New Madrid, MO Earthquake of 1811-1812

Janelle E Kizer

Geology 101

Spring 2012

1. Introduction:

During 1811 – 1812, four earthquakes occurred in New Madrid, Mississippi River Valley, which are considered to be some of the most humongous earthquakes in the U.S. since the settlement by the Europeans. The first two was at 1811, December 16, Northeast Arkansas, Magnitude 7.2-8.1. The next one was at January 23, 1812 right at New Madrid, Missouri and the magnitude was 7-7.8. The last one occurred at February 7 of 1812, 9:45 Coordinated Universal Time (UTC), in New Madrid, Missouri with a magnitude 7.4-8.0. All these earthquakes were 3 times stronger than the Alaska earthquake of 1964, and 10 times stronger compared to the San Francisco earthquake of 1906.

2. Geographic location of New Madrid, MO:

New Madrid was formed in 1808. It is situated on the Mississippi River and interstate 55. It has a population of 3154 residents, and it is considered as a small community in United States.

New Madrid, MO is located at 36.59° North latitude, 89.53° West longitude and about 89 meters altitude above the sea level.

Geographic coordinates:
Latitude: 36.59° North
Longitude: 89.53° West
Altitude: 89 m

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3. General geologic setting:

A state’s general geologic setting basically includes what types of rock has build up the overall region, what structural features that state has, like, mountains and faults. It also includes plate tectonic setting and also an overall geologic map.

3.1. Geologic map:

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3.2. Plate tectonic setting:

The middle of the North American tectonic plate actually contains the new Madrid fault zone. One of the attribute of this plate is, this plate is thinner and weaker near to its center. As a result, it formed a rift zone.

When the pacific plate had a collision against the west side of the North American plate in California, there was a buckling effect near the center of the North American plate. These scenarios might have caused the new Madrid earthquakes.

3.3. Types of rock:

The New Madrid Seismic Zone (NMSZ) is made up of reactivated faults that formed when North America began to rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era (about 750 million years ago). The types of igneous rocks that can be found in Missouri are –

- Granites

- Rhyolites

- Ignimbrites and

- Felsites

These rocks are 1.38-1.48 billion years old. In this region, two more igneous rocks, basalt and diabase, form as dikes and sills. These are very narrow rock bodies which fill the cracks and add character to the story of Missouri geology. These rocks were placed about 1.1 billion years ago. Both of these rocks are durable, but the amount of weathering one sees gives clues to their ancient age.

3.4. Types of structural features:

There are several types of rift, arch and faults can be found in New Madrid. However, the structures which had prominent contribution to the earthquake, are described below-

3.4.1. Reelfoot rift:

This rift basically is the host to the seismic zone of New Madrid. Reelfoot rift is a failed rift which was formed in Late Proterozoic to Early Cambrian times. There was an ocean named Lapetus Ocean, and the rift was off the margin of that ocean. As a result, a triple junction was formed. According to this junction, the successful arms of the junctions are the rift-developing oceans, and the failed arms are the Mississippi embayment and the southern Oklahoma aulacogen /Anadarko basin, respectively. Lapetus Ocean is actually the ancestor of the Atlantic and Gulf of Mexico.

Apart from the triple junction model, there is another model called quadruple junction, which was proposed more northerly and all arms (four) were considered to be fail arms. In 1991 Thomas, with the help of quadruple junction in southern Arkansas, created a model of evolution of the southern North American margin. According to this model, Reelfoot rifts and southern Oklahoma were failed arms in early Cambrian. There were active boundaries in the form of Ouachita rift and Alabama-Oklahoma transform. The Reelfoot rift most probably merges with east-west Rough Creek Graben to the north.

There are lots of model regarding the configurations and evolution of the rift. In all, the Reelfoot rift is a failed rift.

Around the world, so far lots of earthquake occurred in crust which experienced an extensional tectonics. So, in order to understand the earthquake vulnerability of a region, it is important to establish the rifted character of NMSZ crust.

3.4.2. Blytheville arch and intrusions:

The Blytheville arch is a strong upwarp of the Paleozoic strata within a 10-15-krn wide zone that expands to the northeast and is approximately centered on the axis of the Reelfoot rift. However, the reason behind an upwarp of the Paleozoic reflectors is an enigma and an issue of debate. Some say, it’s axial intrusions and according to some experts, it is the diapiric action of less-dense sediments at the sediment-crystalline basement contact which caused this upwarp.

It has been interpreted that the entire arch is made up of shallow intrusions. This phenomenon supports the intrusion mechanism. However, a positive flower structure is another way of getting the less dense flexible sediments to move into the upper carbonate section and to produce a long, linear upwarp of strata.

The Blytheville Arch is very complicated in structure, because some igneous rocks have invaded it. It also has overlying sedimentary units which are up warped. There is an important change in the structure of BA, which had a major influence on the 1811-1812 earthquakes.

3.4.3. Blytheville fault zone (BFZ):

Simply BFZ is an intruded extension of axial fault zone. Means, it is a continuation of Blytheville arch. The extension is to the northeast for 55 km. However, it is unknown whether it is continuous with the arch structures or not.

There is a possibility of the BA being a positive flower structure. If so, then BFZ may present a section that has not developed an arch, because, that section then won’t be under too much compression. The presence of reflectors of disrupted basement is clear on seismic profiles. Less amount of uplift of Paleozoic strata is also very clearly observable. Moreover, it is considered a coincidence that the concentrated zone of seismic activity crosses northeast toward the river.

3.4.4. Reelfoot fault (RF):

The Reelfoot scarp is basically know as RIF. It is a deep, seismogenic fault. The RF has been mapped as 32 km. The RF has not been detected on seismic profiles under Mississippi embayment’s sedimentary rocks. However at 1992, a tabular zone of hypocenters has been resolved, which dips 31° southwest and has a depth of 12 to 14 km that might be the seismogenic expression of the RF in the crystalline basement.

If the 60 to 70 degree dip is used at the depths of 5 km, then the surface projection would reach the surface approximately at the Reelfoot scarp.

4. Detailed geology of the earthquake:

The earthquake was linked with lots of issues like plate tectonic settings, nature of the fault, movements among the plates etc.

4.1. Plate tectonic setting:

The type of tectonic plate settings that caused these earthquakes has already been discussed in paragraph no. 3.2. However, a new paper in Geophysical Review Letters suggests that tectonic plate events on west coast millions of years back might have caused the new Madrid quakes.

Some of the ocean floor between the Pacific plate and the continental plate of North America were made up of a tectonic plate named Farallon plate. During the Cretaceous period, about 70 million years ago, it met the continental plate and was forced underneath it, or subducted. The Farallon plate went under at a shallow angle, and hence the subduction process was long and complicated. The plate scraped along the underside of the continent for awhile, and the resulting volcanoes formed the Sierra Nevada in California. Due to motions in the mantle, underneath the crust, the continental plate moved westward over the subducted plate; the progress of the Farallon plate under the continent was instrumental in forming the Rocky Mountains. And all these millions of years later, the plate is evidently still descending, and as it moves it affects the flow of molten rock in the mantle beneath parts of the eastern US.

In order to predict what will happen in the future, this information is very valuable. This info also illustrates a very interesting fact. This fact sheds light on the connection between some so old and far away, and something much more close to us.

4.2. Nature of the fault along which movement took place:

The natures of some of the NMSZ faults have been obtained through some seismograph recordings of the frequent small earthquakes. In order to identify active faults in the MNSZ some trends have been used from the measured locations of microseismic earthquakes. The trends indicate a four-segment, zigzag fault system with a length estimated to be 125 miles stretching from Marked Tree, Arkansas northeast through Missouri, Tennessee and Kentucky to Cairo, Illinois.

All the active faults are not always microseismically active. However, those faults might have generated dangerous earthquakes in recent past or historic times. On the other hand, some silent faults are considered to be more dangerous. Those are containing high build up stress and the two sides of faults have been locked together. This is considered as a prelude to a serious rupture of the fault. Even though, if faults of these types exist in NMSZ, it would be way too difficult to locate them.

However, at that time, the nature of BFZ played a very important role during the earthquake of new Madrid. The BFZ is a bit proximate to little prairie. There is a possibility of Cottonwood Grove fault, BFZ and a sub parallel fault to the northwest of Cottonwood Grove to be part of a single fault system. If this is true, then there is a possibility of BFZ to intersect with Reelfoot fault at the southwest side of Reelfoot Lake. It will cause the BFZ to extend up to 65 km.

4.3. Nature of the first earthquake of December 16, 1811 along with the fault:

This particular earthquake generated Modified Mercalli Intensity, which was greater than or equal to 7, and assumed to be 600,000 square km. It was strong enough to shake an area of 2.5 million square kilometers.

The surface fault got ruptured due to this earthquake. However, that was not detected and reported. During this earthquake there was vertical movement along several ancient, subsurface faults. As a result, there was Lake County uplift. That uplift was about 50 km long and 23 km wide. It is located above the surrounding Mississippi River Valley by 10 meters in parts of southwest Kentucky, southeast Missouri, and northwest Tennessee. There is a strong correlation between prehistoric uplifts and modern seismicity. It actually indicates, those stresses may still exist today, which produced those uplifts.

A famous area of that formed during the February 7 earthquake of 1812 is Reelfoot Lake in Tennessee. It is east of Tiptonville dome on the lower side of the Reelfoot scarp. Depressions there ranged from 1.5 to 6 meters.

Other areas collapsed by as much as 5 meters, although 1.5 to 2.5 meters were more common. Lake St. Francis, in eastern Arkansas, was formed like this during both prehistoric periods and the 1811-1812 earthquakes. It is 64 kilometers long by 1 kilometer wide. Coal and sand were thrown from fissures in the swamp land next to the St. Francis River, and the water level was reported to have risen there by 8 to 9 meters.

Large waves (seiches) were generated on the Mississippi River by seismically-induced ground motions deforming the riverbed. Local uplifts of the ground and water waves moving upstream gave the illusion that the river was flowing backwards. Ponds of water also were agitated noticeably.

4.4. History of earthquake activities:

The date of first earthquake was December 16th, 1811. The time was 8:15 UTC. It hit the Northeast Arkansas. The magnitude was 7.2 to 8.1.

The second earthquake occurred at the same date. The time was 14:15 UTC. The place was the same, Northeast Arkansas. The MM intensity of this earthquake was kind of similar to the intensity of the first one. This means, the force at the epicenter of this earthquake would have been a MM intensity X-XI level, because, the maximum intensity at epicenter level is about the same, because the MM intensity of two earthquakes was the same.

The third one occurred just after one month. The date was 23rd January, 1812, 15:00 UTC. The place was New Madrid, Missouri, with a magnitude of 7.0 to 7.8. The meizoseismal area was characterized by the ground rising, ejections, fissuring, severe landslides, and caving of stream banks.

The occurrence of fourth earthquake was on 7th February, 1812 at New Madrid, Missouri. The magnitude was 7.4 to 8.0. The destruction occurred on that day breaks all the record of the magnitude of previous events.

5. Impact on the surroundings:

All four earthquakes were the reason for mass destruction and had a bad impact on the surroundings. The impacts of each earthquake are as follows-

5.1. Two earthquakes of December 16th:

There was a sparse population in the epicenter area during the earthquake, and that is the reason why the earthquake caused a little or slight damage to man-made structures. What is now Memphis, Tennessee experienced shaking at a level IX on the Mercalli intensity scale. A seismic seiche generated upriver, and Little Prairie (previously Fort San Fernando, and now present day Caruthersville, Missouri) was heavily damaged by soil liquefaction. Several complex physiographic changes occurred as well.

5.2. Earthquake of January 23rd:

Epicenter was in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig accredited this earthquake to a rupture on the New Madrid North Fault. This would have placed excessive strain on the Reelfoot Fault.

5.3. Earthquake of February 7th:

This earthquake actually destroyed the new Madrid. An abundance of houses were completely damaged at St. Louis, Missouri. This disaster was totally attributed to the Reelfoot fault. At Kentucky Bend, temporary waterfalls were created because of the uplift along a section of this reverse fault. As a result, it caused the formation of Reelfoot Lake by blocking the streams of today’s Lake County, Tennessee.

6. Positive effect of earthquake:

On the night of December 16, 1811, George Lewis was killed by Lilburn Lewis and Isham Lewis. This earthquake actually helped to bring those murderers to justice.

The earthquake forced the murderers to hide the corpse in a brick chimney rather than burning. After the earthquake the body was found, and immediately those two murderers were investigated and arrested.

REFERENCES:

Johnston, C., & Schweig, S. (1996). The Enigma of the New Madrid Earthquakes of 1811 –1812. Anna. Rev. Earth Planet. Sci. 1996. 24:339-84

Braile, W. L., Hinze, J. W., Keller, R., Lidiak, E, G., Sexton, J, L. (1986). Techtonic Development of the New Madrid Rift Complex, Mississippi Embayment, North America. (p. 8-11) Amsterdam. Elsevier science publisher, B.V.

New Madrid Fault 1811-1812 Earthquakes (n. d.). Retrieved from http://www.new-madrid.mo.us/index.aspx?nid=102

New Madrid Earthquake and the Farallon Plate. (2007). Retrieved from http://www.science20.com/conscious_matter/new_madrid_earthquake_and_farallon_plate-834