10:45 AM - 11:00 AM
[SSS04-07] Interplate coupling and slow slip events along the northern margin of the Philippine Sea plate estimated from GNSS data
Keywords:Slow Slip Events, Interplate coupling, GNSS, Crustal deformation
In order to detect S-SSEs, we analyzed the data of ~800 GEONET GNSS stations along the Nankai Trough and the Ryukyu Trench. More than 390 possible short-term SSEs with Mw ≥ 5.6 for 19 years were detected by our analysis and they have a variety of characteristic recurrence intervals, magnitudes, durations and coincidental seismic activities. The detected SSEs concentrate in a depth range of 25-40 km and form the ETS (Episodic Tremor and Slip) zone along the Nankai Trough. The detected S-SSEs extend from the ETS zone toward southwest, and then fade away around the subducted Kyushu-Palau Ridge. Although few shallow (depth ≤ 20 km) S-SSEs have been detected along the Nankai Trough, S-SSEs often occur on the shallow plate interface along the Ryukyu Trench. This may be related to the incomplete interplate coupling.
We also estimate back-slip rates expressing interplate coupling as well as inland block rotations from GNSS and GPS-A velocities for a quiet period of crustal activity. Land GNSS data from April 2005 to December 2009 are used to estimate interseismic velocities. GPS-A data from 2004-2012 to 2016 are used after correcting co- and post-seismic displacement of the 2011 Mw 9.0 Tohoku-oki earthquake. The estimated coupling distribution (Figure) shows large heterogeneity in both strike and dip directions. Estimated back-slip rates are the highest off Shikoku and in the Bungo Channel at a depth of 10-30 km and decreases toward east. Back-slip rates off Kii Peninsula show heterogeneous distribution. Epicenters of the 1944 Mw8.0 Tonankai and the 1946 Mw8.3 Nankai earthquakes locate in an area of relatively low back-slip rates. Most S-SSEs occur at the down-dip edge of the transition zone from partial coupling to no coupling except in the Bungo Channel where a high coupling zone extends in a down-dip direction.