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The New Madrid Fault Zone is a source of earthquakes which lies along the Mississippi River.
The New Madrid fault zone lies within the central Mississippi River valley, extending from northeast Arkansas, through southeast Missouri, western Tennessee, western Kentucky to southern Illinois. Historically, this area has been the site of some of the largest earthquakes in North America. Between 1811 and 1812, four catastrophic earthquakes, with magnitude estimates greater than 7.0 on the Richter scale, occurred during a 3-month period. Hundreds of aftershocks followed over a period of several years. The largest 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. In addition to these events, seven events of magnitude >= 5.0 have occurred in the area. Instruments were installed in and around this area in 1974 to closely monitor seismic activity. Since then, more than 4000 earthquakes have been located, most of which are too small to be felt. On average one earthquake per year will be large enough to be felt in the area.
The potential for the recurrence of large earthquakes and their impact today on densely populated cities in and around the seismic zone has generated much research devoted to understanding earthquakes. By closely monitoring the earthquake activity, scientists can hope to understand their causes, recurrence rates, ground motion and disaster mitigation. The probability for an earthquake of magnitude 6.0 or greater is significant in the near future, with a 90% chance of such an earthquake by the year 2040.
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).