Subsurface Cavity and Sinkhole Detection Using Electrical Resistivity Tomography in Afikpo, Ebonyi State

Afikpo in Ebonyi State is underlain partly by carbonate and evaporite-rich sediments that are susceptible to dissolution processes and the formation of subsurface cavities and sinkholes. This study employs electrical resistivity tomography to detect and characterize subsurface cavities and sinkhole-prone zones in Afikpo, contributing to geohazard assessment and land use planning in the area. Data were collected along eight ERT profiles of varying lengths between 200 m and 480 m using a dipole-dipole array with electrode spacing of 5 m. Two-dimensional inversion of apparent resistivity data was performed using RES2DINV software, and anomalous zones were interpreted within the regional geological framework. Air-filled cavities appear as very high resistivity anomalies (greater than 1,000 ohm-m) embedded within a background of moderate resistivity sediment (20 to 200 ohm-m). Water-filled cavities exhibit low resistivity signatures, ranging from 5 to 15 ohm-m, depending on the salinity of the filling fluid. Six discrete cavity anomalies are identified across the study area at depths between 3 m and 22 m. The lateral extents of identified anomalies range from 2 m to 18 m, suggesting a variety of dissolution structure sizes. Correlation of geophysical anomalies with surface expressions confirms the reliability of the ERT interpretation. The three-dimensional spatial distribution of identified cavities is consistent with structural control along northeast-trending dissolution conduits. These findings support the inclusion of cavity mapping in infrastructure development planning for Afikpo.

Keywords: electrical resistivity tomography, subsurface cavity, sinkhole, dissolution, geohazard