Radiomagnetotelluric Survey for Mapping Structural Controls on Groundwater in the Awka Area, Anambra State

Groundwater productivity in the Awka area, Anambra State, is strongly influenced by the distribution of subsurface fractures and faults that serve as preferential flow pathways within the otherwise low-permeability formations of the Imo Shale and overlying sand sequences. This study employs radiomagnetotelluric (RMT) profiling to map structural controls on groundwater occurrence in the Awka area. RMT data were acquired along twelve profiles oriented perpendicular to the dominant structural trend identified from satellite imagery lineament analysis, using commercial FM radio stations as transmitters at frequencies between 50 and 250 kHz. Apparent resistivity and phase data were collected in two orthogonal polarizations at 5 m station spacing. Two-dimensional inversion of the TE and TM mode data was performed using ZondMT2D software. Inverted resistivity models resolve conductive vertical zones interpreted as water-filled fractures and faults embedded within resistive background lithology. Depth of investigation based on skin depth calculations ranges from 15 to 65 m depending on frequency and formation resistivity. A total of nineteen discrete conductive zones are mapped, with depths ranging from 8 to 52 m. Correlation of RMT anomalies with documented spring emergence points and high-yield boreholes achieves an 82 percent success rate, validating the structural interpretation. Preferred borehole targets are identified at intersections between RMT-defined conductive structures and secondary fracture sets mapped from satellite data. This study demonstrates the feasibility of RMT as a rapid and cost-effective tool for structural groundwater targeting in urban and peri-urban settings.

Keywords: radiomagnetotelluric, RMT, fracture mapping, groundwater, structural control