Over the last 1000 years, larger magnitude M~8 earthquakes have occurred every 100-200 years at the Nankai trough, southwest Japan, where the Philippine Sea plate is subducting at a rate of ~60mm/yr beneath the southwestern Japan. In addition to large earthquakes, several transient slip events have been observed in this region, possibly due to spatially varying frictional properties on the subduction interface. Using the dense GEONET continuous GPS network, we estimate the spatial extent of interplate coupling along the Nankai trough. The GPS time series are from the JPL-developed GPS Network Processor, which uses GIPSY-OASIS and cluster computing to quickly and efficiently analyze large quantities of data. Using QOCA to remove non-tectonic signals such as common mode error and seasonal signals, we have determined accurate horizontal and vertical interseismic velocities for the entire continuous GPS network. In this study, we use the results of this analysis to look at steady-state subduction plate coupling in southwestern Japan. We construct plate interface geometry from the west of Shikoku to the Tokai region, based on the composite plate boundary model by Wang et al. . For the inversion procedure, we use both horizontal and vertical GPS site velocities, referenced to the Amurian plate. By employing elastostatic Green's function of triangular dislocation elements [Jeyakumaran et al., 1992] and spatial smoothing based on the Fujuwara operator [Desbrun et al., 1999], we estimate the back slip along the Nankai trough. We find strong coupling at the depth of ~10-30 km on the plate interface beneath Shikoku, Kii Peninsula and Tokai area. There is good spatial correspondence between highly coupled regions with the rupture zones of past large earthquakes (e.g., 1946 Nankai and 1944 Tonankai earthquakes). It appears that there is complementary pattern between short-and long-term slow slip patches [Hirose and Obara, 2005] and strong coupling zone, which may suggest variations in frictional properties on the plate interface.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1209 Tectonic deformation (6924);
- 1240 Satellite geodesy: results (6929;
- 8170 Subduction zone processes (1031;