It's very unlikely that your business needs to plan for something that affects more than about a 20-mile radius.  Events like earthquake or hurricane, or even a nuclear disaster, are fairly localized.  For disasters the optimum separation is about 30 miles*, which lets people who are not involved in whatever happens to the primary (the other shifts) staff the alternate in an emergency.  Add in cost of fiber, latency, etc., and 30 miles is just about perfect.

If your business continuity planning is telling folks anything else, I think perhaps they're not getting what they think.

* unless it's just 30 miles further down the eq fault line or hurricane path :-)  Local conditions change the rule of thumb as to exact distance/direction.

-- Jeff