Abstract

An integrated geophysical survey was carried out within the Precambrian Basement Complex of Omuo Comprehensive High School and its environ in Omuo-Ekiti, Ekiti State, South-west Nigeria to assess buildings in the area that are intensively affected by cracks resulting in structural instability. The geophysical methods adopted for the investigation are the Very Low Frequency Electromagnetic (VLF-EM), Magnetic, 2-D electrical resistivity profiling using the dipole-dipole array and Vertical Electrical Soundings (VES) using the Schlumberger array. The traverses were established E – W direction cutting across geologic strike. A total of five traverses were established with length ranging from 130 – 200m and of varying inter-traverse spacing. The station interval is 10m. Also, a total of thirty-five (35) VES stations were occupied covering the entire study area. The acquired data were processed and interpreted integrally to elucidate the shallow subsurface geology of the study area. The results were qualitatively and quantitatively interpreted and are presented as sounding curves and geo-electric sections. The magnetic interpretation shows relatively uneven bedrock topography with variable overburden thicknesses of between 5m – 15m. However, the VLF-EM results reveal ten (10) conductive zones which manifest as low resistivity zones in the generated geo-electric sections. The characteristic sounding curves obtained from the study area are H, HA, KH, HK, KHK, HAK and QH. The geo-electric sections reveal four subsurface layers which include: The topsoil, with resistivity values ranging from 104 – 4656 ohm-m and thickness of between 0.4 – 1.6 m. The weathered layer is characterized by resistivity values varying from 57 – 381 ohm-m and thicknesses of between 0.2 – 9.0 m. The fractured basements were identified beneath traverses 1, 2 and 5 with resistivity values of 109 - 709 ohm-m and depth range of 5.5 – 15.8m. The fresh basement has resistivity values of betwe