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In the latest 12 months there were 737 quakes
registering at least "1" on the Japanese intensity scale of 1-7
in the quake zone, which runs more than 500 km (300 miles) from
Tokyo's eastern suburbs up the northeast coast nearly to the
northern tip of the main island of Honshu. From 2001 to 2010,
agency data shows, the annual average was 306.
The agency warns that there remains a risk of large aftershocks
in the region, which includes the area of the wrecked Fukushima
nuclear plant. Scientists say that while the quakes are getting
weaker, the numbers are still a concern. Last month alone there
were 64 quakes of magnitude 4 or higher in the quake zone. While
the Japanese scale measures the intensity of shaking on the
surface, with the lowest reading of "1" felt only slightly if at
all, magnitude measures the amount of energy released by a
quake.
"In general, when there are a lot of small quakes that means
it's easier for there to be a larger one as well," said Shinji
Toda, a professor at Tohoku University's International Research
Institute of Disaster Science in Sendai. "Of course, we can't
say when."
While the report focused on the northeast, all of Japan is
effectively a quake zone where three tectonic plates intersect,
generating about one-fifth of the world's magnitude 6-plus
quakes.
In November, a magnitude 6.8 tremor rocked the central Japan
prefecture of Nagano, injuring 13. Toda said areas such as
Fukushima and northwest Japan's Akita prefecture, which sits
outside the region hit directly by the March 11 quake, are still
feeling the impact. "There's the possibility that some of this
could go on for a hundred years," he said.
(Editing by Edmund Klamann and Ryan Woo)
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