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The devastating tsunami that hit Japan in 2011 was not caused by a powerful earthquake alone, but was helped along by an underwater landslide the size of Paris, according to a new study. In most of the affected areas, the tsunami reached about 10 meters (33 feet) high, which could be explained by the 9.0 earthquake that hit 231 miles northeast of Tokyo. But tsunami expert Stephan Grilli of the University of Rhode Island was confused at how it could have reached heights of 40 meters (131 feet) near Japan's Sanriku Coast. "Our model could only get inundation up to 16 or 18 meters, not 40. So we knew there must be another cause.”
His computer models showed that it would have required a massive underwater landslide to create a wave that big. They later found evidence on the seafloor of a landslide with a horizontal footprint about the size of Paris, measuring 40 kilometers by 20 kilometers (25 miles by 12.4 miles), and 2 kilometers (1.2 miles) thick. The landslide created a focused tsunami wave that, when combined with the power of the earthquake, reached epic proportions, he said. The natural disaster resulted in more than 15,000 deaths. Grilli's findings were published this week in the journal Marine Geology.
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