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Air Guns Shake Up Earthquake Monitoring
sciencehabit writes "Petroleum geologists have long used air guns in their search for oil and gas deposits. Sudden blasts from the devices generate seismic waves that they use to map underground rock formations. Could the same technique be used to study earthquakes? A team of Chinese scientists thinks so. The researchers have designed an air gun that could be useful in monitoring changes in stress buildup along fault zones."
... probably cheaper and less risky than dynamite.
Dynamite's pretty safe. Blasting caps can be dangerous. However, most of the blowback wrt using dynamite in this application is it annoys the neighbours, is environmentally unfriendly, and bad guys love to steal the stuff.
As for TFA, it depends. Shear waves (the twisty kind) travel quite a ways, but don't tell you much. Pressure waves don't travel very far but do tell you a lot, dependent upon the range of frequencies transmitted by the wave, and the medium through which they're transmitted. An 8 Hz p-wave will travel farther than a 500 Hz p-wave, but you won't learn much of any interest at 8 Hz.
Unfortunately, TFA says nothing about the frequency range produced by these air guns. I doubt it's anywhere near the range produced by dynamite.
BTW, it's geophysicists who do this stuff, not geologists. The latter are the guys with rock hammers and sample bags.
"Tongue tied and twisted, just an Earth bound misfit
The actual acoustic energy used in this technique is pretty low. 15 MPa is about the pressure you'd expect a very full lecture bottle to be at, and probably something you wouldn't think twice about were you to feel a jet of it against your skin. I've had 2000 psi lines fail near me, and while it hurts your ears like a bitch, it isn't even enough to puncture them. The article says it gives seismometer readings equivalent to a .5 intensity earthquake. A quick look at a seismic activity map will reveal that these happen *literally* all the time. If these airguns were enough to cause, or even influence seismic activitoty, we'd be in danger every time someone dropped a full gas cylinder (not to mention rocket launches should cause massive quakes across the globe).
While measuring something indeed influences it, there are fundamental energetic limits below which this influence is negligible (i.e., shining light on a truck to measure it's position. I believe these air guns fall into this category