One of the worst earthquake horrors that ever happened in the United States did not take place in Alaska or California, but occured in the middle of the country around 200 years ago. It was centered where seven states are linked around the Mississippi River Valley today. Seismologists at the United States Geological Survey think they have found evidence that the New Madrid fault line is still very much alive. That is the region in which the earthquake and numerous aftershocks of 1811 to 1812 happened.
However in that era, there were not many people living in the area. Yet for the ones who were, the earthquakes were most likely a terrible experience, stated Susan Hough. She works as a seismologist with the USGS in Pasadena, California. She authored a paper along with a fellow scientist, Morgan Page, which was printed in the most recent issue of the journal Science. Hough explained due to the fact that there were no seismometers at that time in history, scientists were only able to guess at the strength of the quakes. They believe the strongest was at least at a magnitude of seven.
The earthquakes were felt all the way to the East Coast, explained Hough. There were church bells ringing in Charleston, South Carolina and also in Boston. One of the recorded fatalities occured near Louisville, Kentucky, which was actually fairly some distance from the New Madrid zone. The USGS declared that the first of the quakes hit at around 2 a.m. on Dec. 16, 1811. There were then two others that followed on Jan. 23, 1812 and Feb. 7, 1812. Sporadic shaking went on through March of 1812 and aftershocks strong enough to be felt all through the midwest, continued to occur up to the year 1817.
However if a person looks at a map of the region, the New Madrid fault area appears to be an unlikely place for earthquakes because it sets right in the middle of the North American plate. The state of Alaska and the West Coast of the United States, by contrast, are at the edge of techtonic plates, which are more likely to have high seismic action yet the New Madrid fault has had some major quakes in its history. Researchers have geologic proof of numerous major earthquakes of about magnitude seven and eight hitting the zone over the past 5,000 years.
Out of the various quakes, during one, it was reportedly that the Mississippi River actually ran backwards. Earthquake fissures were reported to have gone as long as five miles and even ended up swallowing some people inside in Earth. However there was not a lot of structural damage because the area was sparingly populated at the time.
After that succession of big quakes and aftershocks, in 1843 and 1895 there were also earthquakes with magnitudes of around six and seven that hit. Some scientists believe that this string of quakes were considered to be a long series of aftershocks coming from the original 1811 quake.
In the study that Hough and Page done, they reexamined the information about the earthquakes and compared it to what usually happens after quakes as defined by the Omori Decay Law. That is an established set of equations which forecasts how the rate of aftershocks should decline with time.
Their calculations, instead shown that for all those post 1811/1812 quakes to have been all aftershocks there should have been an average of around 130 earthquakes of magnitude six or higher between 1811 and 2011. There have not been many quakes of that size but there also have not been any earthquakes that massive in the past 100 years so the two authors state that the hypothesis that any current earthquake movement around the New Madrid region is from aftershocks from the 1811/1812 series is a failure.
If they had been aftershocks, the quakes would have been releasing some strain on the fault and lowering the earthquake hazard in the area. Instead, the new research showed that the strain is continuing to increase in the New Madrid zone, and so the earthquake danger continues to stay high.
By Kimberly Ruble