Abstract:
This research examines the relative effectiveness and imaging capabilities of laboratory 2D
resistivity imaging over two geologic targets with five most commonly used electrode
arrays.This is undertaken to establish the array(s) that is/are most suitable for mapping the
geologic targets. Arrays considered include the Wenner (WNN), Wenner-Schlumberger
(WSC), pole-dipole (PDP), pole-pole (PPP), and dipole-dipole (DPD).
A model tank was carefully built in the Department of Applied Geophysics, Federal University
of Technology Akure. The tank was made of transparent glass and housed within a wooden
plank to withstand the pressure of the sand fill. The tank was filled with well-sieved sand,
saturated with water. Two geological models that simulate an underground tunnel and buried
thin resistive dyke were utilized to examine the imaging capabilities of these arrays. A wall test
effect, involving Wenner array, was carried out to determine the area within which geoelectric
measurements could be taken without significant wall effect. One electrical traverse was
established within the tank. Unit electrode spacing used for the imaging was 2 cm while
expansion factor (N) ranges from 1 to 8 for simulated tunnel and 1 to 6 for the simulated
resistive dyke.
The simulated tunnel and dyke show up as high resistivity anomaly within a relatively low
resistivity host medium for all the arrays.Pole-pole array offers the best horizontal resolution
(0.38 m) with considerable vertical resolution of 0.10 m for the tunnel. The value of the total
resolution (0.16 m) suggests that WSC least resolves the modelled tunnel. The result obtained
for the dyke suggests that WNN and WSChave total resolution of 0.17 m and 0.15 m
respectively. Considering the data coverage, anomaly effect and imaging efficiency of the five
arrays, pole-pole presents higher mapping efficiency over a tunnel while Wenner-
Schlumberger and Wenner present higher mapping efficiency over a buried dyke.
