High-resolution electrical resistivity tomography and seismic refraction for groundwater exploration in fracture hard rocks: A case study in Kanthan, Perak, Malaysia

Abstract

• High-resolution ERT and seismic results were validated by tube-well drillings. • Sharp vertical boundary between high and low resistivity zones indicates fault zone. • Depression zone in seismic refraction depth profile indicates highly fractured rock. • DLS method of Wenner-Schlumberger + dipole–dipole arrays are the most effective. • Groundwater source is discovered at the intersection of major discontinuities . This research article describes the integration of high-resolution electrical resistivity tomography (ERT) and seismic refraction to explore potential groundwater in fracture carbonate hard rocks. Data Levels Synthesization (DLS) method is developed where the data levels of two different optimized arrays were merged to produce one final subsurface resistivity image to achieve high-resolution ERT. Numerical modeling was initially conducted on three different geoelectrical arrays. The results of before and after applied DLS method were compared to evaluate the effectiveness of each geoelectrical array to delineate fracture and anomalies accurately. Lineament map is constructed beforehand to map the major discontinuities which could possibly be the potential target for water-containing and water-conducting zones in the subsurface. Two geophysical survey lines were conducted where each survey line covered both ERT and seismic refraction methods. Two tube wells were successfully drilled exactly on the fracture zone with a flow rate around 1000 L/h. The potential water-containing zones within the subsurface limestone bedrock were identified as zones of low to moderate geoelectrical resistivity values ranging from 10 to 400 Ωm and V p velocities exceeding 2000 ms −1 . The fault zones were determined by sharp vertical boundary between the high and low resistivities zones in ERT image and lateral decrease in the V p velocities of the limestone bedrock and depressions along the overburden-bedrock interface. The DLS method of Wenner-Schlumberger and dipole–dipole arrays had been proven effective in enhancing the horizontal and vertical resolutions to produce high-resolution ERT image validated with seismic refraction, lineament map, and tube well drillings.