Characterization of Fault Systems and Their Impact on Groundwater Flow in the Udi-Nsukka Escarpment, Southeastern Nigeria

The Udi-Nsukka escarpment represents a prominent geomorphological feature in southeastern Nigeria that is underlain by a complex system of faults and fractures, which significantly influence local groundwater flow. This study characterizes fault systems and their hydraulic impact on groundwater in the Udi-Nsukka escarpment using an integrated approach combining lineament analysis from satellite imagery, VLF-EM profiling, and hydrogeological data from existing boreholes. Structural lineaments were extracted from Landsat 8 and Sentinel-2 imagery using directional filtering and PCI Geomatica software. VLF-EM data were collected along nine traverses oriented perpendicular to the dominant structural trend using a Geonics EM16 receiver. Karous-Hjelt pseudosection analysis was applied to the VLF-EM data to identify conductive zones in the subsurface associated with water-saturated fractures. Lineament density mapping reveals three dominant orientations: northeast-southwest, northwest-southeast, and north-south, with the northeast-southwest set being most prevalent and correlated with the regional Benue Trough tectonic grain. VLF-EM conductive anomalies identify twelve discrete fracture zones within 50 to 80 m depth, of which eight exhibit hydraulic connectivity based on spring emergence locations and borehole yield data. Groundwater yields from boreholes intersecting identified fracture zones exceed those from unfractured aquifer segments by a factor of 2.5 on average. These findings have direct implications for groundwater development strategy along the escarpment.

Keywords: fault characterization, VLF-EM, lineament analysis, groundwater flow, Udi-Nsukka escarpment