[S-CG46] Shallow and intermediate depth intraslab earthquakes: seismogenesis and rheology of the slab

[SCG46-04] Effects of long-term slow slip events on in-slab stresses in Tokai region, central Japan

*Saeko Kita¹, Heidi Houston², Sachiko Tanaka³, Youichi Asano³, Suguru Yabe⁴ (1.International Institute of Seismology and Earthquake Engineering, BRI, 2.USC, 3.NIED, 4.AIST)

Keywords:Slow slip, Intraslab earthquakes, Stress inversions, Tokai region, Bungo channel

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.