Probabilistic Assessment of Seismic Hazard and Its Implications for Structural Design in the Benue Trough Region

The Benue Trough, a major intraplate rift structure running through central Nigeria, represents the most seismically active geological zone in the country and has generated several moderate magnitude earthquakes in recent decades, yet structural design practice in the region continues to largely ignore seismic loading. This study presents a probabilistic seismic hazard assessment for selected cities along the Benue Trough in the North Central and South East geopolitical zones, including Makurdi, Lokoja, and Abakaliki, using a logic tree framework incorporating multiple ground motion prediction equations and alternative source models. Seismic hazard curves were derived for spectral accelerations at periods of 0.2 s, 0.5 s, and 1.0 s for exceedance probabilities of 10 percent and 2 percent in 50 years. Site amplification factors were incorporated using VS30 data from available geotechnical investigations in each city. The resulting design spectra were compared against the provisions of the Nigerian National Building Code and Eurocode 8 to identify structural design implications for typical residential and institutional building typologies. Results indicate that peak ground accelerations at 10 percent in 50 years exceedance probability reach 0.06g to 0.11g across the study cities, sufficient to govern structural design of unreinforced masonry construction and soft-storey reinforced concrete frames. The current Nigerian National Building Code underestimates design seismic demands in all three cities by factors of 1.4 to 2.1. The study recommends urgent revision of the seismic zonation map in the Nigerian National Building Code and mandatory seismic detailing requirements for institutional and healthcare buildings in the Benue Trough zone. Keywords: seismic hazard, probabilistic assessment, Benue Trough, ground motion, structural design.