Four quakes, measuring as large as 8.1, hit southeast Missouri from December 1811 to February 1812. They leveled towns and created waves on the Mississippi River so large that observers reported the water was running backward, the Survey said.

http://www.bloomberg.com/apps/news?pid=20601103&sid=am55JSrLum88&refer=us

the above fact would indicate these large scale earthquakes come in relative rapid succession.

This quake was felt so far away, there was a 5.0 earthquake in Evansville, Indiana, but nobody felt it 400 miles away, this one was different somehow, and it was very intense along ways away. The big quake in San Francisco in 1989 was big, but it wasnt' felt 400 miles away like this one was. If this fault area in the midwest produced an 8.0 earthquake, I think it could shake an area many, many times larger than the fault along San Francisco.

These scientists are saying that, well the pressure has been released, so now we are safe, but when you hear the ice cracking, that means it's about to break, same thing with tectonic plates, when it starts cracking that means something big could slip, because now it's resting on new tension points that haven't been proven, so to speak, over the test of time.

If a quake of 8.1 hit the midwest, it would be the most significant natural event in US history, all those skyscrapers would come tumbling down in every city in the midwest. The Richter scale is sort of dumb, an 8.0 earthquake is 60 times more powerful than a 7.0 earthquake. Thus, a 7.0 earthquake is 360 times more powerful than a 5.0 earthquake.