Physicists find way to hide buildings from earthquakes
July 21, 2009
According to the U.S. Geological Survey, there are 500,000 detectable earthquakes every year, of which 100,000 will be felt and about 100 will cause damage. Engineers now use seismic vibration control technology - and base isolation in particular – to make buildings more earthquake-proof. But what about existing structures? Researchers from the University of Liverpool have now developed a means of effectively making buildings “invisible” to the destructive path of a quake.
Earthquakes produce two kinds of destructive seismic activity: body waves, which move through the earth’s interior, and surface waves, which move across it. It’s surface waves which are most destructive and which this technology is intended to address. Basically, it involves fitting a series of concentric plastic rings into the earth around a building. The surface wave would then hit these and be directed around and away from the shielded structure by the curved barriers.
The easiest way to imagine it is to think of a rock in a fast-flowing river. The wave pattern bends smoothly around the rock and reconstructs itself on the other side. For all intents, the rock is invisible to the mechanical waves. It’s exactly the same theory with the seismic waves. (And not that dissimilar to recent work on invisibility cloaks, which aim to bend light waves around objects.)
In a further refinement, the research team believes it will be possible to have a number of pairs of rings, each “tuned” to a differing frequency range for incoming seismic waves. That pair of rings would then take the brunt of a particular wave, vibrating wildly, but effectively diverting the energy.
In fact, the only real drawback is that the rings cannot dissipate or reflect the waves, only redirect them. As Sebastien Guenneau from Liverpool University admitted, “They continue to travel behind it with the same intensity. At this stage, therefore, we can only transfer the risk from one area to another, rather than eliminate it completely.” However, the researchers believe the technique could provide a safe oasis – a football stadium, for example – in earthquake-prone areas.