Centimeter-level positioning on the seafloor

Abstract

Abstract:This Introduction. The space geodetic techniques have already been used in the monitoring of crustal deformations on land not only with high spatial and temporal resolutions but also with centimeter-level accuracy. In Japan, the continuous observation with the Global Positioning System (GPS) Earth Observation Network (GEONET) has been producing amazing results. These results have contributed significantly to the understanding of the complex crustal deformation processes.' The remote sensing from flying vehicles with SAR (Synthetic Aperture Radar) Interferometry technique also achieved great success with its high performance.2~ However, these space techniques are only available on land. Currently, about 70% of the solid earth surface is under the veil of sea water.Around Japan, many great earthquakes have occurred repeatedly beneath the deep ocean floor, at the seismic coupling zone between the descending oceanic crust and overhanging continental crust along the Kuril Trerlcli, the Japan Trench, the Nankai trough, etc. When little or no information is known as to what will happen at the ocean bottom crust, an unexpected attack of a tsunami generated by a great earthquake can develop sea-surface precise positioning with GPS and precise acoustic ranging between sea-surface platform and sea-bottom acoustic transponders (Fig. 1). This is analogous to GPS geodesy on land. In this GPS/Acoustic method, the precise positioning for the platform and the buoy on the sea-surface is realized by kinematic GPS technique which uses phase measurement of carrier Centimeter-level positioning on the seafloor 9

Weak interplate coupling beneath the subduction zone off Fukushima, NE Japan, inferred from GPS/acoustic seafloor geodetic observation

“…This technique has its origins in early work carried out by scientists at the Scripps Institution of Oceanography (Spiess, 1985). Our team at the Japan Coast Guard (JCG) and the Institute of Industrial Science, the University of Tokyo, has been developing this technique using a survey vessel and making repeated campaign observations along the major trenches (Asada and Yabuki, 2001;Mochizuki et al, 2003Mochizuki et al, , 2005Fujita et al, 2006a). Fujita et al (2006a) demonstrated that the repeatability of the position determination reaches an accuracy of a couple of centimeters under good conditions and proved the capability of detecting secular crustal movement at a seafloor reference point located off Miyagi Prefecture.…”

Undersea co-seismic crustal movements associated with the 2005 Off Miyagi Prefecture Earthquake detected by GPS/acoustic seafloor geodetic observation

“…In Japan, our team at the Hydrographic and Oceanographic Department of Japan (JHOD) and the Institute of Industrial Science, the University of Tokyo has been developing this technique using a survey vessel and making repeated campaign observations along the major trenches (Asada and Yabuki, 2001;Mochizuki et al, 2003Mochizuki et al, , 2005Fujita et al, 2006). Fujita et al (2006) have shown that the repeatability of the position determination reaches a couple of centimeters under good conditions.…”

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

“…In order to detect seafloor movements with an accuracy of a few centimeters, GPS-acoustic combination technique has been developed (e.g., Spiess et al 1998;Asada and Yabuki, 2001). 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).…”