The Meteorological Agency plans to forecast long-period earthquake ground motions, which maintain much of their momentum and can violently shake high-rises far from the temblor’s epicenter.
The Meteorological Agency plans to forecast long-period earthquake ground motions, which maintain much of their momentum and can violently shake high-rises far from the temblor’s epicenter.
These long-period ground motions shook some skyscrapers in Tokyo after the Great East Japan Earthquake struck northeastern Japan on March 11.
As early as fiscal 2013, the Meteorological Agency hopes to start issuing forecasts on long-period ground motions before they arrive, officials said.
But before that, at the end of fiscal 2012, the agency plans to begin announcing the possibility that long-period ground motions have occurred. The announcements will come along with information on the focus and the intensity issued when the earthquakes strike.
The agency already issues a number of notices and warnings immediately after the earthquake. It plans to announce the information on long-period ground motions in ways not to cause confusion.
The agency will likely consider compiling indexes to indicate the expected strength of shaking in a manner similar to the earthquake intensity. The indexes are expected to use phrases, such as “furniture may fall down.”
According to a survey, more than half the respondents who were on the 20th or higher floors of buildings around Tokyo Bay after the earthquake struck on March 11 last year said they had to get down on their hands and knees or they could not stand even by holding onto furniture.
Even among those inside buildings that stand on the plateau, about 30 percent of people who were on the 20th or higher floors said they could not stand by holding onto furniture.
In Osaka Prefecture, a high-rise building was shaken about 2 meters across during the Great East Japan Earthquake.
The higher the buildings, the harder they are shaken by long-period ground motions.