Investigations of Boreholes using Seismic Refraction Tomography in Nigerian Defence Academy Kaduna, Nigeria.

Abstract

Seismic refraction tomography is unique in the sense that shot are taken at every receiver position along the spread. In that way, it becomes possible to conduct both forward and reverse shooting simultaneously along the profile lines. Therefore, every point within the subsurface along the profile lines is probed by data were processed with ReflexW software and a conventional forward and reversed travel time curve was plotted for each profile lines. Thereafter joint inversion of the travel times picks was carried out. This resulted in the generation of an iterative model, which was used to generate tomographic sections. The result of seismic refraction tomography showed lateral and vertical variation in velocity along most of the subsurface. Refraction tomography gave accurate depth and thickness of the overburden along the profile and to delineate aquifer potential in the basement topography. The aquifer is estimated to be around 55m to 65m along the entire profile line. In sub profiles lines, the velocity range of the first layer is 600 m/s to 1400 m/s, the thickness range of the first layer is 0.7 m to 2.3 m, the velocity indicate loose materials around the zones. The velocity range of the second layers is from 1500 m/s, with thickness fresh/fractured basement with good aquifer potentials.