DisastersJapan earthquake to increase quake risk elsewhere in the country

Published 27 May 2011

Japan’s recent magnitude 9.0 earthquake, which triggered a devastating tsunami, relieved stress along part of the quake fault but also has contributed to the build up of stress in other areas, putting some of the country at risk for up to years of sizeable aftershocks and perhaps new main shocks

Japan's recent earthquake rest of the country's risk // Source: wcu.edu

Japan’s recent magnitude 9.0 earthquake, which triggered a devastating tsunami, relieved stress along part of the quake fault but also has contributed to the build up of stress in other areas, putting some of the country at risk for up to years of sizeable aftershocks and perhaps new main shocks, scientists say.

After studying data from Japan’s extensive seismic network, researchers from the Woods Hole Oceanographic Institution (WHOI), Kyoto University, and the U.S. Geological Survey (USGS) have identified several areas at risk from the quake, Japan’s largest ever, which already has triggered a large number of aftershocks.

A Woods Hole Oceanographic Institute’s release reports that data from the magnitude 9.0 Tohoku earthquake on 11vMarch has brought scientists a small but perceptible step closer to a better assessment of future seismic risk in specific regions, 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.

The Tohoku earthquake, centered off northern Honshu Island, provided an “unprecedented” opportunity to utilize Japan’s “superb monitoring networks” to gather data on the quake, the scientists said. The Tohoku quake, the fourth largest earthquake ever recorded, was “the best-recorded [large quake] the world has ever known.”

This made the quake a “special” one in terms of scientific investigation, Lin said. “We felt we might be able to find something we didn’t see before” in previous quakes, he said.

The magnitude 9 quake appears to have influenced large portions of Honshu Island, Toda said. At particular risk, he said, are the Tokyo area, Mount Fuji and central Honshu including Nagano.

The Kantu fragment, which is close to Tokyo, also experienced an increase in stress. Previous government estimates have put