An Application of Vertical Electrical Sounding for Subsurface Geophysical Characterization in Geidam Town, Geidam Local Government Area, Yobe State.

Abstract

Abstract

The study utilizes the Vertical Electrical Sounding (VES) technique aimed at exploring the subsurface lithology and hydrogeological framework of Geidam Local Government Area, Yobe State, Nigeria. The study forms part of the Chad Basin, a large inland sedimentary basin composed mainly of Quaternary and Tertiary deposits such as alluvial sands, clays, silts, Bima Sandstone, Gongila Formation, and the Chad Formation. Field data were collected with the aid Schlumberger array with electrode separations (AB/2) between 1 m and 140 m. The computed apparent resistivity values decreased progressively from 24 Ωm at shallow depths to around 2 Ωm at greater depths. The VES curves predominantly show an H-type response, which reflects a resistive surface horizon underlain by conductive strata. Interpretation identifies three principal layers: a resistive sandy topsoil (20–30 Ωm, 3–6 m thick), an intermediate clayey sand unit (8–15 Ωm, 15–30 m thick), and a conductive saturated clay aquifer (2–5 Ωm) extending below the depth of exploration. Quantitative modelling indicates that the Chad Formation is dominant at depth, which corresponds with regional geology. The low resistivity of deeper layers indicate that the groundwater in this locality is likely saline or mineralized, a common feature of Chad Basin aquifers. The study highlights the usefulness of VES in subsurface characterization with relevance to groundwater assessment, geotechnical analysis, and environmental studies. The findings serve as useful guide for groundwater development and sustainable water management in the semi-arid northeastern region of Nigeria.

Keywords

Vertical Electrical Sounding (VES); Apparent Resistivity; Geoelectric Layers; Subsurface Characterization; Chad Basin; Groundwater Potential; Geidam; Yobe State; Nigeria.