HR: 09:15h
AN: G41A-06    [Abstracts]
TI: Seafloor Geodetic Observation Along the Major Trenches Around Japan - Focusing on Results at Off-Miyagi Area -
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: Ishikawa, T
EM: tadashi-ishikawa@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1, Tsukiji, Chuo-ku, Tokyo, 104-0045 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: 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: Katayama, M
EM: masato-katayama@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1, Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Toyama, S
EM: shinichi-toyama@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1, Tsukiji, Chuo-ku, Tokyo, 104-0045 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
AU: Colombo, O L
EM: ocolombo@santafe.gsfc.nasa.gov
AF: G.E.S.T./NASA Goddard Space Flight Center, Code 926, Greenbelt, Greenbelt, MD 20771 United States
AB: We have been developing a system for precise seafloor geodetic observation with the GPS/Acoustic combination technique and deploying about fifteen seafloor reference points on the landward slope of the major trenches around Japan, such as Japan Trench and Nankai Trough. The primary purpose of our observation is to detect and monitor the crustal deformation caused by the subduction of the oceanic plate near the plate boundary where huge earthquakes repeatedly occur. The Off-Miyagi reference point is located about 100km landward from the axis of the Japan Trench, NE Japan, where huge earthquakes have repeated with a relatively regular interval of about 30 to 40 years. Four acoustic transponders are installed as a set on the seafloor with the water depth of about 1700m just above the possible rupture area of the future earthquake on the plate boundary. At this point, we have been carrying out intensive campaign observations with our system since 2001. The data analysis consists of (1) kinematic GPS analysis, (2) acoustic wave analysis to obtain round travel time between the transducer on board and seafloor transponder, and (3) a combination of results from (1) and (2) to get the precise seafloor station position. The last analysis (3) is performed by a linear inversion method based on the least squares estimation. Time series of estimated coordinates of the Off-Miyagi seafloor reference point from six campaign epochs during the period 2002-2004 show a linear trend in time in the horizontal components with the repeatability of several centimeters except for one epoch. The linear reduction of the time series gives a crustal movement of about 7-8 +- 1-2 cm/year WNW relative to the stable part of the Eurasian continent, which is reasonable in view of the expected intraplate deformation rate in this area.
DE: 1208 Crustal movements--intraplate (8110)
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting