EARTHQUAKES IN TENNESSEE
Aug. 17, 1865: The largest single earthquake in Tennessee history, at magnitude 5.0, occurred outside of Memphis, near New Madrid, Missouri. The quake knocked down chimneys in Memphis and sent large waves through the Mississippi River. The shocks were felt through Missouri, Tennessee, Mississippi and Illinois.
1811-1812: Three New Madrid earthquakes rocked up to 3.1 million square miles across Kentucky, Missouri and Tennessee — raising and sinking land masses and creating fissures over 80,000 square miles. The greatest of those tremors registered greater than 7.0 magnitude and created Reelfoot Lake in Northwest Tennessee.
Jan. 4, 1843: Severe earthquakes in Memphis registered an VIII intensity and up to 6.9 magnitude. The shocks were felt sharply in Nashville and as far away as Knoxville, although no significant damage was done in those cities.
March 28, 1913: Earthquakes centered in Knoxville cracked walls and toppled chimneys across 4,300 square miles in East Tennessee. The shocks were rated up to 5.9 magnitude.
Oct. 30, 1973: Cracks in the walls were reported at the University of Tennessee Medical Center in Knoxville after a 4.6 magnitude earthquake south of Knoxville sent rumbles throughout the region. Minor damage to walls, windows and chimneys occurred in Blount County.
Source: U.S. Geological Survey
Meigs County, Tennessee, residents Judy and Bill Emerson have lived on Woods Hollow Road since 1990. Their home is barely 500 yards east of the epicenter of the largest of the seven earthquakes that shook the Southeast Tennessee area early Wednesday morning.
"I thought it was an explosion. I thought the heat pump blew up," Judy Emerson, 65, said. "It was so loud it scared me to death.
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"I was screaming at my husband saying, 'Did you hear that? Did you hear that?'" she laughed. "And he said, 'What? Was that you? Did you fall?' And I said, 'No, I'm not that big!'"
The 4:14 a.m. quake shook open cabinet doors in Emerson's kitchen and rattled all the doors and windows, but nothing was knocked off walls or damaged, she said. Neither of the Emersons heard or felt the second or subsequent quakes.
"It sure did scare me," she said, noting she is a night owl who usually is up reading but wasn't on Wednesday. "If I had been sitting there reading, I'd have come right off that couch!"
The magnitude 4.4 earthquake rocked the area less than 10 miles north of Decatur near the Watts Bar Nuclear Plant at 4:14 a.m. Wednesday, followed less than 15 minutes later by a 3.0 magnitude temblor that struck about a mile closer to the Tennessee Valley Authority facility, the U.S. Geological Survey at the University of Memphis reported.
People felt the larger quake, the strongest in Tennessee in 45 years, as far away as Chattanooga, Nashville, Knoxville and even Atlanta, according to USGS maps.
The 1973 earthquake was slightly stronger at magnitude 4.7. It happened near Maryville, according to the National Weather Service.
The first Meigs quake was focused about half a mile south of State Route 68 near Moore Cemetery Road, and was about 5.6 miles deep, while the second was about 4.2 miles deep and was centered nearer Highway 58, officials report.
The first two quakes were followed by several considerably smaller ones — a magnitude 1.9 at 5 a.m., a magnitude 2.1 at 5:41 a.m., a magnitude 1.7 at 8:51 a.m., and a magnitude 1.8 at 10:06 a.m. — USGS earthquake maps show. All of those quakes were very near the first two larger ones, clustered in the same area around Woods Hollow Road.
But that wasn't the only area hit since Tuesday at midnight.
Several hours earlier — 1:18 a.m. — a magnitude 2.7 quake struck about 7.5 miles northwest of Sweetwater, Tennessee, in Monroe County. It was 13.5 miles deep, records show.
TVA spokesman Jim Hopson said Wednesday morning that Watts Bar and the federal utilities' facilities and dams up and down the Tennessee River reported no damage. Officials continued to run through checklists throughout the day to make sure nothing was overlooked.
As the sun rose Wednesday on rattled Meigs Countians, county Emergency Management Director Tony Finnell said there had been no reports of damage but the county's 911 lines lit up as soon as it happened.
"We got a few calls because people woke up with noise and vibration," Finnell said.
"I heard it at the house. I live down below town," he said, referring to the county seat of Decatur.
Finnell said the Emergency Operations Center also got calls from neighboring counties, but there were no reports of damage elsewhere, either.
But the quake jostled people all over.
"It was pretty widespread," Finnell said of reports from people who felt the earth move. But "unless something else crops up or we have a sinkhole open up, I think we're good."
A magnitude 4.4 quake on the Mercalli Intensity Scale means that, at its epicenter, it was likely to be felt indoors by many people, and outdoors by a few. Some people might have been awakened, and dishes, windows and doors disturbed, according to the USGS website.
At worst, people might feel a sensation like a heavy truck striking the building they're in.
While that doesn't sound too worrisome for most homeowners, the same thing happening at a nuclear plant can conjure scarier images.
Watts Bar units 1 and 2 and one of the two units at Sequoyah Nuclear Plant were running at 100 percent power through both the nearby earthquakes, TVA spokesman Hopson said. The second unit at Sequoyah was already shut down for maintenance, he said.
Watts Bar employees on duty early Wednesday followed protocol that begins with a checklist to make sure online power units remain online and are operating safely, he said.
"All the systems operated exactly as designed and there were no issues at all, so there were no safety concerns for the public or employees," Hopson said around 9 a.m. Wednesday. All three units "remain at 100 percent power."
Personnel make "secondary inspections just to make absolutely certain that any type of seismic event doesn't create any problem that escaped notice on our initial assessment," he said, noting those checks would be completed Wednesday.
Elsewhere, TVA's dams, dikes, enclosures and power plants also had no reports of any impact from the quakes, Hopson said.
Nuclear Regulatory Commission spokesman Roger Hannah said Wednesday's quake was not strong enough to meet the threshold for notifying the NRC.
"The requirement for them to declare an emergency is a seismic event greater than what is called an 'operating basis' earthquake. It's based on the ground motion actually felt at the site," Hannah said.
"If it exceeds a certain threshold they report it as an 'unusual event,' the lowest level of emergency," he said. "The level of seismic activity did not exceed that threshold. I think there was a door that came open or something, but it was not damaged."
All TVA facilities are built to withstand "seismic events," which means the standard is higher than the state's strongest known earthquake back in the 1800s, he said.
U.S. Geological Survey data in its 2014 map showing the level of earthquake hazard indicates an increasing hazard in Southeast Tennessee since the last study in 2008.
Contact staff writer Ben Benton at email@example.com or 423-757-6569. Follow him on Twitter @BenBenton or at www.facebook.com/benbenton1.
HOW’S IT SHAKIN’?
Magnitude / Intensity Comparison
The following table gives intensities that are typically observed at locations near the epicenter of earthquakes of different magnitudes, as classified under the Abbreviated Modified Mercalli Intensity Scale from I to XII.
Magnitude/Typical Maximum Modified Mercalli Intensity
1.0-3.0 = I
3.0-3.9 = II-III
4.0-4.9 = IV-V
5.0-5.9 = VI-VII
6.0-6.9 = VII-IX
7.0 and higher = VIII or higher
Abbreviated Modified Mercalli Intensity Scale
I: Not felt except by a very few under especially favorable conditions
II: Felt only by a few persons at rest, especially on upper floors of buildings
III: Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated
IV: Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably
V: Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop
VI: Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight
VII: Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken
VIII: Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned
IX: Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations
X: Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent
XI: Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly
XII: Damage total. Lines of sight and level are distorted. Objects thrown into the air
Source: U.S. Geological Survey