東日本大震災で、宮城県沖約２００キロの日本海溝付近の海底地盤が南東に約５０メートル移動、約７メートル隆起していたことが、海洋研究開発機構の深海調査でわかった。
移動量としては、これまでの観測で最大という。
同機構は３月下旬、深海調査研究船「かいれい」を使い、同海溝付近で地震に伴う海底地盤の変化を調べ、１９９９年の調査時のデータと比較した。移動した部分は、幅４０キロにわたっていた。こうした海溝付近の大きな動きが、破格の巨大津波を生んだとみられている。
海溝の最深部（深さ約７６００メートル）では、陸側の地盤が幅約１５００メートルにわたって崩れた跡も見つかった。今回の地震で海底地滑りが起きた証拠とみられ、同機構の冨士原敏也技術研究主任は「局所的な地滑りとみられるが、日本海溝にある過去の海底地滑りと比べても大きい」としている。
（2011年4月29日18時56分 読売新聞）
Showing posts with label seabed shifted. Show all posts
Showing posts with label seabed shifted. Show all posts
Tuesday, May 10, 2011
Friday, April 8, 2011
08/04 Earthquake shifted seabed 24 meters
The Yomiuri Shimbun
The seabed near the focus of the March 11 earthquake off Miyagi Prefecture moved about 24 meters east-southeast as a result of crustal movement during the massive temblor, the Japan Coast Guard announced Wednesday.
An earlier survey by the Geospatial Information Authority of Japan showed the Oshika Peninsula in Ishinomaki in the prefecture moved about 5.3 meters east during the earthquake.
The coast guard survey showed crustal movement at a depth of about 1,700 meters and about 120 kilometers off the Oshika Peninsula was more than four times the observed shift of the peninsula itself.
On March 28 and 29, a JCG surveying ship checked a total of eight location markers set in the seabed. It discovered seven of them had moved about 24 meters east-southeast, and the seabed had risen about three meters.
A location marker set in the seabed about 80 kilometers off Fukushima Prefecture had moved about five meters east-southeast.
According to the JCG, a magnitude-7.2 earthquake in August 2005 off Miyagi Prefecture caused the seabed to move about 10 centimeters. The March 11 earthquake measured magnitude-9.
A coast guard official said, "The amount of crustal movement we saw this time is unprecedented in recorded history."
(Apr. 8, 2011)
The seabed near the focus of the March 11 earthquake off Miyagi Prefecture moved about 24 meters east-southeast as a result of crustal movement during the massive temblor, the Japan Coast Guard announced Wednesday.
An earlier survey by the Geospatial Information Authority of Japan showed the Oshika Peninsula in Ishinomaki in the prefecture moved about 5.3 meters east during the earthquake.
The coast guard survey showed crustal movement at a depth of about 1,700 meters and about 120 kilometers off the Oshika Peninsula was more than four times the observed shift of the peninsula itself.
On March 28 and 29, a JCG surveying ship checked a total of eight location markers set in the seabed. It discovered seven of them had moved about 24 meters east-southeast, and the seabed had risen about three meters.
A location marker set in the seabed about 80 kilometers off Fukushima Prefecture had moved about five meters east-southeast.
According to the JCG, a magnitude-7.2 earthquake in August 2005 off Miyagi Prefecture caused the seabed to move about 10 centimeters. The March 11 earthquake measured magnitude-9.
A coast guard official said, "The amount of crustal movement we saw this time is unprecedented in recorded history."
(Apr. 8, 2011)
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