LITTLE ROCK — In the U.S. Geological Survey’s map of seismic hazards, the West Coast burns with red and orange hues, along with coastal areas of Alaska and the Big Island of Hawaii, but so does the northeast corner of Arkansas and the edges of neighboring states like Missouri and Tennessee.
The 2018 map from the federal agency underscores the risks posed by earthquakes, even for people living far from the West Coast, and the inherent dangers famously lurking underground.
Officials reviewed the Geological Survey map as well as others in a review of the hazards quakes present to the central United States during an online seminar Friday meant to increase awareness of the topic.
Polly Sturgeon, an expert with Indiana University’s Indiana Geological and Water Survey, told viewers that “what a lot of people don’t realize is that the central United States is No.3 for earthquake hazards in the United States due to our unique geology and our history of earthquakes.”
Sturgeon and other officials paid special attention to the area surrounding the New Madrid seismic zone, a little-known region of seismic activity notable for a series of large earthquakes that struck in the early 19th century.
The zone of elevated earthquake risk roughly encompasses northeastern Arkansas and the nearby regions of southeastern Missouri, northwestern Tennessee and southwestern Kentucky, according to the U.S. Geological Survey.
A little more than 200 years ago, the New Madrid zone was the scene of a devastating series of earthquakes in the winter of 1811-12. During the historic disaster, tremors tore apart the landscape, forced liquefied soil into deposits known as “sand blows” and caused landslides, the federal agency reported.
SOIL LIQUEFACTION
On Friday, officials from around the south-central U.S. sought to educate residents on the risks, urging them to prepare.
Speakers who took part in the discussion over Zoom included representatives of the Arkansas Department of Energy and Environment’s Geological Survey, the Arkansas Division of Emergency Management, the Central United States Earthquake Consortium, the Missouri State Emergency Management Agency and the Mississippi Emergency Management Agency.
Earthquakes are known to occur in Arkansas. A 4.7-magnitude temblor in 2011 near Greenbrier shook residents, as well as several other states.
In 2017, a 3.6-magnitude quake with its epicenter north of Bergman was followed by two weaker quakes.
Sturgeon told viewers that soil liquefaction represents a hazard relevant to residents of the central United States.
During an earthquake, the sandy or silty soil in an area such as an alluvial plain or the vicinity of a riverbank may temporarily behave like a liquid instead of a solid. The phenomenon can cause structures to become displaced from their foundations, she said.
Liquefaction also can cause a “sand blow,” scattering the sediment into the air and over the ground.
Some people might not be as familiar with liquefaction compared with shaking or ground rupture, Sturgeon said. She said that “we know from geologic evidence that liquefaction has happened in central U.S. earthquakes before.”
Sturgeon also compared seismic waves’ ability to travel when they occur in the central U.S. versus the West Coast.
During an earthquake, the central U.S. experiences “low attenuation,” meaning seismic waves can travel much farther before they lose energy because of the qualities of the underlying earth stemming from the older, denser bedrock of the Midwest.
The significance is that a temblor during the New Madrid quakes could be felt over a much larger region when compared with the San Francisco earthquake of 1906.
“People as far as into New England and Texas felt shaking from the New Madrid earthquake,” Sturgeon said.
LANDSLIDES, RUPTURES
Recalling past events, Sturgeon described the New Madrid earthquakes — three that occurred over about three months in the winter of 1811 and 1812, with their epicenter in the area of what is today southeast Missouri and northeast Arkansas.
During the earthquakes, three in the range of magnitude-7 shook the region, as well as four with magnitudes between 4 and 6, and close to 2,000 smaller aftershocks rolled in, Sturgeon said.
The quakes caused landslides, ground ruptures and riverbank failures, she said.
Based on modeling data, Sturgeon said the odds of another magnitude-7 or higher within the next 50 years were 7%-10%, but the odds of a magnitude-6 or above were about 25%-45% over the same period.
Sturgeon noted officials could not predict earthquakes. Still, she added, “a magnitude-7.0 earthquake similar to the New Madrid scale would affect almost 12 million people and cause at least $200 billion in damage within the central United States.”
Hilda Booth, earthquake program manager at the state Emergency Management Division, said the chances of a large earthquake were “very real.”
She displayed a photo of a house that had nearly toppled during an earthquake in Christchurch, New Zealand. The photo showed the home leaning sideways as debris spilled into the front yard.
New Zealand’s geological pattern is similar to that of Arkansas and the central U.S., Booth said, because both have alluvial soil that could experience liquefaction during an earthquake.
Part of the problem with getting people to prepare for earthquakes is “there’s no warning, and many people have never been in one,” Booth said. “So it’s difficult to get people to pay attention to something that they don’t know much about or that they haven’t experienced.”
“But it’s a real threat, and we need to get busy getting prepared before the shaking starts,” she added.
BE PREPARED
Booth said people should not run outside when they feel shaking start, citing the prevalence of injuries or deaths from falling debris. Instead, she encouraged people to look for ways to make their homes or workplaces safer in case of an earthquake.
“Are there things that could fall over, big amoires and bureaus and things that could fall over and block your exit from a building or a door?” Booth asked.
Additionally, Booth encouraged people to prepare a kit of necessary items based on what they and their family would need during a two-week period of an emergency.
She pointed out that the recent snowstorms that hammered Arkansas along with much of the U.S. in February occurred at the same time as the coronavirus pandemic. Booth described the severe winter weather as evidence for “how things can compound and your needs can so easily not be met.”
During an earthquake, people were encouraged to drop to the floor on their hands and knees wherever they are, crawl under a table or desk, cover their heads and necks and hold on to a table leg or other part of the structure, if such a support is available.
The ability to rebuild and pay for repairs in the aftermath of a catastrophe also was discussed.
Jeff Briggs of the Missouri State Emergency Management Agency said most homeowners in southeast Missouri are unlikely to have insurance coverage for losses from an earthquake. Many may not know that homeowners insurance typically does not include earthquake loss, unlike more common disasters such as fires or tornadoes, he said.
The coverage must be purchased as an endorsement at extra cost, Briggs said.
“But what we’re finding out and what homeowners are finding out is that this is becoming a more and more expensive proposition in the New Madrid seismic zone,” he said.
He cited information from the Missouri Insurance Department on rates for earthquake insurance coverage in the St. Louis area versus the lower rates of coverage in the “boot-heel” of southeastern Missouri, closer to the heart of the seismic zone where risk runs higher.
Briggs suggested the map showing the gap in coverage rates was “a major, major concern for us.” He also described it as an issue not just in Missouri but in areas surrounding the New Madrid seismic zone.
In the aftermath of a large quake, many people are “going to be unnerved about what’s happening in their area,” Briggs said. “They’re going to find they don’t have money to rebuild, and what we’ve learned — as we’ve learned from other major disasters around the world — many will not be able to afford to rebuild. Many will decide to leave the area, in fact.”
Officials in Missouri are working with insurance companies and the Federal Emergency Management Agency to find solutions to make insurance more available and affordable, Briggs said, but he described the efforts as a long-term solution.
For right now, he encouraged residents to find out if they have earthquake insurance coverage and, if not, consider acquiring it.