A new seismic source model for seismic hazard assessment in southeastern Ghana

Abstract

The study presents a revised seismic source model for southeastern Ghana through the integration of geological, tectonic and seismological datasets spanning the period 1615 – 2021. Historical earthquake records obtained from the Ghana Seismological Department and previous catalogs were harmonized into moment magnitude (Mw) and declustered to produce a catalog of 629 independent seismic events. Geological and fault datasets were integrated with earthquake epicenters using Geographic Information Systems (GIS) to delineate and characterize active seismic source zones. Three seismic source zones (A, B and C) were identified based on similarities in tectonic setting, fault distribution and seismicity patterns. Seismicity parameters were estimated using the Gutenberg-Richter frequency-magnitude relationship and the Maximum Likelihood Estimation (MLE) method to evaluate earthquake recurrence behavior and tectonic stress conditions. The results revealed that seismic activity is strongly controlled by the reactivation of inherited crustal structures associated with the Romanche and St. Paul’s fracture systems, particularly along the Akwapim Fault Zone and the Coastal Boundary Fault. Zones A (Accra Region) and B (Gulf of Guinea) exhibited the highest concentration of earthquakes and fault density, while Zone C (Ho Region) recorded fewer events, but lower b-values, indicating higher stress accumulation and greater potential for relatively larger earthquakes. The Gutenberg-Richter analysis yielded b-values of approximately 0.60, 0.60, and 0.40 for Zones A, B, and C, respectively, while the MLE derived b-values were 0.93, 0.93, and 0.86. The proposed seismic source model provides a more realistic representation of seismic hazard conditions in southeastern Ghana and offers an improved framework for probabilistic seismic hazard assessment, infrastructure planning and disaster risk reduction.