Recent seismicity of southern Ghana and re-interpretation of the 1939 Accra earthquake: implications for recurrence of major earthquake

Abstract

The purpose of this research is to re-interpret the 1939 Accra Earthquake, explain the nature and cause of the recent seismicity of the Accra region, and assess the likelihood of occurrence of any major cyclic earthquake in the Accra region and southern Ghana. Combining re-interpretation of historical earthquake data of Ghana with new field data, the nature of the seismicity of the Accra region has been assessed. The results show that the 1939 Accra Earthquake was a shallow-focus tectonic event caused by high-angle submarine strike-slip faults along the eastern extension of the Romanche fracture zone 40 kilometres south of Accra. Recent seismicity in the Accra region has emanated from sources similar to those of the 1939 Accra Earthquake related to the offshore fault systems. The structural setting and mechanism of the 1939 earthquake, however, preclude the likelihood of occurrence of a major cyclic earthquake based on a regional cyclic earthquake phenomenon. The results, however, do not exclude the possibility of occurrence of any significant random earthquake striking Accra region or other parts of southern Ghana now or in the future, as there are many independent active fault systems associated with the fault systems of the region.