Temporal variation in seismic moment release rate of slow slips inferred from deep low-frequency tremors in the Nankai subduction zone

We examined seismic moment release rates as estimated from deep low-frequency tremors at episodic tremor and slip (ETS) zones on the plate interface in the Nankai subduction zone. Excluding periods with long-term slow slip events, we observe no clear temporal variation in the seismic moment release rate in the Tokai, the northern Kii, or Shikoku regions. We also find no variation in the seismic moment release rate related to the 2011 Tohoku earthquake in the southern or central Kii region. These findings imply that the 2011 Tohoku earthquake has not affected slow slip activities in the Nankai subduction zone. For the southern and central Kii regions, a long-term decrease in the seismic moment release rate with time is apparent, irrespective of the occurrence of the 2011 Tohoku earthquake, suggesting that frictional properties on slip planes at the ETS zone on the plate interface have varied over time.