The Japanese government implemented Friday a new alert system in seven coastal prefectures from Chiba to Hokkaido to warn against subsequent earthquakes should a quake of magnitude 7.0 or larger strike in either of two deep-sea trenches in the Pacific Ocean where massive temblors are feared.
The warnings are designed to encourage evacuation preparedness against additional earthquakes arising in the Japan and Chishima trenches off the country's northern Pacific coast.
The government estimates an M9.0 quake in either trench could trigger huge tsunami, producing waves of up to 30 meters in parts of Hokkaido and Iwate prefectures in the country's north.
The M9.0 earthquake in March 2011 that occurred along the Japan Trench was a subsequent earthquake, striking two days after an M7.3 quake in the same vicinity.
The system will be in effect in 182 municipalities in Hokkaido, Aomori, Iwate, Miyagi, Fukushima, Ibaraki and Chiba prefectures that span the country's northernmost point down to the border with Tokyo.
Under the alerts, residents would be requested to take actions including preparing to evacuate at short notice, securing warm clothing and confirming where their nearest evacuation center is.
The Japan Meteorological Agency would issue the alert up to about two hours after an M7.0 or stronger quake strikes. If no subsequent quakes occur, the alert would be lifted a week later.
The Japan Trench stretches from Hokkaido to east of the Boso Peninsula near Tokyo, and the Chishima Trench lies off the Chishima Islands, also known as the Kuril Islands.
The government, while acknowledging that the chances of an M8.0 or higher quake striking are only about one in 100, says it expects an alert to be issued once every two to three years.
In September, the government vowed to expand financial assistance to 108 municipalities in the seven prefectures that are at risk of exposure to a powerful quake from the Japan or Chishima trenches and are in particular need of strong anti-disaster measures.
The government also set a 10-year goal to reduce by 80 percent the potential number of victims in a massive earthquake in the region, for which the central government has projected death tolls as high as 199,000 people.
A government task force reported in March that quick evacuations could reduce fatalities by around 80 percent.
Toru Matsuzawa, a seismology professor at Tohoku University's Research Center for Prediction of Earthquakes and Volcanic Eruptions, said he hopes the new system will offer people "a chance to review their evacuation preparations."
"We cannot discount the possibility that a huge, M9-class earthquake could strike the Japan Trench or the Chishima Trench in the near future. If areas subject to the warnings take countermeasures, they can reduce loss of life including from resultant tsunamis," he said.
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