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Sensors found that one part of the ocean floor had been stretched to a point 24 metres east-southeast of its position before the 9.0 undersea quake, which triggered a massive tsunami that engulfed large areas of Japan's northeast coast.
The undersea movement is more than four times bigger than any observed on land, where part of the Oshika peninsula in Miyagi prefecture was found to have shifted 5.3 metres.
The US Geological Survey (USGS) said in March that the force of the quake moved Honshu -- Japan's main island -- by 2.4 metres.