Vertical deformation of the Japanese islands, 1996-1999

The interseismic vertical deformation field of the Japanese islands is derived from the Global Positioning System (GPS) data between 1996 and 1999. Although vertical components of the GPS velocities have rarely been used as important information because of their higher noise level, information on the vertical deformation field will enable us to separate rigid plate motions from deformation due to interplate coupling because horizontal displacements contain both effects, whereas vertical displacements contain only the interplate coupling effect. The results show that (1) the precision of the vertical velocity is generally better than 2 mm/yr, (2) the existence of clear uplift peaks of about 8 mm/yr in the Shikoku and Tokai regions is consistent with strong coupling with a gradual brittleplastic transition zone at the Nankai and the Suruga trough, respectively, (3) clear uplift peaks do not seem to exist in the Tohoku region because the Japan trench plate boundary is too far oceanward from the GPS sites, (4) significant uplift is obtained in the western part of Hokkaido, which may be associated with the long-term postseismic deformation due to the 1983 Japan Sea and the 1993 Hokkaido-nansei-oki (M=7.6) earthquakes, and (5) uplift in northeastern Japan along the Japan Sea coast is apparently associated with distributed compression due to incipient subduction.