3:00 PM - 4:00 PM
[J07-P-04] Detection of offshore vertical displacements after the 2011 Tohoku-oki Earthquake using GPS/A observations
After the 2011 Tohoku-oki Earthquake, GPS/Acoustic (GPS/A) observations have revealed extensive postseismic displacement pattern [Watanabe et al., 2014, GRL; Tomita et al., 2016, AGU], which provides strong constraints on modeling of the postsesimic deformation processes [e.g., Sun et al., 2014, Nature]. Most of the GPS/A observation results are limited in horizontal components because vertical component has large errors due to the trade-off nature with sound speed in the seawater. However, vertical motions are sensitive to postseismic processes; therefore, in this study, we challenge to estimate vertical displacements after the Tohoku Earthquake, from Sep. 2012 to Nov. 2016, at the 20 GPS/A sites located in the Tohoku-oki region.
In order to estimate vertical motions, numerous acoustic ranging data covering extensive sea-surface points are needed to distinguish the vertical motions and sound speed variation[Sato et al., 2013, J. Geod.]. Although, in our survey style, acoustic ranging was mainly performed at a fixed sea-surface point (the center of each transponder array) with the aim to focus on detecting the horizontal motions [e.g., Kido et al., 2006, EPS], we have also occasionally conducted moving surveys to collect acoustic ranging data covering the minimum extent above each transponder array. Using these data, we calculated displacement rates of the vertical motions.
The obtained vertical displacement rates show a spatially characterized pattern: subsidence above the coseismic rupture area and uplift near the trench, but they have 3-15 cm/yr errors in 1σthat are much larger than the errors in the horizontal components. Due to the large errors, it is difficult to discuss the postseismic deformation processes at the moment. Nevertheless, this study successfully showed the potential capability of our data for detecting vertical motions. Further collection of data and appropriate evaluation of the errors will be required to obtain more accurate results.
In order to estimate vertical motions, numerous acoustic ranging data covering extensive sea-surface points are needed to distinguish the vertical motions and sound speed variation[Sato et al., 2013, J. Geod.]. Although, in our survey style, acoustic ranging was mainly performed at a fixed sea-surface point (the center of each transponder array) with the aim to focus on detecting the horizontal motions [e.g., Kido et al., 2006, EPS], we have also occasionally conducted moving surveys to collect acoustic ranging data covering the minimum extent above each transponder array. Using these data, we calculated displacement rates of the vertical motions.
The obtained vertical displacement rates show a spatially characterized pattern: subsidence above the coseismic rupture area and uplift near the trench, but they have 3-15 cm/yr errors in 1σthat are much larger than the errors in the horizontal components. Due to the large errors, it is difficult to discuss the postseismic deformation processes at the moment. Nevertheless, this study successfully showed the potential capability of our data for detecting vertical motions. Further collection of data and appropriate evaluation of the errors will be required to obtain more accurate results.