On February 7, 1812 the fourth and strongest of a series of earthquakes occurred near the town of New Madrid in present-day Missouri (at the time it was in Louisiana Territory).
The effects were devastating. The town was destroyed. Lakes and sandblows were created across the middle-west. The Mississippi River reversed direction and created new aspects to its path, like the Kentucky Bend.
The earthquake was so massive that it cracked sidewalks in Washington DC and made church bells ring in the city of Boston.
The fault--the New Madrid fault system--slips occasionally. There was one last year that knocked over my DVD racks...in Wisconsin.
The next time there is a big one, cities like Memphis and St Louis will be destroyed to a degree that Katrina will look like a flooded basement. It'll serious damage infrastructure and cities from Colorado to the Atlantic Ocean and from the Canadian border to the Gulf of Mexico.
Luckily, little 1950s Levittown houses like mine tend to bounce around during earthquakes and generally don't fall down.