Near-Surface Seismic Velocity Data: A Computer Program For Analysis

Abstract

A computer program (NESURVELANA) has been developed in Visual Basic Computer programming language to carry out a near surface velocity analysis. The method of analysis used includes: Algorithms design and Visual Basic codes generation for plotting arrival time (ms) against geophone depth (m) employing the Least-Squares approximation to fit the best lines, computing velocities from the reciprocals of the slopes of the lines and determining thickness for multi-layer cases. The program was debugged and test-run on Microsoft Windows XP using a set of two near-surface seismic velocity data acquired by the Up-hole technique within the South-Central Niger Delta, Nigeria. The first set of data showed a weathered two-layer case, where the layer has a thickness of 6.0 m and velocity of 431 m/s and a consolidated layer velocity of 1845 m/s. The second set of data was a weathered three-layer case, where the thicknesses were 4.3 m and 7.7 m with the weathered and second layer with velocities of 513 m/s and 1132 m/s respectively and a consolidated layer velocity of 1756 m/s for the third layer. These results are comparable with those obtained by other researchers for the Niger Delta, Nigeria. The resulting information from this near-surface velocity analysis is essential for static corrections for the accurate mapping of the underlying structures for oil and gas exploration, and geotechnical engineering for foundation works in building houses, bridges, dams and construction of highways.

Keywords: Algorithm design, visual basic codes, least-squares approximation,weathered layer thickness and velocity.

Nigerian Journal of Physics Vol. 19 (2) 2007: pp. 253-266