Interplate locking condition derived from seafloor geodetic observation in the shallowest subduction segment at the Central Nankai Trough, Japan

We monitored seafloor crustal deformation at two observation stations on opposite sides of the Nankai Trough from 2013 to 2016 in order to investigate the interplate locking condition along the Central Nankai Trough. We estimated the seafloor crustal deformation with respect to the Amurian Plate based on five observations. The results for two stations, TCA and TOA, were 38 +/- 25 mm/yr toward N78 degrees W and 5 +/- 21 mm/yr toward N69 degrees W (1 sigma), respectively. The displacement rate at TOA is consistent with the motion of the Philippine Sea Plate with respect to the Amurian Plate using the Euler vector of the REVEL model. The displacement rate at TCA is similar to that at other seafloor geodetic stations, e.g., 48 +/- 10 mm/yr at KUM2 station, on the Kumano Basin. The interplate coupling rate was estimated to be roughly 70 +/- 40% (1 sigma) in the shallowest segment of the Nankai Trough.