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.
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 (SAS300) 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.
Background of Study
The electrical methods are generally classified according to the energy source involved, i.e., natural or artificial.
Thus, self potential (SP), telluric current, magnetotelluric (MT) and audio frequency magnetic field (AFMAG) methods come under natural source methods, while resistivity, equipotential, mise-ả-la-masse, electromagnetic (EM) and induced polarization (IP) methods are artificial source methods.
In this work, the electrical d.c. resistivity method was used in carrying out geophysical investigation of the Centre for Energy Research and Training (CERT), Ahmadu Bello University, Zaria.
The parameters investigated in this area include the depth to the bedrock, distribution of the weathered basement rocks and the subsurface deformational rock systems.
Climate, Vegetation and Geomorphology of the Study Area
Centre for Energy Research and Training, Ahmadu Bello University, Zaria is located in the South-Western region of the Zaria Sheet 102 map (Fig. 1.1). The study area is bounded approximately by longitudes 70 38´58” E and 7042’15”E and latitudes 11008’35’’N and 11008’58’’N within the Zaria Sheet 102 SW map.
Zaria lies in the Guinea Savannah, woodland vegetation characterized by bushes generally less than 3 metres high and scattered trees. The vegetation assumes various shades of green in the wet season and turns brown or pale in the dry season.
Extensive farming usually takes place during the rainy season, but with the presence of rivers like the Kubanni, irrigation farming system is also practised in some areas.
The study area can be reached through the federal high way of Sokoto – Zaria road.
The study area falls within the semi-arid zone of Nigeria (Harold, 1970). The mean annual rainfall over a period of 35 – 40 years for Zaria is 109.2 mm (Olufemi, 1985).
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Ajibade, A.C., Woakes, M. and Rahaman, M.A., (1989): Proterozoic Crustal Development in the Pan African Regime of Nigeria, Review in Geology of Nigeria (ed. C.A. Kogbe), Elizabethan Publ. Co., Lagos, P. 70 – 80.
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Tags: application of electrical resistivity method, electrical resistivity method, electrical resistivity method for groundwater exploration, resistivity array types, resistivity electrode configuration, resistivity profiling, resistivity survey, schlumberger resistivity method