The New Madrid Seismic zone lies within the central Mississippi 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, 4 catastrophic earthquakes, with magnitude estimates greater than 7.0, 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 New Madrid seismic zone is so named because the town of New Madrid, Missouri was the closest settlement to the epicenters of the 1811-1812 quakes. At that time, St. Louis and other major cities in the central U.S. were sparsely settled. At least 3 of the series of earthquakes were felt throughout much of the U.S. and as far away as Quebec. The potential for the recurrence of such 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 50% chance by the year 2000 and a 90% chance by the year 2040. A quake with a magnitude equal to that of the 1811- 1812 quakes could result in great loss of life and property damage in the billions of dollars. Scientists believe we could be overdue for a large earthquake and through research and public awareness may be able to prevent such losses.