HR: 0800h
AN: S51A-0137    [Abstracts]
TI: Spatiotemporal Velocity Changes Around Miyake and Kozu Islands, Central Japan in June,2000 - May,2001
AU: * Hagiwara, H
EM: hagiwara@eri.u-tokyo.ac.jp
AF: Earthquake Research Inst. Tokyo Univ., 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sakai, S
EM: coco@eri.u-tokyo.ac.jp
AF: Earthquake Research Inst. Tokyo Univ., 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Yamada, T
EM: yamada@eri.u-tokyo.ac.jp
AF: Earthquake Research Inst. Tokyo Univ., 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Inst. Tokyo Univ., 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Spatiotemporal velocity changes have been found around Miyake and Kozu Islands, central Japan in June,2000 - May,2001 from seismic tomography method applied to 694,345 arrival times at 122 sites in and around Miyake and Kozu Islands including ocean bottom observations. Due to the high irregularity in the uppermost crust and the difficulties of handling both of the data of seabed and the land simultaneously, station correction is adopted. The arrival time data is divided eleven periods so as to examine the temporal velocity change, taking into account the hypocenter distribution map. We determine Vp,Vs models in each period applying the seismic tomography method. The result indicates that there are mainly two low velocity zones which locate in the west of Miyake Island and the east of Kozu Island and they change temporally their intensity corresponding hypocenter distribution. In the early period ( ~ July 5 ), low velocity zone (LVZ) is limited at Miyake site and that suggests magma is supplied form Miyake Volcano. Next period (July 6 - July 20), LVZ of Miyake site decreases and in reverse that of Kozu site appears with seismic swarm. In the period (July 21 - Aug 14), LVZ of Kozu site is very powerful and expands up to 5km depth with great swarm. This suggests that the new magma intrusion occurs from deeper between Miyake and Kozu Islands. Next, in the period (Aug 15 - Aug 31), LVZ of Miyake site increases with swarm and that indicates the magma flow form Miyake volcano coming again. After that, in the period (Sept.1,2000 - May 6,2001), both LVZs decrease their rates gradually and the seismic activity decrease either. We surmise that those low velocity zones correspond magma intrusion and spatiotemporal changes of magma intrusions cause repeating seismic immigrations between Miyake and Kozu Islands.
DE: 8180 Tomography
DE: 8434 Magma migration
DE: 7230 Seismicity and seismotectonics
DE: 7280 Volcano seismology (8419)
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2004 AGU Fall Meeting