Plus the DC itself might be running, but now you could be running it on a generator (no outside power); better hope you can get a fuel truck to it before the 1-week tank runs out (are there truckable roads outside now?). And connectivity - you might have line slack inside your building, but the fiber cables might be broken in several locations before they even get to next active element (which is also earthquake-proofed? And powered? For how long?); so perhaps you're down to the radio fallback (hope the antennas aren't misaligned too much, let alone that their masts are still upright); again, assuming that the other end of the link is operable.

In other words, preparing for vis major is far harder than it looks. Doable? Yes, if you're willing to go all the way to military-grade resilient comms...for a military-grade budget. Far easier to failover to a DC in a different zone.