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

Yoko Kono,Keita Nakamoto,Yoshihiro Hiramatsu

doi:10.1186/s40623-020-1142-3

Abstract

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.

Highlights

Slow earthquakes such as deep low-frequency tremors, very low-frequency earthquakes, and long-term and short-term slow slip events (SSEs) have been found in many subduction zones worldwide (e.g., Obara and Kato 2016)
The lesser variation in seismicity in areas far from the source area can be interpreted as small Coulomb stress changes induced by the 2011 Tohoku earthquake (e.g., Toda et al 2011)
Seismic moment release rates of slow slips at episodic tremor and slip (ETS) zones were investigated for seven regions in the Nankai subduction zone using data of 2001–2016

Summary

Introduction

Slow earthquakes such as deep low-frequency tremors, very low-frequency earthquakes, and long-term and short-term slow slip events (SSEs) have been found in many subduction zones worldwide (e.g., Obara and Kato 2016). Slow earthquakes, designated as episodic tremor and slip (ETS) (Rogers and Dragert 2003), usually accompany tremors. In the Nankai subduction zone, the average slip rates at the ETS zone have been estimated (Hirose et al 2010b; Ishida et al 2013; Daiku et al 2018) based on an empirical relation between the apparent moment of tremors and. Examining the variation in slow slip activity in the Nankai subduction zone through tremors is interesting, but no marked change in slow slip activity has been observed there geodetically based on data obtained before and after the 2011 Tohoku earthquake

Methods

Results

Conclusion