The latest recommendation I've heard for seismic events is to get at the base of a wall if possible. Has something to do with triangular geometry being the safest bet inside a structure. I think grabbing the corner of the room exposes you to too many structrual junctions, where it is most likely going to come apart, although having perpendicular supports might help prevent collapse. One other thing you did wrong was perhaps not preparing for such an event previous.

As for what to do next, if your wife is ambulatory, I hope you told her where the gas cutoff valve is, and she can get to it before the big boom. Or is that from the propane tanks that have been ruptured? If you can't get the gas turned off soon, or find some way to free your arm, you may have to gnaw it off if you want to survive. Good luck.