Integrated geophysical investigation of remotely sensed suspected fault zones around Iwaraja-Ijebu Ijesa area of Osun state, Nigeria.

Abstract

Magnetic profiling, electrical resistivity 2-D Dipole Dipole imaging and 1-D Vertical Electrical Sounding (VES) were carried out over two suspected remotely sensed delineated mega lineaments in the area around Iwaraja – Ijebu Ijesa in Osun State, Southwest Nigeria. This was with a view to establishing the existence of the mega structures. Total field magnetic and electrical resistivity measurements were carried out along geophysical traverses established across the suspected fault zones. The magnetic measurements, carried out at 10 m interval, were corrected for diurnal variation and offset. The 2-D magnetic models generated along the traverses, delineated uneven magnetic basement relief with overburden thicknesses varying from 3.0 to 90.0 m and suspected steeply dipping magnetic dykes (suspected fault zones) with widths varying between 60 and 200 m. Inverted 2-D Dipole Dipole images and geoelectric sections along the geophysical traverses delineated five geologic layers comprising the topsoil, laterite, weathered layer, weathered/fractured basement and fresh basement. The 2-D Dipole Dipole images identified major low resistivity near vertical discontinuities typical of fault zones that correlated with the magnetic anomalous zones. The widths of the anomalous zones varied between 60 and < 200 m. The study concluded that the suspected mega lineaments are fault zones which were displaced slightly north of the present locations.

Keywords: Geophysical Traverses, Magnetic Profiling, Electrical Resistivity, Suspected Fault Zones