Magnetic hard drives are sensitive to vibration. You can shout at hard drives and measure the effects (video: https://www.youtube.com/watch?v=tDacjrSCeq4).

One of the worst-case scenarios is a head crash. A head crash will damage the media and may result in data loss. https://en.wikipedia.org/wiki/Head_crash

My guess is that earthquakes powerful enough to cause a head crash are powerful enough for widespread destruction anyway, but I’m no expert. I did some quick searches for hard drives damaged by earthquake, and the only results I got were scenarios where the hard drives or the whole rack got knocked over by the earthquake and hit the floor.

- Personnel-level warning to immediately rerack servers, close racks, and get off ladders and away from fall hazards

- Proactively spin up generators to reduce failover in the more-likely event of a power disruption

- Potentially temporarily shut off very large circulation fans so that blades don't collide with the housings

- Potentially stop and carefully restart cooling water loops, in case there's a rupture in the system somewhere

Add to this: initiate failover or zone transfer of distributed servers / services to other DCs outside the likely impacted area.