Everywhere I've looked so far that talks about the possibility the LIGO detection was an earthquake, involves being ruled out due to the large distance between the two LIGO sites. Two identical earthquakes would be necessary is what I'm reading.
I don't think this is correct, because earthquakes are recorded as deep as 800 km below the surface. There's a region in the mantle, I should think, from which earthquakes may register identically at the two locations. Particularly as we're talking very tiny vibrations.
What I would like to ask is, firstly, were deep-mantle quakes controlled for? As a follow-up question, was there a consulting academic seismologist with deep-mantle expertise on the LIGO team?
Response to the decision to mark this question as duplicate 22/08/2016 My question was marked duplicate and I am providing my response here in accordance with site policy: Any replacement of a more detailed specific and explained problem, with a much more generic question that makes no mention nor indicates any awareness of the specific matter it is supposed to replace, is never legitimate. In the rare caseas of exception to this a rationale would be expected.
My question was based on the published characterization of the scope for seismic activity to generate detection events mistaken for gravity waves, in which the possibility of deep mantle (a long way down) seismic events is not considered . There is significant evidence that this isn't a trivial oversight or simply a detail left out for reasons of brevity .
The two LIGO sites come as a solution to the problem of Earth sourced anomaly detections. The argument provided by LIGO is that it would take two identical but independent seismic events for a kLIGO gravity wave detection to be explained this way. The reasoning is apparently airtight and demonstrated in multiple independent ways. Just one is that for the detection to be seismic, an event at one location would have to reach the other at superluminal speeds.
So it's very clear the scope that the LIGO guessed for seismic activity. But the reasoning is flawed because, for example, a seismic event deeper in the mantle, say 100km or 200km, could plausibly reach both sites at the same instant without having to exceed the normal seismic velocities.
A secondary question was whether the LIGO team had been guessing and using common sense about the scope for false readings from seismological sources, or was an academic or professional seismologist retained.
That is a legitimate, unanswered, question for a plausible oversight in the LIGO planning and execution. There's no way that this is replaceable by a naive generic question about a philosophical matter of provability.
Responses to Anna V and Rob Jeffries 22/08/2016 This is my reasoning by way of response to the excellent answers provided by Anna V and Rob Jeffries. In one sense they give the same answer in that both ultimately argue that LIGO would have taken this into account and/or even if they didn't the matter is implausibly unlikely.
The LIGO is cutting edge technology applied to an extremely high standard and there is no suggestion otherwise in my question. But nor is the fact of that a legitimate counter argument. This is because the question can be reformulated at any number of levels. For example, let's say you think LIGO's planning and execution was so high quality that something like this would be 'caught'.
But let's suppose you are correct, is the resulting picture in accordance with the high standards of LIGO? It is simply a logical fact that the arguments provided by LIGO explicitly embed the assumption that quakes only happen near the surface. That is the basis of their reasoning for having 2 sites. So despite the precision damping that you mention, the problem was serious enough to them that they have planned, executed, and written extensively about, the ultimate solution for that problem. And that ultimate solution is flawed at least intellectually, because there is a built in implicit assumption seismic activity occurs near the surface only
I think that's an issue for LIGO on some level. If the detection didn't happen that, then it becomes an issue of an inaccuracy, that spreads from the flawed assumption, all the way through papers and into the public consummation bumpf. Presumably including the elected or other sub-committees of funding/grant decision makers. Failing that, it's just good housekeeping to note down the imperfections of a project for learning purposes.