| Abstrakt: |
Although probabilistic seismic hazard assessment (PSHA) has been carried out in a few countries in West Africa (WA), large-scale PSHA is still lacking in the region. Dearth of earthquake data, sparse or complete absence of a network of seismographic stations, lack of skilled geoscientists, absence of appropriate policies to encourage PSHA, and so on are responsible for the situation. This research therefore is aimed at computing the area-characteristic seismic hazard parameters (b-value, activity rate (λ_4.0), and the regional maximum earthquake magnitude (Mmax)) for Ghana, Nigeria, Benin, Togo, Burkina Faso, and Cote D'Ivoire to assist in future PSHA studies and planning. The earthquake catalogue which covers the 1615–2020 period with magnitudes ranging from 1.5 to 6.8 was compiled from regional stations, publications, and the International Seismological Commission (ISC). The initial catalogue with 259 events was reduced to 98 events after declustering (removal of dependent events) and harmonization of magnitudes into moment magnitude (MW); six subcatalogues were then created from the main one, each representing the respective country. The method of maximum likelihood estimate was adopted in the computation of the parameters. Firstly, the hazard parameters for the whole area were computed using the ZMAP. Secondly, the Ha3 program was utilized to compute the parameters for the subcatalogues. The results of the seismicity parameters for the whole region are b = 0.98, λ_4.0 = 0.631, Mmax=7.21. The results for the parameters for each contributing country are Ghana (b = 0.76, λ_4.0 = 0.081, Mmax = 7.03); Nigeria (b = 0.68, λ_4.0 = 0.026, Mmax = 6.22); Togo (b = 0.96, λ_4.0 = 0.020, Mmax = 5.01); Benin Republic (b = 0.92, λ_40 = 0.024, Mmax = 5.19); Cote D'Ivoire (b = 0.94, λ_4.0 = 0.033, Mmax = 5.28); and Burkina Faso (b = 0.91, λ_4.0 = 0.031, Mmax = 5.10). The return periods and probabilities of exceedance of magnitudes 4.0 to 7.0 for each zone in 1, 50, 100, and 500 years are also presented in this study. The 0.98 b-value for the whole region relates well with the expected b-value characteristic for stable cratonic areas. Besides, the low or high values of the b-values have indicated either a fault-slip-related seismicity (Ghana and Nigeria) or of stress change seismicity (Benin, Burkina Faso, Cote D'Ivoire, and Togo) regions. [ABSTRACT FROM AUTHOR] |
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