Abstract
The Dipole –Dipole array was used for Constant Separation Traversing (CST) to investigate subsurface lithology in Oredide village, Auchi, Edo state with a view to determining the vulnerability or otherwise of the menace of erosion in the area. All the traverses were carried out with electrode spacing of 10 m with a spread of 200 m. The data was obtained using Pasi terrameter (16-GL) and processed with the Dipro software. The results revealed that the subsurface is underlain by the topsoil, lateritic sand, sand and sandstone. 2D results indicate topsoil with resistivity value range of 309 to 40130 Ωm within the depth range of 0 to 5 m. The second layer corresponds to sandy, lateritic sand, sand and sandstone having resistivity values ranging from 2186 to 60350 Ωm to a depth of 10.0 m. The third layer has resistivity values indicating lateritic sand, sand and sandstone layer with resistivity values ranging from 2186 to 60350 within the depth of 20 m. The fourth layer connotes lateritic sand, sand and sandstone to a depth of 30 m. The fifth horizon has resistivity values in the range of 585.2 to 35732.4 Ωm which is representative of sand and sandstone.The maximum depth imaged was 47.7 m.The inverted 2-D resistivity structure shows high resistivity distribution near-surface >1000 Ωm, which are indications of vulnerabilities to erosion in the study area with depth of scouring being 15 m.
Highlights
A more perfect model of the subsurface is a twodimensional (2-D) model where the resistivity varies in the vertical direction, as well as in the horizontal direction along the survey line
It is most unique when the survey line is placed near a steep contact with the line parallel to the contact.Aigbogun et al, (2020) used electrical resistivity tomography to investigate subsurface lithology in Auchi Polytechnic, Auchi, Edo state, Nigeria
The method is repeated for as many combinations of current and potential electrode positions as defined by the survey configuration. 2D resistivity imaging can be seen as continuous vertical electrical sounding (CVES) in which a number of VES conducted in a grid are merged together or as a combination of successive profiles with increasing electrode separation
Summary
A more perfect model of the subsurface is a twodimensional (2-D) model where the resistivity varies in the vertical direction, as well as in the horizontal direction along the survey line. Geoelectrical resistivity imaging has been widely employed to map areas with fairly complex geology(Griffiths and Barker, 1993; Griffiths et al, 1990; Dahlin and Loke, 1998; Olayinka, 1999a; Olayinka and Yaramanci, 1999b; Amidu and Olayinka, 2006).Loke (2001) stated that the major inadequacy of the 2D geoelectrical resistivity imaging is that measurements taken with large electrode separation are often affected by the deeper sections of the near-surface as well as structures at a larger horizontal distance from the line of survey.
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