[S-EM12] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM12-P15] Three-dimensional electrical resistivity structure beneath the northern Kanto region, Japan

*Yoshiya Usui¹、Makoto Uyeshima¹、Tasuku Hashimoto¹、Shin'ya Sakanaka²、Yusuke Yamaya³、Shu Kaneko⁴、Masahiro Ichiki⁵、Toshiki Kaida⁵、Yuki Tomioka⁶、Dieno Diba¹、Yasuo Ogawa⁷、Shohei Kihara⁶、Takao Koyama¹、Koji Miyakawa¹、Masataka Masuda¹、Keiji Hirase⁶、Gosuke Hoshino⁶、Kento Ide⁶、Hayata Sato⁶、Rentaro Shimizu ⁶、Amane Terai⁶、Yuta Yoshie⁶、Kei Nakayauchi⁶、Han Song¹、Takahiro Akiyama¹、Hayato Hitotsumatsu⁸、Norihiro Kitaoka⁷、Takuro Kanetsuki⁶、Ritsu Sakiyama²、Akira Watanabe¹、Takafumi Murakita ⁶、Hiroko Tendo⁶、Yoshiaki Harashima⁶、Shunsuke Yaegashi⁶、Kota Suzuki⁶ (1.Earthquake Research Institute, the University of Tokyo、2.Faculty of Engineering and Resource Science, Akita University、3.Renewable Energy Research Center, Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology、4.Graduate School of Science and Engineering, Chiba University、5.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University、6.Japan Organization for Metals and Energy Security、7.Institute of Innovative Research, Tokyo Institute of Technology、8.Department of Earth Science, Toyama University)

キーワード：Magnetotellurics, Electrical resistivity, Subsurface fluid, Volcano, Subducting slab

Dual subductions of the Philippine Sea slab and the Pacific slab occur beneath the Kanto region in Japan. The seismological studies suggested that the northern edge of the Philippine Sea slab is located under the northern Kanto region. However, geochemical studies based on isotopic ratios of volcanic rocks have suggested that the aseismic Philippine Sea slab extends beyond the seismologically determined northern edge and perturbs mantle flow, enhancing the flux of the slab-derived fluid to the northern Kanto region. The northern Kanto region has several quaternary volcanos and seismically active areas. The interaction between the Philippine Sea and Pacific slabs may play an important role in the tectonics in this region. The subsurface fluid is considered to affect both volcanic and seismic activities significantly, and the fluid may stem from the subducting slabs. Thus, it is important to reveal the subsurface fluid distribution by conducting an electromagnetic induction survey that delineates the electrical resistivity structure. However, the regional electrical resistivity structure in the northern Kanto region has not yet been investigated. Hence, we performed magnetotelluric surveys around the northern Kanto region in 2021, 2022 and 2023. The across-arc survey line in 2021 continues from Mito City, Ibaraki Prefecture, to Nagaoka City, Niigata Prefecture. The survey areas in 2022 and 2023 cover the forearc area of the northern margin of the Kanto region (the northern parts of Tochigi and Ibaraki prefectures). We estimated the 3-D electrical resistivity structure from the uppermost mantle to the upper crust by estimating the MT response functions and performing the inversion using them. The resistivity structure contains the resistive Pacific slab and a conductive area in the mantle wedge, which continues to the crust beneath Nasu and Takaharayama volcanoes. The conductive area may indicate the path of the fluid derived from the subducting slab to those active volcanoes.