Map showing the 11 March 2011 magnitude 9.0 off Tohoku mainshock
and 166 aftershocks of magnitude 5.5 and greater until May 20. Warmer color
indicates more recent events. Larger symbol indicates greater quake magnitude.
(Modified from figure created by the U.S. Geological Survey)
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
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.
Data from the magnitude 9.0 Tohoku earthquake on March 11 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.