Geophysical Mapping of Shallow Faults and Their Hydrogeological Significance in Kaduna State

This study maps shallow faults using combined ground geophysical methods and analyses their hydrogeological significance in Kaduna State, North West Nigeria. Faults in crystalline basement terrain function as either conduits or barriers to groundwater flow depending on their aperture, infill material, and cross-cutting geometry relative to regional flow directions. Understanding whether major structural lineaments in Kaduna State promote or inhibit groundwater movement is critical for interpreting productive borehole site selection and regional aquifer connectivity. This study integrates ground magnetic profiling, electrical resistivity tomography, and seismic refraction along 14 traverses crossing identified aeromagnetic lineaments in Kaura, Sanga, and Kagarko local government areas. Magnetic profiles detect changes in basement lithology at fault zones. ERT provides cross-sectional images of fault geometry and infill material resistivity. Seismic refraction characterises P-wave velocity contrasts across faults. Borehole yield data from 38 adjacent boreholes are compiled and analysed in relation to mapped fault proximity. Findings reveal two distinct fault categories from the geophysical surveys: open fracture zones characterised by low resistivity (5 to 25 ohm-metres) and reduced seismic velocity (less than 1,800 metres per second), which correlate with highly productive boreholes averaging 3.8 litres per second; and clay-infilled fault zones characterised by very low resistivity (2 to 8 ohm-metres) and very low seismic velocity (less than 800 metres per second), which act as barriers and are associated with borehole yields below 0.5 litres per second. Discrimination between productive and barrier fault zones using the combined geophysical signatures achieves 81 percent classification accuracy. The study provides practical geophysical criteria for fault-related borehole targeting in Kaduna State.

Keywords: fault mapping, hydrogeological significance, ERT, seismic refraction, Kaduna State.