (simplified), Bernard et al (2006) and Bell et al (2008). M N 4 superficial earthquakes (focal depth b15 km) focal mechanisms from Kiratzi and Louvari (2003), Kiratzi et al (2008), Hatzfeld et al (1990), and RCMT catalogue (http://www.bo.ingv.it/RCMT/).…”