Is the New Madrid fault system...

in southeastern Missouri shutting down? Some geophysicists think so.

Oddly, this intracratonic location, far from active plate boundaries, is the location of several of the largest historical earthquakes ever experienced in the United States in 1811 and 1812. So powerful was the main temblor that large areas of the land subsided, new lake basins were formed, the course of the Mississippi River was altered, and bells in Boston rung in response to the surface waves.

I recall, as a kid living in a suburb of St. Louis at the time, feeling a small earthquake related to this relict seismic zone. It's the only earthquake I've ever experienced.