Electrical Resistivity and Seismic Refraction Methods of Investigating a Landslide Area: A Case Study of Elu Community, Abia State, Nigeria

This study was carried out to investigate the subsurface structure in a landslide area in a community in Ohafia Abia State, using geophysical data obtained from the subsurface formation of the area. A total of seven stations comprising of three vertical electrical sounding (VES) using Schlumberger electrode configuration and four electrical resistivity profiling (2D) using Wenner array configuration were occupied. Resistivity data were acquired using the Abem terrameter (AGI single R8). The data were smoothened and analyzed using Schlumberger computer automatic iterative software. In the same line seismic critically refracted data were acquired using 12-channel ABEM Terraloc MK III digital seismometer and processed with the Reflexw software into 2D velocity depth models. A two-layer model was delineated by the velocity profile with a range of 338 m/s and 4356 m/s for the entire depth of probe. Results of resistivity model show 6 constrained geo-electric layers covering a total depth of 55.0 m with low resistivity values for the top soil. Increase in resistivity with depth observed in the study indicates increase in compaction and solidification with depth in the subsurface as layers alternates. The resistivity of most of the formation layers are averagely high suggesting a high degree of void spaces inside the rock material. This might have resulted from high erosional activities in the area that gave rise to landslides. Also, the formation lithology for the area is mainly sand/sandstone from the top soil to the survey depth, suggesting non protective or absence of highly compacted clay materials that are more resistant to erosion associated with heavy rainfall in the area