Transient crustal deformation modeled from Japanese GEONET GPS time series

The Japanese continuous GPS network (GEONET) with ~1450 stations provides a unique opportunity to study ongoing subduction zone dynamics, and crustal deformation at different space-time scales. Recently a reanalysis of GEONET data using a GIPSY-based Network Processor yields high precision GPS solutions for the whole network [Owen et al., 2006]. We construct the detailed subduction plate interface along the Nankai trough based on the composite model [Wang et al., 2004] and approximate it with a triangular mesh to better represent the complex 3-D geometry. We derived GPS site velocities in SW Japan relative to the stable part of the Amurian Plate and estimate the interplate coupling along the SW Japan subduction zone. Cleaned GPS position time series also reveal new characteristics of the slow slip events (SSE). For example, the Tokai slow slip event appears to affect a larger spatial distribution of stations compared to previous studies. We applied the extended network inversion filter [MacGuire and Segall, 2003] to model the spatial and temporal distribution of this slow slip event using longer data from 2000.0 to 2004.0. Our initial results show that this SSE involves three sub-events since 2000.0. They all initiated at roughly the same location ~(137.6E, 34.7N) in a weakly coupled zone. The maximum cumulative slip locates at the deeper end of the seismogenic zone with an equivalent Mw~7.1 as of Dec. 2003. We estimate the stress change from these sub-events and investigate possible relations with seismicity rate changes in the region. We also investigate other slow slip events including the 2003 Bungo Channel and discuss their relation with plate coupling as well as imaged structural heterogeneities in the region.