Earthquake activity in southeastern Ghana (1977-1980)

Abstract

Although Ghana is remote from the major earthquake zones, it is moderately active seismically, with a history of earthquakes damaging the capital, Accra. Seismic recording with a variety of instruments during 1977 to 1980 has enabled us to develop a crustal velocity model and locate epicenters. Most of the earthquakes occur in an area to the west of Accra around the junction of two major fault systems, the east-west trending Coastal Boundary fault and the NNE trending Akwapim fault zone. Fault plane solutions suggest a mixture of normal faulting on the Akwapim fault zone (in agreement with geological evidence) and strike-slip faulting, in response to a regional ESE tensional stress perhaps caused by strike-slip movement along the Romanche fracture zone. In view of the high stress suggested by the low b value for the recorded events, precautions against earthquake hazard in Accra would be timely.