WEST LAFAYETTE, Ind., July 30 (UPI) -- U.S. researchers say a new theory may explain how an earthquake fault in the middle of the continent produces large temblors far from a tectonic plate boundary.
Purdue University researchers say energy that produced 7 to 7.5 magnitude quakes in the 1800s on the 150-mile New Madrid fault system that stretches south from Cairo, Ill., through Missouri, Arkansas and Tennessee came from stresses built up in the Earth's crust long ago, a university release said Friday.
Rapid erosion from the Mississippi River at the end of the last ice age washed away sediment and removed weight pressing down on the Earth's crust, allowing the fault to slip and trigger earthquakes, they suggest.
The theory could explain how the fault generated large earthquakes in the recent past but today show no signs of accumulating the forces needed to produce another earthquake, Purdue Professor Andrew Freed says.
"The only way to reconcile the fact that this part of the continent is not deforming but is producing earthquakes is for the stresses to have built up long ago," Freed said.
"Old geologic processes, such as the opening of the Atlantic and the uplift of the Rocky Mountains, may have squeezed the Midwest," he said.
"The resulting stress remained stored for millions of years until uplift associated with the Mississippi erosion event led to the unclamping of old faults lying beneath."
