Mapping Bedrock Topography using Electromagnetic Profiling

Electromagnetic profiling method was used in Echara Unuhu, within the Abakaliki Urban, to map the bedrock topography which also aids us to determine the position of the deepest fractured shale where a productive borehole will be constructed The area under study is within the Abakaliki Shales Geologic Formation. The rocks are packages of thinly layered olive green to dark gray blush black shale, which are frequently calcareous, subordinate fine-grained micaceous sandstone; micaceous siltstone, sandy shales and shelly limestone. Two-man portable Geonics EM 34-3 electromagnetic equipment was used in the profiling normal to the strike. The results show that typical conductivity value of the shallow bedrock (1.51-2.0m) lies between 22.1-53.7 mmho/m while conductivity values from 269-786mmohm/m indicate thicker/deeper (25-30m) fractures with higher moisture contents. Mapping of bedrock topography at Echara Unuhu enabled us to locate a point which on drilling produces good water yield; this technique is recommended for use in formations with similar characteristics