Figure two very distant galaxies collide, and their supermassive black hole centers begin to orbit each other and eventually merge. Billions of years later, would the gravitational waves this sends out trigger one or more earthquakes on the earth. If so, how would we know, and how would we eliminate other causes of earthquakes from the data, such as plate tectonic earthquakes, which probably account for most earthquakes?
I’d imagine that gravitational waves roiling through a subduction zone could trigger quakes, but how would we know?
Very, very unlikely that they would be the cause. But if they were, we’d never prove it.
AFAIK, no one has ever shown that tides have caused any earthquakes. Tides, whether lunar or solar, are a zillion times stronger than any gravity waves we would feel from such an event. Even tides from Jupiter (as felt here on Earth) are probably several orders of magnitude stronger than the gravity waves from those black holes. So the chances of gravity waves causing earthquakes are pretty much nil.
In this article, they are talking about enough gravitational radiation to accelerate a black hole to several million miles per hour. That’s orders of magnitude more energy than anything in the solar system is putting out. Sure, there’s probably enough other radiation from the event to roast us mnay times over, but maybe we’d get lucky and only get hit by the gravitational radiation.
Consider that LIGO phase II will be sensitive enough to detect a distortion between mirrors of 10[sup]-17[/sup]cm. At this point in time we’ve never detected gravity waves, at least not directly. You can imagine just how small an impact a passing gravity wave would have when trucks rumbling past a detector easily swamp out any signals.
Forget about trucks-- You can get significant noise in a gravitational wave detector from the gravity of a tumbleweed blowing past. No, I’m not making that up, nor exaggerating: That really and literally is one of the very many possible noise sources they have to account for at LIGO.
EDIT:
Oh, going the other way, though, works: Gravitational wave detectors are superb seismographs. Any earthquake anywhere in the world will be picked up by all of them (which is, of course, yet another noise source, and a lot bigger one than the tumbleweeds).
Scientists have invented a new clock that is waaaay more accurate than the clocks currently used by NIST (NIST clocks are good to 1 second in 300 million years, this clock is good to 1 second in 5 billion years). It is so sensitive that it is impossible to get two of these clocks to agree if they are on earth (moving one up one centimeter will change how time passes for it and be detectable…the earth moving below them will be detectable).
They suggest that such clocks, in space, could make good gravity wave detectors. Any idea if these would be more sensitive than LIGO?
Set up as clocks, no. The problem is that gravitational waves are periodic: One clock might be slowed down while the other is sped up, but a very short time later, the first will be sped up while the second is slowed down, and the net effect is that they’ll be the same on average over usefully-measurable timescales. It’s likely, though, that some of the same technology that goes into those clocks also goes into GW detectors, just arranged differently.
