Friday, June 24, 2016

Is Middle America Due For a Huge Earthquake?

As I drove across the I-40 bridge into Memphis, I was reassured: chances were slim that a massive earthquake would wrest the road from its supports, and plunge me more than a hundred feet into the murky Mississippi. Thanks to a recently completed $260 million seismic retrofit, the bridge—a chokepoint for traffic in the central U.S.—is now fortified. It’s also decked out with strong-motion accelerometers and bookended by borehole seismometers to record convulsions in the earth.
The bridge passes a glass colossus, the Memphis Pyramid. Originally built as a nod to the city’s Old Kingdom namesake, the pyramid now enshrines a Bass Pro Shops megastore. The city recently spent $25 million to prevent the pyramid from being swallowed, perhaps by Geb, the ancient Egyptian god of earthquakes. Further downtown, AutoZone’s corporate headquarters also stands ready for a tectonic throttling, propped up as it is on top of giant shock absorbers, while, the nearby Memphis VA is similarly inured to temblors after the city spent $64 million dollars removing nine floors of the hospital to reduce the risk of collapse in a catastrophic earthquake.
To those reared on the coasts, with a traditional understanding of earthquakes as arising from titanic disagreements at the edges of tectonic plates, this all sounds quite strange. Indeed, the USGS earthquake hazard map of the United States, might also come as something of a shock. The familiar culprits are there: the entire West Coast predictably lights up as a long, narrow hazard zone—from the cascades to southern California. But in the center of the country there’s also a bewildering, giant fuchsia bullseye—smack in the middle of what should be the stable interior of North America.
In 1999, FEMA identified four hazards in the United States that, were they consummated in all their destructive wonder, would be worthy of the title “catastrophic.” They were: a major earthquake hitting Los Angeles, a major hurricane hitting Miami, a major hurricane hitting New Orleans (check), and a giant earthquake hitting the Central US.

The source of all this anxiety is the fabled New Madrid Seismic Zone. In the winter of 1811 and 1812, three earthquakes of magnitude 7, and possibly as high as 7.7, and countless punishing aftershocks thereafter, rocked the sparsely inhabited frontier of the American Midwest. The earth had slipped somewhere deep under the frontier settlement of New Madrid, Missouri, and the resulting earthquakes opened up chasms, diverted the Mississippi, threw trees to the ground and landslides into the river. It created temporary waterfalls and lasting lakes. Meanwhile, existing lakes were turned inside out, as cracks in the ground spewed volcanoes of sand and water into the air. Boatmen caught in the maelstrom said the Mississippi appeared to run backwards. The quakes woke New Yorkers, rang church bells in Charleston, South Carolina, buzzed bemused Torontonians a country away, and brought down chimneys from St. Louis to Cincinnati. Because the deep rock in the middle of the continent is older and colder than out west, strong shaking was felt over an area 10 times that of the 1906 San Francisco earthquake. An alarmed President James Madison even wrote Thomas Jefferson from DC about the tremors.
The shocks occurred on what today is the least understood seismic zone in the United States. And depending who you ask, another major earthquake here represents either a towering threat for which the Central U.S. is woefully unprepared, or a wildly overhyped phantom costing taxpayers hundreds of millions of dollars in needless infrastructure improvements.
*   *   *
Not far from Memphis and St. Louis, 600 million years ago, the continent tried to rip in half. It failed. But even calling this “the continent” is misleading: North America was probably south of the equator, almost upside down, and had just fractured out of a larger supercontinent called Rodinia. East Antarctica was to the northwest, eastern New England and the Canadian Maritimes were perhaps on a different part of the planet, stitched onto Africa, and a piece that was about to break off of “North America” would eventually end up in the middle of Argentina. This was not our world. This world was still convalescing from the near-death experience of Snowball Earth—having hurtled in and out of planet-wide glaciations, and the first strange whispers of simple animal life had just begun to be etched in ocean rocks.

As the supercontinent Rodinia blasted apart, an ocean not unlike the Atlantic (only a half-billion years earlier) began to grow between the rifting continents. But in “Missouri,” a similar ocean rift stalled. Here the continent tried to divorce but it didn’t take. For hundreds of millions of years this failed rift (called the Reelfoot Rift) has languished as a jagged scar buried deep in the earth. As the ages have passed, it’s been covered far above at the surface by trilobites in shallow seas, later by coal swamps, and later still, by coastal dinosaurs. But it’s never fully healed.
After eons of continental tango, only a few thousand years ago, this rift reawakened. A little over 200 years ago, several faults along this unthinkably ancient gash ruptured, triggering some of the largest earthquakes in American history. Luckily, almost no one lived near Southeast Missouri at the time. But today millions of people do.
*   *   *
In 2009, the Mid-America Earthquake Center at the University of Illinois released a report simulating the fallout from another 1811-1812-style earthquake in a region that today includes Memphis, St. Louis, Nashville, and a Mississippi River lined with industry, people, and levees. The language used to describe the resulting destruction in the study was surprisingly intemperate.
“All hell will break loose,” the study’s lead author Amr Elnashai pronounced. The report’s nightmare vision is best quoted in full:
Nearly 715,000 buildings are damaged in the eight-state study region. About 42,000 search and rescue personnel working in 1,500 teams are required to respond to the earthquakes. Damage to critical infrastructure (essential facilities, transportation, and utility lifelines) is substantial in the 140 impacted counties near the rupture zone, including 3,500 damaged bridges and nearly 425,000 breaks and leaks to both local and interstate pipelines. Approximately 2.6 million households are without power after the earthquake. Nearly 86,000 injuries and fatalities result from damage to infrastructure. Nearly 130 hospitals are damaged and most are located in the impacted counties near the rupture zone. There is extensive damage and substantial travel delays in both Memphis, Tennessee, and St. Louis, Missouri, thus hampering search and rescue as well as evacuation. Moreover roughly 15 major bridges are unusable. Three days after the earthquake, 7.2 million people are still displaced and 2 million people seek temporary shelter. Direct economic losses for the eight states total nearly $300 billion, while indirect losses may be at least twice this amount.
The language in the report is only slightly less dire than that used by the fringe right, which has oddly latched onto the geological curiosity of New Madrid as both an objective correlative for the nation’s political disunion, as well as a sign of the coming apocalypse. Wade into the conspiratorial murk of the cyber hinterlands—that preserve of goldbug popup ads and invidiously cropped pictures of President Obama—and you’ll find eccentric interpretations of the region’s seismology.

The New Madrid Seismic Zone has long suffered from a surfeit of such hype.
I visited the New Madrid Historical Museum in the Missouri Bootheel town that was destroyed in the wild winter of 1811-1812 by the fault it straddles. The museum is housed in an old saloon in the shadow of a giant Army Corps levee that protects the town from the looming Mississippi. It advertises the town’s unofficial—and strangely plangent—motto on billboards, t-shirts and road signs: “It’s Our Fault!”
When I visited New Madrid, the only two people downtown were myself and Sandy Hill, who works at the front desk of the Historical Museum. Hill moved to New Madrid in 1990, when earthquake hype was reaching a crescendo. A prophecy had just been made by an eccentric charlatan named Iben Browning, who falsely claimed to have predicted the 1989 Loma Prieta earthquake in California the year before. Now he was predicting that a magnitude 7 earthquake would strike New Madrid on December 3, 1990. Despite the obvious quackery, and the universal derision of seismologists, news trucks from around the country descended on the town to cover the fictive quake, scaring its residents half to death.
“At that time my husband was principal out at New Madrid Central and they had a girls basketball game that night and the other team wouldn’t let their girls come here because that was when we were supposed to have the earthquake,” says Hill. “A lot of people left for the week and got a motel room. I sent the insurance policies on our houses to my sister-in-law in Florida, and I says, ‘If we go down the sewer you can have a good time.’”

When the day came and went without incident—and the convoy of news vans packed and left—the menace of the earthquake disappeared for many as well. Today in the museum a staticky VHS tape about 1811-1812, called “The Night the Earth went Crazy,”  still plays on a loop. Over the bad tracking and synth-fuzz soundtrack the narrator nonsensically calls the 1812 event “the worst earthquake in recorded history,” which it assuredly was not. But today most people I spoke with in the region seemed to think about their hometown quake more as historical curiosity than existential threat.
But to James Wilkinson, director of the Central U.S. Earthquake Consortium (CUSEC), every year is 1811. His organization, which was created by FEMA, is housed in a small columnated brick building outside the Memphis Airport. CUSEC brings together the emergency managers of the eight states that would be most directly affected by another New Madrid event. Memphis, being the closest city to the fault, and famous for the sorts of attractive historic brick buildings that tend to get demolished by earthquakes, is the major metro area most threatened by a reprise of 1811-1812. But for Wilkinson, the greatest threat might not be the shaking itself but a Mississippi River newly unleashed from its engineered prison of levees.
“The thing that, to me, makes the river scary is how much industry we have along it: there’s power plants, there’s chemical plants, there’s ports,” he said. “And the river might change course altogether.”
Rivers are alive. Bends in them push ever outward over time as the rushing water carves out the river’s outer edge. Give them time and these bends will warp into horseshoes. And when these kinks get too extreme the water finds a shortcut over the land in between, pinching off the horseshoes and stranding these former river bends as oxbow lakes. If viewed in extreme time lapse, over thousands of years, the Mississippi would wriggle like an angry snake, shedding off little crescent lakes. This wriggle has been tamed, for now, by civil engineers.

There is evidence for a previous dramatic shift in the river in the landscape not far from Memphis.
“Crowley’s Ridge is this ridge about 25 to 30 miles west of here that runs right up through the delta for no apparent reason,” says Wilkinson. “So you’re riding through West Memphis as you cross the river and its flat. And then suddenly you just go up on this ridge and its about a half-mile to a mile across before you drop back down. Well, the feeling is that the river used to be on the other side of that ridge.”
“We’re very lucky in a sense,” Wilkinson said as I was leaving his office. “We’ve had earthquakes, we’ve had damage, but nothing like what we’ve seen in other parts of the world. So the clock’s ticking.”
*   *   *
“They’re not scientists!” said Northwestern seismologist Seth Stein. I met with Stein in his office in Evanston, Illinois, and he’d cut me off as soon as I mentioned that I had visited CUSEC.
Stein literally wrote the book on New Madrid and his research over the past three decades has been a gigantic record scratch in the ominous drumbeat of alarm. To Stein, the constant warnings of disaster are dangerous nonsense. To wit, he thinks the University of Illinois study predicting mass casualties is trash.
“Same thing,” he said. “They’re engineers. They know absolutely nothing about earthquakes.”

As for the USGS earthquake hazard map showing a bullseye over the midwest, Stein thinks it needlessly amplifies the threat. And he has nothing but scorn for CUSEC and the federal agency it represents. Understanding Stein’s skepticism requires a little primer on earthquakes.
It’s not enough to say that there are old faults underneath New Madrid and that’s why there are earthquakes. The continent has endured eons of trauma. There are faults everywhere. To the north and west of New Madrid’s jagged Reelfoot Rift is the much larger and even more unthinkably ancient Midcontinent Rift, formed more than a billion years ago when there was nothing more interesting on planet earth than pond scum. It runs from Ontario to Oklahoma. The result of another failed breakup of the continent, today the Midcontintent Rift is exposed most spectacularly as dramatic lava cliffs hanging over Lake Superior in Minnesota and Michigan. But this rift system is quiet.
On the other side of New Madrid, the eastern seaboard is positively riddled with old faults—a shattered underworld of scars from continental collisions that once thrust the Appalachians possibly as high as the Himalayas, and wrenching schisms that would later pull the supercontinent Pangaea apart. As this successor to Rodinia split, the Atlantic Ocean was born 200 million years ago. But before it became a proper ocean, it was a network of narrow rift valley lakes—not unlike today’s East African Rift Valley—and it invited prehistoric crocodiles and dinosaurs to its shores. But the division also left behind a bedrock riven with the geological equivalent of stretch marks. Rumbles, like the one that cracked the Washington Monument in 2011, remind us that ancient scars exist unseen all along the east coast, but for the most part, these old faults  are quiet. To get earthquakes you need not only faults, but strain.
In California there’s plenty of strain. Where the Pacific Plate grinds inexorably against the edge of North America, earthquakes are easy to understand. As the plates try to move past each other, they catch, and strain builds up. When this strain reaches a breaking point, the land snaps back into place. These are earthquakes. And these earthquakes will continue with utter inevitability for the foreseeable future as the two plates continue to plow past each other, guided by the incandescent churn of the mantle far below. Along the San Andreas, the ground is warping at a rate of 40 millimeters per year. The longer California goes without earthquakes, the more strain this motion builds up (as a result, Los Angeles is long overdue for a truly massive earthquake). In Chile, home to the largest earthquakes in recorded history, the Nazca Plate is diving under South America at 80 millimeters per year, or twice that of California.
But when Stein littered the New Madrid Seismic Zone with GPS receivers, he found that the ground was hardly moving at all—less than two millimeters per year and possibly zero. According to seismology 101, no ground motion means there’s no strain building up. And no strain means no earthquakes. New Madrid, Stein reasoned, was safe. But with no plate boundaries, why on earth was there ever strain—and, more importantly, earthquakes—here in the center of the continent in the first place?
“Basically the way to think about the lithosphere—and it’s easy when you live in Chicago—is, imagine you have big chunks—big chunks—of ice floating around on the lake, and those things are sliding by each other. So those are the plate boundary earthquakes, like in California. But then within those big ice sheets you have small cracks. And there are very small motions within them. That’s how the big pieces stay together.”

The continents aren’t rigid and unchanging but rather dynamic and plastic, slowly deforming as distal forces act on them over huge distances. The ancient faults—those wounds from all of earth history—provide weak points in the crust where the incredibly slow deformation of the continent can eventually build up enough strain to unleash massive, unexpected earthquakes.
“So this is, in fact, how continents deform,” Stein says. “We have all these faults that have grown over the whole history of the continent, and the earthquakes move around among them.”
In New Madrid a slew of forces act on the 600 million-year-old Reelfoot Rift, and come from all directions, converging here in the middle of the continent.
First, from below. There’s an odd little tectonic fragment off the coast of the Pacific Northwest, called the Juan De Fuca plate. It’s all that remains of a once gigantic slab of Pacific Ocean seafloor that began diving under North America during the Cretaceous. Today this fragment is responsible for the inevitable mega-quake (outlined in Kathryn Schulz’ Pulitzer Prize-winning New Yorker storylast year) that will pummel Seattle. But the rest of this formerly enormous ocean plate is now mostly underneath the United States, having slid under the continent for tens of millions of years. Far underneath the middle of the country, this ancient slab of the Pacific finally dives down to oblivion, dragging on the earth above and tugging at New Madrid.
Then, from the east. The Mid-Atlantic Ridge is a colossal underwater mountain range in the middle of the Atlantic Ocean that runs from the Arctic to nearly the Antarctic. It has been pushing North America away from Europe and Africa for 200 million years. The stress from that distant mid-ocean push might be transmitting all the way to the middle of the United States. And so New Madrid buckles.
From the north, there used to be tremendously heavy sheets of ice more than a mile thick that covered the top half of North America until a very recent 12,000 years ago. As these ice sheets have retreated, and North America has been relieved of its Ice Age burden, the continent still unbends—a strain that might be tweaking New Madrid.

Finally, from above. The writhing Mississippi River, which whips sediment back and forth throughout the delta, constantly shifts the load atop the ancient faults of the Reelfoot Rift, potentially setting them off.
Whatever the reason, the rift came alive a few thousand years ago. Though New Madrid earthquakes undoubtedly came as a surprise to European settlers in the 19th century, they were a recurring peril for the epic civilization that came before.
*   *   *
From the top of Monks Mound in southern Illinois, the St. Louis Arch is a hazy mirage on the horizon. At almost 100 feet tall the mound itself is a terraced pyramid and the “largest prehistoric earthwork in the Americas.” According to archaeologists, it once overlooked a city, Cahokia, that wouldn’t be surpassed in population until colonial Philadelphia hundreds of years later. Cahokia was just one part of a breathtaking culture that built mounds like this up and down the Mississippi, with trading networks that spanned hundreds of miles. Though Cahokia collapsed a century before Columbus for reasons that remain mysterious (an archeologist on-site told me that fortifications and traumatized skeletons suggested a war-weary end), Indian cultural artifacts elsewhere in the region have helped scientists date a slew of massive pre-Columbian earthquakes.
The sand and water volcano witnesses saw issue from the earth in 1812 came from deposits deep under New Madrid. When shaken, this subterranean slurry acted like a shaken can of soda, bursting through the rock layers above in sandy fountains, some of which spewed more than 30 feet in the air. Today “sand blows” from 1812 can still be seen on Google Maps as pale patches dotting the farmland around New Madrid. But earlier sand blows found underground have been dated—thanks in part to the native pottery shards and charcoal that sandwich them—to 1450 AD, 900 AD and 2350 BC. To many geologists, the recurrence of these huge earthquakes over the past few thousand years is worrying—a sign that 1811-1812 wasn’t a one-off, freak disaster but a consistent, if intermittent, feature of life in the Central U.S. for the past several thousand years. But Stein thinks the New Madrid Seismic Zone is vitiated, having catastrophically relieved the strain that it had built up slowly, over tens of thousands of years. Now, he says, the faults are shutting off.
If this is true, it wouldn’t be the first fault in the region to do so. Hundreds of miles to the west is the Meers Fault in Oklahoma. It’s dead now, but as recently as 1,200 years ago it was producing large New Madrid-style earthquakes.
“If you accept the facts that intra-plate faults turn on and off, and this one turned on, it has to turn off … So it’s kind of working its way down and it has pretty much used up what was in its strain reservoir.”

“Every time there’s a magnitude 4 people like CUSEC are claiming giant earthquake’s on the way! And you think about this, and you look into the rock physics and it says no, it’s the opposite. Those are aftershocks.”
This part of Stein’s message is both comforting from a New Madrid perspective but unsettling for everyone else. That’s because large intra-plate earthquakes, when they disappear on one fault zone, tend to pop up where no one’s looking.
His collaboration with Chinese colleagues has convinced Stein that New Madrid isn’t the sui generis oddball, as its often portrayed, but fits the pattern found on other continents. In China, one doesn’t need to be a paleoseismologist or archaeologist to piece together the record of earthquakes over the past few thousand years. You only need to be able to read Chinese. Government records provide a catalog of giant mid-continent earthquakes in China that go back thousands of years and, unnervingly, almost completely defy any pattern.
Stein pulled up an animation on his computer of a millennium of Chinese earthquakes.
“OK we’re starting at the year 1300,” he said.
In 1303 a magnitude 8.0 lights up Hongtong in the Shanxi province of North China.
“So there’s this huge earthquake here and then you say, ‘Ok well there must be this structure here, maybe the next one will be on it.”
And sure enough, not far away, in 1556, a magnitude 8.3 pops up to the southwest in Huaxian.
“This is another huge earthquake, so then you say, ‘Ok, this is a really dangerous area now.’”

He clicked the next slide.
“And then this is 1668.”
In 1668, 500 miles to the east, a massive 8.5 earthquake pops up out of nowhere.
“Then you say, ‘Oh, well we never even suspected this fault system.’ So if you were building nuclear power plants for the Ming Dynasty you wouldn’t build ‘em here and you wouldn’t build ‘em here,” he said, pointing to the now at least two demonstrated trouble spots.
“But then the next one’s here,” he said, as I followed, the dots dance from one part of the screen to the other. Only 11 years later, the threat had unpredictably migrated hundreds of miles north, to just outside of Beijing, pummeling the region with a magnitude 8 earthquake in 1679. The scattering continued to the present day, as giant earthquakes filled in the blank spaces on the map. In 1966, a sequence of earthquakes alerted officials to a new trouble spot in Xingtai. But then in 1976, 260 miles away, the Tangshan earthquake struck where no one was looking, and killed perhaps a half a million people.
“In most cases these earthquakes are on unmapped faults,” Stein said. “A lot of times the way you find a fault in the mid-continent is that you get a big earthquake on it and then you go out and say, ‘Oh gee, there’s a fault there.’”
To Stein, the implication is clear. He compares the expensive retrofitting of Memphis to staking out the entire police department at the last convenience store that was robbed.
“If you say, ‘OK, the really dangerous place is where the last earthquake was,’ you get into this whack-a-mole situation,” he said.
If the New Madrid Seismic Zone really is shutting down, then it’s someone else’s turn. North America isn’t going to stop deforming and all that strain has to go somewhere. Somewhere in the country, perhaps some fault has been imperceptibly building up strain for hundreds of thousands of years and will soon release it. Perhaps it’s the blank areas of our hazard maps that should worry us. In Nepal, the country’s earthquake hazard map showed the two ends of the country glowing with seismic hazard and a placid interior. Last April an enormous quake struck this unremarkable center of the country and killed more than 8,000 people.

“Shall we say, All this is but a Chance that happens to us or the mere unguided Motion of Matter?” he wrote. “Ah, profane Philistine!””
Three decades later, another earthquake struck off the coast of Gloucester and rocked the city once more. A similar earthquake today might devastate Boston’s Back Bay neighborhood, which is built on landfill that would liquefy during heavy shaking. In New York City, the nearby Ramapo Fault hasn’t had a major earthquake on it, as far as anyone can tell, for hundreds of years. Depending on how you look at it, this is reassuring or nerve-wracking.
But Stein prefers not to worry, taking after the prescription of geologist Charles Richter himself who once scoffed, “I don’t know why people in California or anywhere worry so much about earthquakes. They are such a small hazard compared to things like traffic.”
“A good number to remember is that earthquakes kill about 10 people a year in the United States,” Stein says. “Which is about the same as skateboards.”
But catastrophic earthquakes, like terrorism, have an outsized hold on our brainstems. There’s something especially menacing and Old-Testament-y about the idea of the Earth itself demolishing the pretenses of civilization. Charles Darwin addressed this primal unease, after experiencing the 1835 Concepción earthquake in Chile.
“A bad earthquake at once destroys our oldest associations: the earth, the very emblem of solidity, has moved beneath our feet like a thin crust over a fluid;—one second of time has created in the mind a strange idea of insecurity, which hours of reflection would not have produced.”
But Stein’s interpretation is far from unanimous among seismologists. New Madrid may yet be a menace. In his office at Center for Earthquake Research and Information at the University of Memphis, geologist Charles Langston slumps his shoulders at the mere mention of Stein’s name. He lets out a long sigh and begins to laugh. “Seth,” he mutters.

No one really knows how intra-plate earthquakes work. And no one really knows what on earth is going on down there deep underground. While Stein’s model posits that the ground above would warp in the run-up to an impending quake, other models for New Madrid suggest there would be no deforming at all. As for Langston, he’s been listening to the New Madrid Seismic Zone for the past few years, and what he’s heard has been disquieting. After setting up 81 seismometers in eight states, Langston’s team has been using the sound of large earthquakes from the other side of the planet to map out the earthquake hazard directly below his feet. They found that the sound waves from these distant calamities markedly slowed down as they passed through New Madrid Seismic Zone compared to the earth around it.
“To explain those areas of low seismic velocity, you have to say that the rocks are different in some way and, in fact, they almost have to be molten,” he said. “But since there’s no volcanoes they’re probably not molten. They’re probably hot. You also probably need water at great depth. So there’s some very unusual things going on. So what that all says is that that part of the mantle and the crust is unusually weak compared to the adjacent parts. So it makes sense that the New Madrid Seismic Zone is there. It’s a weak spot in the crust that makes earthquakes.”
I asked Langston if the region was ready for another big earthquake.
“No,” he said.
The earth, that “emblem of solidity,” shifts quietly under our feet until it gives way. Supercontinents shatter and reunite. Oceans peel out of the heartland or fail to form, buried instead as broken lineaments of stone by rivers of life. Hundreds of miles below landlocked farms—or old earthen pyramids—the seafloor dives down to the incandescent abyss. The continents warp and the music on Beale Street plays on. We still live with the legacy of everything that’s ever happened to this planet, and each new earthquake points a way forward. When buildings fall or rivers change course, society rebuilds like an ant colony kicked by a child. But the continents will follow on their aimless course—as they have—until there’s no one left to notice them tremble. Two centuries ago, New Madrid played an infinitesimal part in this story, but no one knows what comes next.
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