Interplate locking condition derived from seafloor geodetic data at the northernmost part of the Suruga Trough, Japan

Abstract

We observed seafloor crustal deformation at two observation sites on opposite sides of the Suruga Trough off Japan from 2005 to 2011 to investigate the interplate locking condition at the source region of the anticipated great subduction earthquake, named Tokai earthquake. We estimated the displacement velocity vectors relative to the Amurian Plate on the basis of repeated observations. Our results at the two points, Suruga northeast and Suruga northwest (SNW) were 42 ± 8 mm/yr toward N94 ± 3°W and 39 ± 11 mm/yr toward N84 ± 9°W, respectively. These directions are the same as those measured at on-land GPS stations. The magnitudes of the velocity vectors indicate a significant shortening of approximately 4 mm/yr between SNW and on-land GPS stations located to the west of the Suruga Trough. The results show that the plate interface is strongly locked (no slip) shallower than the source region of the anticipated Tokai earthquake.

Non-volcanic crustal movements of the northernmost Philippine Sea plate detected by the GPS-acoustic seafloor positioning

“…In Japan, our group first succeeded in detecting seafloor movements caused by interseismic plate convergence at the Japan Trench ) and has continued to monitor the movements including coseismic and postseismic deformation at the seafloor sites along the Japan Trench (e.g., Matsumoto et al 2006;Sato et al 2011a, b;Sato et al 2013b;Watanabe et al 2014) and the Nankai Trough (e.g., Yokota et al 2015). Moreover, other groups in Japan have provided important results (Kido et al 2006;Kido et al 2011;Tadokoro et al 2012;Yasuda et al 2014) to understand the major interplate earthquakes as well. Figure 1 shows a schematic picture of the GPSacoustic positioning system developed by our group.…”

“…The IM subducts beneath the Eurasian plate (EU) along the Suruga Trough, where a large earthquake had occurred in 1854 (Ando, 1975). In order to investigate the accumulation and/or the release of strain on the plate interface, it is necessary to estimate the precise convergence rate of the subducting oceanic plate relative to the continental plates, as Yasuda et al (2014) had directly investigated in the Suruga Trough. They indicated the strong coupling in the shallow portion of the plate boundary from the seafloor geodetic observation.…”

Heterogeneous interplate coupling along the Nankai Trough, Japan, detected by GPS-acoustic seafloor geodetic observation

“…Our past observations near the Japan Trench provided great advantage in understanding the 2005 Off-Miyagi Prefecture earthquake (M7.2) (e.g., Matsumoto et al 2006 andSato et al 2011b), the 2011 Tohoku-oki earthquake (M9.0) (e.g., Sato et al 2011a andSato et al 2013b), and others. Important observations have also been made by other research groups in Japan such as Tohoku University (e.g., Kido et al 2006 andKido et al 2011) and Nagoya University (e.g., Tadokoro et al 2012 andYasuda et al 2014).…”

Interplate Coupling Distribution Along the Nankai Trough in Southwest Japan Estimated From the Block Motion Model Based on Onshore GNSS and Seafloor GNSS/A Observations

“…Since this period includes the 2009 M 6.5 Suruga Bay earthquake and the 2011 M 9 Tohoku‐Oki earthquake, raw observations after these events were affected by coseismic steps and postseismic deformation. Thus, we removed these effects by calculating them as follows: For coseismic steps of the M 6.5 Suruga Bay earthquake, we calculated the elastic deformation on the surface assuming an elastic half‐space and used a revised subfault model (Yasuda et al, ). For postseismic deformation of the M 6.5 Suruga Bay earthquake, we employed the average crustal deformation observed at the GEONET site near Suruga Bay as an approximation.…”