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Magnetotelluric investigations for the seismically active area in Northern Miyagi Prefecture, northeastern Japan

Earth, Planets and Space volume 51, pages 351–361 (1999)Cite this article

Abstract

The ELF- and the ULF-MT surveys were carried out in the northern part of Miyagi Prefecture, northeastern Japan. This area is one of the most seismically active areas in this region, where hypocenters of microearthquakes are distributed on a fault plane at depths from 2 to 16 km. The aim of the present study is to investigate the relationship between electrical resistivity structure and the hypocentral distribution of microearthquakes in the area. The calculated impedance tensor at each site has been obtained from the observed data and decomposed to remove galvanic distortion, provided that the regional strike is N32?E to obtain the 2-D apparent resistivity and phase responses. The resistivity structure obtained by the inversion process using smoothness constraint shows that the relatively electrically conductive layer at depths from 4 to 10 km corresponds to the zone where the microearthquakes occur. The fact that the conductive zone correlates with the hypocentral zone is probably attributed to fluids in the crust. Another more conductive block is found at depths from 1 to 3.5 km and the bottom boundary of this conductor appears to restrict the uppermost depth where the microearthquakes occur. This subsurface conductor is interpreted as a marine sediment deposited during the Tertiary period. In the lower crust, the relatively conductive blocks (lower than 5Ω m) exist below a depth of 15 km.

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Authors and Affiliations

  1. Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan

    Masahiro Ichiki, Naoto Oshiman & Norihiko Sumitomo

  2. Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578, Japan

    Masaaki Mishina

  3. Department of Environmental Earth Science, Faculty of Education, Aichi University of Education, 1 Hirosawa, Igatani, Kariya, Aichi, 448-8542, Japan

    Tadanori Goto

  4. Ocean Hemisphere Research Center, Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan

    Masahiro Ichiki & Hisashi Utada

Authors
  1. Masahiro Ichiki
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  2. Masaaki Mishina
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  3. Tadanori Goto
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  4. Naoto Oshiman
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  5. Norihiko Sumitomo
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  6. Hisashi Utada
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Correspondence to Masahiro Ichiki.

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Ichiki, M., Mishina, M., Goto, T. et al. Magnetotelluric investigations for the seismically active area in Northern Miyagi Prefecture, northeastern Japan. Earth Planet Sp 51, 351–361 (1999). https://doi.org/10.1186/BF03352239

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  • DOI: https://doi.org/10.1186/BF03352239

Keywords

  • Lower Crust
  • Apparent Resistivity
  • Conductive Zone
  • Resistivity Structure
  • Impedance Tensor