Earth Planets Space, Vol. 60 (No. 6), pp. e9-e12, 2008E-LETTER
Yoshihiro Matsumoto1, Tadashi Ishikawa1, Masayuki Fujita1, Mariko Sato1, Hiroaki Saito1, Masashi Mochizuki2, Tetsuichiro Yabuki1, and Akira Asada2
1Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan
2Institute of Industrial Science, the University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
(Received April 30, 2008; Revised June 5, 2008; Accepted June 9, 2008; Online published June 18, 2008)
We have been carrying out GPS/acoustic seafloor geodetic observations at several reference points situated along the Japan Trench, a major plate boundary of subduction. A time series of horizontal coordinates of one of the seafloor reference points, located off Fukushima, obtained from seven campaign observations for the period 2002–2008, exhibits a linear trend with a scattering root mean square of about 3 cm. A linear fit to the time series gives an intraplate crustal movement velocity of 3.1 cm per year in a westerly direction, which is significantly smaller than that at the other seafloor reference point 120 km away along the trench axis. This result implies weak interplate coupling in this region.
Key words: GPS/acoustic, seafloor geodetic observation, back-slip, Off Fukushima, intraplate deformation.