Do you have any concept of what a Mag. 10.0 earthquake is? Keep in mind as well, that this rung the whole plate, not like the relatively itty-bitty quake that spawned the Tsunami last year (and detectibly altered the earth's shape and rotation). The last time the New Madrid fault wnet, it threw the Mississippi several miles...then an aftershock threw it again. The earthquake was felt a thousand miles away.
I'd worry more about a 6.5-7 quake, which would have enough punch to take down unreinforced buildings, but not enough to take down ones built to modern earthquake codes.
The city of St. Louis in particular is full of brick buildings; it would take a hard hit from anything above a 5.8.