Dike intrusion associated with the 2000 eruption of Miyakejima Volcano, Japan |
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| Authors: | K Yamaoka M Kawamura F Kimata N Fujii T Kudo |
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| Institution: | (1) Research Center for Seismology and Volcanology, Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya 464-8602, Japan;(2) Tono Geoscience Center, Japan Nuclear Cycle Development Institute, Izumi, Toki, Gifu 509-5102, Japan;(3) Present address: Earthquake Prediction Research Center, Earthquake Research Institute, University of Tokyo, Yayoi, Bunkyo, Tokyo 113-0032, Japan |
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| Abstract: | The model for the 2000 dike intrusion event between Kozushima and Miyakejima volcano, Japan, was reinvestigated. After the sudden earthquake swarm in Miyakejima volcano, a dike intrusion of large volume was detected by the nationwide GPS network (Geonet). The displacements detected with GPS stations over an area with a radius of about 200 km shows a distribution that is consistent with the dike source being located near Miyakejima volcano.The dike was intruded northwestwards between Miyakejima and the neighboring Kozushima volcano. We searched for the parameters in the models that reproduce the regional displacements due to dike intrusion between Miyakejima and Kozushiima islands. We tested three models, (1) the model with a single dike, (2) the model with a dike and a point dislocation source which represents a creep dislocation source and (3) the model with a dike and a deflation source which represents a magma reservoir. Though all three models can match the horizontal displacements near the source area, model 1 fails to reproduce the regional displacements in the central part of Japan. Both models 2 and 3 can reproduce the regional displacement for horizontal components. Model 3 produces slightly better results than model 2 for vertical components. The balance in the volume budget for models 2 and 3 is also consistent with the observations. These results show that we cannot distinguish between the two models using only GPS observation. As there is no direct evidence for such a large creep or ductile source (corresponds to M7 or more) as proposed in model 2 and the active seismic region migrated back and forth within the linear swarm region, the model with a dike and a deep magma source is preferable. For the deflation point source, we obtained a deflation volume of 1.5 km3 at the depth of 20 km below the dike. An additional ~0.95 km3 of volume loss through caldera collapse and edifice deflation took place at Miyakejima. We conclude that the magma that intruded the dike came in part from below Miyakejima and in part from below the sea floor between Miyakejima and Kozushima, perhaps from reservoirs at the Moho.Editorial responsibility: S Nakada, T Druitt |
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| Keywords: | Earthquake swarm Magma reservoir Izu islands Magma plumbing system Dike intrusion Miyakejima Crustal deformation |
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