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Sand Muddies Clarity of Quake Predictions

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FAYETTEVILLE - A University of Arkansas researcher and his colleagues believe that a recent study showing a build-up of stress in the New Madrid Seismic Zone is inconclusive. They call for more instrumentation in the region to determine the potential future of earthquake activity in the area.

   Glen Mattioli, professor of geosciences in the J. William Fulbright College of Arts and Sciences, and his colleagues wrote a brief letter that appeared in the journal "Nature." It detailed another interpretation for the results generated by scientists who believe that their research demonstrates a build-up of strain within the New Madrid Seismic Zone. This type of strain typically precedes earthquake events.

   "Our conclusion was that there may be some deformation going on in the New Madrid Seismic Zone, but if there is, it's close to or below the level of detectability," Mattioli said.

   Mattioli and his colleagues drew this conclusion by re-examining the data collected by a research group at the Center of Earthquake Research and Information at University of Memphis using global positioning systems from various stations set up along part of the rift in eastern Arkansas, southern Missouri and western Tennessee. Robert Smalley Jr. and his colleagues have measured tiny movements along the fault and drew their conclusions from these findings.

   However, when Mattioli and his colleagues examined the same data, they arrived at a different conclusion.

   "We didn't see any motion that differed significantly from random motions in the rest of the continent," Mattioli said.

   One thing both researchers agree on: Enhancing the current network of GPS hardware on the ground may help develop a clearer picture of what is occurring in the New Madrid Seismic Zone. And more accurate information could help people who live in the New Madrid Seismic Zone make informed decisions about safe buildings and other structures.

   "This whole thing is a big enigma," Mattioli said. "As far as we know, the reason we get earthquakes is because of applied stress related to the motion of plates."

   But in the nation's heartland, this reason does not apply, and no theory has fully explained why large earthquakes may have occurred there. The Mississippi River basin further complicates regional studies, because the unstable, shifting sand and mud make it difficult to isolate any significant movement from the "noise" surrounding it.

   However, evidence from sand blows and liquefaction seem to show that large earthquakes have shaken the region over time, including the well-documented New Madrid earthquake events of 1811 and 1812, which changed the course of the Mississippi River and were felt as far away as Boston. People who live in cities in the earthquake zone would like to know more about the possibility of future quakes in the region.

   Mattioli, Smalley and Eric Calais of Purdue University have proposed creating a bigger network of GPS stations in the area to obtain high-precision data that will help better determine what is happening in the New Madrid Seismic Zone.

    "In the long run, this may give the U.S. Geological Service a way to assess earthquake hazard in continental interiors where earthquakes and their cycles are not very well understood," Mattioli said.

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