Displacement and maintenance of control points at Okinotorishima Island on Philippine Sea Plate

Abstract

Okinotorishima Island is the southernmost island of Japan, located on the Philippine Sea plate. On the island, Geospatial Information Authority of Japan (GSI) set triangulation points and a GPS continuous observation station in 1989 and 2005, respectively, and has conducted GPS surveys since 1992 for surveying and crustal deformation monitoring. This report describes the displacement of Okinotorishima Island from 2005 to 2013 as a result of re-analyzing GPS data using GAMIT software. The displacement suggests that Okinotorishima Island has moved WNW at Vns = +21.6 mm/year and Vew = -58.0 mm/year, or moved N66.8 deg W at 61.9 mm/year. The rate of collection of data at the island is lower than that of the GSI's other GNSS stations because the station is an extremely isolated island in the Pacific Ocean. In order to monitor the movement of Philippine Sea plate, it is necessary to continue the maintenance of observation devices and enhance the station's data availability.