M. O. ALILE

This study examined the use of Electrical Resistivity Tomography (ERT) to investigate the subsurface lithology in Ugbogiobo, Ovia North East Local Government Area of Edo State. The research aimed to determine the variation in subsurface materials and identify geological structures that may influence groundwater potential, engineering suitability, and environmental conditions in the study area. The study adopted a geophysical survey approach using the ERT method, where resistivity measurements were taken along selected profiles to generate two-dimensional subsurface images. Data obtained were processed and interpreted using standard inversion software to produce resistivity models that reveal variations in lithological units. The results showed distinct subsurface layers characterized by varying resistivity values, indicating differences in soil composition, moisture content, and degree of weathering. The near-surface layer was generally composed of lateritic and sandy materials with relatively high resistivity values, while deeper zones exhibited lower resistivity indicative of clayey formations and possible water-bearing zones. The study also identified potential fracture zones and areas of structural weakness, which are important for groundwater accumulation and civil engineering planning. The study concludes that Electrical Resistivity Tomography is an effective non-invasive geophysical tool for subsurface investigation in Ugbogiobo. It provides reliable information on lithological variations and groundwater potential. The research recommends the integration of ERT surveys in site investigation studies before construction and borehole drilling to improve decision-making, reduce failure rates, and enhance sustainable groundwater development in the area.