[S-EM15] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM15-09] Approach to specifying high potential zones of geothermal recourses by combining satellite image analysis and MT/AMT resistivity model

★Invited Papers

*Taiki Kubo¹, Yuji Yamada¹, Heriawan Mohamad Nur², Iskandar Irwan², Kakeru Miyazaki¹, Koki Kashiwaya¹, Tada-nori Goto³, Katsuaki Koike¹ (1.Graduate School of Engineering, Kyoto University, 2.Institut Teknologi Bandung, 3.Earth-Science Laboratory, Graduate School of Science, University of Hyogo)

Keywords:Indonesia, Remote sensing, Geochemistry, Caldera

To promote the utilization of geothermal resources, which are expected to play a more significant role in the future, it is essential to develop exploration methods for assessing and evaluating their potential. Remote sensing analysis using satellite imagery enabling the estimation of surface mineral distribution and the detection of vegetation anomalies is an effective tool for large-scale investigations. Furthermore, integrating remote sensing data with geophysical exploration methods allows for a more detailed understanding of geothermal systems by providing two- and three-dimensional insights into subsurface structures. This study introduces two case studies. The first focuses on the Wayang Windu geothermal area in Indonesia, conducted as one of a SATREPS project supported by JICA and JST. In addition to satellite image analysis, surface surveys—including soil gas radon concentration monitoring and geochemical measurements—were performed. Vegetation anomalies and topographical lineaments identified through satellite analysis corresponded with known geothermal manifestations and fault distributions. A geothermal potential map, created on a 100 × 100 m grid, was derived by integrating remote sensing results with radon gas concentrations from over 20 monitoring wells (5 m depth) and geochemical data from approximately 30 sampling points. The subsurface structures of the promising geothermal sites identified in the potential map were then compared with resistivity cross-sections obtained through TEM and AMT surveys. The analysis revealed that low-resistivity zones were distributed along fractures, highlighting their role in geothermal fluid circulation. The second case study examines the Sanzugawa Caldera area in Yuzawa City, Akita Prefecture, which is divided into a southern region with active geothermal manifestations and operational power plants, and a northern region with minimal geothermal activity. Using HISUI satellite imagery, available since 2022, vegetation anomaly detection revealed that the distribution of anomalous zones aligned with fault structures along the caldera's outer edge. This suggests that geothermal fluids, such as hot water and gas, reach the surface through fractures. By comparing these findings with MT resistivity distributions from Ishizu et al. (2022) and the NEDO survey, the deep geothermal fluid flow pattern was estimated, revealing structural heterogeneity in both the outer and central parts of the caldera. These case studies demonstrate that a comprehensive understanding of the relationship between surface geothermal manifestations and deep resistivity structures enhances the efficiency of geothermal resource exploration.

Ishizu, K., Ogawa, Y., Nunohara, K., Tsuchiya, N., Ichiki, M., Hase, H., Kanda, W., Sakanaka, S., Honkura, Y., Hino, Y., Seki, K., Tseng K.H., Yamaya, Y., Mogi, T. (2022). Estimation of spatial distribution and fluid fraction of a potential supercritical geothermal reservoir by magnetotelluric data: A case study from Yuzawa geothermal field, NE Japan. Journal of Geophysical Research: Solid Earth, 127, e2021JB022911. https://doi. org/10.1029/2021JB022911