Earth Planets Space, Vol. 55 (No. 6), pp. e13-e16, 2003E-LETTER
Meilano Irwan1, Fumiaki Kimata1, Naoyuki Fujii1, Shigeo Nakao2, Hidehumi Watanabe2, Shinichi Sakai2, Motoo Ukawa3, Eisuki Fujita3, and Koji Kawai4
1Graduate School of Environmental Studies, Research Center for Seismology and Volcanology, Nagoya University, Nagoya, Japan
2Earthquake Research Institute, University of Tokyo, Tokyo, Japan
3National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan
4Japan Hydrographic Department, Marine Preservation, Tokyo, Japan
(Received February 28, 2003; Revised June 13, 2003; Accepted June 16, 2003)
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.
Key words: Miyakejima, rapid deformation, kinematic GPS.