Earthquakes in Knoxville? How often they occur in East Tennessee and why | Know Your Knox
Have you ever felt a rumble underneath your feet and wondered, “What was that?” Was it caused by ecstatic Vols fans at Neyland Stadium or did the earth really quake?
Both things are entirely possible in Knoxville. Forty-two earthquakes occurred in East Tennessee between the beginning of 2023 and Dec. 7, including four near Knoxville, according to the U.S. Geological Survey earthquake database. The quakes ranged from 1.4 to 2.8 in magnitude.
These are categorized as “weak” or “light” earthquakes by USGS and most go unfelt by people. But Knoxville sits in one of the most active earthquake areas in the Southeast: the East Tennessee Seismic Zone.
“You guys are in earthquake country, you're in tornado country. And we always tell people when they feel an earthquake, think of that as a wake-up call,” USGS geophysicist Thomas Pratt told Knox News.
“Given the amount of seismicity out there, you wouldn't be surprised, at any time, that you get a magnitude 4 to 5 earthquake,” he added.
A magnitude 4 can often be felt 60 miles from where it occurred. Moderate quakes begin with magnitude 5.
East Tennessee has up to a 36% chance of experiencing a quake that causes at least slight damage within the next 100 years. That chance increases up to 74% for the far west region of the state.
What does magnitude measure?
The Richter scale so many people associate with earthquakes isn't really used anymore. Instead, geologists use seismometers to measure ground motion and grade that on a magnitude scale.
The AP Stylebook, a trove of information for journalists, describes magnitude simply and provides a handy link to the USGS earthquake calculator.
"When comparing quakes, every increase of one number means that the quake is 10 times bigger and releases 32 times more energy. For example, a magnitude 7 quake shakes 10 times as hard and is 32 times stronger than a magnitude 6 quake. To determine the difference in size and strength, use the U.S. Geological Survey’s calculator: earthquake.usgs.gov/education/calculator.php."
The strongest earthquakes in East Tennessee
The East Tennessee Seismic Zone extends across Tennessee, northwestern Georgia and into northeastern Alabama. The area is not known to have major earthquake, but hundreds of earthquakes too small to be felt have been recorded in recent decades.
A 4.7 magnitude tremor shook Alcoa in November 1973, and a magnitude 4.4 magnitude occurred in Decatur, Tennessee back in 2018.
Top 10 largest East Tennessee earthquakes (since 1900)
4.7 magnitude – Alcoa (1973)
4.5 magnitude – Greenville (1928)
4.4 magnitude – Decatur (2018)
4.2 magnitude – Vonore (1987)
4.1 magnitude – Luttrell (1913)
4.1 magnitude – New Tazewell (1956)
3.8 magnitude – Tazewell (1997)
3.8 magnitude – Fincastle (2020)
3.7 magnitude – Ducktown (1979)
3.7 magnitude – Tellico Plains (1995)
Tennessee is in two seismic zones: the East Tennessee zone and the New Madrid zone. There had been 191 earthquakes in Tennessee in 2023 as of Dec. 15, according to USGS data. Thirteen of those were 2.5 magnitude or higher.
How well do you Know Your Knox? We answer the questions you really want to know
Why are there earthquakes in East Tennessee?
The ground shakes when there is a sudden slip on a fault. The sudden slip releases energy in waves that travel through the earth's crust, according to USGS.
Some fault systems, like San Andreas in California, have been well-studied and can help determine what specific fault caused an earthquake. But that’s not the case in East Tennessee.
“(The East Tennessee Seismic Zone is) a seismic zone we know the least about … and yet it's one of the largest ones in the Eastern U.S.,” Pratt said. “So, it's a concern because it's long enough that it could have a pretty good size earthquake on it if the whole thing ruptures.”
Earthquakes in East Tennessee often occur so far underground (as far as 20 miles deep in recent cases) that it's extremely difficult to study the fault system and determine patterns. Some of the recorded quakes don’t reach the surface.
“The best guide to earthquake hazards in (this specific) seismic zone is the earthquakes themselves,” USGS stated in a summary of the 2018 Decatur tremor.
Pratt also noted that faults tend to be in valleys where rocks erode more easily. But when the Tennessee Valley Authority intentionally flooded parts of the valley in the early 20th century, that made it difficult to study those areas.
“So it could be that there's evidence for earthquakes down in some of those valleys, but they were flooded in the 1930s and '40s and so we will never know,” Pratt said.
Earthquakes in the Eastern U.S. can be felt at greater distances than those that occur in the west, USGS states. The Decatur quake was felt over a 310-mile span.
Is 'the big one' coming to East Tennessee?
Although the East Tennessee Seismic Zone is very active, our region is not known to have earthquakes that cause significant destruction. The region has been steady and stable, Pratt said. Largely unfelt tremors regularly occur and quakes in the magnitude 4 range happen once or twice a year.
Pratt did say, however, magnitude 6 quakes are possible in Eastern states, but they typically occur only once every 2,000 to 3,000 years.
Pratt advises people to stock up on emergency supplies. Recommended supplies include water for several days, nonperishable food, flashlights, a battery-powered radio, first aid kit and a whistle to signal for help, according to the Tennessee Emergency Management Agency.
Other tips for earthquake preparedness include securing items that could topple over or fall, having an emergency plan and a place to meet if your family is separated and considering an earthquake insurance policy, which can lessen financial burdens in the aftermath of an earthquake.
Traditional homeowners and business insurance policies do not cover earthquake damage, according to the Tennessee Department of Commerce and Insurance. But earthquake insurance is available to purchase in Tennessee from licensed insurance producers.
Know Your Knox answers your burning questions about life in Knoxville. Want your question answered? Email knowyourknox@knoxnews.com.
Devarrick Turner is a trending news reporter. Email devarrick.turner@knoxnews.com. On X, formerly known as Twitter @dturner1208.
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This article originally appeared on Knoxville News Sentinel: Has Knoxville ever had an earthquake?
