One of my first tasks when I was hired ten years ago was to investigate creation of a disaster recovery site for our mainframe computer systems. I had already had some experiences with disasters and recovery. Here are some examples of a few that we included in our plans.
Major Earthquake - Those of us who live in California understand earthquakes. I've personally been through at least five significant quakes (6.8 or greater) without suffering any damage at all. In many people's mind, a major earthquake is disaster scenario.
One day "big one" will come (in California) and who knows what will happen at that time. In fact, my boss and I were able to convince CEO of our company to create a "hot site" (a duplicate site which is already ready to take over in event of a disaster) because of a recent significant earthquake.
One of first things that we did is contact Caltech (the experts on earthquakes) to commission a study to determine where we should place our disaster site. The primary criteria was that site be relatively close (within 50 miles) but on a different geologic plate so earthquake would not flatten both locations.
As we studied possibility of this disaster, we realized that building and computers might emerge from earthquake entirely intact, but infrastructure (power, phone lines and so forth) might be destroyed. In addition, a major earthquake is a unique disaster because it's more likely that your people will be in complete shock and more interested in their families and homes than in restoring your computer operations.
The thing to do here is be sure you've got infrastructure issues covered cold. This includes phones, power and network. Make sure you have a disaster site (or very good backups kept off-site) ready to go. Rehearse your disaster plan, and make sure your people know what to do.
Minor Earthquake - A minor earthquake might be easy to survive (we've been through several of them with no issues) and it might introduce some interesting quirks on it's own. The power might be out, phone lines might be down and take weeks to repair, and general infrastructure (roads, food shipments and so on) might be disabled. In addition, earthquakes tend to put people into a state of shock, so it might be difficult to get people to recover and get back to work.
Biological Event - When envelops fill of anthrax started appearing on news, we were suddenly confronted with a new type of disaster. What if a biological attack or event occurred in our building? What if receptionist opened an envelop contaminated with anthrax? We would then be confronted with a unique situation. The building would be sealed and off-limited for days, weeks or even months; and we would not be allowed back in under any conditions for any reason for that time.