Geologists found in the Eastern United States the most powerful traces of ancient earthquakes

© Illustration RIA Novosti . Alina Planinarska on the territory of the States of Tennessee and AlabamaGeologists found in the Eastern United States the most powerful traces of ancient earthquakes© Illustration RIA Novosti . Alina Polyanina

. The rift on the border of the States of Tennessee and Alabama, considered the early source of weak earthquakes was one of the most seismically restless points in North America in the last 25 thousand years, say scientists in an article published in the journal Bulletin of the Seismological Society of America.

«It is possible that a massive earthquake here occurred only at the end of the ice age, and that they stopped will no longer occur. While we have insufficient data to make such statements — it is possible that occasional episodes of geological activity will occur here in the future for other reasons,» said Randall Cox (Randel Cox) from the University of Memphis (USA).

This fault, located at the southern spurs of the Appalachian mountains, is today one of the most active centers of seismic activity on the territory of Eastern United States. Here periodically there are relatively weak earthquake, whose strength never exceeded a magnitude of 4.8 points on a scale of MMS. In other words, these stimuli will always remain invisible to the inhabitants of the cities of Tennessee and Alabama, are located near this area.

Cox and his colleagues accidentally discovered that it was not always so, and that the region in the relatively recent past was one of the most hectic parts of North America, studying the traces of an unusual «landslide» on the bottom and banks of the artificial lake, Douglas in the North-East of Tennessee.

This reservoir, created by the state authorities during the Second world war for the construction of HPPs, shallow and almost completely dries up during the winter, which allows scientists to study the geological history of the Appalachians and the entire Eastern United States without arranging to do this large-scale excavations.

Studying these cracks, the scientists came to the conclusion that it was not created landslide, a powerful earthquake, according to the age of the surrounding rocks, about 15 and 25 thousand years ago. The power of these tremors, according to the calculations of geologists, was about 6 or 7 points on a scale of MMS. It is comparable in strength with the earthquake in Los Angeles in 1994, or the earthquake in Spitak in 1988, that caused widespread destruction and death of thousands of people.

How could these earthquakes? Scientists believe that they could be associated with the processes that occur inside the earth’s crust after the retreat of the glaciers to the North and a gradual rise in North America, flattened with a shield of ice during the glaciation. This process has not been completed until now and therefore scientists do not exclude that in the future, these tremors may recur.

Why is it important? As noted by Cox, in the vicinity of the fault built several nuclear power plants and hydroelectric dams, which can fail if they are not prepared for powerful aftershocks. Therefore, scientists will continue to study the lake bottom in search of other traces of ancient earthquakes, and plan to start looking for traces of them in other regions of the fault.

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