Good point. I've only seen it once so far, so I will keep an eye out for it the next time. My interpretation was that the initial shockwave had hit the building, and was causing all the structural damage that we saw as they were leaving the building. The shockwave passed, at which point they were trying to get to the ship and leave before the larger danger of "the horizon is missing" reached them.

My feelings on it were that the building was shaking due to seismic activity at a low level on the outskirts of the rock wave. The sheer size of the rock wave might make it seem closer than it was. The problem is that we have little indication how far away the base was from the initial blast point. My thought it was quite a distance away since they had X-Wings parked out front in the open.