日本地球惑星科学連合2019年大会

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[E] 口頭発表

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-CG48] Science of slow earthquakes: Toward unified understandings of whole earthquake process

2019年5月30日(木) 10:45 〜 12:15 コンベンションホールA (2F)

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)、波多野 恭弘(東京大学地震研究所)、座長:氏家 恒太郎(筑波大学生命環境系)、ウォリス サイモン(Nagoya University)

11:00 〜 11:15

[SCG48-23] Generation of high fluid pressure at the base of the shallow mantle wedge—evidence from serpentinite of the Sanbagawa belt, SW Japan

*ウォリス サイモン1纐纈 佑衣2横田 麻莉1,2 (1.東京大学、2.名古屋大学)

キーワード:流体圧、深部スロー地震、蛇紋岩、三波川帯

Serpentinite units derived from the mantle wedge in the Sanbagawa subduction-type metamorphic belt record interaction between the shallow mantle-wedge and the flow of SiO2-bearing fluids at two different depths in the paleo subduction zone. The mineralogy and geochemistry of two units indicate there was a major increase in the fluid flow perpendicular to the subduction boundary with decreasing pressure. The rate of flow can be related to the presence or absence of a thick shear zone. Estimates of fluid flux from subducted slabs combined with experimentally determined permeability of serpentinite suggests that the presence of a zone of gently dipping strongly foliated serpentinite is a key component of developing high fluid pressures at depths of 30–50 km in subduction zones—a key requirement for the development of slow earthquakes. Most of the SiO2 in these subduction fluids will be absorbed in the serpentinite and is unlikely to be available for precipitation and formation of an impermeable cap at higher levels in the system.