TY - JOUR
T1 - Electrical Resistivity Structure Around the Atotsugawa Fault, Central Japan, Revealed by a New 2-D Inversion Method Combining Wideband-MT and Network-MT Data Sets
AU - Usui, Yoshiya
AU - Uyeshima, Makoto
AU - Ogawa, Tsutomu
AU - Yoshimura, Ryokei
AU - Oshiman, Naoto
AU - Yamaguchi, Satoru
AU - Toh, Hiroaki
AU - Murakami, Hideki
AU - Aizawa, Koki
AU - Tanbo, Toshiya
AU - Ogawa, Yasuo
AU - Nishitani, Tadashi
AU - Sakanaka, Shin 'ya
AU - Mishina, Masaaki
AU - Satoh, Hideyuki
AU - Goto, Tada nori
AU - Kasaya, Takafumi
AU - Mogi, Toru
AU - Yamaya, Yusuke
AU - Shiozaki, Ichiro
AU - Honkura, Yoshimori
N1 - Funding Information:
We thank local landowners for providing us their properties for the wideband‐MT and the Network‐MT measurements. We also thank the staff of Nippon Telegraph and Telephone Corporation and its related companies for their assistances with Network‐MT measurements in the Chubu region. Special thanks are given to Tomohumi Uto, Hironori Kanezaki, Yuji Mochido, Tomoe Mogami, Makoto Harada, Shigeru Koyama, Hiromine Mochizuki, Setsuro Nakao, Yasuo Wada, and Yasuyoshi Fujita for performing the observations and for obtaining the data set. We thank Alan D. Chave (Woods Hole Oceanographic Institution) for his robust remote reference magnetotelluric (RRRMT) code. We also acknowledge Junichi Nakajima (Tokyo Institute of Technology) for giving us the data of the seismic velocity structure around the Atotsugawa fault system. Some figures were created using Generic Mapping Tools (Wessel et al., 2013 ). In addition, we would like to thank two anonymous reviewers and the editor in charge for their valuable comments that significantly improved the manuscript. This work was funded by “The Program of Research and Observation for Prediction of Earthquake and Volcanic Eruption” of the Ministry of Education, Culture, Sports, Science and Technology of Japan and “The Cooperative Research Program” of the Earthquake Research Institute. This study is also carried out with research grants (nos 19540442 and 25400443) from JSPS. We used the computer systems of the Earthquake Information Center of the Earthquake Research Institute at the University of Tokyo.
Funding Information:
We thank local landowners for providing us their properties for the wideband-MT and the Network-MT measurements. We also thank the staff of Nippon Telegraph and Telephone Corporation and its related companies for their assistances with Network-MT measurements in the Chubu region. Special thanks are given to Tomohumi Uto, Hironori Kanezaki, Yuji Mochido, Tomoe Mogami, Makoto Harada, Shigeru Koyama, Hiromine Mochizuki, Setsuro Nakao, Yasuo Wada, and Yasuyoshi Fujita for performing the observations and for obtaining the data set. We thank Alan D. Chave (Woods Hole Oceanographic Institution) for his robust remote reference magnetotelluric (RRRMT) code. We also acknowledge Junichi Nakajima (Tokyo Institute of Technology) for giving us the data of the seismic velocity structure around the Atotsugawa fault system. Some figures were created using Generic Mapping Tools (Wessel et al., 2013). In addition, we would like to thank two anonymous reviewers and the editor in charge for their valuable comments that significantly improved the manuscript. This work was funded by “The Program of Research and Observation for Prediction of Earthquake and Volcanic Eruption” of the Ministry of Education, Culture, Sports, Science and Technology of Japan and “The Cooperative Research Program” of the Earthquake Research Institute. This study is also carried out with research grants (nos 19540442 and 25400443) from JSPS. We used the computer systems of the Earthquake Information Center of the Earthquake Research Institute at the University of Tokyo.
Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.
PY - 2021/4
Y1 - 2021/4
N2 - The Atotsugawa fault is one of the most active faults in Japan, and the strain accumulation at the fault is considered to be caused by an aseismic shear zone in the fluid-rich lower crust. To identify the shear zone and investigate the origin of the aqueous fluid in the lower crust, we deployed a Network-MT survey in addition to a conventional wideband-MT survey around the fault and performed an inversion combining both the MT data sets. In the inversion, by modifying a conventional inversion algorism, we accurately represented kilometer-scale dipoles of the Network-MT measurement to provide constraints on the electrical resistivity structure. In the lower crust under the study area, there are localized conductive anomalies below the Atotsugawa fault, the Ushikubi fault, and the Takayama-Oppara fault zone. Comparing our electrical resistivity structure with the seismic velocity structure, we interpreted that the lower-crustal conductors are localized ductile shear zones with highly connected fluid. We considered that the localized ductile shear zones are responsible for the strain accumulation along the respective active faults. In addition, in the mantle wedge above the subducting Philippine Sea slab and its downward extension, a highly conductive portion is detected, which may be attributed to the fluid dehydrated from the Philippine Sea slab and/or the Pacific slab. The existence of the large conductive area supports the suggestion of previous seismic and geochemical studies that the fluid of the lower crust around the Atotsugawa fault originated from subducting slabs.
AB - The Atotsugawa fault is one of the most active faults in Japan, and the strain accumulation at the fault is considered to be caused by an aseismic shear zone in the fluid-rich lower crust. To identify the shear zone and investigate the origin of the aqueous fluid in the lower crust, we deployed a Network-MT survey in addition to a conventional wideband-MT survey around the fault and performed an inversion combining both the MT data sets. In the inversion, by modifying a conventional inversion algorism, we accurately represented kilometer-scale dipoles of the Network-MT measurement to provide constraints on the electrical resistivity structure. In the lower crust under the study area, there are localized conductive anomalies below the Atotsugawa fault, the Ushikubi fault, and the Takayama-Oppara fault zone. Comparing our electrical resistivity structure with the seismic velocity structure, we interpreted that the lower-crustal conductors are localized ductile shear zones with highly connected fluid. We considered that the localized ductile shear zones are responsible for the strain accumulation along the respective active faults. In addition, in the mantle wedge above the subducting Philippine Sea slab and its downward extension, a highly conductive portion is detected, which may be attributed to the fluid dehydrated from the Philippine Sea slab and/or the Pacific slab. The existence of the large conductive area supports the suggestion of previous seismic and geochemical studies that the fluid of the lower crust around the Atotsugawa fault originated from subducting slabs.
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U2 - 10.1029/2020JB020904
DO - 10.1029/2020JB020904
M3 - Article
AN - SCOPUS:85105018454
VL - 126
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - 4
M1 - e2020JB020904
ER -