Three-dimensional resistivity model of the southeastern part of Gangwon Province, Korea, using integrated AMT and electrical resistivity surveys

We present a three-dimensional (3D) geological model of the south-eastern Gangwon Province, Korea, using integrated geophysical datasets. The study area has historically hosted numerous coal and metal mines, many of which are now abandoned. Recently, renewed interest in critical minerals has driven active mineral exploration. In addition, the area has been selected as a potential site for underground research laboratory for high-level radioactive waste disposal and cosmic particle research. 

In this study, audio-magnetotelluric (AMT) data acquired at grid-distributed measurement stations were analyzed. A total of 49 AMT survey stations were deployed in a generally non-uniform grid configuration. Measurement stations were densely distributed at approximately 100 m intervals around the candidate site for underground research facility, while station spacing increased to approximately 250–350 m toward the outer areas. For remote reference measurements, a remote reference station was operated at a distance of approximately 12–14 km from the survey area.

Three north–south profiles, three east–west profiles, and additional virtual two-dimensional profiles oriented in the northeast–southwest and northwest–southeast directions were defined. Two-dimensional inversion was performed along these profiles to obtain a preliminary geological model for subsequent 3D inversion. These models, together with two-dimensional inversion results derived from electrical resistivity survey lines, were used as initial models to facilitate faster convergence in 3D inversion. Furthermore, near-surface electrical resistivity obtained from inversion of electrical resistivity data was incorporated into the initial model to minimize static effects caused by by near-surface resistivity inhomogeneities.

The geological model derived from the 3D inversion was validated through comparison with airborne magnetic survey data and available borehole information from the study area. Continuity of geological features, including coal seams and lithological boundaries between limestone and granite, was confirmed on individual two-dimensional sections, leading to the construction of a new 3D geological model. The developed 3D resistivity model provides a reliable geophysical framework for mineral exploration and for site characterization of underground research facilities in this region.