By Lorrie Ross
Staff Writer
Minutes after the ground shook with unusual rumblings on Saturday morning, May 10, social media posts were rampant. “What was that?” and “Was there an explosion of some kind?” One post speculated the mine near Highway 69 was blasting bigger sections than usual, while some thought it was an approaching thunder storm. Several people said they thought a medical chopper was landing on their house.
According to the United States Geological Survey, when the land trembled at 9:04 a.m. eastern time, it was actually a 4.1 magnitude earthquake centered in east Tennessee, but felt in multiple states. The USGS information said the earthquake originated near Greenback, Tenn., about 30 miles southwest of Knoxville. Folks throughout eastern Tennessee, western North Carolina and north Georgia, reported feeling the quake. Some even reported feeling the earthquake south of Atlanta.
Other than scaring folks, there were no reports of injuries or property damage locally, although uncertain Clay County residents called and texted friends to find out if they had felt it, too. In addition, Clay County Emergency Management Director Jeff Ledford said emergency services did not receive any emergency reports from the earthquake.
Meanwhile, the Clay County 911 Communications Center received 16 calls. “Along with several reports on non-emergency phone lines about the earthquake,” Clay County 911 Communications Director Kevin Sellers said. “There were no injuries or property damage reported to the Clay County 911 Center after the earthquake was felt throughout the county.”
Central United States Earthquake Consortium executive director Brian Blake said Saturday’s earthquake was the largest in East Tennessee in more than 30 years. Blake said there is an active seismic zone in the area, known as the Eastern Tennessee Seismic Zone. Also known as the East Tennessee seismic zone and the Southern Appalachian seismic zone, the ETSZ is a geographic band which stretches from Tennessee, south into northwestern Georgia and northeastern Alabama and north into southwestern Virginia.
Despite being one of the most active earthquake zones in the eastern United States, the ETSZ is not known for major earthquakes. Hundreds of small earthquakes have been recorded in recent decades, which are detected by instruments, yet too small to be felt by residents. Earthquakes are not as unusual as one may think. In the past 30 days, Tennessee has recorded more than 20 earthquakes of lesser magnitudes.
Earthquakes large enough to feel the impact occur approximately once every year in the ETSZ. Some damaging earthquakes have happened in the ETSZ. The largest historic earthquakes in the zone were a 5.1 magnitude, on April 29, 2003 near Fort Payne, Ala. and on Aug. 9, 2020 near Sparta, N.C. However, the USGS has said earthquakes as large as magnitude 7.5 may be possible in the Eastern Tennessee Seismic Zone.
Saturday’s earthquake was considered a shallow quake by the USGS, since it was only about 15 miles deep. Magnitude 4 earthquakes can often be felt 60 miles from where they occur. Moderate quakes start at magnitude 5.
At magnitude 4.1, the May 10 earthquake was the seventh earthquake of 4.0 magnitude or greater in Tennessee since 1900. It was the first Tennessee earthquake stronger than 4.0 since 2018 when a 4.4-magnitude quake hit Decatur, Tenn. In Nov. 1973, Alcoa, Tenn. was shaken by a 4.7 magnitude earthquake. Over the past year in Tennessee, only three other earthquakes exceeded a magnitude of 3.0, according to USGS data.
The source or sources of the ETSZ seismic activity is unknown, though it has been investigated. The ETSZ is far from the edge of the North American Plate and represents an intraplate or mid-continent earthquake zone. The faults which are known in the ETSZ are considered to be ancient with no known active faults reaching the surface.
In late 2024, KnoxNews.com quoted U.S. Geological Survey geophysicist Thomas Pratt. “You guys are in earthquake country, you're in tornado country,” Pratt said. “We always tell people when they feel an earthquake, think of that as a wake-up call.”
In case you are ever in a stronger earthquake, know earthquake safety guidelines. Central United States Earthquake Consortium has seven steps to prepare at Seven Steps to Earthquake Safety found at: https://cusec.org.