日本地球惑星科学連合2018年大会

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[EE] Evening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-CG53] Science of slow earthquakes: Toward unified understandings of whole earthquake process

2018年5月23日(水) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:井出 哲(東京大学大学院理学系研究科地球惑星科学専攻)、廣瀬 仁(神戸大学都市安全研究センター)、氏家 恒太郎(筑波大学生命環境系、共同)、波多野 恭弘(東京大学地震研究所)

[SCG53-P18] Estimation of pore fluid overpressures for tensile cracking at depth of shallow slow earthquakes

*大坪 誠1氏家 恒太郎2Hardebeck Jeanne L.3最首 花恵1宮川 歩夢1山口 飛鳥4 (1.産業技術総合研究所、2.筑波大学、3.米国地質調査所、4.東京大学)

キーワード:スロー地震、応力、亀裂、流体、沈み込み帯

Pore fluid pressure Pf is important for understanding slow earthquake mechanics. In this study, we estimated the pore fluid pressure during the formation of foliation-parallel quartz veins filling mode I cracks in the Makimine mélanges, eastern Kyushu, SW Japan. In the coastal region of the Makimine mélanges (Late Cretaceous Shimanto accretionary complex of SW Japan; temperature = 300–350°C, Palazzin et al., 2016), the mélange preserves quartz-filled shear, foliation-parallel veins and tension vein arrays. We applied the stress tensor inversion approach proposed by Sato et al. (2013) to estimate stress regimes by using foliation-parallel vein orientations. The estimated stress is a reverse faulting stress regime with a sub-horizontal σ1-axis trending NW–SE and a sub-vertical σ3-axis, and the driving pore fluid pressure ratio P* (P* = (Pf – σ3) / (σ1 – σ3)) is ~0.1. When the pore fluid pressure exceeds σ3, veins filling mode I cracks are constructed (Jolly and Sanderson, 1997). The pore fluid pressure that exceeds σ3 is the pore fluid overpressure ΔPfPf = Pf – σ3). To estimate the pore fluid overpressure, we used the poro-elastic model for extension quartz vein formation (Gudmundsson, 1999). Pf in the case of the Makimine mélanges are ~280 MPa (assuming depth = 10 km, density = 2750 kg/m3, tensile strength = 5 MPa and Young’s modulus = 7.5–15 GPa). The normalized pore pressure ratio λ* (λ* = (PfPh) / (PlPh), Pl: lithostatic pressure; Ph: hydrostatic pressure) is ~1.03 (Pf > Pl).