Tennessee has been touched by "some of the most significant events in U.S. history," according to the U.S. Geological Survey.
* Aug. 17, 1865: The largest single earthquake in Tennessee history occurred outside of Memphis, near New Madrid, Mo. The quake threw down chimneys in Memphis and sent large waves through the Mississippi River. The shocks were felt through Missouri, Tennessee, Mississippi and Illinois. That quake registered at 5.0 magnitude.
* 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
Ahead of time:
Secure your hot water heater, secure bookshelves to the walls and invest in cutoff valves for natural gas and water lines.
• Put together an emergency preparedness kit.
• Download the state's Ready TN mobile app at www.tnema.org/ReadyTN/
In case of an earthquake:
• Stop what you are doing and get under something sturdy. Most injuries associated with earthquakes are from objects falling on people
Source: Tennessee Emergency Management Agency
East Tennessee got a lot more colorful on the national seismic hazard map between 2008 and 2014.
More color signifies a higher earthquake hazard for a region that rarely registers notable seismic activity.
The U.S. Geologic Survey's most recent map updates an area of Southeast Tennessee to include a patch of red, indicating it has been placed in the second-most hazardous tier out of seven that the USGS uses in its national map that is released every six years.
"The 2014 map when compared with the 2008 map does indicate that we should be a little more concerned - not that we have a huge hazard - but we should be somewhat concerned," said Jonathan Mies, a geology professor at the University of Tennessee at Chattanooga.
The potential for seismic activity in East Tennessee pales in comparison to the potential for it on the western side of the state, where much stronger quakes occur in the New Madrid region.
Still, the Volunteer State was deemed one of the 16 states at highest risk for an earthquake by USGS. And even though Mies said many nearby earthquakes happen deep underground, they still happen.
Thirty-six earthquakes of magnitude 1.5 or greater have been recorded in Eastern Tennessee in the past year, with two of those just about a week ago.
Geological survey sensors detected a 1.9 magnitude quake about 5:15 p.m. last Saturday in Soddy-Daisy. The day before, a 1.8 magnitude tremor cropped up near Etowah around 12:46 a.m.
More serious earthquakes do occur in Eastern Tennessee, though.
In 1973 a 4.6 magnitude earthquake south of Knoxville caused minor damage and shook towns in Tennessee, Georgia, Kentucky and North Carolina.
An earthquake must register above a 2.0 for people in the immediate area to actually feel something, said Cecil Whaley, earthquake manager for the Tennessee Emergency Management Agency.
"It's not uncommon for us to see one or two events a week," Whaley said. "But they are very small and difficult to record."
Regardless, the Tennessee Valley Authority takes no chances when it comes to securing its dams so that a natural disaster does not lead to flooding.
TVA officials say their structures are designed to withstand an earthquake and that the agency continually monitors things like seismic activity and how it could affect dams and power plants.
"The dams themselves are designed to exceed the maximum probable earthquake for the area and still maintain their structural integrity," said Jim Hopson, a TVA spokesman. "The dam safety program is designed to continually re-evaluate the health of the dam to ensure they're meeting the current standards and not the standards they were designed for up to 100 years ago."
The East Tennessee fault line, which runs from Chattanooga, through Knoxville and into North Carolina, is only part of a larger seismic zone, and it's pretty active, Whaley said.
But there's no need for residents to panic.
"They don't need to be excited about the fact that there are many more earthquakes [recorded] here than there have been in the past," Whaley said. "We are constantly adding new monitoring equipment that helps us see activity when it happens."
Mitch Withers, an associate research professor at the University of Memphis Center for Earthquake Research and Information, said the updated maps represent an uptick in information more than activity.
"We can't predict earthquakes. The earth is much too complicated and our knowledge is much too thin to be able to do that," Withers said. "But we try to make predictions through probability of major events."
Contact staff writer Louie Brogdon at firstname.lastname@example.org or 423-757-6481.
Contact staff writer David Cobb at email@example.com or 423-757-6731.