|San José State University|
& Tornado Alley
Some of the most severe earthquakes in the United States occurred not on the Pacific Coast but in the middle of the continent in southeastern Missouri near the town of New Madrid. There are many things that were unusual about the New Madrid earthquakes of 1811-1812. First, their location is a surprise. There were centered at the southeast corner of Missouri far from the seismic active zones of the mountain chains on the edges of continents, which are the boundaries of techtonic plates. Second, their magnitudes were unusually high; in the range of 8.1-8.3. Third, the pattern was unusual in that there were three shocks of about the same magnitude separated by weeks in time. The table below gives the timings of the three major shocks. There were numerous aftershocks following each major shock.
|The New Madrid Earthquakes of 1811-1812|
|Date||Time of Day||Magnitude|
|December 16, 1811||2 A.M.||8.2|
|January 23, 1812||8.1|
|February 7, 1812||3:15 A.M.||8.3|
The estimated locations of the epicenters of these earthquakes are shown below:
Several towns, including New Madrid, shown on the above map were destroyed by the quakes. In Little Prairie fifteen minutes after one aftershock on December 16th water rose to waist level and the towns people had to walk through this water eight miles to reach high ground. They went on another twenty six miles over a three day period seeking refuge in New Madrid only to find it had been destroyed.
In addition to these three major quakes there were inumerable minor ones, following and sometimes preceding the major ones. One careful observer noted an average of about forty per day over a three month month period. There was a notably strong quake on January 7 but it was not of a level 8 magnitude.
The magnitudes of the quakes were estimated from the descriptions of their effects. Some of these effects were:
This map shows the range over which the effects of the quakes were felt. The dark red zone is where the severe shaking was felt. The lighter red is where shaking was felt but without damage.
There were other things that occurred such as flashes of light, loud noises and smelly gases spreading over the land. Watery sand spouts were particularly wide spread. The water was warm. Holes were created in the ground and sometimes sand cones where the sand spouted out and then came down. Sometimes chunks of wood or coal as heavy as 20 pounds were blown out of these sand spouts. The map below shows the area in which sand spouts occurred.
Wild animals were disturbed by the quakes, seeming to lose their fear of humans. Horses reacted to the quakes by stop moving or proceding as if they were walking on ice.
The major puzzle concerning the New Madrid earthquakes is why they occurred in midcontinent. The answer seems to be that a break in the North American plate was developing along the route of what became the Mississippi Valley. A rift valley was developing but the fissure ended in the region of New Madrid.
(To be continued.)
Norma Bagnall, The New Madrid earthquakes of 1811-1812, Columbia, MO: University of Missouri Press, c1996.
Jay Feldman, When the Mississippi ran backwards : empire, intrigue, murder, and the New Madrid earthquakes, New York : Free Press, c2005.
F.A. McKeown and L.C. Pakiser (eds.), Investigations of the New Madrid, Missouri earthquake region, Washington : U.S. Government Printing Office, 1982.
Jake Page and Charles Officer, The Big One: The Earthquake that Rocked Early America and Helped Create a Science, Boston: Houghton Mifflin Co., 2004.
James L. Penick, The New Madrid earthquakes of 1811-1812 Columbia, MO : University of Missouri Press, 1976.
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