Our seismic zone is active, but tremors have been weak
Dude, Where’s My Greenway?
Where the sidewalk ends in Turkey Creek
Wednesday, May 24
For those who saw the pullout map, it’s not as bad as it looks, according to geologists and engineers who’ve appraised the seismology of this region over the years. The eye-catching map, entitled “Danger Zones” and employing color shadings to depict earthquake risk around the world, showed the East Tennessee Seismic Zone as riskier than Russia’s Kamchatka Peninsula, which sustained a quake measured at 7 on the magnitude scale shortly after the map was published. Such a quake could cause near-catastrophic damage around here.
But there hasn’t been such a quake in East Tennessee in recorded time, and one isn’t likely, according to Pete Lemiszki, the state geologist based in Knoxville.
The map had to be interpreted in terms of the risk to people and infrastructure from a major quake. Our region is much more densely populated and built-up than the easternmost Russian peninsula. The ETSZ, which roughly centers on the Appalachian Trail and follows the mountains for about 300 kilometers from the Virginia and Kentucky borders into a bit of northern Georgia and a corner of northeast Alabama, has a lot of small tremors, but has never experienced one measured at magnitude 6. The strongest quakes in the zone, which is roughly 50 kilometers wide and includes Knoxville, have been in the high 4 range since accurate measurements became possible in the late 1800s. Most of the quakes that can be felt around here are in the 3s, says Lemiszki.
Since the scale is logarithmic, each increasing number represents a 10-fold release of energy at hypocenter, the underground point where the earth shift originates.
The undersea quake that caused the devastating South Asian Tsunami in 2004 was a 9. That’s stronger than the quakes that have caused widespread damage on the U.S. West Coast over the years or the calamitous Alaska quake of the 1960s, or even the estimated magnitude of the celebrated New Madrid quake when the earth’s undulations changed the course of the Mississippi River along Tennessee’s western border in 1811-12. The Indonesian tremor that killed thousands last week measured less than 6.5, but it happened in a highly populated, vulnerable area.
The strongest quake recorded in the ETSZ in this century was in the high 4 range at Fort Payne, Ala., southwest of Chattanooga, in April, 2003. It shook buildings and cracked foundations near its epicenter, the point on the surface directly above the hypocenter, but caused no injuries. Quakes of slightly lesser magnitude have been measured in the Maryville-Alcoa area south of Knoxville in 1973 and in Western North Carolina in the mid-’90s. They, like the many smaller quakes experienced annually in this zone, were felt in and around Knoxville but damage was minimal, even near their epicenters.
The reason that quakes are felt over a very wide area around the ETSZ is that the hardness of the crust transmits the energy flow much farther than do softer, more easily fractured formations elsewhere, says Bill Doll, a geophysics research specialist who has studied seismic activity in this region for Oak Ridge national Laboratory. The ETSZ quakes also occur deep below the surface, from five to 25 kilometers down, with most in the 10- to 12-kilometer depth range, according to Lemiszki’s records.
The Fort Payne quake was felt in 12 states, though damage was restricted to a radius of a few kilometers from the epicenter. And Knoxville has often experienced shaking sensations from even mild tremors in the Carolinas and Virginia, Kentucky and Georgia.
Doll says geologists don’t know much about the fault or faults lying deep beneath the ETSZ. “It’s an area of higher uncertainty,” he says, but the fact that no major quakes have occurred around here in modern times means that no catastrophic tremors seem likely in the near future. Lemiszki points out that the latest report from the U.S. Geological Survey offices says quakes of up to magnitude 7.5 could occur in the ETSZ “infrequently.” He acknowledges that infrequently is a vague term, but to a geologist, it could mean every 500 years or so.
The East Tennessee faults near the surface are termed inactive or “dead” by such authorities as Robert Hatcher, professor of geology and tectonics at UT, but that doesn’t mean they can’t come to life. Though there are no plate shifts going on here like there are on the West Coast, there is some activity in the underground rock formations. The geological establishment concludes that the data is too “young” in terms of measured activity and the bedrock is too hard and deep to show all the telltale signs of its ancient upheavals.
Hatcher, like other students of the region’s seismicity, says it’s not possible to predict whether a major quake might occur here. There are no known predictors in the data that’s been collected so far.
“We just don’t know,” Hatcher says.
Dude, Where’s My Greenway?
“The greenway’s such a super-asset,” he continues, “one that’s going to get so much better as we continue to transcend into having the entire area built out. We’re excited about the future.”
Ross is the founding member of Tennessee’s Izaac Walton League (IWL), the current manager of the greenway and the adjacent wetland. He says that the IWL works quietly with developers, contractors, the city and even the EPA to address conservation problems.
“It’s evolving into a better wetland all the time,” says Mark Campen of the IWL. “Looking back at photos from the ’60s and ’70s, there was a lot more dry land then.”
True, it’s not uncommon for passersby to see muskrats and even beavers during a leisurely walk along the Turkey Creek greenway. Ross recalls the story of a man from Alabama: “He said, ‘I saw my first beaver here.’ And he said, ‘Imagine, all these years wanting to see a beaver, and I see one right here inside a major development.’”
Back in 1995, before it was filled with retail, restaurants and office parks, the area was farmland, a vast, empty space of foliage and one of the region’s largest wetlands. Kerry Sprouse, John Turley and Jim Nixon, the makeup of Turkey Creek Land Partners (TCLP), saw something different; they saw possibility.
The partners proposed a 2.5-mile road extension through the property, to continue Parkside Drive and connect with Campbell Station Road. The city then allocated $4.1 million to build the road, sewers and any other necessary utilities.
“That was one of the commitments from the beginning, to build a greenway,” says Will Skelton, who was the chair of the city’s greenway commission back in ’95. “The city spent a lot of money on infrastructure for the developer. This is one of the things the developer was doing to make up for that, I guess.”
TCLP had agreed to turn the greenway over to the city upon completion, but no easement was ever placed on the entire stretch of land. “It’s been a problem,” Skelton continues, “the easement wasn’t properly documented. When they develop something adjacent to it, they close it down. They don’t seem to pay too much attention to the users of the greenway when they want to build something next door to it.... I’m hoping that the developers will do what they said they would do, and turn over a properly constructed greenway with adequate legal easements.”
Now, if the TCLP still plans to turn the greenway over to the city, they have to get individual easements from all of the businesses that have built nearby. (TCLP could not be reached for comment by press time.)
“Instead of putting the easement on the entire greenway,” Campen says, “it was chopped up in parcels.”
But Ross does not see the current legal debacle as a terrible inconvenience. “When the [greenway] is turned over to the public, when your tax dollars will have to pay for it, it’ll meet the standards that a greenway needs to meet. If the city doesn’t have this as part of their greenway system, then they shouldn’t be required to pay for maintenance on it. Right now, it just doesn’t meet the standard.”
Ross argues that the easiest thing for the developers would have been to not build a greenway until all the commercial projects were finished. “But,” he says, “they knew that when people came to shop, while this area was developing, that there’re all kinds of groovy things to see out here [in the wetland and surrounding environs]. They just said, ‘We’ll foot the bills until we are ready for the transition of a first-class thoroughfare.’”
The only question that remains is, of course, when will that be?
“I do not know why the greenway has not yet been turned over to the city,” former mayor Victor Ashe writes, via email. “I do not have the documents in front of me here in Poland, and it has been 11 years since I dealt with the issue. Therefore my recollection of the details is not fresh.”
There is one thing that everyone agrees on: 11 years is a long time, long enough for the details of a huge, multi-million dollar development to become foggy.
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