9:00 AM - 9:15 AM
[J07-1-03] Postseismic deformation of the 2011 Tohoku Earthquake measured by GPS/Acoustic observations
The postseismic displacements after the 2011 Tohoku Earthquake measured by offshore geodetic studies [e.g., Watanabe et al., 2014] unveiled a deformation pattern significantly different from that onshore geodetic observations showed [e.g., Ozawa et al., 2012], which provided strong constraints on modeling postseismic deformation processes [e.g., Sun et al., 2014, Nature]. Furthermore, Tomita et al. [2016] revealed the along-trench variation of the postseismic displacements from GPS/Acoustic (GPS/A) observations. In this study, we show updated results of the GPS/A observations and discuss the spatiotemporal variation of the postseismic deformation.
We have carried out repeated campaign surveys from Sep. 2012 to Sep. 2016 at 20 GPS/A sites located in Tohoku-oki region. We estimated the displacement at each site for each survey by means of Kido et al. [2006] and then estimated the horizontal postseismic displacement rate at each site.
The displacement rates demonstrate clear spatial variation: slight trenchward motions (<~5 cm/yr) in the north region of the primary rupture area (PRA), significant trenchward motions (5-15 cm/yr) in the south region of PRA, and significant landward motions (10-15 cm/yr) above PRA. The observed landward movement can be roughly explained by the viscoelastic relaxation model (VR model, Sun et al., 2014), but it cannot be fully accounted for, which may indicate a contribution of interplate locking producing further landward motions. In the north region of PRA, both of the observed and the VR modeled motions are small. This suggests trivial contributions of other processes (e.g., afterslip and interplate locking). In the south region of PRA, the observed trenchward motions are much larger than the VR modeled motions. It indicates that the contributions of afterslip is major in this region with showing temporal decay of afterslip, while such a temporal decay is not detected where contributions of the viscoelastic relaxation are dominant.
We have carried out repeated campaign surveys from Sep. 2012 to Sep. 2016 at 20 GPS/A sites located in Tohoku-oki region. We estimated the displacement at each site for each survey by means of Kido et al. [2006] and then estimated the horizontal postseismic displacement rate at each site.
The displacement rates demonstrate clear spatial variation: slight trenchward motions (<~5 cm/yr) in the north region of the primary rupture area (PRA), significant trenchward motions (5-15 cm/yr) in the south region of PRA, and significant landward motions (10-15 cm/yr) above PRA. The observed landward movement can be roughly explained by the viscoelastic relaxation model (VR model, Sun et al., 2014), but it cannot be fully accounted for, which may indicate a contribution of interplate locking producing further landward motions. In the north region of PRA, both of the observed and the VR modeled motions are small. This suggests trivial contributions of other processes (e.g., afterslip and interplate locking). In the south region of PRA, the observed trenchward motions are much larger than the VR modeled motions. It indicates that the contributions of afterslip is major in this region with showing temporal decay of afterslip, while such a temporal decay is not detected where contributions of the viscoelastic relaxation are dominant.