Assessment of long-term variation in displacement for a GPS site adjacent to a transition zone between collision and subduction

A transition and subduction zone adjacent to the Ryukyu Arc, Ryukyu Trench, and Okinawa Trough, extends between southern Japan and northeastern Taiwan. It is generated during the northwestward subduction of the Philippine Sea Plate, which lies the Eurasian Plate along the Ryukyu Trench. The movement of the Philippine Sea Plate is hindered at the northeastern corner of Taiwan, which causes complicated structure of the Philippine Sea Plate at the western end of the Ryukyu subduction zone. Development of the active subduction and transition boundary near the western Ryukyu Arc is evaluated statistically by using displacements derived from GPS site data. The statistical model shows that the absolute displacement derived from GPS measurements of nearly 8 years indicates a maximum spatial variation of 0.625 m. Three trends are observed for such long-term progress, and use of linear regression also reveals quite good consistency between the data and statistic models. Such rate is also elevated following the trend development. Southeastern and nearly horizontal movement is suggested to the main development of for the site movements, it is likely related to the tensional activity adjacent to this boundary.