Investigation of Seismicity in Parts of African Plate

Abstract

This study investigated seismicity in parts of African plate to examine the pentad and annual variation of seismicity and to determine b-values for a period of 45 years. The data set for this work were obtained from the Advanced National Seismic System (ANSS), a website owned by Northern California Earthquake Data Centre, Berkeley UC, USA. The selected data consisted of earthquakes with Mb ≥ 0.2 for the study area from 1st January 1971 to 31st December 2015 with focal depth from 0 – 700km.  A total of 40,481 earthquake events were used in the study with North Africa having 39,068; South Africa 957; East Africa 448 and West Africa 8.  A comparison of the patterns of seismicity in the regions of the study showed that seismicity is very high in North Africa, moderate in South Africa, low in East Africa and very low in West Africa. It was also found that the seismic activity in the different regions of Africa does not vary uniformly with time. Series in the four regions are fluctuating and no similarity among them. Analysis of the correlation among the four regions was stronger between North Africa and East African regions with correlation coefficient, r = 0.53. This shows that there might be a similarity between the two regions in the process of stress accumulation or release. The b - values in the study area were determined to be; North Africa: 0.49; South Africa: 0.47; East Africa: 0.69 and West Africa: 1.58.  This indicates that West Africa region has reduced stress and hence more stable than other regions of Africa since it is related to the West African Craton. Therefore, North Africa, South Africa and East Africa are more vulnerable to earthquake hazards than West Africa.