How a 'Seismic Cloak' Could Slow Down an Earthquake 101
Daniel_Stuckey writes "The United States is currently gripped in a bout of earthquake mania, following a series of significant tremors in the West. And any time Yellowstone, LA, or San Francisco shakes, people start to wonder if it's a sign of The Big One to come. Yet even after decades of research, earthquake prediction remains notoriously hard, and not every building in quake-prone areas has an earthquake-resistant design. What if, instead of quaking in our boots, we could stop quakes in their tracks? Theoretically, it's not a crazy idea. Earthquakes propagate in waves, and if noise-canceling headphones have taught us anything, it's that waves can be absorbed, reflected, or canceled out. Today, a paper published in Physical Review Letters suggests how that might be done. It's the result of French research into the use of metamaterials—broadly, materials with properties not found in nature—to modify seismic waves, like a seismic cloaking device."
Interesting .... (Score:5, Interesting)
For some reason, this article made me think of that story about Tesla and his "oscillator" experiment:
http://www.angelfire.com/scifi... [angelfire.com]
I wonder if, rather than relying on these "metametals" in special soil, one could station units similar to these at strategic locations along fault lines, designed to pick up an earthquake's resonant frequency and generate a corresponding one tuned to cancel it out?
Re:Interesting .... (Score:2, Interesting)
The difficulty in wave cancellation is that you have to work with the interference patterns. Unless the source and countersignal are in exactly the same location, the interference will lead to both flat regions and double-amplitude regions. Noise-cancelling headphones work by exploiting a chokepoint where the signal strength involved is low enough that the constructive interference will be miniscule and in (for the numbers involved) harmless locations.
If you can't artificially dampen the quake, the next most viable method would be to surround vulnerable locations with possible countersignal generators and turn on those that would interfere favorably for the protected area. This may have dramatic and destructive side-effects elsewhere...
From reading the actual article, this could work (Score:5, Interesting)
The primary problem with this concept is that you have to know very precisely the composition of the ground where you install this barrier. Another problem is that environmental changes - soil moisture, temperature, are going to affect the material properties somewhat (but maybe not enough to matter).
Essentially, extremely low frequency waves that trash buildings don't perceive the ground as atomic, the waves act over their wavelength, which is very long, and so if you put things into the ground, it changes the material properties. Carefully drilled holes apparently can change the properties in dramatic ways. The word "cloak" is sexy, but the more interesting bit mentioned at the end of the paper was the prospect of building a bandstop damper with the low corner at 0 Hz.
It doesn't do you much good if your earthquake prevention device reflects the energy somewhere else dependent on the epicenter, and it also doesn't do you much good if it doesn't block enough frequencies to stop it from trashing your buildings. A bandstop filter would operate over a broad enough band to attenuate all the frequencies, and it wouldn't reflect energy to other buildings (which could have obvious liability concerns.) Imagine a plaintiff's attorney showing a standing wave pattern of destruction emanating from a field of holes drilled by the defendant's firm.
The other satisfying nature of this tech is that it's proactive. Instead of building structures that will probably collapse if a magnitude 8 happens anyway, you go out there and build armor that will stop the earthquake entirely. Also, a field of holes and concrete and various pertubations, all buried, is a lot less ugly than the structural changes needed to reinforce a building against a major earthquake.
It would be expensive to do the detailed surveys and compute the solution, but it would create more high education jobs, and it's probably worth doing.