| Скачать .docx |
Реферат: 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 ones. Next day four
such, and on the 7th about 4 o’clock A.M., a concussion took place so
much more violent than those that had proceeded it, that it was
dominated the hard shock. The awful darkness of the atmosphere, which
was formerly saturated with sulphurious vapor, and the violence of the
tempestuous thundering noise that accompanied it, together with all of
the other phenomena mentioned as attending the former ones, formed a
scene, the description of which would require the most sublimely
fanciful imagination.
At first the Mississippi seemed to recede from its banks, and its waters
gathering up like a mountain, leaving for the moment many boats, which
were here on their way to New Orleans, on bare sand, in which time the
poor sailors made their escape from them. It then rising fifteen to
twenty feet perpendicularly, and expanding, as it were, at the same
moment, the banks were overflowed with the retrogade current, rapid as a
torrent – the boats which before had been left on the sand were now
torn from their moorings, and suddenly driven up a little creek, at the
mouth of which they laid, to the distance in some instances, of nearly a
quarter of a mile. The river falling immediately, as rapid as it
had risen, receded in its banks again with such violence, that it took
with it whole groves of young cotton-wood trees, which ledged its
borders. They were broken off which such regularity, in some
instances, that persons who had not witnessed the fact, would be
difficultly persuaded, that is has not been the work of art. A great
many fish were left on the banks, being unable to keep pace with the
water. The river was literally covered with the wrecks of boats, and
’tis said that one was wrecked in which there was a lady and six
children, all of whom were lost (http://www.hsv.com/genlintr/newmadrd/
accnt1.htm).
This is a very powerful account of the first and second primary shocks. Having
never been in an earthquake I cannot imagine “the earth visibly waving as a gentle sea”.
There are several other published accounts, however, none as descriptive and powerful as
this one.
References
http://www.eas.slu.edu/Earthquake_Center/NewMadrid/General.html
http://www.eas.slu.edu/Earthquake_Center/Nuttli.1973/Intensity.html
http://www.eas.slu.edu/Earthquake_Center/Street/rstreet.html
http://www.hsv.com/genlintr/newmadrd/accnt1.htm
http://www.slu.edu/Earthquake_Center/ Nuttli.1973/Magnitudes.html
http://wwwneic.cr.usgs.gov/neis/eqlists/bigten.lis