HR: 0830h
AN: V51J-0401    [PDF]
TI: Repeated Seafloor Geodetic Observation west off Miyake-jima volcanic island
AU: * Mochizuki, M
EM: moma@iis.u-tokyo.ac.jp
AF: Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505 Japan
AU: Sato, M
EM: mariko-sato@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Fujita, M
EM: masayuki-fujita@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Katayama, M
EM: kata@rose.freemail.ne.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Yoshida, Z
EM: zengo@iis.u-tokyo.ac.jp
AF: Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505 Japan
AU: Yabuki, T
EM: tetsuichirou-yabuki@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Asada, A
EM: asada@iis.u-tokyo.ac.jp
AF: Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505 Japan
AB: An intensive earthquake swarm started under Miyake-jima island, 180 km south off Japan main island, on June 26, 2000. The earthquake swarm migrated towards northwest off Miyake-jima island, where numerous earthquakes, more than 100,000, were detected within about two months and an extensive crustal deformation was observed by on-land geodetic observations. Inst. of Industrial Science, Univ. of Tokyo and Hydrographic and Oceanographic Dept, Japan Coast Guard deployed three seafloor geodetic reference stations (St.A, St.B \& St.C) in triangle area surrounded by three islands, Miyake-jima, Nii-jima and Kouzu-jima islands, in November and December, 2000, and have been conducting observations using these three stations to monitor seafloor deformation for the better understandings of underground magmatic activities. The observations have been conducted thirteen times until present. Fast and quickly varying ocean current in this area prevented us from stable observation. The surface current makes the pole, which connects the GPS antenna and the ship-board transducer, bend. This bending of the pole gave uncertainty to the analyses of locating the positions of the seafloor geodetic reference stations. The pole was replaced new, more rigid pole to overcome the problem in August 2002. The first observation with this new system was conducted at the reference station in the Sagami-bay. Smaller amount of bending with the new pole than that with the old one against both roll and pitch components could be seen in the data from this observation. This shows that the replacement of the pole provided stability to the observation system. We started to adopt the new system to the observation at the three stations west-off Miyake-jima island area, too. Station C, that is located nearest one to the Miyake-jima island, is one where we had most frequent observation after improvement of the system. The observations with the new system have been conducted four times in September, December 2002, April and August 2003 there. We have been processing and analyzing the data from these four observations at Station C. More stable analyses have been done with the data from the observations which the new system was employed than with ones observed by the old system. In this poster, we will present the repeatability of the observation system with the new pole, as well as discuss the preliminary results from them.
DE: 1206 Crustal movements--interplate (8155)
DE: 1242 Seismic deformations (7205)
DE: 1294 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting