HR: 0800h
AN: G51B-0827    [Abstracts]
TI: Earthquake-Induced Seafloor Displacement at Kumano-Nada in Nankai Trough, Detected by Repeated GPS/Acoustic Surveys
AU: * Kido, M
EM: kido@aob.geophys.tohoku.ac.jp
AF: PCPEV, Tohoku Univ., 6-6 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: PCPEV, Tohoku Univ., 6-6 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Tsuka, K
EM: kentarot@cc.kochi-u.ac.jp
AF: Natural Env. Sci., Kochi Univ., Akebono-cho, Kochi, 780-8520 Japan
AU: Tabei, T
EM: tabei@cc.kochi-u.ac.jp
AF: Natural Env. Sci., Kochi Univ., Akebono-cho, Kochi, 780-8520 Japan
AB: Since 2004, we have started seafloor geodetic surveys at Kumano-nada in Nankai Trough, where the Philippine Sea Plate is subducting beneath the Japan Island. We employed GPS/Acoustic joint approach with a towed buoy communicating with transponders installed on seafloor. Target of the survey is to detect in-situ co-seismic displacement as well as to observe inter-seismic secular displacement which contribute estimate of distribution of asperities along the subduction zone. In November 2004, S.E.off~Kii-pen.earthquake occurred just adjacently to the south of our survey site. According to the GPS measurement of crustal deformation on land and studies of seismic waveform inversions, the earthquake is expected to consist of multiple failure, and its fault mechanism is still in controversial. In-situ measurements of crustal displacement close to the fault can reveal the earthquake mechanism. Fortunately, we have conducted surveys twice just before and after the earthquake and found 20--30cm southward displacement, which is much larger than that observed on land. This supports the combined two faults model. Our survey site consists of neighboring two transponder arrays. Displacement vectors of the two arrays slightly differ to on another. This may suggest local deformation within a small distance, which is supported by the fact that the post-seismic activities extend to just beneath the two arrays. We have made much effort to achieve high precision, such as passive estimate of sound velocity change with travel-time analysis, active monitoring of it by using self echo sounder equipment, and so on. However quantification of the accuracy of the measurement is rather difficult. One of the way to confirm the accuracy is repeatability of observations. We have made a survey again in this August, whose results are still processing. In the presentation, we will show the survey configuration, analytic technique, and results with the new survey.
UR: http://www.aob.geophys.tohoku.ac.jp/dmg/
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1209 Tectonic deformation (6924)
DE: 1222 Ocean monitoring with geodetic techniques (1225, 1641, 3010, 4532, 4556, 4560, 6959)
DE: 3075 Submarine tectonics and volcanism
DE: 3094 Instruments and techniques
SC: Geodesy [G]
MN: Fall Meeting 2005