HR: 11:20h
AN: T22E-05    [Abstracts]
TI: Diving surveys of small seamounts on the outer rise of the Japan Trench, and replacement of benchmarks for seafloor geodesy
AU: * Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578, Japan
AU: Kirby, S
AF: USGS, Middlefield Road, Menlo Park, CA, United States
AU: Abe, N
AF: JAMSTEC, Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Hino, R
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578, Japan
AU: Kido, M
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578, Japan
AU: Osada, Y
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578, Japan
AU: Tsushima, H
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578, Japan
AB: Geodetic experiments and diving surveys of the outer rise of the Japan Trench off Northeastern Japan were carried out during the Kairei KR07-07 cruise in June 2007 using the ROV KAIKO 7000 II. The cruise aimed at three objectives. The first was diving surveys of small seamounts on the outer rise. A new type of seafloor volcanism called gpetit spoth was recently found near the Japan Trench (Hirano et al., 2006). Since each of diving surveys to three seamounts found fresh basalts, the survey area can be a potential locality for another petit spot volcanic field (Abe et al., this meeting). The second objective was diving surveys of the seafloor in the source region of the 2005 M7.1 outer rise earthquake. It was the largest outer rise earthquake recorded off the Japan Trench since the 1933 M8.4 Sanriku- oki tsunami earthquake. Although we could not find any indication of deformation on the seafloor during the survey, we are interested in the observation that the aftershock distribution (Hino et al., this meeting) was overlapped with the area of the small seamounts. The seamounts may have resulted from young volcanism like gpetit spoth caused by oceanic plate flexure (Hirano et al., 2006). Bathymetric maps show graben structures near the small seamounts sub-parallel to the trench axis suggesting normal faults in the outer rise region. We can suppose that the normal faults can be another mechanism for the young volcanism near the Japan Trench, or that the gpetit spoth volcanism may have induced the large intra-plate normal fault earthquake. Anyway the seamounts can be related to intra-plate earthquakes. The third objective was renewal of acoustic seafloor benchmarks deployed on the outer rise. Three precision acoustic transponders (PXPs) were deployed in 2002 to observe the motion of the pacific plate near the subduction plate boundary, and somehow exhausted the batteries after a few short observations. Each of two PXPs was replaced with a new one after cm-order observation of the relative positions. A new PXP was deployed from the sea surface near the third PXP. We plan to combine the geodetic observations with the old PXP net with future works based on the data of precise relative positioning.
DE: 1209 Tectonic deformation (6924)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8178 Tectonics and magmatism
DE: 8415 Intra-plate processes (1033, 3615)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting