March 13, 2009

New Madrid fault may coming to halt

U.S. scientists say the New Madrid seismologic fault system in the Midwest and South may be in the process of shutting down.

Purdue and Northwestern University researchers have been using global positioning system measurements to determine the earthquake risk to parts of Illinois, Indiana, Tennessee, Arkansas and Kentucky. The fault motion has been much less than expected, Purdue researchers said Friday.

The last major earthquake in the New Madrid seismic zone was in 1812.

Our findings suggest the steady-state model of quasi-cyclical earthquakes that works well for faults at the boundaries of tectonic plates, such as the San Andreas fault, does not apply to the New Madrid fault, lead author Eric Calais, a Purdue professor of earth and atmospheric sciences, said in a release.

Co-author Seth Stein, a professor at Northwestern, said the slower the ground moves, the longer it takes until the next earthquake. If the ground stops moving, the fault could be shutting down, he said.

We can't tell whether the recent cluster of big earthquakes in the New Madrid is coming to an end. But the longer the GPS data keep showing no motion, the more likely it seems, Stein said.

The findings are published in the journal Science.