Comparative Analysis Between 2D-Electrical Imaging and Seismic Refraction Tomography at National Animal Production Research Institute (NAPRI), Zaria. Kaduna State, Nigeria

Abstract

Understanding subsurface structure is crucial in geotechnical, environmental and engineering investigations. Two widely used geophysical methods are: 2D Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT). They offer complementary insights into subsurface conditions. ERT is sensitive to electrical properties (e.g. moisture, clay content), while SRT excels in detecting mechanical contrasts (e.g. rock hardness), combing both methods enhances subsurface imaging accuracy, especially in complex geology like fault zero or weathered profiles. The two methods were carried out to investigate the depth to basement complex in National Animal Production Research Institute (NAPRI), Zaria. The major instruments used for this survey where Terraloc Mark6 digital seismography, sets of vertical geophones, SAS4000 Terrameter and Electrode Selector ES 464. The geometric arrangement positioned both the geophones and the source along a straight line. The 24 geophones and the source were set at 5 m intervals, covering a distance of 120 m. Besides the initial shot location, shots were detonated at each geophone location. For the 2D electrical survey, the electrodes were arranged along the profiles with a 5.0 m electrode spacing between the 41 electrodes, resulting in a total spread of 200 m. In each of the profiles, geo-electric tomography managed to penetrate to a maximum depth of 29.3 m with optimal current injection into the subsurface. The geo-electric tomography was unable to reach the basement rock except at locations where the basement complex is found at a depth of 29.3 m or less. In contrast, seismic refraction tomography achieved a penetration depth of over 40m. It was possible to identify the basement tomography at depths exceeding 40m along the profiles.