The Earthquakes Of 1811 And 1812 In

The Mississippi River Valley Essay, Research Paper

When one thinks of earthquakes, the Mississippi river valley (MRV), does not

frequently come to mind. One usually thinks of one of California’s numerous faults or

somewhere in Alaska. However, little known to the general public, there were two

massive earthquakes in the MRV, which rank among the top three in the contiguous

United States and in the top ten for the entire United States (http://wwwneic.

cr.usgs.gov/neis/eqlists/bigten.lis). Starting in the early morning hours of December 16,

1811 a violent shaking of the earth began, which continued on for three months,

producing two of the three largest quakes in the contiguous US, this particular quake

registered an 8.0 in magnitude on the Richter scale. There was a second quake on

February 7, 1812 which registered 8.2 (http://wwwneic.cr.usgs.gov/neis/eqlists/

bigten.lis).

The plate which is responsible for this activity is named the New Madrid Seismic

zone, it is named for the only populated city that was in existence in the time and the area

of these earthquakes, New Madrid, Missouri. The New Madrid Seismic zone lies in the

central MRV, starting in southern Illinois and ending in southeast Missouri, western

Tennessee.

Usually an earthquake consists of a principal shock and then the aftershocks, the

1811-1812 earthquakes didn’t follow the usual pattern. There was the first primary shock,

at and then it’s aftershocks, however the aftershocks from the first quake hadn’t subsided

before the second principal shock hit. Following suite, the aftershocks from the second

quake had not terminated when the third and largest principal shock hit (http://www.eas.

slu.edu/Earthquake_Center/Nuttli.1973/intensity.html). It is difficult to gage the actual

intensity of the earthquakes due to the lack of technology, however, the strength can be

estimated by the damage caused by the quakes and also by the journals of the people

settling this part of the country. Fortunately, a man by the name of Jared Brooks, who

was a resident of Louisville KY, kept a journal of the seismic activity from December 16,

1811 to May 5, 1812. He had devised his own system of measuring intensities with a set

of horizontal pendulums from 1 to 6 inches in length and a set of vertical spring- mass

systems. Devising his own instruments, he also created his own categories of intensities,

with six levels. The first is comparable to an eight on the Modified Mercalli scale, second

level is a five to a six, third is a four to five, fourth is a three, the fifth level is comparable

to a two on the MM, the sixth is a one (http://www.slu.edu/Earthquake_Center/

Nuttli.1973/Magnitudes.html). With the assistance of these measurements scientist have

been able to devise approximate strengths of these earthquakes. The following is a map

with the MM intensity values for the December 16, 1811 earthquake. Map

(http://www.eas.slu.edu/Earthquake_Center/Nuttli.1973/Intensity.html)

Through some in depth research about ground motions and intensities of these

earthquakes, if has been concluded that the epicenter of the first earthquake (December

16, 1811) was closer to the northeast Arkansas near the southern end of the lake formed

by the St. Francis River. The lake in the area was raised as much as 12 ft. up higher than

the surrounding country. The water in the lake was drained and replaced by white sand.

It was stated by the Louisiana Gazette that the river itself rose as much as 25 to 30 feet

above it’s banks (http://www.eas.slu.edu/Earthquake_Center/Nuttli.1973/Intensity.html).

There are several published personal accounts of these earthquakes, the following

is an collection of excerpts from a letter found in a book entitled, “Lorenzo Dow’s

Journal,” published by Joshua Martin, printed by John B. Wolff, 1849, on pages 344-346.

On the 16th of December, 1811, about two o’clock, A.M., we were visited

by a violent shock of an earthquake, accompanied by a very awful noise

resembling loud but distant thunder, but more hoarse and vibrating,

which was followed in a few minutes by the complete saturation of the

atmosphere, with sulphurious vapor, causing total darkness. The screams

of the affrighted inhabitants running to and fro, not knowing where to

go, or what to do – the cries of the fowls and beasts of every species -

the cracking of trees falling, and the roaring of the Mississippi – the

current of which was retrogade for a few minutes, owing as is supposed,

to an irruption in its bed — formed a scene truly horrible.

There were several shocks of a day, but lighter than those already

mentioned until the 23d of January, 1812, when one occurred as violent

as the severest of the former ones, accompanied by the same phenomena as

the former. From this time until the 4th of February the earth was in

continual agitation, visibly waving as a gentle sea. On that day there

was another shock, nearly as hard as the proceeding

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