Research of strain field of the Japanese Islands using GPS

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The present project aims at examining straining process of overall Japanese Islands. It is important to find and monitor crustal straining process of this region especially in terms of both tectonics and prediction studies. In order to tackle this problem, we employed GPS interferometry. Most of Japanese researcheres participated in the project and have conducted three year of the nationwide campaign titled as GPS JAPAN project. Major activities and results obtained in the study are;(1) Nationwide GPS observations have been done three times since 1990. More than 100 stations have been occupied during the campaign. Moreover, surrounding countries, China, Korea, Taiwan etc.participated in the campaign.(2) All of acquired data were stored onto MO discs which are located in the temporal data center established at ERI. These data are shared among participated researchers for baseline analysis.(3) Major VLBI/SLR sites were collocated with GPS and coordinates at these primary sites have been acquired referring to VLBI/SLR coordinates.(4) Database for sites were established.At this moment, all of acquired data were distributed and used for baseline analyses for clarifying strain change of the Japanese Islands. Partial results are;(1) Relative plate motion between the Philippine Sea plate and the Eurasian plate have been found by preliminary examination in the southwestern part of the Islands,(2) Regional crustal deformations have been found in Shikoku and Sagami Bay region. These deformations are compatible with pre-estimated plate motion models or long term triangulation /trilateration data.(3) Precise orbits of satellites have been acquired over Japan. Through these results, capability and importance of GPS technique have been established and further researches are going on to delineate the strain process of overall Japan with fairly high temporal resolution.