SUBSURFACE RESISTIVITY INVESTIGATION AT THE CENTRE FOR ENERGY RESEARCH AND TRAINING (CERT), AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA

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Date
2011-06
Authors
IDOWU, FADELE SUNDAY
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Abstract
Electrical resistivity method was used in carrying out geophysical investigations at the Centre for Energy Research and Training (CERT), Ahmadu Bello University, Zaria, with a view to determining the depth to the bedrock, thickness of weathered basement and the structural deformation of the subsurface rocks. The Vertical Electrical Sounding (VES) using Schlumberger array was carried out at forty (40) stations. ABEM terrameter (SAS 300) was used for the data acquisition. The field data obtained were analysed using a computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity data. Results from the interpretation suggest three (3) layers in most parts of the study area. However, there is a case of two (2) layers at a station. The resistivity value for the topsoil varies from 2 to 738Ωm with thickness ranging from 1.00 to 3.90 metres. The weathered basement has resistivity values ranging from 32 to757Ωm and thickness of between 0.52 and 23.00 metres. The fresh basement (bedrock) has resistivity values as high as 6,036Ωm. The topsoil is characterized by fine grain rocks (clayey), associated with weathering of sulphide minerals from the underlying granitic rocks. They have great amount of dissolved salts resulting to their low resistivity values. The weathered basements are medium to fine grain, porous or fractured rocks containing water. They are referred to as the aquiferrous zone. Highly fractured areas here have low resistivity because of its high degree of saturated water implying that their resistivity is greatly influenced by underground water. The geologic sections derived, suggest that the weathered basement entirely represent a promising aquifer which can serve as the source of water to the area throughout the year. The fresh basement rocks are coarse, close grained (plutonic or intrusive) rocks, constituting the rock forming minerals which are poor conductors resulting to their high resistivity values. The parameters of investigation have helped in identifying strategic areas for siting high-rise buildings, potential positions for the siting of boreholes and possible depth of sewage system in order to avoid groundwater contamination since the area is generally a shallow fresh basement. A borehole log was provided for the only borehole present in the area. Azimuthal sounding plots have revealed the existence of resistivity anisotropies, trending NW-SE, NE-SW and E-W directions. These structural trends conform with the Orogenic events that took place in the Basement Complex of Nigeria, implying that the study area was affected by the two major Orogenic events that took place in the Nigeria Basement Complex, that is, the Pan-African (600 ma) and Eburnean Orogeny (1950±50 ma).
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A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA IN PARTIAL FULFILLMENT FOR THE AWARD OF MASTER OF SCIENCE IN APPLIED GEOPHYSICS DEPARTMENT OF PHYSICS AHMADU BELLO UNIVERSITY, ZARIA.
Keywords
SUBSURFACE,, RESISTIVITY,, INVESTIGATION,, CENTRE FOR ENERGY RESEARCH AND TRAINING,, AHMADU BELLO UNIVERSITY,, ZARIA,, NIGERIA
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