Seismic Hazard Assessment for a Proposed Dam Site in Plateau State

This study assesses seismic hazard at a proposed small dam site in Plateau State, North Central Nigeria. Infrastructure projects including dams and bridges require seismic hazard assessment as part of their engineering design process, particularly in areas where historical seismicity records are sparse. Plateau State lies within Nigeria's basement complex where tectonic lineaments and anthropogenic activities including mining have generated local seismicity. This study collects seismic noise data at 12 stations distributed across a 2-kilometre radius around the proposed dam site using three-component seismometers deployed for 24-hour recordings. HVSR analysis extracts fundamental resonance frequency and amplification factor at each station. Peak ground acceleration is estimated using attenuation relationships appropriate for the West African tectonic setting, calibrated to the local HVSR site response. Active fault mapping is conducted from high-resolution satellite imagery. Available historical earthquake catalogue data for the region are compiled from the NEIC and ISC international databases and the OAU Ile-Ife seismological station bulletin. Findings reveal that the area experienced 14 seismic events of magnitude 1.5 to 3.8 within a 50-kilometre radius from 2000 to 2023, mostly associated with mining activities in the Bukuru-Jos area. Site resonance frequencies of 4 to 7 hertz with amplification factors of 2 to 4 are measured, indicating moderate site amplification. Estimated peak ground acceleration for a 475-year return period event is 0.06g, confirming the dam requires Seismic Design Category B provisions under appropriate engineering codes. The study recommends continued strong motion monitoring during dam construction.

Keywords: seismic hazard, dam site, HVSR, Plateau State, peak ground acceleration.