2009 Volume 55 Issue 1 Pages 39-51
We have conducted observations of the seafloor crustal deformations around the Nankai Trough using a GPS/Acoustic technique. In the Kumano Basin, there are two seafloor benchmarks that are located about 60 and 80 km away from the deformation front of the Nankai Trough, respectively. The observations from 2005 to 2008 have illustrated that these benchmarks are moving at rates of about 5-6 cm/yr with uncertainties of 1-3 cm/yr relative to the stable Amurian plate. In this study, in order to estimate interplate coupling along the Nankai Trough, we calculated surface deformations accompanied with plate subduction in an elastic half-space and compared them with on- and offshore GPS velocities obtained by GPS/Acoustic technique. Then, we investigated the effect of observation for the seafloor crustal deformations on slip resolution on the plate interface. We conclude that offshore crustal deformation data provide good constraints for the estimation of fault slips at the shallower part of the plate interface, especially at the depths of 10-20 km, where slip resolution is low without using offshore geodetic data. Future additional crustal deformation observations on the seafloor would lead to the better estimation of seafloor velocities, which help us reveal strain accumulation process in the seismogenic subduction zone during interseismic period.
