Japan earthquake appears to increase quake risk in other parts of country

Washington, May 26 (ANI): Scientists have said that Japan's recent magnitude 9.0 earthquake, which triggered a devastating tsunami, could increase risk of sizeable aftershocks in other parts of the country for years.

Researchers from the Woods Hole Oceanographic Institution (WHOI), Kyoto University and the U.S. Geological Survey (USGS), studied data from Japan's extensive seismic network, and identified several areas at risk from the quake, 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.

"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 wrote.

Using a model known as Coulomb stress triggering, Lin and his colleagues found measurable increases in stress along faults to the north at Sanriku-Hokobu, south at Off Boso and at the Outer Trench Slope normal faults east of the quake's epicentre off the Japan coast near the city of Sendai.

"Based on our other studies, these stress increases are large enough to increase the likelihood of triggering significant aftershocks or subsequent main shocks," the researchers said.

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," he explained.

Lin added that aftershocks, as well as new mainshocks, could continue for "weeks, months, and years".

The paper will be published in the Tohoku Earthquake Special Issue of the journal Earth, Planets and Space. (ANI)