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Going deep to learn the secrets of Japan's earthquakes
A subsequent cruise by JAMSTEC's RV Kaiyo 7-8 months after the earthquake collected additional high-resolution reflection seismic images in the area. Fortunately, the researchers also had data from a similar study that had been done in 1999 in the same region.
The data showed them that the landward seafloor in the trench area slipped as much as
50 metres horizontally, said Yasuyuki Nakamura, Deputy Group leader in JAMSTEC's Center for Earthquake and Tsunami Structural Seismology Group.
"This was a big slip in the trench axis area," he said. "For comparison, the 1995 Kobe earthquake, which killed more than 6000 people and was a magnitude 7.3, had an average slip of 2 metres."
Another magnitude 8 earthquake in 1946 in the Nankai area in southern Japan that destroyed 36,000 homes had a maximum slip of 10 metres, Nakamura said.
"So you can see that
50 metres is a very huge slip," he said. That in itself partly explains why the tsunami wave was so big, he said.
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