Abstract

In order to investigate the subsurface seepage conditions of the Ahmadu Bello University (A.B.U.) farm dam, we have recorded high resolution seismic profiles spanning the entire periphery of the lake. Seismic waves generated from multiple shots were recorded on large number of closely spaced receivers using a 24 channel Abem Terraloc Mk 6 seismograph and the high-quality seismic data were processed using REFLEXW version 3.0 interpretation software. 2D seismic cross sections of the overburden and underlying bedrock were obtained and the physical composition of the subsurface materials was studied from their seismic velocity characteristics. On the basis of analysis of the data, the overburden shows evidence of unconsolidation with a seismic velocity range of 448 - 1875 m/s interpreted to represent lateritic clay material. The underlying bedrock shows evidence of differential weathering and saturation with a seismic velocity range of 1466 - 8061 m/s. Zones of relatively low seismic velocities within the bed rock are interpreted to represent zones of intense weathering and or fracturing and suspected to provide seepage pathway for water from the impounding reservoir.

Key words: Seismic refraction tomography, subsurface seepage condition, artificial lake, Nigeria.