HR: 0800h
AN: G21A-0139    [Abstracts]
TI: An Experiment on GPS/A Seafloor Positioning in the Central Part of Kumano-nada, Central Japan
AU: * Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Sweeney, A
EM: aaron@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Miura, S
EM: miura@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Kido, M
EM: kido@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Osada, Y
EM: osada@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AB: Kumano-nada, northeast of Kii Peninsula in the central part of Japan, is a seismogenic zone of the M-8 class Tonankai earthquakes that occurred repeatedly at an interval of about 100 years. The MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) initiated a 5-year program in 2003 for seafloor observations in and around Kumano-nada. Nagoya and Tohoku Universities initiated experiments on GPS/A seafloor positioning to monitor crustal deformation in the subduction zone with a focus on investigation of the effect of sound velocity structure in the ocean on seafloor positioning (e.g., Tadokoro et al., this meeting). Tohoku group deployed five precision acoustic transponders (PXPs) jointly developed with Scripps Institution of Oceanography in the central part of Kumano-nada at depths of about 2,000m. The deployed PXPs A, B, C, and D form a diamond on the seafloor, and PXPs C, D, and E form a triangle. Although three typhoons were in the way of our 12-day cruise in August this year, we carried out GPS/A observation for several days. After an observation for locating the precise position of each PXP, we tried to keep the buoy near the center of the diamond or the triangle. The vessel held the position within 20-30m from the center, and the buoy_fs position was kept with 100m from the center. Kinematic GPS positioning is now under processing with GEONET data observed in Kii Peninsula. We also tried monitoring the sound velocity structure with 3 sets of inverted echo sounders (IESs) deployed near the PXPs C, D, and E. The IESs can monitor temporal and spatial variation in the sound velocity structure in the triangle array of PXPs. We plan to carry out the second GPS/A observation in November. The result is worthy of notice. Strange earthquakes of magnitude 6.9, 7.4, and 6.4 occurred on the nearest Nankai Trough axis on September 5-7, 2004. Co-seismic crustal deformation observed by the GEONET was about 4 cm near the coast of Kii Peninsula. The seismogenic zone is in the list ocean drilling under the IODP (Integrated Ocean Drilling Program).
DE: 8123 Dynamics, seismotectonics
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting