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

Yoshimura, Ryokei; Oshiman, Naoto; Uyeshima, Makoto; Ogawa, Yasuo; Mishina, Masaaki; Toh, Hiroaki; Sakanaka, Shin’ya; Ichihara, Hiroshi; Shiozaki, Ichiro; Ogawa, Tsutomu; Miura, Tsutomu; Koyama, Shigeru; Fujita, Yasuhito; Nishimura, Kazuhiro; Takagi, Yu; imai, mikihiro; Honda, Ryo; Yabe, Sei; Nagaoka, Shintaro; Tada, M.; Mogi, Toru

doi:10.1186/bf03352771

Cited by 29 publications

(20 citation statements)

References 17 publications

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“…This study shows that the seismogenic zones correspond approximately to resistive zones lying adjacent to conductive zones, or to the conductive-resistive transition zone. These results are consistent with previous magnetotelluric studies conducted across the epicenters of large (>M 6) inland earthquakes (Mitsuhata et al 2001;Ogawa et al 2001;Tank et al 2003Tank et al , 2005Kasaya and Oshiman 2004;Ichihara et al 2008Ichihara et al , 2014Yoshimura et al 2008;Kaya et al 2009;Umeda et al 2011Umeda et al , 2014Chandrasekhar et al 2012) with the exception that aftershocks occur in a thick sedimentary layer (Uyeshima et al 2005). Note here that the dense magnetotelluric observations occasionally image localized subvertical conductors beneath the active faults (e.g., Unsworth et al 1997;Wannamaker et al 2002;Becken et al 2008;Ikeda et al 2013;Sass et al 2014).…”

Section: Discussionsupporting

confidence: 82%

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Aizawa

Asaue

Koike

et al. 2017

Earth Planets Space

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The M JMA 7.3 Kumamoto earthquake that occurred at 1:25 JST on April 16, 2016, not only triggered aftershocks in the vicinity of the epicenter, but also triggered earthquakes that were 50-100 km away from the epicenter of the main shock. The active seismicity can be divided into three regions: (1) the vicinity of the main faults, (2) the northern region of Aso volcano (50 km northeast of the mainshock epicenter), and (3) the regions around three volcanoes, Yufu, Tsurumi, and Garan (100 km northeast of the mainshock epicenter). Notably, the zones between these regions are distinctively seismically inactive. The electric resistivity structure estimated from one-dimensional analysis of the 247 broadband (0.005-3000 s) magnetotelluric and telluric observation sites clearly shows that the earthquakes occurred in resistive regions adjacent to conductive zones or resistive-conductive transition zones. In contrast, seismicity is quite low in electrically conductive zones, which are interpreted as regions of connected fluids. We suggest that the series of the earthquakes was induced by a local accumulated stress and/or fluid supply from conductive zones. Because the relationship between the earthquakes and the resistivity structure is consistent with previous studies, seismic hazard assessment generally can be improved by taking into account the resistivity structure. Following on from the 2016 Kumamoto earthquake series, we suggest that there are two zones that have a relatively high potential of earthquake generation along the western extension of the MTL.

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Section: Discussionsupporting

confidence: 82%

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Aizawa

Asaue

Koike

et al. 2017

Earth Planets Space

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“…Among many aftershocks we selected an M4.3 aftershock for our analyses, which occurred about five kilometers southeast of the observation site, as also shown in Figure 8. The result of magnetotelluric studies made in the focal region indicates a uniform layer with 10 Ωm prevailing to the depth of several hundred meters in the area including our observation site [ Yoshimura et al , 2008]. …”

Section: Observation and Datamentioning

confidence: 99%

A model for observed circular polarized electric fields coincident with the passage of large seismic waves

et al. 2009

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[1] Among electric field variations supposed to be associated with earthquakes, electric field variations coincident with the passage of seismic waves have been well documented and interpreted mostly in terms of the electrokinetic effect. Here we present two examples of electric field variations obtained in association with small artificial earthquakes caused by blasting and three examples for aftershocks of two large earthquakes of magnitude 6.9 and 7.2, respectively. The electric field turned out to be circularly polarized in some cases, whereas linearly polarized cases were also seen. Since it is unclear whether such a peculiar behavior is understood in terms of existing models, we propose another mechanism to explain circular polarization; here we call this mechanism as ''seismic dynamo effect,'' which would be regarded as an extended model of the so-called induction effect. In our model we consider ions motion in pores filled with water in the ground, which is driven by ground motion in the Earth's magnetic field. With this model we show that circular polarization of electric field is realized in association with resonance between the frequency of ground velocity due to seismic wave and the cyclotron frequency of ions, such as HCO 3 À or Cl À contained in pores, for the Earth's magnetic field at the observation site. Ions with positive charge, such as Na + , also seem to be responsible for circular polarization of electric field with rotation direction opposite to that for ions with negative charge. We also show that in this model the magnitude of electric field can be estimated in terms of the number density of ions.

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“…Because electrical resistivity is quite sensitive to the amount of pore fluid and its connectivity in the rocks, a subsurface resistivity structure can be used to image the fluid distribution in the crust. Many resistivity investigations in the inland earthquake zone have found electrical conductors in the lower crust beneath the active fault and high‐seismicity zones [e.g., Ogawa et al ., ; Ogawa and Honkura , ; Tank et al ., ; Uyeshima et al ., ; Yoshimura et al ., ; Ichihara et al ., ; Wannamaker et al ., ; Ichihara et al ., ]. These results support the hypothesis that the strain becomes concentrated in the upper crust above regions of the lower crust weakened by locally present fluids [e.g., Iio et al ., ; Hasegawa et al ., ].…”

Section: Introductionmentioning

confidence: 98%

Three‐dimensional resistivity structure in Ishikari Lowland, Hokkaido, northeastern Japan—Implications to strain concentration mechanism

Yamaya¹,

Mogi

Honda

et al. 2017

Geochem Geophys Geosyst

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The Ishikari Lowland on the island of Hokkaido in northeastern Japan is situated at the end of a westward‐moving foreland fold‐and‐thrust belt from the Hidaka collision zone, where the northeastern Japan and Kurile arcs meet. This activity forms a tectonic zone under an east‐west compression field in this region. A magnetotelluric resistivity survey was performed to investigate the mechanism for the strain concentration in this region. A three‐dimensional (3‐D) resistivity inversion showed a conductive thick sedimentary layer and an underlying resistive basement. Remarkable conductors were found in the resistive basement beneath the Ishikari‐teichi‐toen fault zone (ITFZ) and the Shikotsu caldera. The conductors beneath the ITFZ were interpreted as aqueous fluids that accumulated in the damaged zone in connection with the formation of pull‐apart faults and horst. In contrast, the conductor beneath the Shikotsu caldera corresponds to a magmatic fluid path from the upper mantle. These features suggest that the ductile deformation in the upper crust contribute to the strain concentration in this region. The soft thick sediments allow ductile deformations to occur. Furthermore, local fluid‐rich zones in the basement cause the crustal strength to be heterogeneous. These thick sediments and local fluids in the basement both contribute to the strain concentration in this region.

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

Cited by 29 publications

References 17 publications

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

A model for observed circular polarized electric fields coincident with the passage of large seismic waves

Three‐dimensional resistivity structure in Ishikari Lowland, Hokkaido, northeastern Japan—Implications to strain concentration mechanism

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