Crustal Movement around Sagami Bay Inferred from GPS Observation Network of the Hydrographic Department

Abstract

GPS observations have been continued since May in 1990 at three points around Sagami Bay; Izu-Osima, Manazuru and Turugi-Saki. The network constitutes a nearly regular triangle of about 50 km baseline length. In the spring of 1992, the precision of baseline estimation becomes 1.1-1.8 cm, 0.8-1.2 cm and 2.5-3.1 cm for east-west, north south and vertical components, respectively. Two-year observations have revealed the horizontal movements of observed site although there is some doubt about the accuracy of east-west component because of the poor condition of satellite constellation. By fixing the position of Manazuru site, the movement of Izu-Osima to the northwest is in ferred. The convergence velocity is 2.6 cm per year, which is slightly less than the tectonic motion model of the Philippine Sea plate relative to the continental plate. The movement of Turugi-Saki is to the westnorthwest with the velocity of 2.2 cm per year, which is almost consistent with the tectonic model of strain accumulation associated with the plate convergence along the Sagami trough.