The New Madrid fault system
Introduction
The New Madrid fault system, describes a huge unstable zone largely viewed as the source of earthquakes that take place in the interior of a tectonic plate. The aforementioned fault line, is held responsible for the historically 1811-1812 earthquakes which were unofficially referred to as the earthquakes of New Madrid. The resultant earthquakes, historically termed as the most calamitous earthquakes are known to have hit parts of The Mid Western and Southern parts United States gradually seeing their way into the South Western parts of the United States shifting from New Madrid. Scientists have closely studied the occurrence of past earth quakes evaluating motions taking place on the ground, in an attempt to predict the possibility of earth quakes of the same or greater magnitude taking place in the near future.
Most predictions as to the likelihood of when the next new Madrid fault will take place are generally based on the number of times huge earthquakes are experienced within the zonal area of new Madrid. Research findings present the possibility of the New Madrid fault zone coming up again in the near future, with reports on the occurrence of massive earthquakes that have agitated the core regions of the United States from the year 2001 to 2011. Blame on massive earthquakes is laid on drilling and mining activities which are the most common human activities within the affected regions. A number of scientists have predicted numerous earthquakes within a period of every 200 years which from a geographical perspective support the likelihood of the new Madrid fault coming up again (David Stewart ,103).
1811-1812 Resultant earthquakes of the new Madrid fault line.
A series of three to five major earthquakes believed to have been magnitude 7.0 or larger earthquakes occurred in the New Madrid Seismic Zone in the two month period between Dec. 16, 1811 and Feb. 7, 1812. Several thousand additional “smaller” earthquakes occurred during the three month period from Dec. 16, 1811 to March 16, 1812. These included 15 earthquakes believed to have been magnitude 6.5 to 8.0 and 189 earthquakes magnitude 5.0 to 6.5. Two thousand were felt by people, indicated by crude seismograph instruments and recorded in personal journals at Louisville, Kentucky and Cincinnati, Ohio, which are respectively 250 and 350 miles away.
The first principal earthquake, M7.7, occurred at about 2:15 am (local time) in northeast Arkansas on December 16, 1811. The second principal shock, M7.5, occurred in Missouri on January 23, 1812, and the third, M7.7, on February 7, 1812, along the Reelfoot fault in Missouri and Tennessee. The earthquake ground shaking was not limited to these principal main shocks, as there is evidence for a fairly robust aftershock sequence. The first and largest aftershock occurred on December 16, 1811 at about 7:15 am. At least three other large aftershocks are inferred from historical accounts on December 16 and 17. These three events are believed to range between M6.0 and 6.5 in size and to be located in Arkansas and Missouri. This would make a total of seven earthquakes of magnitude M6.0-7.7 occurring in the period December 16, 1811 through February 7, 1812. In total, Otto Nuttli reported more than 200 moderate to large aftershocks in the New Madrid region between December 16, 1811, and March 15, 1812: ten of these were greater than about 6.0; about one hundred were between M5.0 and 5.9; and eighty-nine were in the four range magnitude. Nuttli also noted that about eighteen hundred earthquakes of about M3.0 to 4.0 during the same period.
The first earthquake of December 16, 1811 caused only slight damage to man-made structures, mainly because of the sparse population in the epicentral area. The extent of the area that experienced damaging earth motion that produced Modified Mercalli (Intensity greater than or equal to VII) was estimated to be 600,000 square kilometers. However, shaking strong enough to alarm the general population (intensity greater than or equal to V) occurred over an area of 2.5 million square kilometers.
Due to the harder, colder, drier and less fractured nature of the rocks in the earth’s crust in the central United States, earthquakes in this region usually shake and damage an area approximately twenty times larger than earthquakes in California and most other active seismic areas.
The frequency of large earthquakes in the New Madrid Seismic Zone is still being debated. Several methods have been used to make estimates. Paleoseismology techniques are used to recognize evidence of large prehistoric earthquakes preserved in geologic materials (soil and rock). From the approximate locations, dates and magnitudes the long term average recurrence interval can be calculated. Currently, paleoseismologists infer two or more seven magnitude or larger, large earthquakes have occurred in the last 2,000 years or less giving recurrence interval estimates of 300 to 1,000 years for the large quakes. Probability models extrapolate the approximate 200 years of recorded history or 100 years of instrumental recordings to estimate frequency.
The New Madrid Seismic Zone appears to be about 30 years overdue for a magnitude 6.3 quake because the last quake of this size had occurred 100 hundred years ago at Charleston, Missouri, on Oct. 31, 1895 and had a magnitude 6.7. A magnitude 6.3 quake near Lepanto, Arkansas, on Jan. 5, 1843, was the next prior earthquake of this magnitude. About 75 percent of the estimated recurrence time for a magnitude 7.6 earthquake has elapsed since the last quake of this size occurred in 1812.
The resultant damage
The earthquakes caused the ground to rise and fall – bending and uprooting trees, and opening deep cracks in the ground. Deep seated landslides occurred along the steeper bluffs and hill slides resulting in large areas of land being uplifted permanently. Still, larger areas sank and were covered with water that erupted through fissures or crater lets. Huge waves also known as seiches, on the Mississippi River overwhelmed many boats and washed others high onto the shore. High banks caved and collapsed into the river and sand bars, and points of islands gave way. During this period whole islands disappeared. However, Surface fault rupturing from these earthquakes has not been detected and was not reported to date. The region most seriously affected was characterized by raised or sunken lands, fissures, sinks, sand blows, and large landslides that covered an area of 78,000 - 129,000 square kilometers, extending from Cairo, Illinois, to Memphis, Tennessee, and from Crowley's Ridge in northeastern Arkansas to Chickasaw Bluffs, Tennessee.
The 1811-1812 New Madrid earthquakes destroyed most or all of the simple buildings in New Madrid and Little Prairie (Caruthersville), the only two towns in the area at the time. The simple, single story log buildings were in fact a very earthquake resistant type of construction. About 5,500 square miles or about 3.5 million acres was also damaged or destroyed by landslides, fissures, sand blows, lateral spreads, subsidence, submergence and uplift. Much of this land became unusable for the subsistence type agriculture of that day. Buildings in St. Louis, 150 miles or more to the north, were slightly damaged. The damage mostly consisted of broken or collapsed stone chimneys and broken stone buildings, a type of unreinforced masonry construction that is especially susceptible to earthquake damage.
