It's a 120-mile-long system of three to five faults stretching from 40 miles northwest of Memphis to southern Illinois, near Cairo.
"The system is capable of producing a quake near 4.0 magnitude every three years," said Gary Patterson, a geologist and information services director for the Center for Earthquake and Research Information in Memphis, Tennessee. "And they'll cause minimal damage."
But New Madrid already has spawned four earthquakes this year of similar size, along with nearly 100 smaller quakes. Patterson said such activity may or may not be the precursor to a much larger quake.
The recent activity is an anomaly, he said.
"It's unusual, and we don't have any reason to believe there is increased risk," Patterson said. "But any time you have this kind of activity in an area that has a 25 [percent] to 40 percent chance of a 6.0 or greater in the next 50 years, it will draw attention."
And the region is ill-prepared for a strong quake, he added.
In the five years I lived down in Carbondale, I only felt one quake and that, believe it or not, was the night before graduation -my last day there.