There is a high likelihood of a magnitude 7 or higher earthquake occurring within the next 30 years at faults along the Japan Trench in the Pacific Ocean, according to the latest assessment by the government's earthquake research committee.
The report released Tuesday updates with new findings the provisional assessments published in November 2011 soon after the Great East Japan Earthquake.
For an earthquake off Miyagi Prefecture, the long-term assessment deemed the probability of a magnitude 7 to 7.5 quake occurring at about 90 percent.
Along a stretch of the Japan Trench from the eastern sea off Aomori Prefecture to the sea off Chiba Prefecture's Boso Peninsula is where an oceanic plate slips under the continental plate. This area includes the focal region of the Great East Japan Earthquake. The latest assessments were based on earthquake records, tsunami deposits and other findings collected after the disaster.
As major earthquakes of magnitude 9 occur every 550 to 600 years, the probability of another in the next 30 years is nearly 0 percent, unchanged from the previous assessment. The committee raised the probability of a magnitude 7.9 quake off Miyagi Prefecture from nearly 0 percent to about 20 percent, and that of a quake off Fukushima Prefecture in the magnitude-7 range from about 10 percent to about 50 percent.
Last year, the government introduced four levels for expressing the probability of trench earthquakes. Applying this system to the latest assessments, almost all areas are at level 3, or high probability.
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