Microseismicity and faulting geometry in the Gulf of Corinth (Greece)

During the summer of 1993, a network of seismological stations was installe d over a period of 7 weeks around the eastern Gulf of Corinth where a seque nce of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal f aulting with the active fault plane dipping at about 45 degrees for both fa ults. The aftershocks of the 1981 earthquake sequence recorded by King et a l. (1985) were processed again and show similar results. In contrast, the o bservations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 (Rigo et al. 1996), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes (Hatzfeld et al. 1996; Bernard et al. 1997) show seismicity dipping at a very low angle (about 15 degrees) northwards and normal faulting mechanisms with the activ e fault plane dipping northwards at about 30 degrees. We suggest that the 8 -12 km deep seismicity in the west is probably related to the seismic-aseis mic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal m echanisms between east and west of the Gulf could be related to the differe nce in the recent extension rate between the western Gulf of Corinth and th e eastern Gulf of Corinth, which rotated the faults dipping originally at 4 5 degrees (as in the east of the Gulf) to 30 degrees (as in the west of the Gulf).