A PLATE MOTION STUDY USING AJISAI SLR DATA

Eight years of Ajisai SLR data were processed to determine the terrest rial reference frame and its time evolution. The typical precision and accuracy of the estimated geocenter position averaged over a year det ermined from a one-year Ajisai SLR data set are 1 cm and 1.5 cm, respe ctively. The baselines between SLR stations away from plate boundaries show rates of change that are in good agreement with NUVEL-1A, ITRF93 and LAGEOS results but significant deviations from geologically deter mined plate motion models are found for stations in plate boundary reg ions. Velocities of the observation stations were estimated by a weigh ted least squares method. The Simosato SLR station, located 100 km awa y from the plate boundary between the Eurasian plate and the Philippin e Sea plate, moves in the direction of the subduction of the Philippin e Sea plate with respect to the Eurasian plate, which infers strong co upling 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 ref erence frame and its variation, thus independent of the previous SLR s tudies most of which were based on LAGEOS SLR analyses.