Earth Planets Space, Vol. 57 (No. 6), pp. 507-513, 2005
Akio Kobayashi 1, Akio Yoshida2, Takeyasu Yamamoto1, and Hiromi Takayama1
1Meteorological Research Institute, 1-1 Nagamine, Tsukuba-shi, Ibaraki-ken 305-0052, Japan
2 Tokyo District Meteorological Observatory, Otemachi 1-3-4, Chiyoda-ku, Tokyo 100-0004, Japan
(Received August 25, 2004; Revised February 16, 2005; Accepted April 8, 2005)
Transient crustal deformation occurred in the regions of Kanto and Tokai during the seismo-volcanic event in the northern Izu Islands in 2000. In our investigation of the observed deformation, we constructed an optimum-source model of the event between Miyake and Kozu Islands. We then made an inversion analysis of the differences between the observed displacement field and the calculated displacement field from the optimum model, assuming that the differences were caused by the changes in the interplate coupling beneath the Tokai region. From the inversion analysis of data for each of three-month periods, May to August, June to September, and July to October, we found decreased interplate coupling in the early stages of the 2000 event. In the first stage, either a slow slip or a temporary suspension of the plate subduction occurred in the focal region of the anticipated Tokai earthquake. The area then extended to the west and, finally, a slow slip exceeded the secular convergence velocity on the plate interface near Lake Hamana in the fall of 2000. We believe this ongoing slow slip began in August or early September 2000.
Key words: Tokai region, slow slip, interplate coupling, crustal deformation.