Subsurface Geological Characterization Using Electrical Resistivity Data

Abstract

Electrical resistivity is one of the most effective geophysical properties for lithological classification because it is strongly affected by rock composition, weathering, porosity, groundwater saturation, and fracture development. This study evaluates the applicability of two-dimensional electrical resistivity tomography (ERT) for distinguishing subsurface lithology in the Byeonsan Peninsula, Korea, where Precambrian gneiss, Jurassic biotite granite, Cretaceous tuff, and Quaternary alluvium are distributed. Two ERT survey lines were established across representative lithologic boundaries. Apparent resistivity data were acquired using a dipole-dipole array with a 2 m electrode spacing and inverted using the DC_2DPro program to obtain two-dimensional inverted resistivity sections. The interpreted resistivity distributions were compared with the existing geological map to evaluate their capability for identifying lithologic boundaries and geological structures. The resistivity sections clearly distinguished the major lithologic units. Precambrian gneiss and fresh biotite granite exhibited relatively high resistivity values (>1,000-1,300 Ω·m), whereas Cretaceous tuff showed moderate to low resistivity values (250-600 Ω·m), and Quaternary alluvium displayed the lowest resistivity values (50-300 Ω·m). Distinct resistivity transition zones corresponded closely to mapped lithologic boundaries and were interpreted as fault-controlled contacts or fractured zones. In addition, weathered zones and possible buried lithologic boundaries beneath the alluvial cover were identified. The results demonstrate that ERT is an effective tool for lithological classification and subsurface geological interpretation. When integrated with geological mapping, borehole data, and other geophysical surveys, ERT can significantly improve the accuracy of geological mapping, structural interpretation, and engineering site investigations.