DC Resistivity Investigation of Anisotropy and Lateral Effect using Azimuthal Offset Wenner Array. a case Study of the University of Calabar, Nigeria

Abstract

Azimuthal resistivity survey (ARS) was conducted using offset Wenner array to investigate anisotropy and lateral effect for the first time in the University of Calabar environment, Nigeria. Two (2) sites were surveyed within the study area. Data were collected using ABEM terrameter SAS 1000 and its accessories. From a reference point, azimuth was varied with an increment of 15⁰ to 360⁰. Analysis of azimuthal offset Wenner array resistivity data revealed that the study area is homogeneously anisotropic with no lateral effect in all azimuths. The apparent coefficient of anisotropy estimated from the field data ranged from 1.10 to 1.90 with anisotropy in (NW-SE), (NE-SW), (E-W) and (N-S) directions. The homogeneity index ranged from 4.71 to 9.60 and this indicates that the variation due to anisotropy is greater than that due to inhomogeneity within the study area.

Keywords: Anisotropy, Lateral effect, Azimuthal Resistivity Survey, Offset Wenner Array and homogeneity index.