Earthquakes Rattle Western Tennessee in Active Seismic Zone

Two earthquakes rattled portions of western Tennessee earlier today, with the epicenter of both located within an active seismic zone.  Fortunately, while today’s earthquakes were the strongest this month in Tennessee, they were still relatively mild. The first struck at 4am  about 13 km from Ridgely at a depth of 10.5 km; it was measured to be a 2.6 magnitude event. The second struck nearby 40 minutes later 12 km northwest of Newbern; it was measured as a 3.1 magnitude event.

Today’s earthquakes struck just a week after a few struck in the eastern portion of the state. That mild 2.6 earthquake rocked the area outside of Knoxville, Tennessee on May 23.  According to USGS, the earthquake struck at a depth of 9 km just over 5 miles from the town of Garland in the eastern portion of the state.  Last week, 3 earthquakes struck the state: a 2.1 near Ridgely and both  a 2.0 and 1.6  near Tiptonville. Earthquakes that hit nearby in Missouri, Georgia, and Arkansas were also felt in the state over the last 2 weeks. While these earthquakes are light and scattered around the  Tennessee, scientists want people prepare should something far stronger strike.

While many people associate earthquakes with western states moreso than Tennessee, one of the largest earthquakes to strike the United States struck not far away. And scientists are concerned that residents in this area aren’t properly prepared for the next major earthquake to strike this area.

On December 16, 1811, at roughly 2:15am, a powerful 8.1 quake rocked northeast Arkansas in what is now known as the New Madrid Seismic Zone.  The earthquake was felt over much of the eastern United States, shaking people out of bed in places like New York City, Washington, DC, and Charleston, SC.

The ground shook for an unbelievably long 1-3 minutes in areas hit hard by the quake, such as Nashville, TN and Louisville, KY. Ground movements were so violent near the epicenter that liquefaction of the ground was observed, with dirt and water thrown into the air by tens of feet.

President James Madison and his wife Dolly felt the quake in the White House while church bells rang in Boston due to the shaking there.

But the quakes didn’t end there. From December 16, 1811 through to March of 1812, there were over 2,000 earthquakes reported in the central Midwest with 6,000-10,000 earthquakes located in the “Bootheel” of Missouri where the New Madrid Seismic Zone is centered.

Damage-range comparison between a moderate New Madrid zone earthquake (1895, magnitude 6.8), and a similar Los Angeles event (1994, magnitude 6.7). Yellow indicates where shaking was felt; red indicates at least minor damage to buildings and their contents. Image: USGS
Damage-range comparison between a moderate New Madrid zone earthquake (1895, magnitude 6.8), and a similar Los Angeles event (1994, magnitude 6.7). Yellow indicates where shaking was felt; red indicates at least minor damage to buildings and their contents. Image: USGS

The second principal shock,  a magnitude 7.8, occurred in Missouri weeks later on January 23, 1812, and the third, an 8.8, struck on February 7, 1812, along the  Reelfoot fault in Missouri and Tennessee.

The main earthquakes and the intense aftershocks created significant damage and some loss of life, although lack of scientific tools and news gathering of that era weren’t able to capture the full magnitude of what had actually happened. Beyond shaking, the quakes also were responsible for triggering unusual natural phenomena in the area: earthquake lights, seismically heated water, and earthquake smog.

Residents in the Mississippi Valley reported they saw lights flashing from the ground. Scientists believe this phenomena was “seismoluminescence”; this light is generated when quartz crystals in the ground are squeezed.  The “earthquake lights” were triggered during the primary quakes and strong aftershocks.

Since 1974, there have been more than 4,000 earthquakes near the New Madrid Seismic Zone. Scientists believe a large earthquake here in the future isn’t a matter of if but when. Image: USGS

Water thrown up into the air from the ground, or the nearby Mississippi River, was also unusually warm. Scientists speculate that intense shaking and the resulting friction led to the water to heat, similar to the way a microwave oven stimulates molecules to shake and generate heat. Other scientists believe as the quartz crystals were squeezed, the light they emit also helped warm the water.

During the strong quakes, the skies turned so dark that residents claimed lit lamps didn’t help illuminate the area; they also said the air smelled bad and was hard to breathe. Scientists speculate this “earthquake smog” was caused by dust particles rising up from the surface, combining with the eruption of warm water molecules into the cold winter air. The result was a steamy, dusty cloud that cloaked the areas dealing with the quake.

The area remains seismically active and scientists believe another strong quake will impact the region again at some point in the future. Unfortunately, the science isn’t mature enough to tell whether that threat will arrive next week or in 50 years. Either way, with the population of New Madrid Seismic Zone huge compared to the sparsely populated area of the early 1800s, and tens of millions more living in an area that would experience significant ground shaking, there could be a very significant loss of life and property when another major quake strikes here again in the future.

Tennessee isn’t the only state experiencing earthquakes in the eastern United States. Virginia, North Carolina, and South Carolina have all seen several earthquakes over the last few weeks.