by Elizabeth K. Gardner

The Great Earthquake at New Madrid. A nineteenth-century woodcut from Devens' Our First Century (1877)
A new theory developed at Purdue University may solve the mystery of why the New Madrid fault, which lies in the middle of the continent and not along a tectonic plate boundary, produces large earthquakes such as the ones that shook the eastern United States in 1811 and 1812.
The theory suggests that the energy necessary to produce the magnitude 7-7.5 earthquakes came from stored stress built up in the Earth’s crust long ago. Rapid erosion from the Mississippi River at the end of the last ice age reduced forces that had kept the New Madrid fault from slipping and triggered the temblors.
Eric Calais, the Purdue professor of earth and atmospheric sciences who led the study, said the theory is the first to explain how a fault could have had large earthquakes in the recent past but today show no signs of accumulating the forces needed to produce another earthquake.
“We understand why earthquakes happen at the contact between tectonic plates, like in California, but it has always been a puzzle as to why earthquakes occur in the middle of the continent as well, and with no visible surface deformation,” Calais said. “Our theory links an external climate-driven process, the melting of the ice sheet, and earthquakes.” (more…)


















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