Combined Use of Electromagnetic and Magnetic Survey for Hydrogeophysical Characterization of Ijapo Housing Estate, Akure

Abstract

Very Low Frequency Electromagnetic (VLF-EM) and ground magnetic studies were carried out in Ijapo Housing Estate, Akure, with the aim of delineating hydrogeologic associated structures. The area is underlain by the precambrian basement complex rocks of southwestern Nigeria. VLF-EM profiling was undertaken along 19 traverses with lengths ranging from 180 to 1,200m. Ground magnetic data were acquired along 35 traverses with lengths varying between 120 and 1,060 m. VLF-EM data were plotted as profiles and also inverted into 2D-sections using Karous-Hjelt filtering software. Ground magnetic data were reduced and inversed using automated euler-deconvolution software to estimate depths to basement. VLF-EM readings vary from – 110.3 to + 99.9% in the filtered real and imaginary components. VLF-EM depth-structure map enables the classification of the area into zones of shallow and deep fractures. Relative magnetic values vary from -1290.38 to +835.38 nT. Estimated depth to basement from the geomagnetic section was used to generate magnetic depth-structure map which enabled the classification of the study area into shallow and deep fracture zones. Correlations of results show that area classified as deep structure zone from VLF-EM coincide fairly well with that of ground magnetic. This is the high groundwater potential zone. Groundwater development programme within crystalline basement complex should be limited to high groundwater potential zone, because of the localized nature of its occurrence. Therefore, detailed geophysical survey should be carried out prior to drilling.