Sand Signs Could Predict Future of Earthquakes in Tennessee

July 28, 2009

Floating down Tennessee’s Sequatchie River, graduate student Chris Howard and geology researcher Steve Obermeier are looking for sand blows — signs of ancient earthquakes, indicators of the big one.

During two days of paddling this month, they didn’t find much.

“That would suggest at least at this point that there haven’t been any major quakes in the Sequatchie Valley within the last 10,000 or 20,000 years,” Howard said. “We saw quite a wide range of ages of sediment, and we didn’t see any evidence of a strong earthquake in any of it. Which is good for the people who live here, I guess.”

But they still have lots of flood plains to cover. Howard and Obermeier are doing earthquake field research for Dr. Bob Hatcher, designer of a new study intended to help the Nuclear Regulatory Commission understand the frequency and pattern of large quakes.

The $129,000 study is timely, with “a number of applicants” wanting to put nuclear power plants in the region, according to NRC geoscientist Dr. Gerry Stirewalt.

Most people don’t know it, but East Tennessee is the heart of the second-most-active quake zone in the eastern portion of the nation.

The East Tennessee Seismic Zone is a 30-mile wide swath of folded land that stretches 185 miles up the Tennessee mountain ranges from Alabama to Virginia and runs right through the Chattanooga and tri-state area.

Seismographic records show that, east of the Rockies, the land from Northwest Georgia through most of East Tennessee is shakier than everything except the New Madrid Seismic Zone, which runs from Memphis to Missouri.

Despite a whole lot of shaking — mostly in tiny quakes that almost no one can feel — the Appalachian tremors are the least studied, Hatcher said. He is a Distinguished Scientist in Earth and Planetary Sciences at the University of Tennessee in Knoxville.

The mountain quakes are so deep they haven’t caused much surface damage or fear, Hatcher said. They haven’t stirred much research funding interest, either.

“Basically nothing bad has happened yet,” he said.

Generally earthquakes at or below 3.0 in magnitude have little human impact.

But quake researchers such as Hatcher believe the East Tennessee Seismic Zone has seen some big ones. If they can find geologic evidence, they can learn more about the region’s ancient quake size and frequency.

That could allow them to project future quake potential.

“We still don’t know the capability of the maximum-size earthquake that the East Tennessee Seismic Zone could produce,” Hatcher said. “We have estimates, but they are just guesses because we have no data to go from.”

So Howard and Obermeier are paddling low-flowing rivers looking at exposed rock shelves. They’re searching for signs of what once was sand shaken hard enough to liquefy and be squeezed in a flow to the surface.

In the fall, Howard said he and Obermeier will be looking on rivers in North Georgia. Another research crew will be on the Chickamauga Reservoir portion of the Tennessee River in coming months.

If they find a sand flow — also called a liquefaction feature — they will have a clue frozen in time just as fossils were.

Obermeier said he hopes also to talk to local archaeologists and cavers.

“They might have seen these features and just not know what they are. They can point us to them,” he said.

Hatcher describes what’s left of the bygone quakes as a “mantle of sand (now stone) on the ground’s surface — usually white sand.

“It’s pretty obvious when you see it,” he said.

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