Top Earthquake Risk States: #11-16

Rounding out the top 16 states in the U.S. with the highest earthquake risks are Arkansas, Illinois, Kentucky, Missouri, South Carolina, and Tennessee. The biggest threat to these states is the New Madrid Seismic Zone.

New Madrid Seismic Zone, depicting area of damage and extent of shaking felt

Arkansas

The biggest earthquake risk in Arkansas lies in the New Madrid Seismic Zone. The 19 counties in northeast Arkansas, those that stretch out from the Seismic Zone, are at greatest risk.

A magnitude 7.7 New Madrid earthquake would likely damage 162,000 buildings and 1,100 bridges. The number of casualties could be as high as 15,300, and direct economic losses might top $40 billion.

In 1976, a magnitude 5.0 earthquake struck Poinsett County, Arkansas.

Illinois

Southern Illinois is near two significant earthquake zones. The most notable is the New Madrid Seismic Zone, which poses a high risk to several states. The second fault zone is the Wabash Valley Seismic Zone, where a magnitude 5.2 earthquake shook the area in April 2008. Prior to that, a 5.3 quake caused some damage in 1968.

A large earthquake in the New Madrid Seismic Zone could have 6,300 casualties and possibly damage 45,000 buildings and 160 bridges. It could have a $44 billion economic impact on the state.

Kentucky

Kentucky is also at risk from the New Madrid Seismic Zone. A large 7.7-magnitude earthquake in the New Madrid Seismic Zone would likely cause a $53 billion economic loss for Kentucky. Among the losses would be damage to 68,400 buildings and 250 bridges. The number of casualties could be 6,900.

Within Kentucky’s borders, the largest recorded earthquake was a magnitude 5.2 that hit on July 27, 1980 in Bath County. The shaking caused an estimated $3 million in damages in Maysville. A smaller 4.2-magnitude tremor shook Perry County in 2012. 

Missouri

Missouri is another state that would be severely affected by a major earthquake in the New Madrid Seismic Zone. In fact, the seismic zone is named after the Mississippi River town of New Madrid, which was part of the Louisiana Territory when the 1811 earthquake hit and is now part of Missouri.

A repeat of the 1811 earthquake would likely damage 87,000 buildings and 1,000 bridges. There could be 14,100 casualties, and the state could face $49 billion in direct economic losses.

Because of the below-ground geology of the region, a major earthquake in the New Madrid Seismic Zone could cause destruction over an area 20 times larger than a similar quake in Southern California (Jackson County, Earthquake Threat). It’s estimated that these major quakes occur probably every 200 to 300 years.

A study at the University of Illinois determined that a magnitude 7.7 New Madrid rupture would leave more than 7 million people in the region homeless and would leave large parts of St. Louis, Missouri, and Memphis, Tennessee, uninhabitable. The St. Charles County Division of Emergency Management puts the odds of another major New Madrid quake happening before 2040 at 25 percent.

More information for earthquake preparedness can be found on the Missouri Department of Public Safety, State Emergency Management Agency page for Earthquakes

South Carolina

In the 2014 U.S. Geological Survey Hazards Map, Charleston, South Carolina has a high risk of a damaging earthquake within 50 years. The area was hit by a magnitude 7.0 (or higher) tremor in 1886. A smaller, 5.5-magnitude quake struck near the town of Union in 1913. 

Like much of the Midwest and eastern United States, the frequency of large earthquakes in South Carolina is a best guess due to the lack of visible evidence. But increased research is improving estimates. Large ruptures are estimated to occur about every 200 to 250 years, with larger events, like the one in 1886, happening between 250 and 500 years. However, moderate tremors are likely much more frequent, with a probable frequency of about every 125 years. 

According to a 2016 HAZUS report released as part of the South Carolina emergency management plan, if South Carolina were to experience a magnitude 7.3 earthquake, more than 4 percent of the buildings would be damaged beyond repair. Among those would be 13 hospitals, 30 fire stations, and two emergency operations centers. Of the 83,961 buildings that would likely experience complete damage, more than half would be single-family homes. The most vulnerable of the structures are unreinforced brick masonry buildings (Expectations for Charleston’s next great unexpected disaster). More than 2,000 bridges would be at least moderately damaged.

Initially, an estimated 166,675 households would be without potable water. A week later, 94,500 would still be without water.

The HAZUS report estimates 213,063 households would be without power, and one month later, more than 53,000 would still be without electricity. Three months later, there would still be 1,341 households without power.

Nearly 94,000 households would be displaced, and 62,464 residents would likely need temporary shelter.

Depending on when the earthquake strikes, a midday tremor would likely result in 2,877 fatalities and leave another 1,553 with life-threatening injuries.

Tennessee

Wednesday, December 12, 2018, a small magnitude 4.4 earthquake shook eastern Tennessee. A 3.3 magnitude aftershock followed. While these were not quakes to worry about, they do provide the reminder that the state has earthquake risk.

Like other midwestern states, Tennessee’s greatest earthquake risk is the New Madrid Seismic Zone. A repeat of the 1811 event would result in major economic losses and thousands of fatalities, including several thousand in Memphis. Like nearby states, tens of thousands of structures would be damaged in the event, and vital infrastructure, such as water supply, would be affected. 

Some of the Tennessee-specific impacts of a magnitude 7.7 New Madrid earthquake include:

33,000 injuries

1,300 deaths

710,000 households without power

510,000 households without potable water

265,000 buildings damaged

107,000 buildings completely damaged

55 hospitals damaged and unable to provide service

250 fires stations and 125 police stations damaged and unable to provide service

40 airports damaged and not operational

1,000 bridges damaged, with 250 completely unusable

50 dams and 7 levees damaged

21 million tons of debris requiring 850,000 truckloads to remove

What isn’t really mentioned in the analysis of a possible repeat of the 1811 New Madrid earthquake is how the quake could affect the Mississippi River. It is entirely possible that the series of levees could fail in one or more places, causing the river to invade the spaces civil engineers have tried to protect. Even worse is if the river were at or near flood stage. Water, especially large amounts of it, wants to flow through the path of least resistance. The result of a flood would not only affect Memphis but also have consequences in western Kentucky, southern Missouri, and parts of Arkansas. 

Besides the New Madrid Seismic Zone, there is another risk for tremors in Tennessee. Near the eastern border of the state is the lesser-known Southern Appalachian Seismic Zone, which stretches from northeastern Alabama into southwest Virginia and east Tennessee. Most earthquakes in this seismic zone are small, with magnitude 4.6 tremors occurring in 1973 near Knoxville and in 2003 in nearby Fort Payne, Alabama. It’s estimated the seismic zone can produce a magnitude 7.5 rupture, which would be as devastating as an earthquake in the New Madrid Seismic Zone. 


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