Change of recurrent slow slip event behaviors along the Nankai trough, Southwest Japan

Abstract:

Recurrent slow slip events (SSEs) have been regularly recorded by a continuous GNSS network (GEONET) in the Bungo Channel region, Nankai trough since 1996. Past studies suggest complex interactions between slow slip transients, large seismic events, downdip low frequency earthquakes and up-dip very low frequency earthquakes. In this study, we model recent slow slip events in the region using re-analyzed GEONET GNSS position time series. Thanks to the improved processing strategy, our multi-decades long GNSS position time series show good consistency and reduced scattering. Our time-dependent slip inversion analysis shows two recent events in 2014-2016 and 2018-2020 display different spatiotemporal patterns as compared to previous events. The change in slip and the repeat interval between these events suggest a possible change in slow slip behaviors. One mechanism for such change is the stress perturbation of large earthquakes and their postseismic processes. We investigate how external stress perturbation affects the changes in the SSE pattern through rate-and-state friction based earthquake cycle simulations. In all events considered we find slow slip exerts temporal modulation on the downdip low frequency earthquakes (LFEs). Both slow slip and LFEs are spatially overlapped, suggesting LFEs may be loaded directly by aseismic slip.