Probabilistic seismic hazard assessment for West Africa region

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Abstract

West-Africa is a region of low-to-moderate seismicity, with only a few known earthquakes of moment magnitude greater than 5, notably the 1939 Mw 6.4 Accra (Ghana) earthquake. An effort has been made to perform a seismic hazard assessment for the region enclosed within latitudes 2°N and 16°N and longitudes 18°W and 15°E using a probabilistic approach within a logic-tree framework. Ground-motion scaling relationships are selected to account for epistemic uncertainty. The compiled catalogue from 1615 to 2018 and homogenised to moment magnitude (Mw). We present hazard result values on rock site conditions, in terms of seismic hazard curves, peak ground acceleration and uniform hazard spectra, for the study region and four selected cities. We estimate the maximum PGAs of 10%, and 2%, chances over 50 years at 0.10 and 0.26 g respectively, in Accra. Finally, a deaggregation of the Accra site was carried out to identify the dominant earthquake scenario for the chosen site for a 475-year return period. Results showed that the prevalent scenario characterised by seismic events between magnitudes 5.5-6.0 and at a distance less than 60 km. Findings from these assessments will help to contribute to the safe development of the region.

Bibliographical metadata

Original languageEnglish
JournalGeorisk
DOIs
Publication statusPublished - 15 Jul 2021