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Matsunaga, Keita*; Aizawa, Koki*; Asamori, Koichi; Ogawa, Hiroki*; Utsugi, Mitsuru*; Yoshimura, Ryokei*; Yamazaki, Kenichi*; Uchida, Kazunari*; Matsushima, Takeshi*; Inoue, Tomohiro*; et al.
Tectonophysics, 915, p.230880_1 - 230880_11, 2025/11
Times Cited Count：4 Percentile：80.74(Geochemistry & Geophysics)Usui, Yoshiya*; Ueshima, Makoto*; Hase, Hideaki*; Ichihara, Hiroshi*; Aizawa, Koki*; Koyama, Takao*; Sakanaka, Shinya*; Ogawa, Tsutomu*; Yamaya, Yusuke*; Nishitani, Tadashi*; et al.
Journal of Geophysical Research; Solid Earth, 129(5), p.e2023JB028522_1 - e2023JB028522_22, 2024/05
Times Cited Count：16 Percentile：90.71(Geochemistry & Geophysics)We elucidated the crustal heterogeneities beneath a strain concentration area on the back-arc side of the northeastern Japan Arc based on electrical resistivity. By deploying magnetotelluric surveys, we revealed the three-dimensional electrical resistivity structure in the crust, suggesting the coexistence of two types of strain-concentration mechanisms in the strain-concentration area. The shallow conductive layers and lower-crustal conductors appear to act as low-elastic-modulus and low-viscosity areas, respectively, and are responsible for the strain concentration. We found a spatial correlation between the edges of the lower-crustal conductors and the epicenters of large intraplate earthquakes. Weak shear zones in the conductive lower crust may cause stress loading on faults in the brittle upper crust, resulting in large earthquakes. We also identified vertical conductors ranging from the lower crust to Quaternary volcanoes, which may indicate fluid paths to these volcanoes.
Ito, Takayoshi; Harjo, S.; Osamura, Kozo*; Hemmi, Tsutomu; Awaji, Satoshi*; Machiya, Shutaro*; Oguro, Hidetoshi*; Nishijima, Gen*; Takahashi, Koki*; Matsui, Kunihiro; et al.
Materials Science Forum, 681, p.209 - 214, 2011/05
Times Cited Count：1 Percentile：48.67(Materials Science, Multidisciplinary)Motoyama, Aoi*; Ogawa, Yasuo*; Uyeshima, Makoto*; Asamori, Koichi; Uchida, Toshihiro*; Hase, Hideaki*; Koyama, Takao*; Sakanaka, Shinya*; Yamaya, Yusuke*; Aizawa, Koki*; et al.
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no abstracts in English
Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Shiozaki, Ichiro*; The 2001 Research Group for Crustal Resistivity structure*
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Matsunaga, Keita*; Aizawa, Koki*; Asamori, Koichi; Ogawa, Hiroki*; Utsugi, Mitsuru*; Yoshimura, Ryokei*; Yamazaki, Kenichi*; Uchida, Kazunari*; Matsushima, Takeshi*; Inoue, Tomohiro*; et al.
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no abstracts in English
Usui, Yoshiya*; Ueshima, Makoto*; Hase, Hideaki*; Ichihara, Hiroshi*; Aizawa, Koki*; Koyama, Takao*; Sakanaka, Shinya*; Ogawa, Tsutomu*; Yamaya, Yusuke*; Nishitani, Tadashi*; et al.
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In the back-arc area of the southern Tohoku region, there are several quaternary volcanos and active faults that have the potential to cause M7-class inland earthquakes. In the vicinity of some of the volcanoes, deep low-frequency earthquakes occur, implying the transfer of melt or aqueous fluid. So as to reveal the magma supply system around the area, it is important to reveal the distribution of the subsurface fluid. Also, understanding the fluid distribution helps elucidate the earthquake generation process. To delineate the subsurface electrical resistivity structure, the authors estimated the resistivity structure in the area by performing magnetotelluric surveys and generating the 3-D resistivity structure model with high resolution. In this study, the authors show the resultant electrical resistivity structure and discuss the subsurface fluid distribution as well as its relationship with the volcanic and seismic activities around the study area.
Harjo, S.; Aizawa, Kazuya; Ito, Takayoshi*; Abe, Jun; Osamura, Kozo*; Hemmi, Tsutomu; Jin, X.*; Nakamoto, Tatsushi*; Awaji, Satoshi*; Takahashi, Koki*
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Motoyama, Aoi*; Ichiki, Masahiro*; Ogawa, Yasuo*; Uyeshima, Makoto*; Asamori, Koichi; Uchida, Toshihiro*; Koyama, Takao*; Sakanaka, Shinya*; Hase, Hideaki*; Aizawa, Koki*; et al.
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We compiled the magnetotelluric (MT) and geomagnetic transfer function (GDS) data which were acquired by Uchida (2004), Umeda et al. (2008), Asamori et al. (2011), Uyeshima (private comm.) and Ogawa (private comm). The 118 observation sites locate in the study area. Both MT and GDS frequency response was used to model three-dimensional resistivity distribution of the southern Tohoku district, NE Japan. The resultant resistivity model reveals no conductor beneath the onshore forearc in Fukushima prefecture. The model rather shows resistor there with over several-thousand ohm-m, which corresponds to the Abukuma batholiths. Thus, our model indicates that the area only around Iwaki-city is peculiar forearc, where fluid migrates upward from deep crust.
Matsunaga, Keita*; Aizawa, Koki*; Ogawa, Hiroki; Utsugi, Mitsuru*; Yoshimura, Ryokei*; Yamazaki, Kenichi*; Uchida, Kazunari*
no journal, ,
no abstracts in English
Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Shiozaki, Ichiro*; The 2001 Research Group for Crustal Resistivity structure*
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We show the resistivity structure around the focal region of the 2000 Western Tottori Earthquake (M7.3). The purpose of this study is to investigate the relationship between the rupture of the mainshock and the resistivity structure, which was not discussed in the previous study. By using the broad-band MT data, Umeda et al. (2011) imaged a deep conductive body in the middle crust to the upper mantle on the southwestern side of the mainshock rupture fault. However, they did not investigate the spatial relationship between the resistivity structure and the slip distribution. Therefore, in this re-analysis, we have spatial attention to the shape and uniqueness of the conductors. In addition to the previous broad-band MT data, we use broad-band MT data at 12 sites obtained by Universities (The 2001 Research Group for Crustal Resistivity structure, Japan, 2001). We use full components of the impedance tensor and geomagnetic transfer functions to image preliminary 3-D resistivity structure, and investigate its relationship to the slip distribution of the mainshock and also occurrence of the aftershocks.
Matsunaga, Keita*; Aizawa, Koki*; Asamori, Koichi; Ogawa, Hiroki; Utsugi, Mitsuru*; Yoshimura, Ryokei*; Yamazaki, Kenichi*; Uchida, Kazunari*
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We estimated the 3-D resistivity structure around the epicenter of the 1997 Kagoshima Prefecture Northwestern Earthquake doublet in Japan by using broadband magneto-telluric (MT) data. The resistivity structure shows low-resistivity zones near the eastern and western edge of the aftershocks at depths of 5-10 km. The hypocenters of the M6 earthquakes are located near the edge of the low-resistivity zones. It is interesting that a prominent high resistivity zone is sandwiched by two low-resistivity zones at a depth of 0-3 km, and its location coincides with the distribution of the granodiorite body.
Matsunaga, Keita*; Aizawa, Koki*; Asamori, Koichi; Ogawa, Hiroki*; Utsugi, Mitsuru*; Yoshimura, Ryokei*; Yamazaki, Kenichi*; Uchida, Kazunari*; Yamaguchi, Masahiro*; Inoue, Tomohiro*; et al.
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Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Inoue, Tomohiro*; Usui, Yoshiya*; Ichihara, Hiroshi*; Yamaguchi, Masahiro*; Uto, Satoshi*; Hataoka, Hiroshi*; et al.
no journal, ,
Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Shiozaki, Ichiro*; Inoue, Tomohiro*; Usui, Yoshiya*; Ichihara, Hiroshi*; Yamaguchi, Masahiro*; Uto, Satoshi*; et al.
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