Geophysical Determination Of Depth To Basement And Velocities Of Electromagnetic Waves In Akamkpa L.G.A South Eastern Nigeria Using Ground Penetrating Radar (GPR)

ABSTRACT

A subsurface survey was carried out in Akamkpa Local Government Area South Eastern Nigeria, which is part of Oban Massif belonging to the Precambrian. Basement Complex of Nigeria. The study was carried out with a MALA made Pro Ex system Ground Penetrating Radar (GPR) with a pair of unshielded OPTICAL model antennas 50MHZand 100MHzfrequencies and its other accessories. A profile length of 500m to 1km with readings taken at intervals of 3m, in each of the eight locations chosen. (Figure 6). The objectives of the study were to determine the depth to the basement of each location and to calculate the velocities of the reflectors in such locations. The technique for GPR utilizes the transmission of electromagnetic waves in the radio frequency range into geological media through its transmitter antenna on the surface. The reflected wave energy is picked up by a receiver antenna on the surface and recorded in a computer. In locations 1 and 2 the signal from the 100MHZfrequency antenna did not get to the bedrock because of the high conductivity of the overburden in the two areas causing the signal to be attenuated. Hence no subsurface reflections appeared on the radargrams and no depth to bedrock was determined. In locations 3 to 8 where 50MHzfrequency antenna was used, the overburden of the locations were of low conductivity hence the signal was less attenuated. The signal was able to reach the depth to basement with subsurface reflections appearing showing contrast, in dielectric constants. The depths to basement of these locations were determined from radargrams which have been processed for clearer vision using RAMAC ground vision 2 software. The result showed that for the six locations the average depth to the basement was I 6.0m and the average velocities were 0.034, 0.03 1, 0.035, 0.032, 0.033 and 0.033mns for Aniking, Okom-Ita, Nsan 1, Nsan 2, Ayiebam 1 and Ayiebam 2 respectively.