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Rupture Process and Aftershocks Relocation of the 8 June 2008 M_w 6.4 Earthquake in Northwest Peloponnese, Western Greece

Institute of Geophysics, National Central University, Taoyuan County, Jhongli, 320 Taiwan kkonst{at}ncu.edu.tw

N. S. Melis

Institute of Geodynamics, National Observatory of Athens, Athens, Greece

S.-J. Lee

Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

C. P. Evangelidis and K. Boukouras

Institute of Geodynamics, National Observatory of Athens, Athens, Greece

Online Material: Spatiotemporal evolution of the aftershock sequence of the 8 June 2008 mainshock, sensitivity tests to the mainshock slip inversion, color versions of figures, relocated aftershocks catalog, classification scheme for the moment tensor solutions, and moment tensor inversion description.

On 8 June 2008 at 12:25 (GMT) an M_w 6.4 strong earthquake occurred in the area of northwest Peloponnese, western Greece, causing the death of two people and extensive damage to the surrounding area. The main event and its aftershocks were recorded by one nationwide and three regional networks equipped with three-component broadband seismometers. Initial locations of the earthquake sequence comprising 438 aftershocks showed a linear northeast–southwest trend and that the mainshock was located at 22 km depth. After the relocation using catalog and differential travel times, most events form three distinct clusters at depths 15–25 km. Moment tensor solutions for the main event and its largest aftershocks exhibited a pure strike-slip mechanism with one nodal plane orientated northeast–southwest in accordance with the relocated seismicity. A parallel, nonnegative least-squares inversion technique utilizing multiple-time windows was used to derive the spatiotemporal slip distribution of the main event. The resulting slip distribution model revealed a large slip patch (maximum slip 150 cm) between 10 and 20 km depth at the northeast part of the fault that also coincides with the area that suffered most of the damage. Another patch exhibiting smaller amounts of slip (20–50 cm) is located to the southwest direction at the same depth range, and smaller patches exist at 25–30 km depth. Most aftershocks are located in areas of low slip (<25 cm) filling the regions of slip deficit. The 8 June earthquake occurred at an area where no previous seismological or other observations indicated the existence of a seismogenic fault at that depth and with this strike. This, and the fact that the event nucleated in the middle to lower crust, may be interpreted as the reactivation of a fault structure that was inherited from previous tectonic phases.