Electrical resistivity tomography and VLF- EM technique for locating groundwater prospect in basement complex terrain of Ibadan south-west, Nigeria.

Abass, Olusegun K. and Bello,, MA and Williams,, I Electrical resistivity tomography and VLF- EM technique for locating groundwater prospect in basement complex terrain of Ibadan south-west, Nigeria. SEG Global Meeting Abstracts.

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Abstract

Delineating optimal drill location for groundwater prospect in basement complex terrain is an element of concern. The study area which is situated in the hard rock landscape of Ibadan, South-west, Nigeria is posed with water scarcity due to frequent seasonal variation. To address this dilemma, integrated geophysical technique with geological observation was adapted. A major lineament direction in the study area was found parallel to the geologic strike trending in the NW-SE direction. A total of eight (traverses 1, 3, 5 and 7 parallel to the strike direction while traverse 2, 4, 6, and 8 is perpendicular to it) 250 m long very lowfrequency electromagnetic (VLF-EM) profile integrated with 2-D electrical resistivity tomography (ERT) along the VLF traverses were collected to optimize the subsurface target zone. The result interpreted from the integrated geophysical technique with two open hand dug wells constitutes three layers overlaying the fresh basement rock. The top soil, weathered saturated layer and dry weathered basement. The aquifer region is the weathered saturated zone resulting from the low resistivity value between 90 - 370 Ωm and positive Karous-Hjelt current density distribution with depth variation from 4 – 13 m. Data consistency was observed along the lineament direction parallel to the geologic strike (NW-SE) which correlated well with the hand dug well II (NW) along traverse 3. Thus, the use of integrated geophysical approach along with geologic investigation is a reliable tool to predict groundwater bearing zones in hard rock terrains.

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