It's not just the bump and grind of plates that make earthquakes. If that was true, the midwest would have nohing to worry about but drunken cheese heads. Intracontinental faults also cause a buttload of earthquakes. It's like if you have a plate of dry fudge and start pressing, pulling, and sliding them around against each other. Cracks will appear within each piece of fudge and even if nothing is really moving on the edges of the fudge, pressure will make the cracks split or move independantly of the fudge edges.
The New Madrid fault is one of the intracontinental faults. It's released pressure fairly routinely so while the quakes it gives off will be fairly sizable, they won't be catastrophic. The intracontinental faults that stretch from Ohio, through New York, and into Canada have only released minor pressure, in the 1700's and 1800's. Neither of those were really enough to do anything and compared to the pressure built versus pressure released of the New Madrid, that fault is going to be catastrophic when it goes. Now, it might give off a couple farts of pressure here and there, but unless the releases are at least a 7.0, when the big one happens, it will be catastrophic.
Everyone worries about California and, to a lesser extent, the New Madrid, but it's the ones we don't expect that will really nab us. That whole hubris thing again. "There's a major fault running through New York? Silly person, this is The Big Apple! Nothing like that happens here!"
*hourglass icon*
