Subsurface Structural Characterization Using 2d Electrical Resistivity Tomography At National Animal Production Research Institute (napri) Zaria Nigeria.

The method adopted for this research work was the 2D Electrical Resistivity Tomography(ERT), using the ABEM LUND Imaging System. A Wenner configuration was carried out tomap the electrical properties as an aid to characterizing the subsurface conditions. Eight profileswere occupied in the study area. For each profile, the layout geometry for the electrical imagingwas such that two reels of cables were laid collinearly with 5m intervals between the takeoutelectrodes. Each reel had 20 takeout electrodes. However, the two innermost electrodes of thetwo reels of cables were connected together thus yielding effectively 41 electrodes and a spreadlength of 200m. The data obtained using ABEM Terrameter SAS4000 with electrode selectorwere processed using RES2DINV software. From the interpretation of the electrical imagesobtained in the study area, the depth to the fresh basement is generally well beyond 29.3m. Thestudy reveals the presence of two distinct layers; the topsoil and the weathered basement withresistivity ranges of 20-400m and 30-470m respectively. These two layers constitute theoverburden with a minimum thickness of 29.3m as revealed by the pseudosections. This is themaximum depth of probing achieved in the present study. The topsoil, composed of laterite andbrownish sandy clay, has a thickness of about 5.0m to 7.0m. The weathered basement underliesthe topsoil with a thickness of about 22.3m to 24.3m and this is the good aquifer in the studyarea. This layer has a relatively low resistivity due to the presence of water. The layer is highlyweathered and the degree of weathering increases towards the fresh basement. This increasedthickness of bedrock weathering is a proof of the capability of this layer to provide a good waterreservoir with a high probability of the presence of fractures in the weathered basement. Themaximum depth of probing achieved in the present study is 29.3m; this is less than the depth tothe fresh basement. Hence, there is no information about the fresh basement.

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