[S-CG50] Dynamics in mobile belts

[SCG50-14] Effects of ETS on seismicity and stress in the subducting oceanic plate

*Saeko Kita¹, Heidi Houston², Suguru Yabe³, Sachiko Tanaka⁴, Youichi Asano⁴, Takuo Shibutani⁵, Naoki Suda⁶ (1.Building Research Institute, 2.University of California, 3.AIST, 4.NIED, 5.DPRI, Kyoto University, 6.Hiroshima University)

Keywords:Slow slip, intrslab earthquake, stress field, seismicity, the southwestern Japan, Kii peninsula

Slow slip phenomena appear related to geofluids, but the detailed relationships among slow slip, geofluids, and intraslab earthquakes remain unknown. Here we report changes in seismicity rates, b-values, and stresses in the oceanic slab before and after slow slip episodes beneath Kii Peninsula, Japan. One month before slow slip occurrence, the seismic rate and b-value become high, consistent with the effects of fluid-induced seismicity. Intraslab stress orientations below the plate interface in the ETS zone change only slightly, whereas below the plate interface updip of ETS, the intraslab stress orientations rotate by a larger amount, suggesting that transient aseismic slip occurs on the interface updip. The existence of repeating earthquakes and seismicity on the plate boundary also implies that aseismic slip occurs on the updip zone after the ETS, which could reset the stress state of the slab and the boundary to its prior condition. The proposed methodology, which is based primarily on intraslab earthquakes, may help monitor plate boundary conditions and slow slip phenomena, which can signal the beginning stages of megathrust earthquakes in subducting plates.