Kozu Island volcano, one of the active volcanoes in Izu islands, erupted on a massive scale about 1,000 years ago. After that no volcanic eruption and activity has been recorded in Kozu Island. As the horizontal displacements observed by GPS measurements at Kozu GPS station show a disagreement with the plate motion estimated from the plate model of the Philippine Sea plate, we occupied local GPS network in Kozu Island to discuss the crustal movements. Four GPS campaigns have been repeated since July 1996 to November 1997. Through the campaigns, the horizontal displacements of one to five cm/yr and the vertical movements of two cm/yr are detected in the network. As observed convergence vectors at Zenisu reef and Hachijo Island located south of the Kozu Island show good consistency with the displacements estimated by a plate motion model, local displacements are deduced from the displacements estimated by the plate model and the observed displacements at Kozu Island. Local displacements suggest the south- or southwestward displacements of three to five cm/yr. Tilting of 5×106 radian/yr to the south is also detected by the measurements. The location of the source for the crustal movements is estimated in the northeastward in or off Kozu Island.
