Is Middle America Due For a Huge Earthquake?
In the early 19th century, a series of massive quakes rocked Missouri. Some experts predict that the state could be in for another round of violent shaking, while others warn that a big quake could strike elsewhere in the center of the continent.
By Peter Brannen
Jun 23, 2016
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.
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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.
Continued at:
http://www.theatlantic.com/science/archive/20...ke/486623/
