Seismic fault geometry and kinematics of the 13 May 1995 Western Macedonia (Greece) earthquake

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During the devastating earthquake of 13 May 1995, in the Kozani-Grevena area (Western Macedonia, Greece), many surface ruptures formed in the epicentral area. Most of these fractures were due to faulting, but some were secondary ground ruptures and landslides. Geological field work in the area has shown that the Aliakmon river neotectonic fault consists of several (three or more) fault strands: the Servia, the Rymnio and the Paleochori-Sarakina strands. Using geological criteria, all of these fault strands were judged to be active faults affecting recent (Holocene) deposits and scree. The main new surface fractures caused by the earthquake, and particularly those clearly of tectonic origin, follow systematically the traces of the last two neotectonic fault strands, forming a new fracture line. This tectonic line, trending ENE-WSW (N 70 °), coincides with the focal mechanism solution and the satelite image major lineament. Both the geological and instrumental seismological data suggest that the seismogenic fault is a segment of the Aliakmon river neotectonic fault zone situated among the villages of Rymnio, Paleochori, Sarakina, Kentro and Nisi. The total length of the reactivated fault segment is about 30km long overall and is separated from the non-activated Servia fault segment by a geometrical seismic segment barrier near the village of Goules. The seismic fault is a normal fault trending ENE-WSW and dipping to NNW, with high angle at the surface and low angle at depth. The majority of the epicentres of the seismic sequence were distributed on the hangingwall of this reactivated fault segment. Additionaly a series of subparallel antithetic surface fractures, mainly striking E-W or ENE-WSW and dipping to the South, following previous neotectonic strike-slip faults, were reactivated during the earthquake with the geometry of normal faults antithetic to the main seismic fault. The most important of these are the Chromio-Varis-Myrsina fracture line (length 15km), along the Vourinos corridor dextral strike-slip structure and the Felli fracture line (length 6 km) along the Felli sinistral strike-slip fault. An interpretation of the geometry and kinematics of the reactivated faults is shown in the proposed geological model with simplified cross sections.