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Roger Weller, geology instructor
New Madrid Earthquakes
by Nancy R. Chase
New Madrid Earthquakes
There are several facts about the New Madrid series of earthquakes during the
winter of 1811-1812 that command respect. First, the three-month sequence
included at least six earthquakes of Magnitude equal to or greater than 7 and
four earthquakes estimated at M 8 or higher, constituting the most powerful
seismic event recorded in U.S. history. There are varying estimates of the
magnitude for the earthquakes in the series, but the United States Geological
Survey places the three main shocks at the intensity level of XII on the
Modified Mercalli scale, the maximum that scale allows. Second, this
catastrophic event occurred toward the center of the continent, far from the
plate boundaries that are commonly the active seismic zones. There are no other
recorded earthquakes in the Stable Continental Regions worldwide that match this
series. (This SCR category includes two-thirds of all continental crust.)
Third, there has been continued activity in the New Madrid Earthquake Seismic
Zone until the present day, although currently on a greatly reduced scale.
The New Madrid Seismic Zone (NMSZ) in red. USGS image.
These earthquakes are named for the riverboat town of New Madrid (pronounced
MAD-rid), all of whose buildings were destroyed, located on the western bluffs
of the Mississippi River near what would become the “boot-heel” of southeastern
Missouri when it later became a state in 1821. New Madrid was the biggest river
town between St. Louis and Natchez in 1811, with a population estimated
variously at several hundred to 2,000 people. (The size of the local Native
American population at that time is not known, although it is known that there
existed a rich and insightful heritage of tales and explanations of natural
disasters among these peoples.) Shipping on the river was already extensive,
although in its technological youth, by 1811. Boats were drift- and pole-barges
as well as canoes and keelboats, with the first steamboat making its inaugural
voyage at the very point in time between the first two of the New Madrid
earthquakes. The Mississippi River was then the frontier of the fledgling
United States of America, with virtually no reporting of the event from any
distance west of the river, and hence little way of estimating damage in that
direction. East of the Mississippi, however, eyewitness reports were very
numerous and well recorded, with the quakes creating a sensation throughout the
growing U.S. population. Church bells were rung in Boston and pendulum clocks
were stopped in Washington, D.C. by the quakes.
Extent of effects of the New Madrid earthquakes of 1811-12 .
There were horrific reports originating from both near the epicenter and many miles from it, with one account coming from no less a personage than John James Audubon, naturalist, ornithologist and artist, who was about two hundred miles away (as the crow flies) in Kentucky. He stated, in part:
“…I heard what I imagined to be the distant rumbling of a violent tornado, on which I spurred my steed, with a wish to gallop as fast as possible to the place of shelter; but it would not do, the animal knew better than I what was forthcoming, and, instead of going faster, so nearly stopped, that I remarked he placed one foot after another on the ground with as much precaution as if walking on a smooth sheet of ice. …he all of a sudden fell a-groaning piteously, hung his head, spread out his four legs, as if to save himself from falling, and stood stock still, continuing to groan.
“I thought my horse was about to die,…but at that instant all the shrubs and trees began to move from their very roots, the ground rose and fell in successive furrows, like the ruffled waters of a lake, and I became bewildered in my ideas, as I too plainly discovered that all this awful commotion in nature was the result of an earthquake. …
“The fearful convulsion, however, lasted only a few minutes, and the heavens again brightened as quickly as they had become obscured; my horse brought his feet to the natural position, raised his head and galloped off as if loose and frolicking without a rider.
“. . .Shock succeeded shock almost every day or night for several weeks, diminishing, however, so gradually as to dwindle away into the mere vibrations of the earth.”
From The New Madrid Compendium, CERI, University of Memphis.
The New Madrid Seismic Zone, which is still active in a subdued way at the present time, is part of the Reelfoot Rift, a “failed rift” called an aulacogen. The word comes from the Classical Greek word aulax, meaning “furrow,” and from the suffix –gen, meaning “producing” or “giving birth to.” This occurs when a large piece of continental crust begins to diverge from the main mass, then ceases outward movement and is reunited with the continent, an action which leaves complex segmented faults. This type of seismic zone seems to generate earthquakes in multiples of huge events closely linked in time, as opposed to the single large quake followed by a series of smaller aftershocks which is typical of the most famous American seismic area, the San Andreas Fault of California.
The Reelfoot Rift. USGS image.
Geophysicist Maria Beatrice Magnani of the Center for Earthquake Research and Information (CERI) at the University of Memphis in Tennessee, characterizes this failed rift seismic zone in the following way:
“The New Madrid Seismic Zone is an area where deformation is subtle and
more challenging to understand because evidence is controversial and difficult
to reconcile. Intraplate seismicity and deformation is one of the last
frontiers of plate tectonics, as we still have to understand the fundamental
processes responsible for the large earthquakes that occurred away from plate
boundaries. …In the middle of the continent, seismic waves travel very far
because the continent is old, cold and rigid, and the energy released by the an
earthquake is not attenuated much or dissipated very quickly. This is different
from California, for example where the crust is hot and attenuates seismic waves
much more efficiently. The interior of the continent is like a bell that rings
for long distances and for a very long time.”
The Reelfoot Rift inside the structurally disturbed belt is still active with small quakes.
from Putnam’s Geology, Fifth Edition, by Birkeland and Larson, Oxford U. Press, 1989
A very few years after the quakes of 1811-12, the boundaries of the new state of Missouri were set and the area which makes the “boot-heel” of the state was included, incorporating a huge area that had been devastated by the earthquakes. This provides an intriguing sidelight on how politics can follow the lead given by geography and geology. John Hardeman Walker was a cattleman and local landowner of note in 1811. He was also an acquisitive man. After every building in New Madrid and nearby Little Prairie had been destroyed by the earthquakes, people were left destitute by the loss of their homes and by the helter-skelter dispersal of livestock. Many people also faced the ruination of their cropland caused by flooding, by extensive liquefaction and by what remains to this day the world’s largest single area of sandboil or sandblow (referred to as “the beach” by geology students who have not yet reached the age of sense). At this juncture Walker began to buy up huge tracts of land in the vicinity from those who were abandoning the area. (In fact, only two families remained on the site of New Madrid.) When the issue of Missouri statehood was debated in 1818, Walker lobbied to alter the proposed use of the 36 degree 30 minute parallel to delineate the southern boundary of the new state. This commonsense and simple boundary line proposal would have made the southern state line the same as the line between Kentucky and Tennessee, but it would have left Mr. Walker languishing in the territory of Arkansas, a fate which failed to exert the slightest charm over him. After extremely successful lobbying (of an undisclosed nature) both in Missouri and in Washington, D.C., Walker was able to have the border placed 50 miles south, lying along an east-west line extending about 30 miles, and jumping back up to 36 degrees 30 minutes at the next convenient river. To Walker’s complete satisfaction, when Missouri became a state in 1821, it included this “boot-heel” in its southeastern corner, and the Arkansas Territory lost 627,000 acres.
The Missouri Bootheel is in the southeast corner of the state. USGS image.
Johnston, Arch C. et al., New Madrid Compendium, The Enigma of the New Madrid Earthquakes
Update Newsletter:: CERI’s Magnani discovers major fault line in area:: University of Memphis
USGS Earthquakes Hazards Program: Historic Earthquakes: New Madrid Earthquakes 1811-1812
USGS: Earthquake Hazards Program: Missouri, Earthquake History
USGS: Uncovering Hidden Hazards in the Mississippi Valley
Kentucky Geological Survey: Precambrian Rift Basins of Eastern North America, 2000
Missouri State Archives :: Missouri History :: The Bootheel”
Birkeland, Peter W., and Larson, Edwin E., Putnam’s Geology, Fifth Edition, Oxford University Press, New York and London, 1989