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Magnetotelluric observations around the focal region of the 2007 Noto Hanto Earthquake (Mj 6.9), Central Japan

  • Ryokei Yoshimura17Email author,
  • Naoto Oshiman17,
  • Makoto Uyeshima27,
  • Yasuo Ogawa37,
  • Masaaki Mishina47,
  • Hiroaki Toh57,
  • Shin’ya Sakanaka67,
  • Hiroshi Ichihara77,
  • Ichiro Shiozaki87,
  • Tsutomu Ogawa27,
  • Tsutomu Miura17,
  • Shigeru Koyama27,
  • Yasuyoshi Fujita17,
  • Kazuhiro Nishimura17,
  • Yu Takagi17,
  • Mikihiro Imai67,
  • Ryo Honda77,
  • Sei Yabe17,
  • Shintaro Nagaoka37,
  • Mitsuhiro Tada17 and
  • Toru Mogi77
Earth, Planets and Space200860:BF03352771

Received: 30 June 2007

Accepted: 10 September 2007

Published: 19 February 2008


On 25 March 2007, a damaging earthquake (Mj 6.9) occurred near the west coast of the Noto Peninsula, Central Japan. A wideband magnetotelluric (MT) survey was carried out in the onshore area of the source region immediately after the mainshock, with the aim of imaging the heterogeneity of the crustal resistivity structure. The final observation network had consisted of 26 sites. As a preparatory step for imaging three-dimensional features of the resistivity around the focal region, we constructed two-dimensional resistivity models along five profiles using only the TM mode responses, in order to reduce three-dimensional effects. Four profiles are perpendicular to the fault strike, and a fifth profile is parallel to the strike through the mainshock epicenter. Significant characteristics of the resistivity models are: (1) beneath the mainshock hypocenter, there is a conductive body which spreads to the eastern edge of the active aftershock region; (2) a resistive zone is located in the gap of the aftershock distribution between the mainshock hypocenter and the largest eastern aftershock; (3) one of the largest aftershock occurred at the boundary of the resistive zone described above. These results suggest that the deep conductors represent fluid-filled zones and that the lateral heterogeneity could have controlled the slip distribution on the fault plane.

Key words

Resistivity structurewideband magnetotellurics2007 Noto Hanto Earthquake