Three-dimensional resistivity structure in the focal region of 2000 Western Tottori Earthquake

Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Shiozaki, Ichiro*; Inoue, Tomohiro*; Usui, Yoshiya*; Ichihara, Hiroshi*; Yamaguchi, Masahiro*; Uto, Satoshi*; Hataoka, Hiroshi*; Shigematsu, Hiromichi*; Nagayama, Yushi*; Honda, Takayuki*; Yamada, Tomoki*

We estimate a three-dimensional resistivity structure based on high-density magnetotelluric (MT) observations in the focal region of the Western Tottori earthquake to clarify the relationship between subsurface fluid distribution, seismic activity, and rupture processes. We compiled a dataset consisting of 100 MT stations, integrating 52 sites used in the previous study, 13 additional existing stations, and 35 newly acquired MT observations conducted between October and December 2024. As a result of three-dimensional resistivity analysis, a low-resistivity body was imaged extending from directly beneath the mainshock hypocenter (depth 10 km) to the lower crust. The low-resistivity body beneath the mainshock is interpreted as a fluid-rich region, suggesting that fluids may have facilitated rupture initiation by reducing fault strength.