[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM14-04] Two-dimensional electrical resistivity structure beneath the northern Kanto region

*臼井 嘉哉¹、上嶋 誠¹、坂中 伸也²、小山 崇夫¹、市來 雅啓³、山谷 祐介⁴ (1.東京大学地震研究所、2.秋田大学大学院国際資源学研究科、3.東北大学 大学院理学研究科附属地震・噴火予知研究観測センター、4.産業技術総合研究所福島再生可能エネルギー研究所再生可能エネルギー研究センター)

キーワード：電気比抵抗構造、流体分布、MT法、関東地方、沈み込み帯、マグマ供給系

The tectonics of the Kanto region in central Japan is dominated by the dual subduction of the Philippine Sea (PHS) slab and the Pacific (PAC) slab. The PHS slab subducts under the continental Okhotsk plate, and the PAC subducts below the PHS and the continental plates. It is thought that the interaction between the two slabs plays an important role in the magma generation and the seismogenic process under the region. Geochemical study based on isotopic ratios of volcanic rocks (Nakamura et al. 2018) suggested that aseismic PHS slab extends to the north of seismically determined slab edge and perturbs mantle flow, enhancing the flux of the slab-derived fluid to the northern margin of the Kanto region. In order to elucidate the transport of the slab-derived fluid and its relationship with volcanic and seismic activities, it is important to reveal the subsurface fluid distribution by conducting an electromagnetic induction survey that delineates the subsurface electrical resistivity structure. Since the electrical resistivity of subsurface fluid is generally lower than that of dry rocks by more than several orders of magnitude, the electrical resistivity is sensitive to the interconnected fluid in subsurface rocks. Therefore, the authors performed a magnetotelluric survey around the northern margin of the Kanto region. In the central part of the survey line, there are active volcanos, Takaharayama and Hiuchigatake. The volcanic rocks of Takaharayama show a high contribution of the fluid originating from both the PHS and PAC slabs (Nakamura et al. 2018). After we determined the impedance tensor, the vertical magnetic transfer function, and the inter-station horizontal magnetic transfer functions, we estimated the two-dimensional resistivity structure. In this study, we show the resultant resistivity structure and discuss the subsurface fluid distribution as well as its relationship with the volcanic and seismic activities around the study area.