Mitsui Fudosan

Tokyo seems overdue for a major quake. The last one was 90 years ago, when the Great Kanto Earthquake killed more than 100,000 people, and scientists say a big one may strike soon.

Buildings are better made today, yet over 6,000 people died in the Great Hanshin Earthquake that hit Kobe in 1995.

Now, two Japanese companies want to install giant pendulums on skyscraper rooftops to reduce the swaying caused by major earthquakes by 60 percent.

Real estate developer Mitsui Fudosan and construction firm Kajima said they have developed a 300-ton pendulum that will act as a counterweight to long-period seismic waves.

It's a variation of tuned mass damper technology, used in many towers, bridges, and buildings to reduce seismic vibration amplitudes.

The companies plan to spend about $51 million installing six such pendulums atop the Shinjuku Mitsui Building, a 55-story skyscraper in Tokyo completed in 1974.

The building swayed as much as 6 feet during the magnitude-9.0 quake that centered on northeast Japan in March 2011.

While the pendulums probably won't save lives, swaying can cause injury and damage to tall buildings.

Japan's first skyscraper was erected in 1968, and since then various vibration-dampening technologies have been used. Pendulum know-how has been used in newer high-rises, but the Mitsui-Kajima device could be retrofitted to older structures just by installing it on roofs.

It could also calm nerves. I was on the 20th floor of a Tokyo building in 2011 when seismic waves from a distant 7.0 quake hit, and the swaying wasn't something I'd like to experience again.

(Via Asahi Shimbun)