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