VELOCITY LAYERING IN THE MIDDLE BENUE TROUGH NIGERIA USING SEISMIC REFRACTION DATA

Abstract

Seismic refraction data was acquired in the Middle Benue Trough which is located in the north central Nigeria with latitude 07.5-08.5oN and longitude 08.00-09.30oE. The aim was to find out how velocity vary in the near-surface layers in the area using seismic refraction data. The seismic survey was investigated at 14 acquisition stations. Two overlapping reversed profiles were shot into 14 stations. Each acquisition station was primed with 0.20kg dynamite loaded at 1.5m below the surface. The recording equipment was McSeis-160MXTM, and monitor record was processed with Microsoft Excel software to determine the velocities from both the forward and reversed shot-points. The results show two distinct layers cases. The thickness of the topmost layer varies between 2.75m and 5.45m with a mean of 4.1m. The velocity of this topmost layer varies between 399.0 ms-1 and 767.0ms-1 with a mean of 604.8ms-1. The velocity of the underlying layer (V1) varies between 1212.5ms-1 and 3257.0ms-1 with a mean of 1757.9ms-1. The velocity increases with depth into the subsurface. The results are useful in locating groundwater aquifer, and in the design of source-receiver arrays for reflection seismic.