[S08] AM-1

[S08-16] 東海地方および豊後水道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変化

*北 佐枝子¹、Houston Heidi²、矢部 優³、田中 佐千子⁴、浅野 陽一⁴、木村 武志⁴ (1. 国立研究開発法人　建築研究所　国際地震工学センター、2. 南カリフォルニア大学、3. 国立研究開発法人　産業技術総合研究所、4. 国立研究開発法人　防災科学技術研究所)

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) of several years’ duration. Such relationships were compared for the Bungo channel by Kita et al. [2022, SSJ meeting]. A stress-tensor inversion method of focal mechanisms of 20 years of in-slab events was applied and temporal changes of stress axis relative to the duration times 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 the Median Tectonic Line which corresponds to the boundary between Aichi and Shizuoka prefectures. The Sigma 3 axes are close to vertical in western portion, whereas they are horizontal in the eastern portion. The stress ratio R of the inversion became maximum (0.53 to 0.55) during the period between the two L-SSEs in both of the regions. This suggests that the fault plane became more locked in the period, compared to periods of L-SSEs slip. During the periods of the two L-SSEs slips, the plunges of Sigma 1 axes decreased, becoming less vertical in the western portion and close to the plunge of the plate interface in the eastern portion. The stress ratio R decreased during the periods of slip in the both of the regions, which was also observed in three L-SSEs in the Bungo channel. These results suggest to detect in-slab events to monitor ongoing reduction in locking of the plate boundary by aseismic slip.