[S-EM14] Electromagnetic Induction in the Earth and Planetary Interiors, and Tectono-Electromagnetism

[SEM14-02] Three-dimensional resistivity structure of the Tarumae volcanic region using MT data

*Takaya Yamagiwa¹, KENTARO AOYAMA¹, Koichi Suzuki¹, Toru Mogi², Yusuke Yamaya³ (1.Hokkaido University, 2.Faculty of Science, Tokyo Institute of Technology, 3.National Institute of Advanced Industrial Science and Technology)

Keywords:Geophysical Exploration, MT method, Mt.Tarumae

Mt. Tarumae is an active volcano located in the southwestern part of Hokkaido, Japan. 2D resistivity inversion using magnetoterullic (MT) data and 3D resistivity forward modeling using audio-magnetoterullic (AMT) data were performed in this area by Yamaya et al. (2005 and 2009), respectively; however, the structure of the deep subsurface remained unexplored. In this study, we modeled the magma chamber and flow path of hydrothermal fluids and volcanic gases that exist beneath Mt. Tarumae using a recently developed MT 3D inversion method. We used 70 stations to conduct the inversion: 28 stations near Mt. Tarumae and 42 stations in the east of Ishikari lowland, distant from Mt. Tarumae. In the analysis software ModEM (Egbert and Kelbert, 2012), we attempted an iterative calculation using the initial resistivity, the undetermined Lagrange multiplier, and the covariance of the smoothing term as variable parameters. The selected optimal model had the smallest root mean square residual. Consequently, we identified two low resistivity zones—one corresponding to the ascending path of hydrothermal fluids and volcanic gases beneath the summit of the Tarumae volcano and the other leading the Ishikari lowland low-resistivity zone—and a high-resistivity zone corresponding to the Pre-Tertiary strata.