Mapping Of Structural Features in Basement Complex Part of Southwestern Nigeria Using Integrated Geophysical Methods

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Author(s) Babafemi E.M | Bamidele O.E | Sangodiji E.E
Pages 218-227
Volume 5
Issue 5
Date May, 2016
Keywords Geoelectric Layers, Structural Features, VES, VLF-EM
Abstract

Integrated geophysical investigation involving Magnetics, Very Low Frequency Electromagnetic (VLF-EM), Schlumberger Vertical Electrical Sounding (VES) and dipole-dipole configuration of electrical resistivity methods were carried out along a traverse near the Akure-Ilesha highway, Akure, Southwestern Nigeria. The study is aimed at mapping the presence of subsurface structural feature(s) and characterizing overburden materials. The magnetic data, Very Low Frequency Electromagnetic (VLF-EM), dipole-dipole electrical resistivity and Schlumberger Vertical Electrical Sounding (VES) were all obtained along the same profile which is 500 m long. Twenty-six (26) VES stations were occupied with maximum half-current electrode separation (AB/2) of 150 m; with inter VES spacing of 20 m and dipole spacing of 5 m and expansion factor n ranged from 1-5. Magnetic and VLF-EM data were taken at interval of 5 m. The VLF-EM profile and 2-D model generated shows anomalies interpreted in terms of subsurface structures which correlate with the Magnetic anomalies (dykes) revealed on the profile. From the quantitative interpretation the number of the interpreted geoelectric layers ranges from three (3) to five (5). Geoelectric sections generated from VES results showed that the study area is underlain by clayey/sandy clay topsoil, clayey weathered layer, partly weathered/fractured basement and the presumably fresh bedrock. The dipole-dipole resistivity profiling thus present a general morphology of the concealed basement in form of undulating topography. The subsurface structural feature(s) and overburden materials delineated in the study area are inimical to civil engineering structures but suitable for groundwater abstraction and could reduce environmental pollution. This study has therefore demonstrated that the combination of geophysical methods has greatly improve the quality of the basement structure investigation, and also that geophysical survey techniques are necessary for developing a reasonable model of the subsurface features.

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