An earthquake in Middle Tennessee? What you need to know about history, possibility

Given last week's headlines about a 4.8 magnitude earthquake in New York and New Jersey, many people might be wondering if it could happen in the Nashville area?

Middle Tennessee is susceptible to damage from large earthquakes and a big one could be coming to the area sooner than we think, according to Geologist Gary Patterson, director of education and outreach at the University of Memphis Center for Earthquake Research and Information.

So, how long do we have to prepare? Patterson says we can’t be certain of when it will happen, but a big earthquake is projected to hit the New Madrid Seismic Zone – an abundant source of intraplate earthquakes in the Southern and Midwestern United States – every 500 years.

The data is based on about 1,200-1,500 years’ worth of recorded geologic seismic activity in the area, meaning no one can be certain when it will hit.

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But that may not be our greatest threat, Patterson says.

An earthquake in a neighboring state could just as easily prove catastrophic if it's large enough, he said, noting that shockwaves can travel up to as many as 1,200 miles away.

“When we think about seismic hazard, it's not just about the earthquakes in your area but the larger earthquakes that are outside your area that will have (or) could have considerable impact on Middle Tennessee. When large earthquakes occur there, they don't recognize state boundaries, so the hazards are not just driven about by local earthquakes, it's about (the) potential for ground motion based on large earthquakes that have occurred further away,” he explained.

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What happens during an earthquake?

Struggling to remember that fourth grade science lesson on earthquakes?

Here's a quick lesson: An earthquake is the rapid release of energy when two pieces of land move past each other along a fault line, according to the U.S. Geological Survey, or USGS for short.

The definition is "important because that implies that there's a threshold," Patterson said. "Once you reach that threshold, the fault breaks and it gives off vibration and has an earthquake.

“A small earthquake can happen just about anywhere at any time … (but) the capability of producing an earthquake is limited by the size of the fault it occurs on. You can't have a big earthquake on a little fault."

Tennessee is home to thousands of faults, but most of them haven't moved for 350 million years, scientists say.

“We know where most of the active faults are and their size, so that tells us a lot about their capacity to generate a large earthquake," Patterson said.

How are earthquakes measured?

Magnitude is the size of the earthquake, recorded by seismometers and expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 is a moderate earthquake, and a 6.3 is a strong earthquake, according to the USGS Earthquake Hazards Program.

The Richter scale is something most people have heard of, but it is not commonly used any more, except for small earthquakes recorded locally, officials said.

As the first widely-used method, the Richter scale was developed by Charles F. Richter in 1934, the Michigan Technological University states. But it isn’t able to provide accurate estimates for large magnitude earthquakes.

The moment magnitude scale is a more accurate measure of earthquake size.

It was developed in the 1970s, according to Encyclopaedia Britannica, by Japanese seismologist Hiroo Kanamori and American seismologist Thomas C. Hanks and is the only scale capable of reliably measuring the magnitudes of the largest, most destructive earthquakes greater than a magnitude 8.

While magnitude scales have no upper limit and can be used to describe earthquakes small enough to be expressed in negative numbers, there are six categories officials typically use to describe an earthquakes’ magnitude and effects, according to the Michigan Technological University

Those recorded at a magnitude of 2.5 or less are usually not felt, while a magnitude of 2.5 to 5.4 is often felt and can cause minor damage.

Earthquakes measuring 5.5 to 6.0 are prone to causing slight damage to buildings and other structures.

Highly populated areas may experience a lot of damage from 6.1 to 6.9 magnitude earthquakes.

And, although earthquakes measuring 7.0 to 7.9 can result in serious damage, those that are 8.0 or higher can destroy entire communities near the epicenter, or point of origin.

‘A series of catastrophic earthquakes’

Tennessee’s middle region has only experienced a handful of 2.5 magnitude or higher earthquakes between 1924 and 2024, including Murfreesboro in 1997 and Franklin in 2001, according to the USGS Earthquake Catalog.

But time and time again, Nashville has been hammered by the effects of larger earthquakes with epicenters across state lines.

More: Here are the most powerful Tennessee earthquakes from the last 100 years

In 1886, the effects of ground shaking from a large earthquake in Charleston, South Carolina could be felt as far away as New York City, New York, Chicago, Illinois and St. Louis, Missouri, USGS Circular 985 said.

Before that, a series of catastrophic earthquakes destroyed parts of West Tennessee and the Mississippi River Valley between December 1811 and February 1812 after the first of many earthquakes erupted in New Madrid, Missouri and was felt as far away as London, according to the Tennessee State Library Archives.

The Mississippi River briefly flowed backwards during a massive 1811 earthquake, forming Reelfoot Lake in West Tennessee among other lasting geographic effects.

“Big earthquakes here in 1811 were felt 1,200 miles away or 1,300 miles away into Canada. Big earthquakes today in Los Angeles are barely felt in Tahoe (and) Reno,” Patterson said, noting the unique geologic makeup of the seismic zone.

“The earthquakes here are much different in terms of the area and the impact for the same magnitude compared to California."

A magnitude 5 earthquake may affect 5-15 times larger of an area in the New Madrid Seismic Zone compared to California, largely due to the crustal geology of the two areas.

“(California is) shattered with faults, so when an earthquake occurs in that environment, a lot of the energy dissipates quickly because it's hitting all this nonconstructive, destructive interference and its path waves are bouncing into each other, bouncing around and losing energy at distance,” Patterson said.

“The crust here 10-20 miles deep and is relatively cold, dense and hard compared to California, so earthquake waves travel more efficiently here.”

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Geologists estimate that similar New Madrid Seismic Zone earthquakes like the ones in 1811 and 1812 have a 7–10% chance of reoccurring within the next 50 years.

The probability of a magnitude 6 earthquake increases to between 28-46% during that same time period, according to the Arkansas Division of Emergency Management.

As for which natural disasters may pose the greatest risk to Tennesseans, Patterson said that while weather related hazards occur more frequently, a possible earthquake in the New Madrid Seismic Zone potentially offers the worst-case scenario.

“It could have very extensive short-term and long-term impacts and if we don't have plans in place, it could hurt us for a long time," he explained, adding that multi-hazard preparedness is essential for Tennesseans.

The Tennessee Emergency Management Agency’s Tennessee Hazard Mitigation Plan identifies more than a dozen hazards for long-term disaster planning, including earthquakes and severe weather.

Everyone is encouraged to prepare for an earthquake before it happens.

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An emergency plan can help keep everyone safe when a disaster strikes and should consider the unique needs of each family, including culture, religion, diet and medicine.

Discuss how each person can assist with communication, childcare or operating medical equipment and include children in the disaster preparedness conversations, especially when it comes to reviewing communication, evacuation and reunification plans at home and school, officials said.

Once created, the emergency plan should be kept in an easily accessible location and practiced periodically to ensure family members know what to do before, during and after a disaster.

Immediate help may not be available, so supply kits can provide families access to resources in the hours and days after a disaster. According to TEMA, a basic emergency kit should include:

• Water (one gallon per person/pet for several days)

• Food (at least a several-day supply of non-perishable food)

• Flashlight

• Battery-powered radio

• NOAA Weather Radio

• Extra batteries

• First aid kit

• Important medications

• Whistle to signal for help

• Moist towelettes, garbage bags for personal sanitation

• Wrench or pliers to turn off utilities

• Manual can opener for food

• Local maps

• Cell phone with charger or solar charger

• Cash or traveler’s checks and change

For more information, visit www.tn.gov/tema/prepare.

Katie Nixon can be reached at knixon@gannett.com.

This article originally appeared on Nashville Tennessean: Middle Tennessee earthquakes: Experts talk Nashville possibility