ABSTRACT:

The basement complex of southwestern Nigeria has undergone severe tectonic deformation over the geologic past, resulting in various degrees of fracturing and folding, even to the extent of complete obliteration of primary structures except for some places. This study focuses on Akoko area which is dominated by hills of crystalline rocks that have made groundwater resource exploration difficult, thereby affecting the socio-economic activities of the inhabitants. High-resolution multispectral ASTER imagery acquired at the peak of the dry season was used to delineate fractures. Additional characterization employed electrical resistivity soundings. Results indicate the existence of four sets of fractures mostly occurring within the central and north-eastern parts. More fracture intersections occupy the central part. Ground truthing shows that the fractures mostly occur in gneisses, granites and quartzites, while geophysical data interpretation revealed fracture depths typically ranging between 32 and 65 metres. In this hard rock terrain with only a veneer of weathered materials, these fractures are the targets of most groundwater exploration activities. This study further asserts the effectiveness of integrated approach to fracture characterization and its usefulness in groundwater exploration especially in a terrain that had hitherto been hydrogeologically classified as difficult.