Geophysical Support for Urban Land Use Planning and Risk Reduction in Abuja Federal Capital Territory

Rapid physical expansion of Abuja has resulted in construction on geologically diverse terrain, including areas underlain by complex basement rocks, deep weathering profiles, and active structural lineaments, creating geotechnical risks inadequately captured by existing land use plans. This professional study integrates aeromagnetic interpretation and ground electrical resistivity data to develop a geophysical risk classification map for urban expansion zones in the Abuja FCT, covering a 200-square-kilometre priority area in Kuje and Gwagwa districts. Publicly available Nigerian Geological Survey aeromagnetic data were processed using structural enhancement filters to delineate basement geological boundaries and lineament trends. Ground resistivity measurements at 75 sites provided verification of the aeromagnetic structural map and quantified weathering depth, bearing capacity indicators, and drainage-related hazard factors. A geophysical risk index was computed for each surveyed site by combining standardised scores for weathering depth, structural complexity, resistivity variability, and proximity to mapped lineaments. The resulting risk map classifies the study area into four risk zones, with approximately 18 percent of the surveyed area designated as high to very high risk for building development without additional site-specific investigation. The study concludes with recommendations for integrating geophysical investigation requirements into the Abuja Environmental Impact Assessment framework for all development proposals exceeding 0.5 hectares. Keywords: urban planning, geophysical risk, Abuja FCT, aeromagnetic, basement geology