It’s not a secret that Chattanooga is located in an active seismic zone, but new research suggests this zone has the potential to produce a larger, more devastating earthquake than previously thought.
Dr. Chris Powell, with the Center for Earthquake Research and Information (CERI) and the University of Memphis, addressed the growing seismic concern in the area with a presentation called "The Eastern Tennessee Seismic Zone: Scientific Curiosity or a Hidden Danger?"
Using plate tectonics, seismic hazard maps and tomography—the latter is a sort of CT scan for the earth—Powell compared the Eastern Tennessee Seismic Zone to New Zealand’s Alpine Fault, a right-lateral strike-slip fault that has produced at least seven major earthquakes since 1848.
Thus far, the ETSZ has produced only two “damaging” earthquakes—Knoxville in 1973 and Ft. Payne, Ala., in 2003—both 4.6 magnitude. And according to the U.S. Geological Survey, magnitude 7.5 earthquakes are possible in the zone. New research indicates the ETSZ may be associated with the New York-Alabama Lineament, which suggests the presence of a deeply buried strike-slip fault not unlike the active San Andreas Fault.
CNN reported a 7.1 magnitude earthquake in the Philippines that left 49 people dead on Tuesday, Oct. 15.
But until a large earthquake occurs in the area, the threat of the zone cannot be elevated on seismic hazard maps, which show the potential risk to an area. According to Powell, the ETSZ is known as “The Rodney Dangerfield” of zones because it has not produced a major earthquake and, therefore, “gets no respect.”
Nooga.com sat down with Dr. Powell after the lecture to discuss and assess the potential risk for Chattanooga and why she believes a Shakeout— a city-wide earthquake drill—would be beneficial.
What is the Eastern Tennessee Seismic Zone?
The Eastern Tennessee Seismic Zone is just a cluster, a group of earthquakes. And they happen to be concentrated in one spot. That’s why it’s called a zone. So, they’re deep...way below the mountains; at least two miles down and then deeper. And they form a very distinct band. They’re not just random. They occur in sort of a rectangle. And one side of that rectangle is associated with a very strong magnetic anomaly that we know tells us that there is a feature, like a fault—something you see in our velocity models, for example. That fault forms one side of this zone, which makes us think the zone is there because the feature is a pre-existing weakness in the crust. So, it’s all reactivating there. And that’s why we have the earthquakes.
How new and revelatory is this information?
It’s a few years old. We’ve known for a very long time the zone exists; we’ve known for a very long time that is has characteristics that make it dangerous ... meaning that the earthquakes line up. But the recent discovery, using tomography, is the presence of this distinct change in velocity: low velocity one side and high velocity on the other. That extends down to at least 15 miles below the crust. And that’s brand new. It shows us that the magnetic anomaly really is telling us there is a major fault in the crust. And that fault is forming one side of, one boundary of the seismic zone.
Assess for us the true risk in 2013 of a potential damaging earthquake?
The risk has to be based on what the zone has done previously. So, we would say that based on what has happened previously, the risk is not that high. But, there is so much evidence pointing toward the capability of the zone to produce a damaging earthquake, although we can’t put this risk in a seismic hazard map because it hasn’t produced a damaging earthquake.
Isn’t that frustrating? You see it in sports where the rules don’t change until someone gets seriously hurt…
That’s an excellent analogy. That’s what is going on here. As a scientist, I’m telling you this is a dangerous zone. I’m telling you the risk is pretty high.
Knowing this information, that the risk is high, what can we do as Chattanoogans? Have a Shakeout?
Yes. Do it. I think a full-blown Shakeout here is necessary. And, you know, it’s not just for earthquakes. It’s for anything else that happens. Get prepared. Learn as a community how to help one another because you’re on your own. If something like this happens, you can’t expect help. Have shelters and have the population know where they are. You have a major river here. How do you get across the river with the bridges gone? Have emergency plans in mind. Just plan it. Planning, getting ready, preparing yourselves with emergency food and supplies. That’s about it. Now you can, if you wish, beat on people to adopt stricter building codes ... you might be able to get your new construction built to a stronger code. Retrofitting is prohibitively expensive and you have a beautiful city here filled with chimneys. I don’t know if you can really do much about that.
If someone is reading this and wanting to get involved. What is the best way to do that?
I think what we need to do here is to find out who the appropriate contact people are to get emergency management involved. People who do the building, code issues, politicians involved. It’s a hard sell. I think, frankly, going the building code route is something that’s going to be very hard. The preparedness route is probably your best bet. You know, because then you’re not making people invest in new buildings ... but at least you can be prepared as a community. That’s where I encourage people to contact emergency management personnel and ... get a full-blown shakeout here. This is where we teach our children in schools, if nothing else, what to do during earthquakes.
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