Application of Magnetotelluric (MT) Methods in Geothermal Exploration and Geostructural Investigation: A Case in Tatun Volcano Group, Northern Taiwan

Geothermal systems become viable when conditions, like appropriate temperature ranges, geological structures, and petrophysical properties, exist less than 3-5 km near surfaces. Assessing these factors is crucial for identifying economically viable geothermal resources. A key aspect of this evaluation is understanding subsurface electrical resistivity, which plays a pivotal role in characterizing geothermal systems. This study focuses on investigating geothermal resources and sites for geothermal power plants in the Tatun Volcano Group (TVG) in Northern Taiwan. Magnetotelluric (MT) methods, in particular, have emerged as a fundamental and powerful tool in geothermal exploration and subsurface architecture beneath geothermal areas. By performing 3D resistivity inversion of MT data collected from 47 measurement stations, this research develops a comprehensive model of subsurface electrical resistivity. Cross-sections and maps at various elevations are generated from this model to identify resistivity patterns essential for geothermal sites and to construct geological cross-sections for advancing geothermal exploration, such as further drilling.

The study highlights three potential geothermal areas with a high-resistivity core beneath a low-resistivity clay cap. Moreover, this study establishes several cross-sections across the north tip of Taiwan. A comparison between magnetization-derived airborne magnetic surveys, gravity-derived density models, and current 3D resistivity models leads to completing these cross-sections. They manifest subsurface architecture and elucidate the structural development. These results offer important new information for developing geothermal research in the TVG area.