Smooth passage. In simulations, specially designed and concentric rings conduct seismic waves harmlessly (right panels).

M. Farhat et al., PRL 103 (2009)

A "Cloaking Device" for Earthquakes

Researchers say they have found a way to make buildings essentially invisible to earthquakes. If perfected, the technique could protect skyscrapers and homes alike from even the most devastating temblors.

Earthquakes, sunlight, and radio all share a common factor: They propagate via waves. The only difference is that earthquake waves are so powerful--their energy can equal several nuclear bombs--that they literally shake apart rigid structures.

Researchers at Aix-Marseille Université in France and at the University of Liverpool in the U.K. have now developed a barrier that keeps buildings from feeling these waves. They took a cue from stealth aircraft, which employ combinations of specially shaped and fabricated materials that absorb radar signals and deflect them off course. For earthquakes, the concept is the same: Using computers, the team modeled a device composed of layered, concentric rings of plastic, copper, and four other materials of varying flexibility and stiffness--all designed to harmlessly deflect earthquake waves.

In a series of simulations, the team bombarded the rings with the equivalent of earthquake surface waves of standard frequencies ranging from 30 to 150 hertz, or vibrations per second. The rings absorbed and redirected the waves around a central protected zone essentially without disturbing it (see illustration), the researchers report this month in Physical Review Letters. A building of the future might have such an earthquake "cloaking device" incorporated into its foundation to protect it from harmful tremors rolling across the ground.

"The idea is revolutionary," says theoretical physicist John Pendry of Imperial College London. Physicist Ulf Leonhardt of the University of St. Andrews in the U.K. agrees. "It is fantastic how diverse and interesting research on cloaking has become in such a short time," he says. Three years ago, Pendry, Leonhardt, and colleagues published the first proposals on wave invisibility in separate papers in Science. "Now we are talking about cloaking against sound, water waves, or perhaps even earthquakes," Leonhardt says. But both add that it may be a while before any prototypes can be tested. "This may remain science fiction [for some time]," says Leonhardt.

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