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

Eddy Ferdinand Mbossi,Jean Marcel Abate Essi,Bekoa Ateba,Delair Dieudonné Etoundi Ndibi,Tabod Charles Tabod,Pauline Wokwenmendam Nguet,Edouard Olivier Biboum Ntomb,Jacques Dili-Rake

doi:10.4236/ojer.2021.102006

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 (Mw). 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.

Highlights

West Africa spans the area between latitude 0 ̊N to15 ̊N and longitude 20 ̊W to 10 ̊E
The outlined technique was applied to West Africa to estimate the earthquake hazard parameters
The seismic events of Mw ≥ 3.0 have been detected in neighboring countries and Gulf of Guinea (GOG) [13]. In spite of these constraints and the choice done by Musson [13] to do not include them in the seismicity of West Africa, we considered these earthquake events and extended the time period (1615-2021) in order to obtain an accurate seismic hazard assessment of West Africa

Summary

Introduction

West Africa spans the area between latitude 0 ̊N to15 ̊N and longitude 20 ̊W to 10 ̊E. The tectonics of the Western Africa plate have revealed several continental or oceanic fracture zones. These fracture zones are often interpreted as Atlantic passive margins, the site of seismic strain rates and active deformation [1] [2] [3]. The Atlantic Ocean has extended along these faults, especially in its southern part where there is junction of the oceanic fracture zones with the West African continental margin in the Gulf of Guinea (GOG) and continental faults [6]. The GOG region consists of several tectonic structures which are linked to the pan-African Proterozoic orogeny [7] [8]. Kutu et al [12] show the continental active tectonics seems to be linked with the oceanic transform faults in the Gulf of Guinea. Several continental faults may generate large earthquakes (Mw ≥ 6.0) and can be associated with the Romanche, Chain and Saint Paul transform faults [4]

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