In December of 1811, a the largest earthquake ever recorded in American History started. This earthquake, called the New Madrid Earthquake because of its primary location on the New Madrid Fault, near New Madrid, Missouri. From the effects of the 1811-1812 earthquakes, it can be estimated that they had a magnitude of 8.0 or higher on the not yet invented Richter scale. Large areas sank into the earth, new lakes were formed, and the Mississippi River changed its course due to the earthquakes. More info at New Madrid quakes
The quake was felt as far away as Boston, where it caused some church bells to ring!
It was a series of 4 major quakes over about 2 months. Whats truly awesome about it is that the accounts say the ground was in continuous motion for the last 2-3 weeks between the two peak quakes, at times the land could be seen to be rolling in waves. Sounds biblical. Do a web search. Great reading.