Regional Geoelectrical Survey Across Some Parts of Anambra and Niger Delta Basins, South-Eastern Nigeria.

A regional geoelectrical study was embarked upon covering some major towns within the Niger Delta and Anambra basin. Some of the towns include; Owerri, Umuahia, Ohafia, Aba, Umuosu, Ngwa, Mbaise, Okigwe, Lekwesi, etc. About 100 Vertical Electrical Sounding points were established along two long profiles running perpendicularly to each other at North-South and East-West directions covering a distance of about 110km in each traverse. The maximum electrode spread was 500metres, AB/2. The schlumberger array was adopted on the field. The ABEM Terrameter SAS 4000 was used for the data acquisition. The purpose of the study is to examine the variability in lithological units both vertically and horizontally from the North to South and East to West along these profiles because there have been reported cases about land degradation like; gully erosion, landslide, minor subsidence, road failure, etc within the study area. The field data were processed with computer softwares. Iso-resistivity values at AB/2 equals 1m, 4m, 8m, 15m, 50m, 150m, 250m and 350m at surface electrode spacings were plotted and processed for each VES point in order to reveal the variation in resistivity with depth and variability changes in lithological units with depth. This procedure was repeated for all the VES stations on the East-West profile and North-South profile. Results show that the top soil contour has resistivities between 200Ωm and 9000Ωm while at AB/2 = 4m, resistivities are 500 - 1000Ωm (Aba), 1000 - 5000Ωm (Owerri), 2000 - 2500Ωm (Afikpo). Results were also obtained for AB/2 = 8m, 15m, 50m up to 250m. These resistivity values were interpreted as clay, shale, sand, etc, accordingly. From the correlation of the VES points, other geologic structures like faults, boundaries, flood plains, landsides are identified. Other environmental implications are highlighted.