15:30 〜 16:30
[J07-P-05] Little evidence of shortening motion across the Japan Trench after the 2011 Tohoku-oki earthquake from direct-path acoustic ranging
After the 2011 Tohoku-oki earthquake, large postseismic deformation in ocean has been detected by GPS/Acoustic observations both the landward and oceanward slope of the Japan trench, which mainly attributed to the viscoelastic relaxation induced by the mainshock (e.g. Sun et al., 2014, Nature; Watanabe et al., 2014, GRL; Tomita et al., 2015, GRL) especially in the large slip region (off-Miyagi). Crustal deformation near the trench axis play important role on a huge earthquake, whose rupture area extend to the trench. However, convergence rate just at the trench axis is not clear from GPS/A observation. Therefore, we have carried out seafloor acoustic direct-path ranging across the frontal wedge to reveal locking state.
Direct-path acoustic ranging measures two-way travel times between a pair of instruments installed on the seafloor continuously for more than one year and as precisely as ~ 1 mm/yr for 1 km baseline. So far, we have completed three periods of observation, during 2013–2014, 2014–2015, and 2015–2016, in the region where significant coseismic slip was observed (e.g. Iinuma et al., 2012, JGR). In this paper, we show results of the long-term continuous observations from 2013 to 2016. All of results show little evidence of shortening motion across the trench after the Tohoku-oki earthquake.
Furthermore, we are planning to install another instrument in the Fukushima-oki region, where relatively large postseismic slip is expected (Sun and Wang, 2015, JGR) to reveal heterogeneous locking state. It will be planned to deploy in March 2017 and to recover in 2018. We expect that spatially heterogeneous convergency speed that will be caused by postseismic slip can be detected by this additional observation.
Acknowledgement: This observation is supported by JSPS KAKENHI (26000002). The installation and recovery of the instruments were executed during the KAIREI (KR15-15) and SHINSEIMARU (KS-16-14) cruises.
Direct-path acoustic ranging measures two-way travel times between a pair of instruments installed on the seafloor continuously for more than one year and as precisely as ~ 1 mm/yr for 1 km baseline. So far, we have completed three periods of observation, during 2013–2014, 2014–2015, and 2015–2016, in the region where significant coseismic slip was observed (e.g. Iinuma et al., 2012, JGR). In this paper, we show results of the long-term continuous observations from 2013 to 2016. All of results show little evidence of shortening motion across the trench after the Tohoku-oki earthquake.
Furthermore, we are planning to install another instrument in the Fukushima-oki region, where relatively large postseismic slip is expected (Sun and Wang, 2015, JGR) to reveal heterogeneous locking state. It will be planned to deploy in March 2017 and to recover in 2018. We expect that spatially heterogeneous convergency speed that will be caused by postseismic slip can be detected by this additional observation.
Acknowledgement: This observation is supported by JSPS KAKENHI (26000002). The installation and recovery of the instruments were executed during the KAIREI (KR15-15) and SHINSEIMARU (KS-16-14) cruises.