海底地殻変動観測の包括的精度評価と東北日本沖における海底地殻変動の解明

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タイトル別名
  • Elucidation of Seafloor Crustal Movements off Northeastern Japan by GPS/Acoustic Technique with Comprehensive Evaluation of Positioning Precision
  • カイテイ チカク ヘンドウ カンソク ノ ホウカツテキ セイド ヒョウカ ト トウホク ニホンオキ ニ オケル カイテイ チカク ヘンドウ ノ カイメイ

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説明

This paper summarizes the author's research on positioning precision of GPS/acoustic seafloor geodetic technique and observed seafloor movements off northeastern Japan before and associated with the M9.0 earthquake on March 11, 2011. In regard to the former, it is shown that positioning precision has been greatly improved by the introduction of the sailing observation with a hull-mounted system in 2008, compared with the drifting, uncontrollable way as before. The repeatability for the sailing observation is about 2 cm in the horizontal component and better at the seafloor reference points along the Nankai Trough than those along the Japan Trench. Besides, the precision of height determination has also been improved, though it is still inferior to that of horizontal positioning. In regard to the latter, spatio-temporal change of seafloor crustal movements off northeastern Japan has been detected, based on observation data for about nine years before the 2011 event. Particularly, off Miyagi Prefecture, a series of crustal movements indicating strain accumulation-release process has been observed. Interplate coupling off Miyagi Prefecture during interseismic periods was relatively weaker since 2007 than before 2005, while interplate coupling off Fukushima Prefecture was significantly weaker than that off Miyagi Prefecture. Furthermore, from the observations before and after the 2011 event, the huge co-seismic displacements of up to 24 m have been observed just above the focal region.

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