Japan To Start Issuing Alerts For Long - Period Ground Motions In February
Japan's Meteorological Agency says it will start issuing alerts in February for long and slow tremors that can sway skyscrapers, as part of its early warning system for powerful earthquakes.
The current emergency warning system issues alerts for expected strong quakes with intensities of lower 5 or more on the Japanese scale of zero to 7.
Alerts for long-period ground motions will be added to the system on February 1.
The agency ranks long-period ground motion intensity on a four-level scale.
It plans to issue alerts to areas where the two highest intensities, Class 3 and Class 4, are projected. The second highest, Class 3, means people will find it difficult to remain standing. Class 4 means people will have to crawl to move.
Agency officials say that after alerts are issued in areas near epicenters, additional alerts can be issued in other areas where long-period ground motions are projected. Such prolonged shaking can sway high-rise buildings even far from an epicenter.
The March 2011 huge earthquake in northeastern Japan caused skyscrapers to shake as far away as Tokyo and Osaka.
Officials say Japan has had 33 earthquakes accompanied by long-period ground motions of Class 3 or Class 4 since 2000.
They say more people are likely to be subject to such tremors, as the number of urban skyscrapers is on the rise.
The officials are calling on people in high-rise buildings to stay calm after receiving alerts, and take steps to ensure safety.