2D electrical resistivity imaging of fracture zones in Isu-Awaa, Enugu State, Southeastern Nigeria

Abstract

2D electrical resistivity imaging technique has been used to investigate the nature and dimensions of the fracture prone zones in Isu-Awaa, Enugu State, Nigeria. The study area lies within Latitude 06° 14 I 0 II N to 06° 17 I 0 II N and Longitudes 007° 23 I 0 II E to 007° 28 I 0 II E, with an area extent of about 51 Km 2 . The area is underlain by three main geological units (Enugu Shale, Owelli Sandstone and Mamu Formation). The study area is topographically undulating with high ridges surrounding the area. 2D electrical resistivity data was acquired with Wenner configuration, employing the roll-along technique to image the subsurface. A total of four (4) number 2D electrical resistivity imaging traverses were carried out. Data was processed and interpreted using RES2DINV. Measured and calculated apparent resistivity pseudo sections were convolved to generate the inverse model resistivity section, which was the diagnostic interpretative model used. Discontinuities in the layering are possible fracture zones. Major discontinuities were observed at distances of 48 and 87, 52.5, 106, 8.0 and 26 m at traverses A, B, C and D respectively. Fracture trend azimuth rose diagram, shows pre-dominant trend to the SE direction with minority to the SW and NW, and relicts to the NE directions. This conforms to the regional lineaments map of Nigeria. The use of 2D electrical resistivity imaging tool has proved useful in the mapping of fracture prone zones in the study area.