HR: 0800h
AN: V11A-0367    [Abstracts]
TI: FEM Modeling for Magma Chamber of Unzen Volcano Causing 1990-1995 Eruption Inferred From Seismic and Ground Deformation Data
AU: * Kohno, Y
EM: yuhki-k@sevo.kyushu-u.ac.jp
AF: Institute of Seismolgy and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama, Shimabara, 855-0843, Japan
AU: Matsumoto, S
AF: Institute of Seismolgy and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama, Shimabara, 855-0843, Japan
AU: Matsushima, T
AF: Institute of Seismolgy and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama, Shimabara, 855-0843, Japan
AU: Uehira, K
AF: Institute of Seismolgy and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama, Shimabara, 855-0843, Japan
AU: Umakoshi, K
AF: Faculty of Environmental Studies, Nagasaki Universiy, 1-14 Bunkyo-machi, Nagasaki, 852- 8521, Japan
AU: Shimizu, H
AF: Institute of Seismolgy and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama, Shimabara, 855-0843, Japan
AB: The eruption during 1990~1995 of Unzen Volcano located in Kyushu, Japan, was caused by ascended magma from deep part beneath Chijiwa Bay, lying in the 15 km west from crater of the Volcano. Hypocenters of the earthquake swarm occurring around Unzen area during 1989~1990 were migrated to eastward from deep part of Chijiwa Bay. We propose a model of magma chambers for the eruption using seismic and geodetic observation data. Three types of ground deformation data, leveling, GPS and tidal data were applied in our previous study, and four major point sources beneath Unzen area were founded. The magma sources were arranged as ascending start from 15km depth part beneath Chijiwa Bay toward the crater. Stress distribution around magma source could give us constraint about the shape of magma chamber. Therefore we also performed stress tensor inversion using polarities of first onset of P wave for many earthquakes around the Volcano. The minimum principal stress axes in deeper part (> 15 km) obtained by this method have North-South direction, that is similar with the tension axis of tectonic stress field around Unzen Volcano. On the other hand the axes of maximum principal stress in shallower part of the region have directions toward the conduit of magma, suggesting expansion of conduit occurred from magma intrusion. Based on these geophysical implications we carried out a simulation by Finite Element Method (FEM) to get accurate model during eruption (1990~1995) until present. In previous study we applied semi-infinite media and regarded magma source as point spherical source (Mogi source), in this study we considered topography and shape of magma source obtained by stress distribution. As the result we obtained best-fitted model to the leveling data, the GPS data, and the tidal data around Shimabara peninsula as well as stress data around Unzen Volcano.
DE: 0545 Modeling (4255)
DE: 1299 General or miscellaneous (1709)
DE: 7280 Volcano seismology (8419)
DE: 8168 Stresses: general
DE: 8419 Volcano monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting