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Abstract:
No in-depth seismic hazard (SH) study for West Africa (WA) has ever been conducted, as the regional earthquake catalogues are incomplete. Such lack of comprehensive SH study has negatively affected planning and development of critical infrastructure and disaster risk management in WA. This study aims to bridge the knowledge gap by applying modern techniques to updating the existing catalogues and assessing the seismic hazards for the region. We updated the current catalogue for WA from International Seismological Centre, publications and data from seismic stations in WA. Different studies considered the seismotectonic setting of WA as stable continental crust and a region of shallow crustal seismicity. We investigated both schools of thought and compared results. For each scenario, three different ground-motion models (GMMs) were combined to produce each hazard map using logic tree formalism with equal weights. WA was divided into five source zones for the computation of earthquake recurrence parameters and for the entire WA region. Computed Gutenberg–Richter b-value, activity rates(λ), and regional maximum possible magnitudes(mmax) for the zones ranged from 0.84 to 1.0, 0.3–2.1, and 5.2–7.0, respectively. Calculated b-value, λ, mmax for the region were 0.77, 4.1, and 7.2. The estimated b-value (0.77) falls within generally accepted range for tectonic seismicity. SH predicted by GMMs for stable continental areas was higher than that predicted for shallow crustal seismicity. Therefore, our results confirmed that WA is characterized by a stable continental crust. The highest hazard levels were observed in parts of Ghana, Togo, Cameroon etc., ranging between 0.02g and 0.03g.
