Yes, it's indeed hard to predict an earthquake to take out the external power and the subsequent tsunami to take out the backup generators on a coastline facility.
(Note: This was sarcasm)
(Note: This was sarcasm)
Sarcasm aside, it is easy to predict that the facility would be at risk for an earthquake/tsunami combo. The hard part is to predict how much of one to prepapre for. Remember, even in this neck of the woods, the was a quake of historic proportions.