The Federal Capital Territory(FCT), is located within latitudes 8° 25˝ and 9° 25˝ North, and longitudes 6° 45˝ and 7° 45˝ East, covering an area of about 8000 square kilometers. Geoelectric resistivity investigation was carried out in the Territory. A direct current resistivity survey employing the vertical electrical sounding was used and a total of 86 sounding points were established. The Schlumberger four electrode array was used with a maximum half current electrodes separation of 215m for the survey in the sedimentary area and 156m for the survey in the basement area. The ABEM Terrameter SAS300 was used in the survey. The Zohdy computer program was used for the interpretation of the curves. Interpretation of the data collected suggests that the VES curves obtained comprise of 3 to 6 geoelectric layers with the thickness varying from 1m to 60m. The solid bedrock has a high resistivity of more than 2000Ω-m in the basement area, while the Sandstones occupy the third geological formation in the sedimentary area. The structural trend maps delineate series of bedrock ridges(basement area only) and depressions within the survey area. The thickness of this layer is between 1m and 10m and varies from location to location, depending on the processes that have taken place and the type of parent rock. The resistivity values for this layer vary from 20Ω-m for clay to over 3000Ω-m for laterite. The resistivity varies from 40Ω-m to a maximum of 650Ω-m in the basement area with a maximum thickness of 52m, while the resistivity values vary to 2000Ω-m in the sedimentary area with a maximum thickness of over 80m. The fractured basement rocks which occur within the basement environment constitutes the third geological formation beneath the area and has resistivity values lying between 700Ω-m and 2000Ω-m. Where the fractures/joints are connected and open, this layer could serve as a good aquifer. The solid bedrock has a high resistivity of more than 2000Ω-m in the basement area. The structural trend maps delineate series of bedrock ridges (basement area only) and depressions within the survey area. The bedrock overburden being groundwater collecting centres are priority areas for groundwater development. The depth to basement map and the isopach map revealed that the central area has a high groundwater potential.
Keywords: Geoelectric resistivity, surbsurface characteristics, vertical electrical sounding