Scientists from the Woods Hole Oceanographic Institution, Kyoto University and the U.S. Geological Survey, studying data from Japan's extensive seismic monitoring network, say they have identified several areas at risk from the quake, Japan's largest ever, which already has triggered a large number of aftershocks.
"Research over the past two decades has shown that earthquakes interact in ways never before imagined," the researchers wrote in an article for the journal Earth, Planets and Space.
"A major shock does relieve stress -- and thus the likelihood of a second major tremor -- but only in some areas. The probability of a succeeding earthquake adjacent to the section of the fault that ruptured or on a nearby but different fault can jump" significantly, they said.
The magnitude-9 quake appears to have influenced large portions of Honshu Island, Shinji Toda of Kyoto University said.
At particular risk, he said, are the Tokyo area, Mount Fuji and central Honshu including Nagano.
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