3:00 PM - 4:00 PM
[J07-P-03] Recent seafloor movement in and around the rupture zone of the 2011 Tohoku-oki earthquake detected by GPS-Acoustic seafloor geodesy
The Hydrographic and Oceanographic Department of Japan Coast Guard has been developing a system for precise seafloor geodetic positioning with the GPS-Acoustic combination technique and deploying seafloor observation sites on the landward slope of the major trenches around Japan, such as the Japan Trench and the Nankai Trough.
After the 2011 Tohoku-oki earthquake (M9.0), we directly measured huge coseismic seafloor displacements at seafloor sites just above the source region (Sato et al., 2011). These displacements were more than four times larger than those at any onshore GNSS station. It provided definitive evidence of huge coseismic deformation beneath the ocean.
We have repeatedly performed the GPS-A seafloor geodetic observation to monitor the postseismic movement in and around the rupture zone. In contrast to the coastal GNSS sites where trenchward-upward movements were reported, the offshore seafloor sites above the main rupture zone exhibit landward displacements with significant subsidence(Watanabe et al., 2014).
Although the terrestrial movements were reasonably interpreted by afterslip beneath the coastal area, the offshore results are rather consistent with effects predicted from viscoelastic relaxation in the upper mantle, providing definitive evidence of its occurrence.
In this presentation, we will report and discuss the most recent results of postseismic seafloor movement obtained after the paper by Watanabe et al., (2014).
Acknowledgements: We thank the Geospatial Information Authority of Japan (GSI) for high-rate GPS data for kinematic GPS analysis, and for daily coordinates of the sites on the GSI website.
After the 2011 Tohoku-oki earthquake (M9.0), we directly measured huge coseismic seafloor displacements at seafloor sites just above the source region (Sato et al., 2011). These displacements were more than four times larger than those at any onshore GNSS station. It provided definitive evidence of huge coseismic deformation beneath the ocean.
We have repeatedly performed the GPS-A seafloor geodetic observation to monitor the postseismic movement in and around the rupture zone. In contrast to the coastal GNSS sites where trenchward-upward movements were reported, the offshore seafloor sites above the main rupture zone exhibit landward displacements with significant subsidence(Watanabe et al., 2014).
Although the terrestrial movements were reasonably interpreted by afterslip beneath the coastal area, the offshore results are rather consistent with effects predicted from viscoelastic relaxation in the upper mantle, providing definitive evidence of its occurrence.
In this presentation, we will report and discuss the most recent results of postseismic seafloor movement obtained after the paper by Watanabe et al., (2014).
Acknowledgements: We thank the Geospatial Information Authority of Japan (GSI) for high-rate GPS data for kinematic GPS analysis, and for daily coordinates of the sites on the GSI website.