Abstract
Abstract 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.
Highlights
The northeastern part of Japan, where the Pacific Plate is subducting beneath the continental plate at a rate of 9–10 cm/year (DeMets et al, 1994), is a seismically active region, especially in the area off-shore Miyagi Prefecture, where large interplate earthquakes with magnitudes of about 7.5 occur repeatedly at an average interval of about 37 years
Based on the fact that the only major event known to have taken place within the last 400 years is a group of several earthquakes with magnitudes of approximately 7.5 that occurred in 1938, the recurrence interval of large earthquakes in this region is assumed to be 400 years or longer
We present and discuss the crustal movement that we have detected at our seafloor reference point FUKU based on our observations from 2002 to 2008
Summary
The northeastern part of Japan, where the Pacific Plate is subducting beneath the continental plate at a rate of 9–10 cm/year (DeMets et al, 1994), is a seismically active region, especially in the area off-shore Miyagi Prefecture, where large interplate earthquakes with magnitudes of about 7.5 occur repeatedly at an average interval of about 37 years (the Headquarters for Earthquake Research Promotion, 2000). Based on the fact that the only major event known to have taken place within the last 400 years is a group of several earthquakes with magnitudes of approximately 7.5 that occurred in 1938, the recurrence interval of large earthquakes in this region is assumed to be 400 years or longer (the Headquarters for Earthquake Research Promotion, 2002). The GPS/acoustic combination technique for precise seafloor geodetic observation has been successfully used to book steady progress in filling in the gaps in information on crustal deformation in the sea area. This technique has its origins in early work carried out by scientists at the Scripps Institution of Oceanography (Spiess, 1985). For more details on the methodology, the reader is referred to Fujita et al (2006a)
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