On the morning of Feb. 7, 1812 people along a stretch of the Mississippi River, near where Kentucky, Missouri, and Tennessee meet, awoke to find that the river was running backward. According to eyewitnesses, it was traveling "at the speed of a fast horse."
Trees collapsed as the air filled with sulphur and coal dust. The New Madrid fault had erupted, thrusting up a bulwark to dam the Mississippi, and reverse its course for a few hours.
The Feb. 7, 1812 earthquake was only the last in a series of four monumental explosions that radiated across the American heartland over seven and one-half weeks beginning on December 16, 1811. It pummeled a significant portion of the Mississippi River Valley.
No one knows exactly how powerful these earthquakes were; seismologists leave them somewhere in the magnitude 8 plus/minus range. Regardless of magnitude, this quartet of earthquakes warped the ground, created fissures, caved in river banks, and forced from the ground torrents of ejecta that saturated the air with a blanket of noxious vapors sufficient to cause darkness. The gloom obliged people to light lanterns, except in those places where great arcs of dazzling "earthquake lights" were splayed from the horizon into the sky almost halfway to zenith.
The intensity of these tremors sent out seismic waves ranging over 1,000 miles — knocking books, plates and glasses off shelves on the East Coast, cracking sidewalks in Washington D.C., and setting church bells ringing in Boston and Toronto. Sleeping residents in Pittsburgh and Norfolk were awakened; chimneys toppled as far away as Louisville.
The New Madrid Fault Zone differs in some important ways from other seismically-active regions. The most obvious contrast being that there are no plate boundaries running through the mid-section of the North American continent. And yet, good sense dictates that should be necessary in order to produce seismicity, and something indeed is found beneath the Earth’s crust here to account for that.
What is now the North American continent used to be part of the supercontinent Rodinia.
Some 600 million years ago plate tectonics had split Rodinia asunder and the surface under what is now Missouri, Arkansas, and Tennessee, in response to such enormous pressure, also began to rift but didn’t have quite the impetus to pull it off.
What remains of this foiled attempt to tear North America apart is a primeval geologic scar, a fractured weak zone in the bedrock, the demarcation line of something that might have been but ended up stillborn.
This rift would be considered relatively seismically quiescent, but yet can be reactivated ever so often, brought back to life by the east-west compressive forces the continent undergoes as it drifts. The North American plate isn’t sitting calmly undisturbed. It's engaged in a constant shoving match with adjoining plates. These immense shocks and tensions cause compressions that undulate across the length and breadth of the continent.
The only place for it to buckle is in its weakest region, its Achilles’ heel, lying hidden beneath what is now the central Mississippi River Valley.
Populations in this region are probably far less interested in primordial geologic history than in how future events might unfold. Certainly, there will be more earthquakes in the central U.S., big and small, yet the results need not necessarily mirror seismic events in other earthquake-prone areas.
In Californian cities, for example, special construction codes have evolved, retrofitting bills have been passed; foundation and home inspection services prosper. The citizenry is inculcated with the need for emergency preparedness, all in response to having put down roots in an extremely active seismic zone.
In actuality, the West Coast is better prepared for whatever mistreatment the San Andreas or Cascadia might dole out. For that reason alone, San Diego might shrug off the same sort of jolt that could conceivably cause quite a bit of damage in Evansville, Indiana, or Jonesboro, Arkansas.
Nature, too, has stacked the deck.
There is a real difference between the crust in the eastern U.S. — as opposed to the west. It’s older, colder, and more dense. Seismic waves traveling through this medium are stronger and range much further.
There’s reassuring news, however, to note in all this too. According to probabilistic risk assessments determined by the US Geological Survey in 2003, as found in, "Scientists Update New Madrid Earthquake Forecasts." The odds of an 1811-12 magnitude caliber repetition are fairly long — between a seven to 10 percent chance in the range of years from 2003 to 2053. So while Los Angeles, San Francisco, and Seattle garner much more official interest in preparation for seismicity, the expedient of banking on the likelihood it simply won’t happen in Memphis, St. Louis — or Owensboro, Kentucky — seems to be the most practical resort with resources that are obviously not unlimited.
David Nabhan is a science writer, the author of "Earthquake Prediction: Dawn of the New Seismology" (2017) and three previous books on earthquakes. Nabhan is also a science fiction writer ("Pilots of Borealis," 2015) and the author of many scores of newspaper and magazine op-eds. Nabhan has been featured on television and talk radio all over the world. His website is www.earthquakepredictors.com. To read more of his reports — Click Here Now.
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