An integrated geophysical investigation of a spring in Ibuji, Igbara-Oke, southwestern Nigeria

Abstract

An integrated geophysical investigation involving the magnetic and electrical resistivity methods was  used to investigate a spring in Ibuji, near IgbaraOke, southwestern Nigeria. This was with a view to  determining its nature and source and the feasibility of developing it as a groundwater resource. Magnetic profiling and 2-D subsurface resistivity imaging with the dipole-dipole array and thirteen Schlumberger  Vertical Electrical Soundings (VES) were carried out along three traverses. The total field magnetic  measurements were taken at 5 m interval and corrected for diurnal variation and offset. Magnetic   anomaly that is typical of a thin dipping dyke model (suspected to be a fault/fracture or shear zone) was delineated along each of the three traverses. Quantitative interpretation of the magnetic anomalies gave depths to the magnetic basement bedrock of between 13.2 and 20.1 m. The geoelectric sections and the inverted 2-D resistivity structures delineate maximum of four subsurface geological units consisting of the topsoil, weathered layer, the fractured basement and the fresh basement rock. The VES gave depths to basement bedrock of 7.4-25.1 m. Also the resistivity structures identify a major low resistivity  vertical discontinuity (F1) typical of a fault zone across the three traverses and another suspected strike slip fault (F2) across fault zone F1 on which the Ibuji Spring is located. The width of the anomalous zone varies from 10-17.5 m. It can be concluded that the Ibuji Spring is structurally controlled. The 10-17.5 m wide suspected fault zone F1 is favourable to groundwater development.

Keywords: Geophysical, Investigation, Fracture Delineation, Spring, Ibuji.