Subsurface electrical resistivity modelling over a suspected fault zone at Ojirami, Southwestern Nigeria
Tóm tắt
The subsurface of a suspected fault zone at Ojirami Southwestern Nigeria was investigated using the four-electrode array model of the electrical resistivity method of geophysical prospecting. Measurements were taken along four traverses using the 1-D and 2-D electrical resistivity field techniques. The Schlumberger and dipole–dipole electrode configurations were respectively utilized for each of the techniques. The 1-D data were interpreted by partial curve matching and computer iteration using the IPI2Win® software. The data obtained from the 2-D ERI were processed and migrated using the Dipro for Windows® 4.0 inversion software. Inversion was done using the finite element modelling (FEM) method. The second-order smoothness constraint was used and five iterations were carried out on each data set. Three 2-D resistivity models and one geoelectric section were generated from the inverted resistivity data. A resistivity depth slice map of the depth range of 2.5–5 m was also generated for the assessment of the spatial configuration of the suspected fault zone. Geoelectric units which include the topsoil/outcrop, weathered/faulted bedrock and the fresh bedrock were delineated by the 2-D resistivity models and the geoelectric section. The suspected fault zone manifested as zone of comparatively low resistivity (8–81 Ω-m) within two resistive (800 to > 5000 Ω m) basement bedrocks on the resistivity images and geoelectric section. The resistivity depth slice map also revealed the fault zone to be a low resistivity discontinuity within two flanks of fresh bedrocks. The study concluded that the study area is indeed a fault zone.
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