Measurement of Velocity Gradients of Beds At Unwana, Nigeria

Seismic compressional waves have been used in Unwana to measure velocity gradients of beds. The seismic refraction method was employed. Unwana is situated within latitude 5 0 50 ' to 5 0 55 ' N and longitude 7 0 50 ' to 7 0 57 ' E. It has an area of about 48km 2 . A digital type signal enhancement seismograph was the equipment used along with its accessories. Forward and reverse shootings were carried out along the same profile line and the seismic velocities and thicknesses of underlying layers were estimated. The velocity gradients of the refracting beds were hence evaluated. The primary wave velocities for both forward and reverse shots were found to be 315m/s and 300m/s respectively for the first layer and 608 and 600m/s respectively for the second layer. The thickness measured from both forward and reverse ends of the profile line were 2.1m and 2.0m respectively for the first layer and 7.3m and 4.7m respectively for the second layer. These gave values of velocity gradients as 149s -1 and 150s -1 respectively for layer 1 and 83s -1 and 127s -1 respectively for the second layer. The result indicates that the materials of the first layer in Unwana are laterally homogenous and are flatlaying while those of the second layer are dipping although with no lateral inhomogeneity.