hollow earth have reports wich predates your descent there by, iirc, 187 years and some months, anyway the difference is minimal, and also, we are totally unsure of what really powers up ALL of the actual underrail part (while we know that lemco had underwater geothermal power plants).
I have surely missed a good part of the in-game lore, but something tells me that the Omega thing had something to do with Tanner: he's him to send you to get back the buildings at the first mission, wich were omega, and it's again him to send you, along with gorsky, to find what happened into omega... then you go to junkyard and, after that, the cube "vanishes"...also: tanner asked to see what is in gsm compound, wich was omega too, and after that, gorsky "flee" from sgs, never to return...is gorsky fleeing from tanner? Maybe he didn't approve what was done to omega, wich were wiped EXACTLY a bit before the earthquake? Maybe Tanner then found the cube and opened it for a bit, so the faceless tracked it nearby and provoked the earthquake?