The New Madrid Earthquakes - Research Paper Example

? An investigation into the New Madrid Earthquakes of the 18th century, its effects on the victims involved and the possibilities of recurrence Abstract The New Madrid Earthquake of 1811-1812 was the strongest series of earthquakes ever felt in American history! (essortment.com). It rocked the Mississippi Valley and welcomed devastation into the lives of many. On December 16, 1811, the populous of New Madrid Missouri was shaken dull, from their beds at 2:00 am by a violent earthquake. Huge cracks split the ground and the waters of Mississippi rose up with the characteristics of a great tide. Giant waves rose up and swept north giving the impression it was flowing backwards. Boats along the river were engulfed, capsized and their crew drowned. They were many unusual factors about the New Madrid Earthquake of 1811-1812. The first surprising was their location. They were centered at the southeast corner of Missouri far from the active seismic zones of the mountain chains on the edges of the continents, which are the boundaries of tectonic plates. Secondly, their magnitudes were unusually high; in the range of between 8.1-8.3 on a Richter scale. Thirdly, the pattern was unusual in that there were three shocks of about the same magnitude separated by weeks at a time. As mentioned before, the first one occurred on December 16, 1811, with an 8.2 magnitude at 2:00 am. The second one occurred January 23, 1812 at an undisclosed time with an 8.1 magnitude and the third one occurred February 7, 1812 with the highest recorded magnitude of 8.3 at 3:15 am. The impact of that this disaster had on victims far and near was indescribable and sad to say possibilities of it happening again is a certainty! What is New Madrid Seismic Zone? With reference to cusec.org the New Madrid Seismic Zone (NMSZ) is the most active seismic area in the United States east of the Rocky Mountains. The NMSZ is located in southeastern Missouri, northeastern Arkansas, western Tennessee, western Kentucky and southern Illinois. Southwestern Indiana and northwestern Mississippi are also close enough to receive significant shaking from large earthquakes occurring in the NMSZ. Analysis of the New Madrid Seismic Zone The active faults in the NMSZ are poorly understood because they are not expressed at the ground surface where they can be easily studied. The faults are hidden beneath 100- to 200-foot thick layers of soft river deposited soils called alluvium. Fault scraps and traces in the soft alluvium erode in a very short time or may be rapidly covered by new deposits thereby quickly hiding evidence of earthquake fault lines. Faults in places like California, where rocks are at or near the ground surface, are much easier to study because the faults are readily found, seen, measured and analyzed. (Cited from cusec.org) Knowledge about some of the NMSZ faults is obtained by seismograph recordings of the frequent small earthquakes. St. Louis University, University of Memphis, the U.S. Geological Survey and University of Kentucky operate more than 30 seismograph stations to monitor earthquake activity in the NMSZ and Central U.S. Micro seismic earthquakes (magnitude less than 1.0 to about 2.0), measured by seismographs but not felt by humans, occur on average every other day in the NMSZ (more than 200 per year). The measured locations of micro seismic earthquakes show some trends that have been used to identify active faults in the NMSZ. The trends indicate a four-segment, zig-zag fault system with a total length of about 125 miles stretching from Marked Tree, Arkansas northeastward through Missouri, Tennessee and Kentucky to Cairo, Illinois. In the past 25 years, scientists have learned that strong earthquakes in the central Mississippi Valley are not freak events but have occurred repeatedly in the geologic past.  Earthquakes in the central or eastern United States affect much larger areas than earthquakes of similar magnitude in the western United States.  For example, the San Francisco, California, earthquake of 1906 (magnitude 7.8) was felt 350 miles away in the middle of Nevada, whereas the New Madrid earthquake of December 1811 rang church bells in Boston, Massachusetts, 1,000 miles away.  Differences in geology east and west of the Rocky Mountains cause this strong contrast. In 1811, the central Mississippi Valley was sparsely populated. Today, the region is home to millions of people, including those in the cities of St. Louis, Missouri, and Memphis, Tennessee.  Adding to the danger, most structures in the region were not built to withstand earthquake shaking, as they have been in more seismically active areas like California.  Moreover, most earthquake preparations also have lagged far behind. (Cited from Sjsu.edu) Recognizing these problems,  CUSEC, the Member States, the Federal Emergency Management Agency (FEMA), U.S. Geological Survey (USGS) and other organizations are joining together to take actions that will greatly reduce loss of life and property in future temblors. Analysis of the New Madrid Earthquake The occurrences of the New Madrid Earthquake took place in an era with limited or no technological advances to document or investigate the matter. Fragmented data is available but provides endless possibilities for legends, myths and scientific disbelief to proliferate the event. However, USGS.gov reported that the December 16th earthquake was so severe it awakened people in cities as distant at Pittsburgh, Pennsylvania, and Norfolk, Virginia. This shock inaugurated what must have been the most frightening sequence of earthquakes ever to occur in the United States. Intermittent strong shaking continued through March 1812 and aftershocks strong enough to be felt occurred through the year 1817. The initial earthquake of December 16 was followed by two other principal shocks, one on January 23, 1812, and the other on February 7, 1812. Judging from newspaper accounts of damage to buildings, the February 7 earthquake was the biggest of the three. In the Mississippi and Ohio River valleys the earthquakes did much more than merely awaken sleepers. The scene was one of devastation in an area which is now the southeast part of Missouri, the northeast part of Arkansas, the southwest part of Kentucky, and the northwest part of Tennessee. Reelfoot Lake, in the northwest corner of Tennessee, stands today, as evidence of the strength of these great earthquakes. Stumps of trees killed by the sudden submergence of the ground can still be seen in Reelfoot Lake (Cited from Otto. W. Nuttli, 1974). Uplift of over 3 meters was reported at one locality several hundred kilometers to the southwest of the epicentral zone where a lake formed by the St. Francis River had its water replaced by sand. Numerous dead fish were found in the former lake bottom. Large fissures, so wide that they could not be crossed on horseback, were formed in the soft alluvial ground. The earthquake made previously rich prairie land unfit for farming because of deep fissures, land subsidence which converted good fields to swamps, and numerous sand blows which covered the ground with sand and mud. The heavy damage inflicted on the land by these earthquakes led Congress to pass in 1815 the first disaster relief act providing the landowners of ravaged ground with an equal amount of land in unaffected regions. Nuttli also reported that some of the most dramatic effects of the earthquakes occurred along rivers. Entire islands disappeared, banks caved into the rivers, and fissures opened and closed in the river beds. Water spouting from these fissures produced large waves in the river. New sections of river channel were formed and old channels cut off. Many boats were capsized and an unknown number of people were drowned. There are some graphic eyewitness descriptions in contemporary newspapers made by the boatmen caught on the Mississippi River near Little Prairie, not far from the present-day town of Caruthersville, Missouri. Although the total number of deaths resulting from the earthquakes is unknown, the toll probably was not large because the area was sparsely populated and because the log cabin type construction that was prevalent at that time withstood the shaking very well. Masonry and stone structures did not fare so well, however, and damage to them was reported at distances of 250 kilometers and more. Chimneys were thrown down in Louisville, Kentucky, about 400 kilometers from the epicentral area, and were damaged at distances of 600 kilometers. The felt areas of the three largest earthquakes were extremely large. They extended south to the gulf coast, southeast to the Atlantic coast, and northeast to Quebec, Canada. The western boundary cannot be established owing to a lack of population. However, it can be estimated that the area of intensity V or greater effects was approximately 2? million square kilometers. This can be contrasted with the 1906 San Francisco earthquake, for which the area of intensity V or greater effects was about 150,000 square kilometers. The large difference in felt areas between the Mississippi Valley and San Francisco earthquakes, which had approximately the same magnitude and focal depth, can be explained by differences in attenuation of earthquake waves traveling through the Earth's outer crust. The crust in the Western United States tends to ``soak up'' earthquake energy, whereas in the central and eastern regions of the country the seismic energy experiences a much lower rate of absorption. Quantitative studies of recent earthquakes confirm this explanation. Can such earthquake occur again? The answer to whether such earthquakes can happen again is yes. Field studies by M. L. Fuller of the United States Geological Survey published in 1912 provided topographic and geological evidence of large magnitude earthquakes predating the 1811-12 sequence. This evidence included ground cracks as large as any caused by the 1811-12 earthquakes in which trees fully 200 years old grew from the bottoms and slopes. Indications of more recent faults and of sandstone dikes filling old earthquake cracks were also found by Fuller. Furthermore, studies of the seismicity since 1812 show that the region is behaving in a manner more or less typical of active seismic zones. However, to predict when it is going to happen is uncertain at this time. Extrapolation of magnitude and intensity recurrence curves is presently the only method of prediction available, but this is full of difficulties because the earthquake record covers far too brief a period of time and because earthquakes do not follow an exact cyclical pattern. Although extrapolations of recurrence curves for the region indicate return periods -- depending on the investigator -- of anywhere between about 400 to 1,000 years for an earthquake the size of the December 16, 1811 event, there is a possibility that such an earthquake might occur as soon as next year or as late as several thousand years hence. It is easier to speculate on the effects that an earthquake the size of the 1811-12 series would have if it were to occur today than it is to predict when it will happen. In the epicentral area, a repeat of the kind of surficial damage experienced in 1811-12 can be expected. However, this would result in a much greater loss of life and property today because of the much larger number of people and man-made structures in the region than were there 162 years ago. Even more awesome is the size of the area that would be affected. The dispersion of the surface waves, combined with their low attenuation, would result in a large amplitude, long duration sinusoidal type of motion with periods in the same range as the natural periods of tall buildings. Although damage to buildings located outside of the immediate earthquake zone would be mostly nonstructural in character, the monetary amount should be expected to be very large. The emotional and psychological effects of a large earthquake in the central part of the country would probably also be considerable, particularly if the earthquake had a long aftershock pattern as the 1811-12 sequence did. Perhaps the greatest danger of all arises from the sense of complacency, or perhaps total ignorance, about the potential threat of a large earthquake. The frequency of occurrence of earthquakes the size of those that took place in 1811-12 is very low; however, continuing minor to moderate seismic activity in the central Mississippi Valley area is an indication that a large magnitude tremor can someday be expected there again. Works Cited CUSEC, New Madrid Seismic Zone, (2011), retrieved from: http://www.cusec.org/earthquake-information/new-madrid-seismic-zone.html Essortment.com, New Madrid Earthquake of 1811, (2010), retrieved from: http://www.essortment.com/new-madrid-earthquake-1811-60985.html Nuttli, Otto, W., Earthquake Information Bulletin Vol.6 no. 2, (Mar-Apr 1974), San Jose State University, New Madrid Earthquakes, (2011), retrieved from: http://www.sjsu.edu/faculty/watkins/newmadrid.htm USGS.com, New Madrid Earthquakes of 1811-1812, (2011), retrieved from: http://earthquake.usgs.gov/earthquakes/states/events/1811-1812.php Read More