Some parts of the world have little or no history of earth tremors while others are plagued by them. For those building in Iowa, you probably aren't too concerned about earthquakes, whereas those building in California or Tokyo should consider the following:
How often, if ever, do earthquakes occur in the region?
Is the data center site built to withstand seismic disturbances?
Can the data center be located on lower floors where there would be less sway?
Should equipment be held down with seismic restraints?
Can racks be secured to the floor and ceiling as a means of seismic restraint?
Other steps required to ensure the safety of personnel should be outlined in local building codes.