S1, S4: Earth materials science related to igneous processes and plate convergence region (Joint Special Session)

[S1,S4-01] Relationship of slow earthquakes to intraslab and inland earthquakes
in the Nankai subduction zone

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

Keywords:Slow earthquake, Intermediate-depth intraslab earthquake, Stress field, Quartz vein, b-value

We examined time variations in seismicity rates, b-values, and stress regimes in the slab associated with times of episodic tremors and slip (ETS) during 17 years beneath Kii peninsula. At 1 month before the ETS times, seismic rate and b-value become high, which is similar to characteristics of fluid-induced seismicity. Sigma 1 axis in the oceanic crust beneath the ETS zone rotated larger than that updip of the zone just after the ETS times. The results show that monitoring of in-slab earthquakes would be a new technique to detect time change of plate coupling degree and slow slip events.