[S-CG46] スラブ内地震とその発生メカニズム

[SCG46-04] 東海地域下の長期的スロースリップの発生に伴う海洋性プレート内での応力場の変化

*北 佐枝子¹、ヒューストン ハイジ²、田中 佐千子³、浅野 陽一³、矢部 優⁴ (1.建築研究所、2.南カリフォルニア大学、3.防災科学技術研究所、4.産業技術総合研究所)

キーワード：スロースリップ、スラブ内地震、応力インバージョン、東海地域、豊後水道

Relationships between in-slab events and two slow slip events (SSEs) were examined in the Tokai region, where there are in-slab earthquakes and long-term SSEs (L-SSEs) with several years duration. For comparisons, results in Tokai regions were compared with those in Bungo channel by Kita et al. [2022, SSJ meeting]. A stress-tensor inversion method to focal mechanisms of in-slab events for 20 years were applied and temporal change of stress axis relative to the duration time of the two L-SSEs were found. Basically, the Sigma 3 axes of inversion results strike in the east-west direction beneath fault planes of L-SSEs, whereas the strikes of the Sigma 1 axes beneath the fault planes can be divided into two portions by MLT which corresponds to a borderline of Aichi and Shizuoka prefectures. The Sigma 3 stress field axes are close to vertical in western portion, whereas those are horizontal in the eastern portion. The stress ratio R of the inversion results became maximum (0.53 to 0.55) during a period between two L-SSEs durations in both of the regions. It implies that the fault plane become relatively locked in the period, comparing to periods of L-SSEs durations. During the periods of the two L-SSEs durations, the Sigma 1 axes became less vertical in the western portion and those become close to the plunge of the plate interface in the eastern portion. The stress ratio R decrease during the periods of the durations in the both of the regions, which were also observed in three L-SSEs of the Bungo channel. During the time of the Bungo channel L-SSE from 2010, time change of the strike of Sigma 1 rotates following those of the slip direction of the hanging-wall side of the fault plane relative to the foot-wall side estimated by Seshimo et al. [2022]. These results suggest that detection of temporal change of in-slab events monitor ongoing reduction in locking of the plate boundary by aseismic slip.