Stress changes during the rapid deformation of Miyakejima volcano on 26-27 June 2000

Deformation often signals the occurrence of magmatic processes within volcanoes, such as the intrusion of new magma bodies and inflation or deflation, of existing bodies. Stress change induced by magmatic activity can drive propagation of dike and earthquake activity. Conversely, by relieving stresses from previous intrusive processes, can establish stress states favorable to new or continued intrusion. In this research we have modeled stress transfer effects during the dikes intrusion sequence in Miyakejima volcano on 26-27 June 2000. On 26-27 June 2003, a kinematic GPS analysis of data from the the Miyakejima volcano captured a fast developing event 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 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 the submarine eruption at 09:00 on 27 June 2000. The non linear inversion of GPS data 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. This research attempts to identify and delineate stress interactions and to develop a consistent model of magmatic processes in Miyakejima volcano.