Temporal stress variations along a seismogenic megasplay fault in the subduction zone: An example from the Nobeoka Thrust,southwestern Japan |
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| Authors: | Ryoji Kawasaki Yoshitaka Hashimoto Makoto Otsubo Asuka Yamaguchi Yujin Kitamura Jun Kameda Yohei Hamada Rina Fukuchi Gaku Kimura |
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| Institution: | 1. Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan;2. Faculty of Science, Department of Applied Science, Kochi University, Kochi City, Japan;3. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba City, Japan;4. Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa City, Japan;5. Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University, Kagoshima City, Japan;6. Earth and Planetary System Science, Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo City, Japan;7. Kochi Institute for Core Sample Research, Japan Agency for Marine‐Earth Science and Technology, Nankoku City, Japan |
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| Abstract: | The Nobeoka Thrust, an ancient megasplay fault in the Shimanto Belt, southwestern Japan, contains fault rocks from the seismogenic zone, providing an accessible analog of active megasplay faults in deep subduction settings. In this study, the paleostress along the Nobeoka Thrust was analyzed using multiple inversion techniques, including k‐means clustering of fault datasets acquired from drillcores that intersected the thrust. The six resultant stress orientation clusters can be divided into two general groups: stress solutions with north–south‐trending σ1 axes, and those with east–west‐trending σ1 axes. These groups are characterized by the temporal changes for the orientations of the σ1 and σ3 principal stress axes that involve alternation between horizontal and vertical. The findings are probably due to a change in stress state before and after earthquakes that occurred on the fault; similar changes have been observed in active tectonic settings, such as the 2011 Tohoku‐Oki earthquake (Japan). |
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| Keywords: | drillcore earthquake
Nankai subduction zone seismic cycle seismogenic zone stress inversion |
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