2D Geoelectric Imaging of the Uneme-Nekhua Fracture Zone

Abstract

We have employed 2D geoelectric imaging to reveal the geometry and nature of a fracture zone in Uneme-Nekhua, southwestern Nigeria. The fracture zone is discernable from an outcropping rock scarp and appears to define the course of a seasonal stream. Data were acquired using the dipole-dipole survey array configuration with electrode separation of 6 m and a maximum dipole length of 60 m. Three traverses with lengths varying between 72 m and 120 m were laid orthogonal to the course of the seasonal stream. 2D geoelectric images of the subsurface along the profiles imaged a north-south trending fracture zone. This fracture zone appears to consist of two vertical fractures with more intense definition downstream. The eastern fracture is buried by recent sediment, while the western fracture appears to have experienced more recent tectonic activity as it appears to penetrate through the near surface. Perhaps at some point, deformation ceased on the eastern fracture and further strain was transferred to the western fracture. The fracture zone generally defines the course of the north-south seasonal stream with the exception of the downstream end where the fracture appears to have died out entirely. Two associated basement trenches lying parallel to and east of the fracture zone are also imaged.

Subsurface electrical resistivity imaging and electromagnetic conductivity profiling at a proposed construction site at Adekunle Ajasin University campus, Akungba-Akoko, South-Western Nigeria

“…Interpretation criteria for resulting 2D subsurface resistivity structure of the subsurface followed similar criteria to that utilized in Aminu et al (2014), Aminu (2015a) and Aminu (2015b). High laterally and or vertically continuous resistivities (usually above 1000 Ohm-m) were interpreted to indicate unfractured basement rock.…”

“…In construction site investigations, they offer semi-continuous and sometimes continuous profiling of structures inimical to civil works projects (Soupios et al, 2002;El-Qady et al, 2005;Chavez et al, 2014;Yassin et al, 2014). They also provided information on the thickness of the regolith and depth to competent bedrock or formations (Robineau et al, 2007), morphology and spatial distribution of underlying geofeatures (Aminu, 2015a), groundwater regimes (Rizzo et al, 2004;Bufford et al, 2012;Aminu et al, 2014) and ground corrosivity (). They sometimes provide quantitative estimates of insitu geo-technical properties (Anderson, 2006;Cosenza et al, 2006) of the subsurface geologic strata and clues to the tectonic history of surveyed areas (Bufford et al, 2012;Aminu et al, 2014).…”

“…They also provided information on the thickness of the regolith and depth to competent bedrock or formations (Robineau et al, 2007), morphology and spatial distribution of underlying geofeatures (Aminu, 2015a), groundwater regimes (Rizzo et al, 2004;Bufford et al, 2012;Aminu et al, 2014) and ground corrosivity (). They sometimes provide quantitative estimates of insitu geo-technical properties (Anderson, 2006;Cosenza et al, 2006) of the subsurface geologic strata and clues to the tectonic history of surveyed areas (Bufford et al, 2012;Aminu et al, 2014). They therefore present some advantages over conventional geotechnical methods which are generally more expensive, time consuming and often (as a result of prohibitive cost) sparsely sample the subsurface.…”

Electrical Resistivity Imaging of a Thin Clayey Aquitard Developed on Basement Rocks in Parts of Adekunle Ajasin University Campus, Akungba-Akoko, South-western Nigeria

“…In basement complex regions such as the southwestern region of Nigeria, the provision of water for domestic and industrial consumption frequently relies solely on the exploitation of groundwater residing in fractures and weathered overburden. Major faults and fracture systems in the bedrock serve as groundwater collectors and pathways (Lines et al, 2012;Mohamed, Brasse, Abdelgalil, & Kheiralla, 2012;Moustafa, Ibrahim, Elawadi, Metwaly, & Al Agami, 2012;Aminu, Akande, & Ishola, 2014b) during the rainy season and continually recharge the weathered overburden during the dry season. Unfortunately, overburden thicknesses are frequently very thin to prevent long periods of storage.…”

“…In electrical resistivity imaging, the subsurface is charged by means of two current electrodes at the ground surface and the resulting resistivity response of the earth is measured via another set of two potential electrodes. The response obtained is used along with the layout configurations of the survey to create an image of the subsurface within the survey area (Aminu et al, 2014b). Robineau, Join, Beauvais, Parisot, & Savin (2007), utilised electrical resistivity tomography (ERT) to study the nature of a thick regolith within supergene nickel ore deposit developed on ultramafic rocks in New Caledonia (southwest Pacific).…”