抄録
A continuous GPS observation network with 5 stations using single frequency receivers around Usu volcano was installed two days before the 2000 eruption, which took place at the western part of the volcano on 31 March 2000. The cumulative displacements in the radial direction from the center of the volcano reached 1.2 m before the eruption at station HKG located north of the central Usu volcanic massif and 2.3 m at station KNP located 500 m northeast from one of the new craters formed by this eruption. Both displacements were monotonously increasing with time. However at station IZM located closest to the crater, the displacement was only 0.2 m in the NW direction up to the noon 30 March and then changed its direction of SE. After the eruption till the end of April, the cumulative displacements at KNP and IZM exceeded about 1.8 m and 8.9 m, respectively, while the small amount of about 0.2 m was observed at HKG. New 20 GPS stations were installed by early May around the Nishiyama crater in order to monitor the remarkable doming phenomena which started near Nishiyama crater after the eruption. The observation up to the end of May 2000 shows displacements at all stations characterized by both upheaval and outward radial direction from the Nishiyama crater. By August 2000 the displacements at all stations had turned in the direction towards the Nishiyama crater and started to subside.
