8:30 AM - 8:45 AM
[J07-1-01] Observational Results of Seafloor Crustal Deformation Near the Nankai Trough Axis
invited
The Central Disaster Management Council, Japanese government extended the presumed source region of the Nankai mega-thrust earthquake to the trough axis in 2012. It is, therefore, essential to understand interplate locking condition near the trench axis, also for the anticipated mega-thrust earthquake at the Nankai Trough.
We installed three seafloor benchmarks for the seafloor crustal deformation measurement with the GNSS/acoustic technique in the vicinity of the Nankai Trough axis. Two benchmarks, TCA and TCB, are located about 15 and 35 km landward from the trough axis on the Amurian plate, respectively. The other benchmark TOA is located about 25 km seaward from the trough axis on the subducting Philippine Sea Plate. We can directly “measure" the slip deficit and the motion of the subducting Philippine Sea Plate through observations at the three benchmarks.
We performed campaign observations seven times at TCA and TOA benchmarks, and six times at TCB until the end of 2016. The worm ocean current, Kuroshio, flows over the observation sites, and we estimated heterogeneity of sound speed in the sea for the precise seafloor benchmark positioning. We, then, derived steady horizontal displacement rate with relative to the Amurian Plate from the time series of benchmark coordinate. The horizontal displacement rate is measured at 56+/-21 mm/y in the direction of N69+/-14W at TOA benchmark. The predicted motion of the Philippine Sea Plate is 60-61 mm/y in the direction of N59W at the position of TOA benchmark, which coincides with our measurement at TOA within the error interval. The measured horizontal displacement rates are 38+/-19 mm/y toward the west-northwest and 72+/-25 mm/y in the direction of N48+/-21W at TCA and TCB benchmarks, respectively. These results are the strong evidence for interplate locking, with coupling ratios of more than 40% on the basis of the back-slip model, at the most-shallowest segments of plate interface.
We installed three seafloor benchmarks for the seafloor crustal deformation measurement with the GNSS/acoustic technique in the vicinity of the Nankai Trough axis. Two benchmarks, TCA and TCB, are located about 15 and 35 km landward from the trough axis on the Amurian plate, respectively. The other benchmark TOA is located about 25 km seaward from the trough axis on the subducting Philippine Sea Plate. We can directly “measure" the slip deficit and the motion of the subducting Philippine Sea Plate through observations at the three benchmarks.
We performed campaign observations seven times at TCA and TOA benchmarks, and six times at TCB until the end of 2016. The worm ocean current, Kuroshio, flows over the observation sites, and we estimated heterogeneity of sound speed in the sea for the precise seafloor benchmark positioning. We, then, derived steady horizontal displacement rate with relative to the Amurian Plate from the time series of benchmark coordinate. The horizontal displacement rate is measured at 56+/-21 mm/y in the direction of N69+/-14W at TOA benchmark. The predicted motion of the Philippine Sea Plate is 60-61 mm/y in the direction of N59W at the position of TOA benchmark, which coincides with our measurement at TOA within the error interval. The measured horizontal displacement rates are 38+/-19 mm/y toward the west-northwest and 72+/-25 mm/y in the direction of N48+/-21W at TCA and TCB benchmarks, respectively. These results are the strong evidence for interplate locking, with coupling ratios of more than 40% on the basis of the back-slip model, at the most-shallowest segments of plate interface.