By Bud Grimes
If you stand atop Fish Gap Hill in Obion County, Tennessee, a peaceful scene spreads before you. The floodplain sprawls westward toward the Mississippi River, and Reelfoot Lake rests placidly among acres of southwestern Kentucky and northwestern Tennessee farmland. But beneath the surface lies the potential to change all that.
A series of earthquakes in 1811 and 1812 formed Reelfoot Lake and arranged the landscape as we see it today. Could it happen again? Experts agree it’s not so much a question of if it will happen as when.
Preparedness will largely determine how the region fares in a quake’s aftermath, says Dr. Stan Dunagan, a UT Martin earthquake authority. Dunagan (Martin ’93, Knoxville ’98) sometimes takes students to Fish Gap Hill. There he can do more than teach them about earthquakes; he can show them where portions of the bluff gave way under the rolling force of the long ago quakes. Back in his geology classroom, he uses a simple illustration to explain a complex set of actions that lead to earthquakes. It’s like bending a pencil, he says: apply force and the pencil bends. Apply enough force and it will crack.
“Rocks act that way when enough force is placed on them. Just like that pencil will break, the rocks will eventually break,” he says. “And when rocks break, they release energy. That release of energy is an earthquake.”
Quakes occur all the time, whether people feel them or not, Dunagan says. In fact, the New Madrid Seismic Zone, which includes West Tennessee, has the greatest amount of seismic activity and the greatest potential for large quakes in the eastern United States. “Interestingly, East Tennessee is second [the East Tennessee Seismic Zone],” he says. “They don’t have big earthquakes, but they have lots of very small ones, magnitude typically less than 2.0. There are lots of faults in East Tennessee.” The U.S. Geological Survey (USGS, http://www.usgs.gov) recorded 25 earthquakes from March to July 2008 in East Tennessee, a fact that may surprise a lot of people, Dunagan says. Middle Tennessee stands on firmer footing. Based on history and available geologic information, that area is the least likely of the Volunteer State’s three grand divisions to experience a disastrous quake.
West Tennessee, more than any area of the state, faces significant consequences from a large-magnitude temblor. “Geologists view the New Madrid Seismic Zone as one that’s low probability but high consequences,” Dunagan says. “In other words, if there is an earthquake, there’s a chance it could be a big one.”
USGS and the University of Memphis maintain the Center for Earthquake Research and Information at the Memphis campus. The center says the probability of an earthquake measuring 7.7, which is comparable to the 1811–12 quakes that formed Reelfoot Lake, occurring over the next 50 years is 7 to 10 percent.
As for the location of greatest damage if such a quake occurs, Dunagan says, “It depends.” He sketches the shape of the New Madrid Seismic Zone as a crooked S that begins in the Missouri Bootheel and Western Kentucky and winds south to Memphis. The scope of damage would be determined by where the earthquake occurred along the fault, he says. “It’s certainly possible that it would occur along faults that we already have identified, but there may be additional faults that we’re not aware of that it could occur along.
“Memphis is a major concern, because it’s the largest city in this area and because of the important transportation routes that run through it.” Dunagan says Memphis Light, Gas, and Water—in cooperation with the National Science Foundation, the Army Corps of Engineers, and University of Memphis researchers—recently performed surveys along the Mississippi River to locate faults and assess the seismic potential.
But people in major seismic zones aren’t the only ones who should be concerned about major earthquakes. “If there’s a large earthquake, most of West Tennessee will have significant damage,” he says. “There’s lots of soft sandy sediment beneath us. That blesses us with high-quality water resources, but in terms of earthquakes, that’s not where you want to be.”
The important work of monitoring seismic activity is largely coordinated through USGS and several consortiums. UT Martin, which has a seismic station, is part of a network that includes St. Louis University and the University of Memphis center. Another project called EarthScope uses hundreds of GPS and seismic devices across the country to better understand the earth’s structure in a way that might help identify the potential for earthquake hazards. EarthScope plans to move portable instruments into West Tennessee in 2011 and into the rest of the state the following year, Dunagan says.
Predicting and preparing for earthquakes may be the last thing on your mind as you take in the scenery from atop Fish Gap Hill. But this panoramic view of Reelfoot Lake exists only because of what happened when the earth shook in the early 1800s. Stan Dunagan’s advice offers a sobering reminder to be prepared when the earth shakes again.
While history might help identify a pattern that could predict a major quake, Dr. Stan Dunagan advises “not to get bogged down” with such details. “There will be an earthquake one day, and the question is are you prepared when it happens? There are lots of things you can do to get prepared and to mitigate potential losses, whether it’s injuries, loss of life, or property losses.”
Preparing for an earthquake is similar to preparing for other natural disasters such as floods or tornadoes, he says.
- Have a family emergency plan and a communications plan. Practice “drop, cover, and hold on,” identify a safe place in every room of your home (under a sturdy piece of furniture, against an inside wall), and choose an out-of-town family contact.
- Stockpile supplies such as food, water, and medication. Have a battery-powered flashlight and radio and extra batteries.
- Know how to turn off utilities.
- Consider earthquake insurance.
- Secure appliances, bookshelves, and large furniture. “Most injuries are not due to shaking. Most injuries are due to things hitting people and falling on people in an earthquake,” Dunagan says. “Everyone can take an L-bracket and screw it to a piece of furniture and back into the wall.” Gas appliances also should be secured.
If you’re building a new home, you might consider some steps Dunagan and his family took when they built their house near Paris, Tennessee. He had corner bracing added when the house was being framed, as well as some additional horizontal blocking and bracing. He also had the top wooden structure bolted to the basement in multiple places. “The last thing you want, if you have some serious shaking, is one part of your house go one way and the other go the other direction. And if it’s not firmly tied on, that will certainly occur,” he says.