• Time-series analysis;
  • Transient deformation;
  • Subduction zone processes


We model the crustal deformation caused by two long-term subduction slip transients in southwest Japan, which we refer to as the 2000–2004 Tokai and the 2002–2004 Bungo Channel slow slip events (SSEs). We use re-analysed GEONET position time-series, and a Kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998–2004.67 and 2000–2005. Both events are found to have complex slip histories with multiple subevents. In addition to a newly identified slip subevent in 2002–2003, we find that the major event in the Bungo Channel SSE initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward, in contrast to the slip characteristics suggested by other studies. The re-analysed GPS data in the Tokai region shows a renewed slip activity for the Tokai SSE in early 2003–2004 at a similar location as in the period of 2001–2002. The equivalent Mw for both the Tokai and Bungo Channel SSEs are about 7.0. Our results show that the Tokai SSE appears to start before the Miyaki-Kozu seismovolcanic event. Integrating plate coupling and SSEs shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes (LFEs). At least part of the interseismic slip deficit is released by episodic SSEs beneath the Bungo Channel region. We find excellent temporal correspondence between transient slip and adjacent LFEs for both SSE, suggesting that they are closely related and possibly reflect that long-term slow slip may modulate the occurrence of LFEs.