Distribution of fault rocks in the fracture zone of the Nojima Fault at a depth of 1140 m: Observations from the Hirabayashi NIED drill core |
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| Authors: | Kenta Kobayashi Satoshi Hirano Takashi Arai Ryuji Ikeda Kentaro Omura Hiroyuki Sano Takashi Sawaguchi Hidemi Tanaka Tomoaki Tomita Naoto Tomida Tatsuo Matsuda Akiko Yamazaki |
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| Institution: | Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan (email:;),Frontier Research Program for Subduction Dynamics, Japan Marine Science and Technology Center, Yokosuka 237-0061, Japan,;Graduate School of Science and Technology, Shinshu University, Matsumoto 390-8621, Japan,;National Research Institute for Earth Science and Disaster Prevention, Tennodai 3-1, Tsukuba 305-0006, Japan,;Graduate School of Science, University of Tokyo, Tokyo 113-0032, Japan,;Department of Earth Science, School of Education, Waseda University, Tokyo 169-8050, Japan,;Department of Geo/Biospheric Sciences, Faculty of Science, Ehime University, Matsuyama 790-8577, Japan and;Graduate School of Science and Engineering, University of Tsukuba, Tsukuba 305-8572, Japan |
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| Abstract: | Abstract Characteristics of deformation and alteration of the 1140 m deep fracture zone of the Nojima Fault are described based on mesoscopic (to the naked eye) and microscopic (by both optical and scanning electron microscopes) observations of the Hirabayashi National Research Institute for Earth Science and Disaster Prevention (NIED) drill core. Three types of fault rocks; that is, fault breccia, fault gouge and cataclasite, appear in the central part of the fault zone and two types of weakly deformed and/or altered rocks; that is, weakly deformed and altered granodiorite and altered granodiorite, are located in the outside of the central part of the fault zone (damaged zone). Cataclasite appears occasionally in the damaged zone. Six distinct, thin foliated fault gouge zones, which dip to the south-east, appear clearly in the very central part of the fracture zone. Slickenlines plunging to the north-east are observed on the surface of the newest gouge. Based on the observations of XZ thin sections, these slickenlines and the newest gouge have the same kinematics as the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake), which was dextral-reverse slip. Scanning electron microscopy observations of the freeze-dried fault gouge show that a large amount of void space is maintained locally, which might play an important role as a path for fluid migration and the existence of either heterogeneity of pore fluid pressure or strain localization. |
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| Keywords: | 1995 Hyogo-ken Nanbu earthquake clay microstructure core drilling fault gouge fault rocks freeze-drying method Nojima Fault |
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