You have learnt about earthquakes right? Any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks, earthquakes mostly occur when masses of rock suddenly fracture and slip when straining against one another.
Even though about 50,000 earthquakes that can be noticed without instruments happen around the world annually, it is about 100 of these that cause a lot of damage. The strongest of these happen about once a year on average and it is these that are often remembered even years later. The New Madrid earthquakes is one such series of earthquakes that is remembered even now, over 200 years after it took place.
Three large earthquakes
A series of earthquakes that occurred near New Madrid, Missouri, U.S. between December 1811 and February 1812, it included three large earthquakes and several other tremors through the months. Even though it has been agreed upon that the number of lives lost was not great as the region was sparsely populated, there is no denying the fact that it caused widespread damage and disrupted lives.
The first of these three major earthquakes began at about 2.15 a.m. on December 16, 1811 and was followed by at least three major aftershocks in the following 48 hours. The magnitude of this event is believed to be in the range of 6.7-8.1 and despite its strength, it only caused minor damages to man-made structures.
Felt far and wide
The second major earthquake in this series, the smallest of the three, took place on January 23, 1812 with an estimated magnitude of 6.8-7.8. The third of the principal earthquakes took place on February 7, 1812 with a magnitude of about 7.0-8.8.
Tremors during these earthquakes were felt far and wide with eyewitness accounts stating that bells were shaking as far away as Boston. While the number of lives lost through the New Madrid earthquakes is put at below 1,000, there was large-scale damage to the landscape.
Mississippi runs backwards
Lands sunk or were lifted and there were many landslides to go with it as well. The third earthquake, which matched or even exceeded the first in strength, caused a so-called fluvial tsunami in the Mississippi River, forcing it to run backwards for hours.
While most earthquakes take place along the major fault lines of the world that are located at the edges of the tectonic plates making up the Earth’s crust, that isn’t the case with the New Madrid earthquakes. The New Madrid Seismic Zone (NMSZ) lies far from a tectonic plate boundary, but has seen a number of major earthquakes, including events dated around 2350 BC, 900 AD and 1450 AD, apart from the one which took place in 1811-12.
A number of theories
Researchers and scientists studying the event have hypothesised a number of possible reasons that could have led to it. These range from fault movements due to mantle flow and an underground hot-spot to fault movements caused by continued stress on the region owing either to continental drift or the glacial retreat.
While understanding the reasons that lead to such drastic events remains a huge priority, equally important is to prepare or thwart a modern earthquake risk in the same region. What with the growth of modern cities and towns in the region going hand-in-hand with an increased population density, the losses in terms of lives and property for an earthquake like in 1811-12 is unimaginable.
The U.S. Geological Survey predicted that there is a 7-10% chance for a repeat of the 1811-12 disaster in NMSZ in the 50 years following 2003. That number rises to 25-40% for an earthquake of magnitude 6.0 in NMSZ in the 50 years from 2003 – weaker than the New Madrid earthquakes but bound to be devastating. These numbers instill fear in us. But they also enable us to prepare for the worst.
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Recent seismic activity in the NMSZ
This map shows the New Madrid Seismic Zone activity from the years 1974-2011.
Primarily located in Arkansas, Missouri and Tennessee in the central United States, the map shows over six thousand tremors that took place during this period.
Most of the tremors indicated in this map, however, were below the threshold of human sensitivity.
