TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 64 (No. 12), pp. 1093-1099, 2012

Constraints on the early-stage rupture process of the 2011 Tohoku-oki earthquake from 1-Hz GPS data

Yukitoshi Fukahata1, Yuji Yagi2, and Shin'ichi Miyazaki3

1Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan
2Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan
3Graduate School of Science, Kyoto University, Kyoto, Japan

(Received December 27, 2011; Revised September 8, 2012; Accepted September 20, 2012; Online published January 28, 2013)

Abstract: From the comparison of observed 1-Hz GPS data with simple forward computation that evaluates near and intermediate field terms, we put constraints on the early-stage rupture process of the 2011 Tohoku-oki earthquake. Mainly based on the time difference of the onset of large eastward displacements at stations along the northern coast of the source region, we estimate that the first significant moment release started around 35 km west of the hypocenter determined by JMA. The moment release occurred approximately from 20 s to 35 s after the initiation of the earthquake. Significant moment release around the hypocenter and in the near-trench region started from 25 s, and 35 s, at the earliest, respectively. Before about 20 s, the moment release of the 2011 Tohoku-oki earthquake must have been so small that any substantial displacements were not observed on land. The clear opposite motion that follows the large eastward displacement observed at many stations is due to the intermediate S-wave term.
Key words: The 2011 Tohoku-oki earthquake, 1-Hz GPS, rupture process, near field term, intermediate S-wave term.

Corresponding author E-mail: fukahata@rcep.dpri.kyoto-u.ac.jp

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