2D ELECTRICAL RESITIVITY TOMOGRAPHY AS AN INSTRUMENT TO DETERMINE STRATIGRAPHIC LAYERS IN UNIVERSITY OF BENIN-UGBOWO AREA OF EDO STATE

ABSTRACT

This study investigates the effectiveness of two-dimensional (2D) electrical resistivity tomography (ERT) as a geophysical tool for determining stratigraphic layers within the University of Benin (UNIBEN)-Ugbowo area, Benin City, Nigeria. The primary motivation for this project stemmed from the need for a non-destructive and costeffective method to map the subsurface lithology and identify potential variations in geological formations across the study area. 2D ERT offers a valuable approach to achieve this objective by measuring the variations in electrical resistivity of the subsurface. The investigation involved the deployment of ERT surveys along designated lines within the study area. The data acquisition process utilized a specific electrode configuration (Wenner array) to inject electrical current into the ground and measure the resulting potential difference at various electrode separations. This approach allowed for the creation of 2D inverted resistivity imaging models at an approximate depth of about 30m, which visually represent the distribution of electrical resistivity variations with depth along the survey lines. By correlating these variations with resistivity ranges of known geological formations, I was able to detect more than ten distinct subsurface layers ranging from Alluvium soil, Shale, Slate, Sandstone, Quartz, Marble, Basalt, and Granite with apparent resistivity values ranging from 131 Ωm to 2378 Ωm. It will be observed, that there is an increase in the coarse nature of the Lithology, rocky materials which is a reflection from the increase in resistivity of the rock types as we go deeper into the earth subsurface of the study area in all the profiled lines. The findings of this research will contribute to a more comprehensive understanding of the subsurface geological framework within the study area and can serve as a valuable resource for future infrastructure development or environmental investigations. It is worth noting that the data interpretation is based on the first 30 meters of the subsurface. Heavy construction projects might require foundations that extend much deeper. Additional investigation techniques (e.g., deeper boreholes) would be necessary to assess the suitability of the subsurface beyond the reach of this ERT survey