Seismicity pattern of African regions from 1964–2022: b-value and energy mapping approach

Abstract

The African continent is one of the few tectonic plates where very few earthquakes have been reported. Sporadic poor data have jeopardized efforts to assess seismic hazards. In light of the tectonic setting, a review of the continent’s seismicity is crucial for predicting seismic hazards. For this study, seismicity data from USGS and ISC catalogs were collected from 1964–2022, in the latitude range of 40oS-40oN and longitude 20oW-52oE, from the surface to 700 km deep. Gutenberg’s parameters as well as the spatial variation of seismic energy were then analyzed as an assessment of Africa’s seismicity. The results show that NE Africa is at a higher stress level in terms of energy release than NW Africa. The Richter and Guttenberg’s constants of a = 5.61, b = 0.59; a = 6.55, b = 0.77; a = 6.44, b = 0.78; a = 7.41, b = 0.92; a = 5.94, b = 0.86; a = 5.97, b = 0.77 with the corresponding magnitude of completeness, mc, observed to be 3.7, 4.1, 4.4, 4.7, 4.8 and 4.6 were found for regions NW, NE, southern, eastern, western and central Africa, respectively. The distribution of focal depths vs. magnitude revealed that most of the seismicity is inherently shallow in its nature with an average focal depth of 21.22 km. In comparison, NW experiences relatively more profound events with an average depth of 32.19 km. A substantial rise in focal depth in North Africa is associated with the collision boundary. This information as a constraint on the tectonic plate near convergent boundary could be useful in plate modeling. Key Policy Highlights The higher stress observed in the North Africa and East Africa continent is vital for policy makers for sustainable built environment The estimated minimum magnitude cut-off Mw 3.7 reveals that the recording facilities in African continent is now improving. An increased focal depth distribution of events in North Africa infers there is plate convergence and can be used to constrain African tectonic plate for plate modeling.