Is the Ryukyu Subduction Zone in Japan coupled or decoupled?-The necessity of seafloor crustal deformation observation

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We have started the observation of sea floor crustal deformation to detect the inter-plate coupling in the central Ryukyu trench. Five campaign observations were carried out for the period from January 2008 to November 2009. The result shows that the benchmark moved to northwest direction for two years at a rate of 7cm/yr. The estimated width of interplate coupling area is 30-50km from the Ryukyu trench. The interplate coupling in the central Ryukyu Trench and tsunami earthquake (which occurred 300km southwest of our site near the Ryukyu Trench) suggests that interplate coupling occurred up-dip of the seismogenic zone in the Ryukyu subduction zone.