JpGU-AGU Joint Meeting 2017

講演情報

[EE] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG62] [EE] 変動帯ダイナミクス

2017年5月23日(火) 15:30 〜 17:00 ポスター会場 (国際展示場 7ホール)

コンビーナ:深畑 幸俊(京都大学防災研究所)、Robert Holdsworth(Durham University)、Jeanne Hardebeck(USGS)、岩森 光(海洋研究開発機構・地球内部物質循環研究分野)

[SCG62-P13] Fault zone development in the aftershock area of the 2016 Kumamo earthquake, Kyushu, Japan

*小林 健太1高橋 啓太2鈴木 俊2大橋 健治1香取 拓馬2皆美 まどか1津久井 脩平1井村 朱里1加藤 悠人1髙橋 直希1 (1.新潟大学理学部地質科学科、2.新潟大学大学院自然科学研究科)

キーワード:Kumamoto Prefecture, Hinagu fault, active fault, fault rocks

The Futagawa and the Hinagu fault zones were activated at the time of the 2016 Kumamo earthquake. To understand how fault zones have developed over a long period of time, it is necessary to observe fault zone structures at the macro to microscope scales. We carried out field surveys in the NE-SW trending aftershock area of the earthquake, and analyzed the development of fractures, slip senses, and mineral assemblages at the fault zone.
The main shock (Mw7.0, April 16) occurred along the ENE-WSW trending Futagawa fault. On the other hand, the foreshocks (Mw6.2, April 14; Mw6.0, April 15) occurred along the NE-SW trending Hinagu fault. After the earthquake, many NE-SW~ENE-WSW trending surface ruptures were found along the Hinagu fault. They indicated dextral slip sense. In addition, a bed composed of lower terrace deposits was folded at the north end of the Hinagu fault. The fold hinge was plunging to NE.
Brittle fault rock zones were distributed in the Higo metamorphic rocks (Permian-Triassic). Andesite dikes (Neogene?) were intruded, also deformed along the faults. Most fault planes with NNW~NNE strike, indicated dextral, sinistral, normal and reverse slip senses. XRD analysis showed that the foliated cataclasite derived from pelitic-psammitic gneiss is mainly composed of smectite, kaolinite, chlorite and laumontite. The foliated gouges are abundant in smectite, contain chlorite and laumontite. NE-SW striking remarkable brittle shear zone was also recognized in the Hinagu Formation (Early Cretaceous), indicated dextral slip sense.
Viewed from the kinematics and the alteration process, the macroscale fault zone in the aftershock area has a long history of deformations. Parts of them were selected, and activated at the time of the 2016 Kumamo earthquake.