A microearthquake study in the Gulf of Patras region, western Greece, and its seismotectonic interpretation

Abstract

SUMMARY The seismicity of the Gulf of Patras region was monitored from 1983 May to 1984 April by a six-station microearthquake network with 30 km aperture. Over 650 events were located using the revised version of the HYPO71 computer program for determining hypocentral locations. Of these, a subset of 73 well-located events was identified for detailed study. Analysis of these 73 events reveals a local pattern of seismicity with two main features: firstly, a gap in seismicity in the central and western parts of the Gulf, despite the local presence of active faulting affecting the seabed; secondly, a zone of high seismicity in the northeast part of the Gulf where offshore seismic surveys reveal a zone of intense structural complexity. A northeast dipping, diffuse zone of seismicity extending to a depth of about 25 km has been identified in the northeastern corner of the Gulf, centred on the Rio–Antirrio Channel between the Gulfs of Patras and Corinth. It is postulated that the active faults in the central part of the Gulf, which are apparently aseismic, are linked via a shallow decollement surface under the Gulf to a deep, WNW-ESE trending fault zone defining the southern margin of the Corinth graben, and extending westwards to Trichonis Lake. The dipping zone of seismicity is related to the latter fault zone, and aseismic faulting in the Gulf of Patras is attributed to the shallow surface of decollement into which the faults sole. A transfer fault zone trending approximately NE-SW is postulated to account for the offset of the Corinth and Patras grabens.