Rapid ground deformation of the Miyakejima volcano on 26-27 June 2000 detected by kinematic GPS analysis

抄録

A kinematic GPS analysis of data from the Miyakejima volcano captured a fast developing deformation event on 26-27 June 2000 in unprecedented spatial and temporal detail. Initial ground deformation toward east and upward was observed in the southeastern part of the volcano at 18 : 00 on 26 June 2000, almost simultaneous with earthquake swarms. Some time after 21 : 30 on 26 June 2000 the displacements at these sites turned from eastward to westward. Three hours later the displacement rates increased gradually at GPS sites in the western part of Miyakejima as the seismicity migrated and approached the west coast, and reached a climax with submarine eruption at 09 : 00 on 27 June 2000. A Genetic Algorithm was used to explore the parameter space and to find the best fitting source geometry. This analysis leads to an interpretation that the 18 : 00 26 June earthquake swarm was caused by a dike intrusion near the Oyama crater. Starting from 21 : 30 this dike deflated and a new dike intruded near the west coast. Following the propagation of this dike to the offshore, a spherical source began deflating in the southwest of Oyama crater.