Wednesday, September 28News That Matters

Rivers can cause earthquakes, geologists claim

Dec. 21 (UPI) — New research suggests river erosions can explain the pattern of earthquakes faraway from plate boundaries, like the 4.4 magnitude quake that shook Eastern Tennessee last week.

Geologists Ryan Thigpen and Sean Gallen designed a model to simulate how the removal of 500 feet of rock influences crust behavior in the Tennessee Valley. The model’s results match the pattern of earthquakes in the region over the last century.

“We’re taught in introductory geology that the vast majority of earthquakes occur at plate tectonic boundaries, such as in Japan and along the San Andreas fault zone,” Thigpen, an assistant professor at the University of Kentucky, said in a news release.

But the traditional earthquake mechanisms can’t explain the rumbles among seismic zones of East Tennessee and New Madrid, a town near St. Louis. As such, Thigpen and his colleague Gallen, assistant professor at Colorado State University, looked for unexpected mechanisms unique to the geology of East Tennessee and New Madrid.

“Previously, geologists have speculated about some of the driving mechanisms behind the seismicity but new and sometimes radical ideas are now allowing us to consider this from an entirely new perspective,” Thigpen said.

As Scientific American reported, an intraplate earthquake requires three ingredients: faults or weaknesses in the crust; an accumulation of stress in those faults; and a mechanism to increase the stress beyond the fault’s ability to stabilize tension.

If earthquakes only required the first two ingredients, the entire East Coast and the many faults created by the creation of the Appalachians would host a regular pattern of earthquakes. But that’s not what the seismic record shows. Instead, earthquakes on the East Coast are more concentrated in certain seismic zones.

Thigpen and Gallen’s model showed earthquakes in East Tennessee are more likely to occur near places where large amounts of sediment have been swept away by rivers, which suggests the loss of rock influences the stability of the crust. Lighter portions of crust can more easily slide along a fault line.

The mechanism that explains the pattern of earthquakes experienced in East Tennessee — detailed this week in the journal Geophysical Research Letters — could explain earthquake patterns in other seismic zones.

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