When most people think of devastating earthquake in the US they think of California or the Cascades region. Little or no attention is given to an area known as the New Madrid fault.
But this area has had very large earthquakes in the past, some over 7.0 on the Richter scale. In the 19th century an earthquake originating from the New Madrid fault struck with such force that it made the Mississippi river run backwards for a while.
An earthquake of a similar magnitude today would cause devastation and untold fatalities. Not far from where the epicenter was in that earthquake, rest some of the biggest cities in America.
The New Madrid fault runs from northern Arkansas into southern Illinois and then Kentucky and Tennessee.
Although earthquakes are to date not predictable, some of them recur with uncanny periodicity. That is why the New Madrid falut is so dangerous. Because it has struck with periodicity, and many events in the past are believed to have been of great magnitude.
Anomalies observed recently by instruments placed along the fault are indicating a possible return to seismic activity. The conclusion by the USGS is that the risk is great, and that the occurrence of a large seismic event could be real in the span of the next 0-50 years.
Recent findings of deformations or changes in the mantle underlying the fault zone point to a weakening of the 'structure'. That weakening could very well be the harbinger of a release, the slippage that occurs when stress from a tectonic plate releases the energy stored in decades of friction.
An earthquake of 6.0 or larger is becoming a very real possibility. Geologists have been able to 'view' rocks in the mantle under the fault that are weaker at greater depths, in respect to other seismic zones in the central United States.
In Missouri, in the 19th century, at a time when population density was very low, four major earthquakes shook the Missouri region, some of them believed to be close to 8.0 Richter. But now, not far from the epicenter lies the city of Memphis, and St. Louis not too far afield. Not only do gas pipelines lie in its course, but also nuclear facilities.
What makes the New Madrid fault particularly difficult to manage and predict is the nature of the soil beneath the fault: it is in fact prone to a phenomenon called soil liquefaction, so that any structure above the stricken soil falls through and cannot be supported by the ground, making it especially deadly. Although most structures have been built to code, soil liquefaction cannot be prevented nor remedied.
Source : Al Jazeera/ 1.5.13
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