The quake originated at Beth's office when they were testing a dragon shout.
By the way, it's because Chuck Norris did a push-up.
Dammit, I knew they shouldn't have hired Chuck Norris as a voice actor, especially dragon shouts.
I hope they are okay.... and alive.
They must have been deperate in trying to make Alduin's roar the epicest. Well, I think it worked.