Earthquakes are of great concern when choosing a location for a data center. Much has been learned from the recent events in Japan. Several large data centers ran on diesel fuel while controlled rolling blackouts were in effect to help conserve power during the crisis.
While mission critical facilities may not have gone offline completely due to backup system, the ideal scenario is to never have a need to revert to generators for extended periods of time
Locating your data center outside of areas known to be a threat to earthquakes, and other natural disasters for that matter, is the best preventative measure possible.