Seismic Activity in south eastern Ghana
by
Paulina Ekua Amponsah
Geological Survey Department, Ghana

Ghana is located on the southeastern margin of the West Africa Craton and is far away from the major earthquake zones that mark the present day lithospheric plate boundaries. It has however suffered from damaging earthquakes dating as far back as 1636. The last three major ones occurred on 1862,1906 and 1939. It has as well suffered from many minor tremors. Most of these earthquakes are located in southeastern Ghana in the vicinity of the capital city, Accra.

The earliest recorded earthquake in Ghana occurred on 18th December, 1636 in the

Axim district in southwestern Ghana. The maximum intensity of this event was 1X. The buildings and underground workings of a gold mine at Aboasi, northeast of Axim collapsed burying many of the miners (Claridge, 1915).

In 1862 a very strong earthquake struck the capital city of Accra and caused considerable damage .Its maximum intensity was IX. The castle (the seat of government) and some forts were rendered uninhabitable, along with all stone buildings (Junner, 1941).

Two severe shocks were felt in Eastern Ghana on 20th November, 1906.The maximum intensity of the shocks was VIII. Many buildings were greatly affected by this event. Most were cracked and some partly destroyed. Ghana's most destructive earthquake, which caused much damage and loss of life, occurred on 22nd June, 1939. Seventeen people were killed, one hundred and thirty- three injured and an estimated one million pounds worth of damage done to buildings (Junner, 1941). The magnitude of this earthquake was 6.5 on the Richter scale and its maximum intensity, IX. All intensities are based on the modified Mercalli Scale of India.

On 11th March, 1964 and 9th February, 1969 earth tremors of magnitudes 4.5 and 4.7 were recorded. Both events were felt in Accra. The latest tremors, which were felt in all the regional capitals, occurred on 8th January, 1997, 14th February, 1997 and 6th March, 1997. These events caused panic among the populace.

Continuous seismic recording since 1973 has confirmed that local seismic activity is continuing at a rate consistent with recurrence of magnitude 6 earthquakes every 50 years or there about. The time lapse since the last major earthquake and the evidence of continuing activity gives ground for concern that another major earthquake may occur in the not too distant future.

Microseismic studies have indicated that the seismicity is associated with active faulting (Essel, 1997) particularly near the intersection between the East - West trending Coastal boundary fault and a NE-SW trending Akwapim fault zone, defined by a number of active fault scarps.

Date received: March 5, 2002

Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caiq-46.