Evaluation of electrical resistivity anisotropy in geological mapping: A case study of Odo Ara, West Central Nigeria
The study of electrical resistivity anisotropy in rocks has become important in increasing the accuracy of geological mapping using electrical resistivity survey. The study area, Odo Ara near Egbe, west central Nigeria, has been surveyed using electrical resistivity soundings. Sixty Radial Vertical Electrical sounding (RVES) measurements were carried out in the study area which comprises of the banded gneiss, amphibolites, schist and intrusive pegmatites. The aim of the study is to use the electrical resistivity anisotropy properties of the area to resolve its geological setup. The VES data showed a significant presence of electrical resistivity anisotropy. The VES curves obtained were predominantly of 3 geoelectric layer of H-type (ρ1>ρ2<ρ3) curves; the topsoil, sandy clay/ clay layer and fractured basement. The pseudo-sections show a good correlation with the geoelectric section. Moreover, the iso-resistivity and isopach maps also show a significant correlation with the lithological and strike of the rocks in the area but due to the non uniqueness of electrical resistivity, the lithologic difference between the banded gneiss and the amphibolite at the south western part of the area could not be totally resolved. However, the combination of the anisotropy polygons and the iso-resistivity map has reduced the ambiguity inherent in using a single geophysical parameter.
Key words: Electrical resistivity anisotropy, radial vertical electrical sounding, anisotropy polygons.