Preliminary Seismic Hazard Assessment in West Africa Based on Incomplete Seismic Catalogs

Abstract

West Africa is considered a region of low seismicity. However, the monitoring of earthquake activity by local seismic arrays began very early (as early as 1914) in West Africa but seismic catalogs are very incomplete. In 1991, Bertil studied the seismicity of West Africa based on networks of seismic stations in Ivory Coast and neighboring countries. The reference work of Ambraseys and Adams as well as the recent earthquakes given by the international data centres on the seismicity of West Africa were also used for the computations of earthquake hazard parameters. Different earthquake event data have been compiled and homogenised to moment magnitude (M w ). The obtained catalog covers a period of over four centuries (1615-2021) and contains large historical events and recent complete observations. The complete catalog part has been subdivided into four complete subcatalogs with each a level of completeness. The minimum magnitude and the maximum observed magnitude are equal to 2.89 and 6.8 respectively for the whole catalog. The seismic code software developed by Kijko was used to calculate the earthquake hazard parameters. The results give a b value of 0.83 ± 0.08 for the whole period and preliminary seismic hazards curves are also plotted for return periods 25, 50 and 100 years. This is a good and practical example showing that this procedure can be used for seismic hazard assessment in West Africa.

The Intraplate Stress Field of West Africa

“…West Africa is a region with a long history of tectonic deformation that spans Precambrian and Phanerozoic tectonics. Far away from the active tectonic boundaries at the mid‐ocean ridges and subduction zones, its continental interior hosts a plethora of earthquakes that are challenging to explain using simple tectonophysics models (Mbossi et al., 2021; Olugboji et al., 2021). These earthquakes are observed in clusters within and across the Neoproterozoic intra‐cratonic failed rifts (i.e., the Gourma Aulacogen (GA) ), the Mesozoic failed rift systems, the passive transform margins, and the Precambrian brittle shear zones across the intra‐cratonic shields (Figure 1b).…”