TOKYO >> Experts are becoming increasingly interested in long-period ground motions, which severely shake high-rise buildings during earthquakes.

Starting in fiscal 2018, the Japan Meteorological Agency (JMA) plans to issue urgent warnings to areas they fear will be hit by strong long-period ground motions. They would be issued in addition to standard earthquake early warnings.

In preparation for strong earthquakes, technologies are being developed to minimize the swaying of high-rise buildings.

Earthquakes cause various kinds of seismic waves, including short-period tremors, which shake low-rise buildings, and long-period tremors, which cause buildings to shake more slowly. Among these long-period tremors, those caused by seismic waves with long cycles are called long-period ground motions.

Long-period ground motions tend to occur if the focus of an earthquake is shallow or if the quake is on a huge scale. These motions shake high-rising buildings, oil tanks and other large structures intensely and for a long time.

Another characteristic of long-period ground motions is that the tremors can reach faraway places. When the Tokachi Offshore Earthquake occurred in 2003, petroleum inside oil tanks in Toma­komai, Hokkaido — about 155 miles away from the epicenter — was shaken so strongly that fires started. Buildings in Tokyo and Osaka were also severely shaken in the Great East Japan Earthquake in 2011.

Damage from such effects is regarded as nothing new. However, Akira Wada, a professor emeritus at the Tokyo Institute of Technology and an expert in anti-seismic engineering, pointed out that “the importance of measures to cope with (long-period ground motions) has been increasing because the number of high-rise buildings that could be affected has grown.”

The JMA has been announcing long-period ground motion levels since 2013 and classifying the intensity of motion into four grades indicating how strongly high-rise buildings and other structures are shaken.