Living in a zone that could expect an earthquake at any time, near the Madrid fault, I can easily say that America is not prepared for a major earthquake. Earthquakes are difficult to prepare for especially when most citizens live pay check to pay check anyway. Yes, some areas have addressed issues with building codes and highway construction, but those efforts are just a drop in the bucket.
We on earth, especially those of us in the United States, take nature way too much for granted, acting as if nothing bad could happen to us here. So even California, which gets a lot of quakes, is basically unprepared, and the rest of the country simply has no clue what would happen or how to react.
There are certain things that can be done to help prepare for a catastrophe to some degree. For example, people can keep a stash of food, water, and supplies like flashlights and generators. Buildings can be built to sway and move to some degree, to help keep them from collapsing in the event of an earthquake. But there's really no way to fully prepare for something unexpected, especially on such a grand scale.
I definitely do not believe America is prepared for a major earthquake. I would be willing to bet that the possibility of an earthquake has never even been discussed throughout most of the mid western states. I would say that of all states, California may be the most prepared for a major quake, especially since it has been predicted for about the last 50 years.