Spatial variations in damage zone width along strike-slip faults: An example from active faults in southwest Japan |
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| Institution: | 1. Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan;2. Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan;1. Dipartimento di Scienze della, Terra Università La Sapienza di Roma, Roma, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia Roma, Italy;3. Dipartimento di Scienze della Terra Università degli Studi di Siena, Italy;4. Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Italy;1. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China;2. Basin & Reservoir Research Center, China University of Petroleum, Beijing 102249, China;3. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China;4. Exploration and Production Research Institute of Northwest Oilfield Branch Company, SINOPEC, Urumqi 830000, China;1. Department of Geology, University of Otago, PO Box 56, Dunedin, 9054, New Zealand;2. School of Geography, Environment, and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington, 6012, New Zealand;3. GNS Science, PO Box 30-368, Lower Hutt, 5040, New Zealand;4. Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin, 9054, New Zealand |
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| Abstract: | Field investigations reveal spatial variations in fault zone width along strike-slip active faults of the Arima–Takatsuki Tectonic Line (ATTL) and the Rokko–Awaji Fault Zone (RAFZ) of southwest Japan, which together form a left-stepping geometric pattern. The fault zones are composed of damage zones dominated by fractured host rocks, non-foliated and foliated cataclasites, and a fault core zone that consists of cataclastic rocks including fault gouge and fault breccia. The fault damage zones of the ATTL are characterized by subsidiary faults and fractures that are asymmetrically developed on each side of the main fault. The width of the damage zone varies along faults developed within granitic rocks of the ATTL and RAFZ, from ～50 to ～1000 m. In contrast, the width of the damage zone within rhyolitic tuff on the northwestern side of the ATTL varies from ～30 to ～100 m. The fault core zone is generally concentrated in a narrow zone of ～0.5–～5 m in width, consisting mainly of pulverized cataclastic rocks that lack the primary cohesion of the host rocks, including a narrow zone of fault gouge (<0.5 m) and fault-breccia zones either side of the fault. The present results indicate that spatial variations in the width of damage zone and the asymmetric distribution of damage zones across the studied strike-slip faults are mainly caused by local concentrations in compressive stress within an overstep area between left-stepping strike-slip faults of the ATTL and RAFZ. The findings demonstrate that fault zone structures and the spatial distribution in the width of damage zone are strongly affected by the geometric patterns of strike-slip faults. |
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| Keywords: | Arima–Takatsuki Tectonic Line Rokko–Awaji Fault Zone Damage zone Core zone Strike-slip fault Seismic faulting |
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