Fair point, although I'd think twice about trusting a subterranean shelter, even so.
Okay, assume the shelter held up through the earthquakes, wasn't inundated with seawater, and the fires have run their course. You need air, and food and water and if underground, the energy to support a viable habitat. The requirements for food alone, for the necessary extended period would require a colossal facility. One would probably have to be planned and prepared long before detection of a threatening object.
Which brings up the question: Is there any evidence that such an undertaking is in the works?
Then again, there's no guarantee that such a shelter wouldn't be within the radius of complete destruction. The only way that I can see to assure the survival of the species is with a self-sufficient off-planet colony.
If something like this were to occur between now and the time that such a colony exists, and it were of the magnitude that we're talking about, that's probably all she wrote, folks, unless isolated, hardy survivors manage to eke out a Stone-Age existance someplace. Disasters are often quirky. I'd expect that there's be a few.
Not that I know of. I do remember a story in the Washington Post two years ago about extensive underground blasting under the Naval Observatory in Washington DC. This is where the Vice President's residence is (remember "Get out of Cheney's House!"?). I understood they where making some terrorist proof bunker.
Anyway, it would be a chance either way.
My screen name is from a book title about folks in a small Florida town surviving a full scale nuclear war and what they did to survive, even flourish after a time. I've always liked these kind of stories. However, if there was a extinction level event heading our way in only two weeks (especially 3 of them), we'd know about it by now.