A plate motion study using Ajisai SLR data

Eight years of Ajisai SLR data were processed to determine the terrestrial reference frame and its time evolution. The typical precision and accuracy of the estimated geocenter position averaged over a year determined from a one-year Ajisai SLR data set are 1 cm and 1.5 cm, respectively. The baselines between SLR stations away from plate bou-ndaries show rates of change that are in good agreement with NUVEL-1A, ITRF93 and LAGEOS results but significant deviations from geologically determined plate motion models are found for stations in plate boundary regions. Velocities of the observation stations were estimated by a weighted least squares method. The Simosato SLR station, located 100 km away from the plate boundary between the Eurasian plate and the Philippine Sea plate, move-s in the direction of the subduction of the Philippine Sea plate with respect to the Eurasian plate, which infers strong coupling of the two plates at the boundary. The motion of other stations at plate boundary regions is also discussed. This study is the first attempt to use Ajisai SLR data to determine the global terrestrial reference frame and its variation, thus independent of the previous SLR studies most of which were based on LAGEOS SLR analyses.