Editor’s Note: Last night (Wednesday, November 17), at 8:53 p.m., an earthquake of 3.7 magnitude struck southeast Missouri — and some Memphians reported feeling it this far away. Some claimed it was a distinct swaying motion, but others felt it as a quick bump, "like my dog jumping up on the bed." How often do these happen, and when should we expect another? Well, Jesse Davis talked with the experts about this in a feature story we published in 2019. Perhaps it will put your mind at ease.
Between December 1811 and March of 1812, more than a thousand earthquakes rocked the area that would one day be known as the Mid-South. The three biggest quakes, usually referred to as the New Madrid earthquakes, were some of the most powerful and devastating seismic events to take place on the North American continent.
The language often used to describe those earthquakes is nothing short of apocalyptic. It was said that the Mississippi ran backward, that the earth near New Madrid, Missouri, opened up and spewed sand and sediment into the air. The sky blackened, and birds were so confused they flew upside down. The most powerful of the earthquakes was supposedly felt as far away as Canada, and though there was little developed land in the region to be disturbed, the earthquakes permanently altered the geography of the area.
Now the states in the New Madrid Seismic Zone (NMSZ), the 150-mile-long seismic zone stretching through five states from which the series of earthquakes takes its designation, are crisscrossed with highways, towns, and cities. So the question is — when will the next “Big One” strike?
The Mystery of History
For seismologists attempting to understand what to expect from the NMSZ, the key to predicting the future may lie in piecing together what happened in the past. It’s no easy feat, though, since the New Madrid sequence preceded the birth of modern seismic science by more than one hundred years.
German researcher Alfred Wegener presented his theory of “continental drift,” which eventually led to an understanding of plate tectonics, in a paper in 1915. What’s more, “there wasn’t a Richter scale for over a century,” says Jeff Grunwald, administrator at the New Madrid Historical Museum, before noting that these days the preferred terminology is “moment magnitude scale.”
That’s where Dr. Kent Moran comes in. Moran, a native of West Tennessee, has been a research associate at the University of Memphis’ Center for Earthquake Research and Information (CERI) for the last 20 years and was a graduate student at the university prior to that. It’s his job to collect information about the NMSZ and the earthquakes of 1811-1812, weed out the rumors and fantasies, and weave what’s left into a coherent narrative by which seismologists can gain a better understanding of the seismic activity in the region.
“I am a historian by trade,” Moran admits, and that vocation serves him well in his seemingly endless search for more information. Grunwald calls Moran “the New Madrid Compendium,” a nickname borne out by Moran’s encyclopedic knowledge of his subject.
“I look for pre-instrumental earthquakes that are hidden in the historic record,” Moran explains. “I love doing research. I love finding stuff. I love the detective work.”
Eight states are potentially at risk if another series of quakes akin to those in 1811-1812 strike, but so little is known about the circumstances surrounding those earthquakes.
He hunts down pre-earthquake maps, which, when compared to post-earthquake maps and geological surveys, begin to paint a picture of the damage done by pre-instrumental earthquakes — like the New Madrid earthquakes of 1811 and 1812. To sharpen the resolve of that picture, Moran uses any and all sources available, including eye-witness accounts and building-damage records. He readily cites records of fallen chimneys, Arkansas archeological excavations, and 200-year-old newspaper clippings. “French explorers mapped the area in the 1700s and did a wonderful job,” Moran says. “The problem is the maps are hard to come by or are in archives somewhere or are mislabeled, or all of the above.”
The cycles on which the NMSZ operates encompass intervals that far exceed the length of recorded history in the area. “The clock sort of runs at 500-year intervals,” Moran says. “It’s like looking at the clock face, and you only see a portion of the clock.”
That’s what makes Moran’s work so valuable. Eight states are potentially at risk if another series of quakes akin to those in 1811-1812 strike, but so little is known about the circumstances surrounding those earthquakes. “It is a spot, geologically, that will give you large-magnitude earthquakes very infrequently,” Moran says before summing up, “but you need to know what it’s tried to do in the past to know what it might be doing in the future, and the only reference point we have for human experience is 1811-1812.”
Photo courtesy of Discovery Park of America
The Discovery Park of America's 4D Theatre illustrates the region of the country affected by the New Madrid Seismic Zone.
Notes on the Underground
Snow, sleet, hurricanes — dangerous weather events are usually visible. Even if we can’t see the wind, its effects are apparent in the swaying of trees and the movement of clouds, and humans have a relatively clear grasp of the pressure systems, climate, and other factors that influence severe weather. Seismic activity, though, presents a more difficult problem because the area of study is, to put it simply, underground. The NMSZ further complicates the issue by its very nature.
The zone is an intraplate fault, meaning the earthquakes take place within the tectonic plate, rather than at the point where two plates meet. Moran says the area is a failed rift zone in the continent that never quite broke, making the NMSZ a flaw of uncertain dimensions within the plate itself.
“I’ve run into people who say it wasn’t a bad earthquake because nothing was damaged. I say nothing was here to be damaged.” — Dr. Kent Moran
“The best analogy I’ve seen is where you have a piece of sheet metal with a flaw in it, and that flaw is where the stress concentrates,” Moran explains. By way of comparison, the researcher suggests that the California fault lines, which result when two adjoining plates scrape against each other, are more like a game of bumper cars on a grand scale.
Moran says that because there were few European settlers in the area at the time of the New Madrid earthquakes, and the accounts of the earthquakes varied in extremes, some people question the common consensus on the magnitude of the quakes.
“Nobody thinks of a hill being broken open,” Moran says. “I’ve run into people who say it wasn’t a bad earthquake because nothing was damaged. I say nothing was here to be damaged. Now we’ve got stuff parked on the area. If you had the same type of earthquake, stuff would be hurt.”
A map of the New Madrid Seismic Zone. Memphis lies right on the southern edge of it.
The Danger in Not Knowing
Both Moran and Grunwald warn of the danger of misinformation. “Our job is to get information out to the public. If you do not fill that void with the right information, the wrong information will show up,” Moran says, his voice taking on a tone of deadly seriousness.
Perhaps the most infamous case of bad information being spread is that of Iben Browning, the climatologist (note: not seismologist) and author who predicted that the next “Big One” would strike the NMSZ on December 2nd and 3rd of 1990. Iben’s unfounded predictions caused a media storm and mass panic, with some schools in the region planning to cancel classes those days, just in case he was right. As it turned out, of course, he was wrong, and this magazine lampooned the doomsday-prophet in the December 1990 issue, calling the earthquake this city’s “Worst Civic Obsession.”
Of course, Iben’s famously inaccurate predictions won’t be the last bad information spread about the NMSZ. The combination of scarcity of reputable sources and a disaster of potentially Biblical proportions lends itself particularly well to the lightning-fast spread of misinformation.
“One of the common myths that we try to dispel here is that these earthquakes rang church bells in Boston,” Grunwald explains. “We’ve never found any proof of that. You would think that if all the church bells in Boston just started ringing on one of these days, at least somebody in some newspaper somewhere would have mentioned it.”
Moran says that even the most unbelievable fantasies often have at their core a kernel of truth. “During the New Madrid earthquakes, the first of the earthquakes, December 16, 1811, at 2:30 in the morning, rang a clock bell in Charleston, South Carolina, for a duration of 10 seconds,” Moran says. “It was the night watch fire watch steeple, and the seismic waves traveling across the country swayed the steeple, rang that bell for about 10 seconds, and they noticed it.”
Moran explains that some months later, when the news circulated up to Boston, a clipping from the Charleston, South Carolina, newspaper was reprinted in a Boston paper. Charlestown, with a “w,” is a suburb of Boston, and somewhere along the way, someone conflated the accounts. In 1912, Myron L. Fuller published a history of the New Madrid earthquakes for the U.S. Geological Survey, and by then, the myth that the earthquakes rang church bells in Boston was considered unassailable canon.
The instance of the Charleston fire-watch bells is a more extreme case of myth and misinformation, though. Grunwald says that, for the most part, despite the challenge of understanding the NMSZ and the earthquakes it produced (and continues to produce, albeit of a lower magnitude), seismologists have reached something of a consensus about the quakes.
“You probably do get some hyperbole, but I would say most folks these days seem to be landing in the same area in terms of the magnitude of these quakes,” Grunwald says. He explains that most researchers place them on a scale somewhere between a 7 and a 7.7 on the moment magnitude scale. Grunwald says that figure “used to be in the high 8s,” though.
“Shockwaves from quakes in this part of the country travel up to 20 times as far as shocks from earthquakes on the West Coast. The reason for that is the bedrock in this part of the continent is much more dense. There’s less fracturing, so waves move through it much more easily and they go a lot further,” Grunwald explains, suggesting that a better understanding of the differences between the geologies of the two seismically active regions may help account for the downgrading of the 1811-1812 quakes’ estimated magnitudes. Still, Grunwald says, “If you’re talking about an area impacted by shaking felt or damage, there’s really little question that these [earthquakes] would have been the largest.”
The Risk Factor
So what are the risks for Memphians and Mid-Southerners today? Will Downtown Memphis liquify? Will we slide into the Mississippi, and will the river run backwards, carrying the Bluff City to St. Louis or beyond?
It’s not likely.
“People have tried to place [the fault] under Memphis,” Moran says. “You’ve heard that one where we’re going to slide into the river. No, we’re not. It’s a comforting thought.”
Moran says that New Madrid County and Memphis have “different soil quality. The soil of the bluffs is loess. It’s not the river sediment of the river itself.” He continues, “Liquefaction happens when the sub-surface, which is saturated with water, can liquify at a certain magnitude, and that happens especially in river sediment areas or areas with a high water table.
“Up toward New Madrid when the earthquakes hit, because you had that river sediment with a high water table, it did liquify,” Moran says, explaining that he’s seen multiple “accounts of liquefaction happening in the area.” The evidence is still visible in the New Madrid area, where aerial photos show white spots in farmland — called “sand blows” — where sand was violently shaken to the surface.
As to predicting the next “Big One,” well, Moran and Grunwald can offer little in the way of firm forecasts, but the situation is nowhere near as dire as Iben Browning would have had Memphians believe in the 1990s. “It’s a 5 to 10 percent likelihood in any 50-year window of a 7 magnitude event,” Grunwald says. “And a 6 magnitude, which is still a powerful quake and could do a lot of damage, that’s actually a 25 to 40 percent likelihood. There has not been a 6 magnitude quake since 1895 in this part of the country.”
Those probabilities — comforting or not — are about as much certainty as Memphians can expect. Moran says that, for all his research, pinpointing when a seismic event will occur is currently beyond seismologists’ capabilities. “It’s howlingly complex because the whole fault’s under stress, but what’s the weakest point? By the 500-year recurrence interval, we have about 300 years to go … if you’re an optimist,” Moran says. “If you’re a pessimist, it’s tomorrow.”
That’s why, given the low percentages quoted by Grunwald and Moran, when it comes to the NMSZ, it pays to be optimistic.