JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

S (Solid Earth Sciences) » S-SS Seismology

[S-SS04] [EE] Subduction zone dynamics from regular earthquakes through slow earthquakes to creep

Wed. May 24, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)

convener:Kyuichi Kanagawa(Graduate School of Science, Chiba University), Kazushige Obara(Earthquake Research Institute, The University of Tokyo), Demian M Saffer(Pennsylvania State University), Laura Wallace(University of Texas Institute for Geophysics)

[SSS04-P07] Direct and precise geodetic measurement across the Japan Trench after the 2011 Tohoku-oki earthquake

*Ryusuke Yamamoto1, Ryota Hino1, Motoyuki Kido2, Chie Honsho2 (1.Graduate School of Science, Tohoku University, 2.International Research Institute for Disaster Science, Tohoku University)

Keywords:2011 Tohoku-oki earthquake, Tohoku Earthquake, seafloor geodesy, acoustic ranging

The 2011 Tohoku-oki earthquake (Tohoku Earthquake: Mw 9.0) caused over 50 m coseismic slip. After then many geodetic observations such as on-shore GNSS, GPS/Acoustic (GPS/A), and others, have been carried out. Especially, GPS/A played important roll to reveal large off-shore coseismic displacement and subsequent postseismic deformation, which can be interpreted by viscoelastic relaxation (Sun et al., 2014, Nature; Watanabe et al., 2014, GRL; Tomita et al., 2015, GRL) and/or afterslip. Because GPS/A observation alone cannot reveal the afterslip of megathrust in the shallow dip of the trench, “direct-path acoustic ranging”, which can measure precise relative distance (e.g., ~ mm/yr precision for 1 km baseline) between two stations, was used across the trench. It periodically measures two-way travel-time and is corrected the calculated sound velocity after the recovery. Prior to this study, the same observations were conducted twice; they were 2013 (~150-days) (Osada et al., 2014, JpGU) and 2014-2015 (~250-days) (Yamamoto et al., 2016, JpGU), respectively. These observations proved the capability to measure as long as ~10 km baseline and found no significant relative motion across the trench.
In September 2015, we installed five instruments at the same, the region of large coseismic slip (e.g., Iinuma et al., 2012, JGR) and recovered in September 2016 (~360-days observation). The result shows no significant movement across the trench axis like as in the previous surveys. This result shows fully locked state and may clarify the absence of postseismic slip in the shallower part in this area and at least 2013-2016.
In March 2017, we plan to install five instruments across the Japan Trench off-Fukushima, where instead large postseismic slip (e.g., Sun and Wang, 2015, JGR; Iinuma et al., 2016, Nature Comm.). This auxiliary observation may reveal spatial variation of convergence rate along the trench axis.
Acknowledgement: This observation is supported by JSPS KAKENHI (26000002). The installation and recovery of the instruments were carried out during the KAIREI (KR15-15) and SHINSEIMARU (KS-16-14) cruises.