著者

大橋 聖和 大坪 誠 松本 聡 小林 健太 佐藤 活志 西村 卓也

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.4, pp.565-589, 2020-08-25 (Released:2020-10-02)

参考文献数

108

被引用文献数

4 5

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The 2016 Kumamoto earthquake occurred in the tectonically complex central Kyushu area where several forcing factors such as the subducting Philippine Sea plate, the Median Tectonic Line and the Nankai forearc sliver, the spreading Okinawa trough, and the migrating volcanic front are involved. Neogene–Quaternary tectonics of central Kyushu are revisited by integrating geological, seismological, and geodetical approaches. Deformation histories of the Futagawa and Hinagu fault zones, the source faults of the Kumamoto earthquake, are also established in an attempt to explain the relationship between geologic structures and rupture processes of the earthquake. The results show that present-day tectonics surrounding central Kyushu are considered to have originated in the last 1 Ma or younger, as a transtensional tectonic zone (Central Kyushu Shear Zone) characterized by combined dextral faults and rift zones (or volcanoes). Reflecting spatiotemporal variations of the crustal stress field and rift activity, the Futagawa and Hinagu fault zones show multi-stage deformation throughout the Neogene–Quaternary periods: normal faulting to dextral faulting for the Futagawa fault zone and sinistral to dextral faulting for the Hinagu fault zone. Those diverse histories of stress and strain fields in central Kyushu possibly led to the complexities of fault geometry and rupture process of the Kumamoto earthquake.

著者

大坪 誠 大橋 聖和 尾方 隆幸 柴田 伊廣

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2019年大会

巻号頁・発行日

2019-03-14

著者

大橋 聖和 竹下 徹 平内 健一

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.4, pp.473-489, 2020-08-25 (Released:2020-10-02)

参考文献数

108

被引用文献数

2 4

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Knowledge of the strength of faults in the continental upper crust is critical to our understanding of crustal stress states, coseismic faulting, and lithospheric deformation. In this paper, we investigate time- and displacement-dependent fault-zone weakening (softening) over geological time caused by the hydrothermal alteration of rock, the development of faulting-related structure and fabric, and changes in the relevant deformation mechanisms. In the shallow portion of the continental seismogenic zone (< 5 km), hydrothermal alteration induced by comminution and fluid flow along fault zones progressively enriches weak phyllosilicates. The development of phyllosilicate-aligned fabric with increasing shear strain leads to an effective weakening with increasing cumulative fault displacement. In the deep portion of the seismogenic zone (> 5 km), frictional–viscous flow occurs in combination with friction contributed by phyllosilicates and the dissolution–precipitation of clasts after the introduction of water, phyllosilicates and anastomosing fabrics all increasing with greater fault displacement. In addition, the water weakening of quartz and feldspar is an important softening process in the deeper portion of the seismogenic zone (> 10 km). The smoothing of fault-zone topography by the shearing of irregularities and asperities, as well as the thickening of the fault zone, leads to a reduction over time in the bulk frictional resistance of a fault as displacement increases. These time- and displacement-dependent weakening processes of fault zones give rise to diverse strength and stress states of the crust depending on its maturity and may provide clues to reconciling the stress–heat flow paradox of crustal faults.

著者

大橋 聖和 小林 健太 間嶋 寛紀

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.114, no.8, pp.426-431, 2008-08-15 (Released:2009-03-25)

参考文献数

8

被引用文献数

3 1

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To make thin sections or polished slubs of the brittle fault rocks like fault gouge and fault breccia without volume loss, is pretty difficult because of its fragility and softness. In general, the reinforcement by resin is performed in such specimens, but it's not so effective for the brittle fault rocks that contain swelling clay minerals. Additionally, detailed and through instructions about how to make thin sections of these rocks have not been published. Therefore, we introduce the grinding method which does not use the water for brittle fault rocks and altered rocks containing swelling clay minerals. With this method, we can make the thin sections, polished slubs, even sections specially prepared for SEM, TEM, EPMA analyses of noncohesive fault rocks containing swelling clay minerals without volume loss.

著者

深畑 幸俊 大橋 聖和 高田 陽一郎 田中 明子

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.128, no.5, pp.685-687, 2019-10-25 (Released:2019-11-15)

参考文献数

9

被引用文献数

2

著者

金木 俊也 大橋 聖和 廣野 哲朗 野田 博之

出版者

日本地震学会

雑誌

日本地震学会2019年度秋季大会

巻号頁・発行日

2019-08-15