Geophysical investigation of crustal structural framework of Ilesha, southwestern Nigeria

Abstract

The interpretation of the aeromagnetic dataset of Ilesha southwestern Nigeria has been carried out to reveal possible future earthquake hazard as well as establish the groundwater potential of the area. The edge detection methods involving the analytical signal amplitude, the total horizontal derivative, the first vertical derivative and the 3D Euler deconvolution were performed on the residual magnetic intensity anomalies to identify the linear structural discontinuities associated with lithological boundaries/ faults in the area. The upward continuation filter and depth estimation procedures of source parameter imaging and radially averaged power spectrum were applied to the residual magnetic intensity data to map geological structures such as faults as well as determine the depth to crystalline basement rocks in the area. The obtained lineaments observed to trend predominantly towards the NE-SW direction indicative of Pan African Orogeny, suggest possible high yield groundwater aquifer zones. The upward continuation filtered maps showed evidence of deep-lying faults to depth beyond 2 km. The 3D Euler deconvolution plots and spectral analysis revealed depth to magnetic sources ranging from 55 m to 345 m and 13 m to 250 m, respectively. The delineated structural discontinuities in the study area revealed stress history similar to Ifewara-Zungeru fault network, suggestive of possible future earthquake occurrence in the area. It is however recommended that further geophysical studies should involve electrical method to establish the groundwater potential as well as the stability of the basement underlying the area.