[S-CG67] [EE] 海溝海側で海洋プレートに生じる過程：沈み込み帯へのインプット

[SCG67-04] 古い海洋プレートの沈み込み直前での屈曲断層掘削計画：ロンドン会議の成果

*森下 知晃¹、山野 誠²、藤江 剛³、小野 重明³、木村 純一³、尾鼻 浩一郎³、中村 恭之³、山口 飛鳥⁴、鹿児島 渉悟⁴、斎藤 実篤³、小平 秀一³、Morgan Jason⁵ (1.金沢大学、2.東京大学地震研、3.海洋研究開発機構、4.東京大学大気海洋研、5.ロンドン大学)

キーワード：Plate bending induced normal fault, Ocean Drilling Project, Earthquake, Water-carbon circulation

Hydration due to plate bending-induced normal faults (bend-faults) in the region between the trench axis and outer rise (outer rise) has also drawn considerable attention (e.g., Grevemeyer et al., 2007; Fujie et al., 2013). Ideally, comparing subduction zones in several contrasting geodynamic states (e.g. Old plate vs Young plate, bend-faults being reactivated abyssal hill faults vs. newly formed horst-and-graben faults, etc.) is likely to be the most promising exploration approach to expand our knowledge of bend-fault hydration processes. In order to deepen our understanding of bend-fault hydration, an IODP pre-proposal: Bending fault hydrology of the Old Incoming Plate (H-ODIN) was developed. The IODP workshop, Bend-Fault Serpentinization, was held in London, 2016, sponsored by CHIKYU IODP Board, the UK-IODP, and ECORD. Horst-and-graben bend-fault structures are well developed in the northwestern Pacific subduction system. The Vp/Vs ratio is high at the outer rise area where bend-faults start to be developed (Fujie et al., 2013). Anomalously high heat flow valuesare found to be pervasively distributed in the off-Tohoku outer rise region (Yamano et al., 2014). The off-Tohoku region also provides a rare opportunity to study a place where the local stress state is likely to have changed significantly since the 2011 Tohoku Earthquake (Obana et al., 2011). Microseismic activity detected by OBS is considered to be related to actively deforming bend-faults (Obana et al., 2012, 2014). The questions on the nature of bend-fault hydration are classified into (1) Bend-fault material and structure, and (2) Bend-Fault Stress State and monitoring stress-state and fluid flow. The Japan Trench site seems best for understanding links between bend-induced hydration and the outer rise seismic cycle. (especially optimal now as we are in a rare phase between a giant megathrust event and its potential outer-rise doublet.). We will present more details in the presentation.