These catastrophic earthquakes occurred during a three-month period in December 1811 and early 1812. They caused changes in the course of the Mississippi River, which rolled backwards temporarily, and were felt as far away as New York City and Boston, Massachusetts, where churchbells rang. Large areas sank into the earth, fissures opened, lakes permanently drained and new lakes were formed, the course of the Mississippi River was changed, and forests were destroyed over an area of 150,000 acres. Many houses at New Madrid were thrown down. "Houses, gardens, and fields were swallowed up" one source notes. But fatalities and damage were low, because the area was sparsely settled. Hundreds of aftershocks followed over a period of several years.
All three major quakes are generally believed to have exceeded 8.0 on the Richter Scale, and some seismologists believe the largest was 9.0 or larger. Scientists estimate that there is a 90% probability of a magnitude 6.0 to 7.0 quake on this fault system before 2040. Because of the underlying geology of the Mississippi River Valley, large quakes here can affect as much as 20 times the land area of major quakes on the west coast.
The largest New Madrid seismic zone earthquakes to have occurred since then were on January 4, 1843 and October 31, 1895, with magnitude estimates of 6.0 and 6.2 respectively. The last major earthquake to occur in this region occurred in Charleston, Missouri, in 1895, and is estimated to have had a magnitude of 6.7 on the Richter Scale.
A request dated January 13th, 1814, by the Territorial Governor, William Clark, asked for Federal relief for the "inhabitants of New Madrid County". This was possibly the first example of a request for disaster relief, which would later become the job of the Federal Emergency Management Agency (FEMA).