May 26th, 2011 by Joshua S Hill
The recent magnitude 9.0 earthquake that struck Japan has increased the risk of earthquakes across the rest of the country, say scientists from the Woods Hole Oceanographic Institution (WHOI), Kyoto University and the U.S. Geological Survey (USGS).
After studying data from the extensive and “superb monitoring networks” in and around Japan, the researchers have identified several areas across the country now at greater risk of earthquakes. The earthquake, which is the largest Japan has ever recorded, has already triggered a large number of aftershocks across the country.
The data collected has brought scientists a “small but perceptible step closer” to understanding the future risk in specific regions, said said Shinji Toda of Kyoto University, a lead author of the study. “Even though we cannot forecast precisely, we can explain the mechanisms involved in such quakes to the public,” he said. Still, he added, the findings do bring scientists “a little bit closer” to being able to forecast aftershocks.
“Research over the past two decades has shown that earthquakes interact in ways never before imagined,” Toda, Jian Lin of WHOI and Ross S. Stein of USGS write in a summary of their paper in press for publication in the Tohoku Earthquake Special Issue of 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.
Toda noted that the magnitude 9.0 earthquake has influenced large portions of Honshu Island, in particular, the Tokyo area, Mount Fuji and central Honshu including Nagano. Previous estimates had Tokyo at being at a 70 percent risk for a magnitude 7.0 earthquake over the next 30 years, but the new data from the Tohoku earthquake has increased those odds to “more than 70 percent” which, according to Toda, “is really high.”
Stein of the USGS emphasized the ongoing risk to parts of Japan. “There remains a lot of real estate in Japan–on shore and off–that could host large, late aftershocks of the Tohoku quake,” he said.
“In addition to the megathrust surface to the north or south of the March 11 rupture, we calculate that several fault systems closer to Tokyo have been brought closer to failure, and some of these have lit up in small earthquakes since March 11. So, in our judgment, Central Japan, and Tokyo in particular, is headed for a long vigil that will not end anytime soon.”
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