Earth Planets Space, Vol. 63 (No. 7), pp. 615-619, 2011
Hisashi Suito, Takuya Nishimura, Mikio Tobita, Tetsuro Imakiire, and Shinzaburo Ozawa
Geography and Crustal Dynamics Research Center, Geospatial Information Authority of Japan, Kitasato 1, Tsukuba 305-0811, Japan
(Received April 7, 2011; Revised June 21, 2011; Accepted June 30, 2011; Online published September 27, 2011)
A sequence of M 7-class interplate earthquakes and transient postseismic slips following each of these earthquakes occurred along the Japan Trench before the occurrence of the giant earthquake on March 11, 2011. Continuous GPS data detected a significant postseismic deformation with displacements that were much larger than that of the coseismic offset. Moreover, the geodetic inversion results using these observations revealed that the total moment released by these transient slips was much larger than the coseismic ones. This differs from our understanding of the postseismic process that the postseismic deformation and slip are smaller than the coseismic ones. These transient processes may help us understand not only the postseismic process but also the pre-seismic signals indicating the occurrence of the giant earthquake.
Key words: Interplate fault slip, postseismic deformation, the 2011 off the Pacific coast of Tohoku Earthquake, pre-seismic signal, the Japan Trench.