UGRC 144 Science and Technology in Our Lives/Geohazards Session 4 – Earthquakes in Ghana Lecturer: Dr. Patrick Asamoah Sakyi Department of Earth Science, UG Contact Information: pasakyi@ug.edu.gh

Session Overview This session introduces students to earthquake history in Ghana, including past occurrences and locations. Most people living in Ghana today have never experienced an earthquake, and Ghanaians may find it difficult to associate earthquake disasters with Ghana. However, evidence based on the history of the Gold Coast/Ghana, modern day seismograph recordings and the geology of Ghana indicates a high earthquake disaster risk for Ghana. Dr. Patrick A. Sakyi, Dept. of Earth Science

Session Outline The key topics to be covered in the session are as follows: Topic One – History of Earthquakes in Ghana Topic Two – Modern Seismographs in Ghana Topic Three – Earthquake Risk in Ghana Topic Four - Earthquake Epicenters and the Regional Geological Structures of Ghana Topic Five – Active Faults in Ghana Topic Six - Earthquake Risk Map of Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

Reading List Unit 1, Section 4 of UGRC 140 II Geohazards – Institute of Continuing and Distance Education Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana Topic One History of Earthquakes in Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana The most significant earthquakes (magnitude 6.0 and above) which caused severe damage are: Elmina (1615) Axim (1636) Accra (1882) Ho (1906) Accra (1939). Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana The 1939 earthquake which was located 40 km offshore to the southwest of Accra shook most of West Africa. Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana Minor Historic Earthquakes Notable minor tremors were also felt in: 1858 1863 1883 1907 1911 1918 1919 1923 1925 1930 1933 1935 Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana Recent Significant Earthquakes Since 1939, no earthquake has caused any major destruction in Ghana. Events that have caused concern since independence have all been centered on Accra. Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana Recent Significant Earthquakes They were of Magnitude 4.5 or less recorded in 1964 1967 1969 1978 1985 1995 Dr. Patrick A. Sakyi, Dept. of Earth Science

History of Earthquakes in Ghana Recent Significant Earthquakes A recent notable event was a magnitude 4.4 earthquake which occurred on Independence Day 6th March1997. Dr. Patrick A. Sakyi, Dept. of Earth Science

Modern Seismographs in Ghana Topic Two Modern Seismographs in Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

Modern Seismographs in Ghana Modern day recording of earthquakes begun in Ghana when a 6-component World Wide Standard Seismograph Station (WWSSS) was commissioned in Kukurantumi in the Eastern Region in March 1973. Later, many more seismographs were installed in south eastern Ghana for the monitoring of earthquakes. Since 1973 scores of earthquakes, some of magnitude as low as one (1) have been recorded in southern Ghana, and their epicentres determined Dr. Patrick A. Sakyi, Dept. of Earth Science

Earthquake Risk in Ghana Topic Three Earthquake Risk in Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

Earthquake Risk in Ghana Earthquake hazard means the probability of occurrence of an earthquake of sufficient Magnitude capable of causing damage to the weakest man-made structure. Risk means the measure of the likelihood of harmful consequences arising from the interaction of a hazard, vulnerable community elements and the environment. Dr. Patrick A. Sakyi, Dept. of Earth Science

Earthquake Epicenters and the Regional Geological Structures of Ghana Topic Four Earthquake Epicenters and the Regional Geological Structures of Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

Earthquake Epicenters and the Regional Geological Structures of Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana Topic Five Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana All the earthquake activity in Ghana can be associated with three major tectonic zones of weakness active in Ghana. - Cote d’Ivoire Fault - Akuapim Fault Zone - Coastal Boundary Fault Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana In the south-west, is the Cote d` Ivoire fault which cuts through Ghana. Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana The north-east trending Akuapem fault which intersects with the Coastal Boundary fault just to the west of Accra . Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana . Near Accra is the Coastal Boundary Fault Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana . Coastal Boundary Fault The CBF is a major fault parallel to the coast just a few kilometers off shore and trending east-west. To the east, this fault most probably strikes inland and continues as the faulted northern margin of the Keta Basin. Dr. Patrick A. Sakyi, Dept. of Earth Science

Active Faults in Ghana . Expected Epicentre Anywhere along the Akwapim–Togo range (along the Akwapim fault zone) Out to sea along the entire coast line of Ghana (on the coastal boundary fault) The intersection of these two faults (near Accra in the area between Weija and Nyanyanu on the coast) would be the most likely location of the next major earthquake in Ghana. The date and time of such an event cannot be predicted. Dr. Patrick A. Sakyi, Dept. of Earth Science

Earthquake Risk Map of Ghana Topic Six Earthquake Risk Map of Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

Earthquake Risk Map of Ghana Dr. Patrick A. Sakyi, Dept. of Earth Science

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