Shake, Baby, Shake

New Madrid Fault - "Not Dead Yet"

The New Madrid fault zone in the nation's midsection is active and could spawn future large earthquakes, scientists reported Thursday.
It's "not dead yet," said U.S. Geological Survey seismologist Susan Hough, who was part of the study published online by the journal Science.

Researchers have long debated just how much of a hazard New Madrid poses. The zone stretches 150 miles, crossing parts of Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee.

In 1811 and 1812, it unleashed a trio of powerful jolts, measuring magnitudes 7.5 to 7.7, that rattled the central Mississippi River valley. Chimneys fell and boats capsized. Farmland sank and turned into swamps. The death toll is unknown, but experts don't believe there were mass casualties because the region was sparsely populated then.
. . .
"Our new results tell us that something is going on there, and therefore a repeat of the 1811-1812 sequence is possible," Hough said.

The USGS estimates there's a 7 to 10 percent chance of that happening in the next 50 years.

But even that isn't as scary as this article on the Cascadia Subduction Zone fault off the California-Oregon-Washington coast: The Really Big One

. . .When the next very big earthquake hits, the northwest edge of the continent, from California to Canada and the continental shelf to the Cascades, will drop by as much as six feet and rebound thirty to a hundred feet to the west—losing, within minutes, all the elevation and compression it has gained over centuries. Some of that shift will take place beneath the ocean, displacing a colossal quantity of seawater. (Watch what your fingertips do when you flatten your hand.) The water will surge upward into a huge hill, then promptly collapse. One side will rush west, toward Japan. The other side will rush east, in a seven-hundred-mile liquid wall that will reach the Northwest coast, on average, fifteen minutes after the earthquake begins. By the time the shaking has ceased and the tsunami has receded, the region will be unrecognizable. Kenneth Murphy, who directs FEMA’s Region X, the division responsible for Oregon, Washington, Idaho, and Alaska, says, “Our operating assumption is that everything west of Interstate 5 will be toast.”

In the Pacific Northwest, everything west of Interstate 5 covers some hundred and forty thousand square miles, including Seattle, Tacoma, Portland, Eugene, Salem (the capital city of Oregon), Olympia (the capital of Washington), and some seven million people. When the next full-margin rupture happens, that region will suffer the worst natural disaster in the history of North America.

That sounds bad. I spent much of my youth travelling up and down the California and Oregon coasts. That's a lot to lose. Not to mention all the friends and family that live in that zone. So just when can we expect this to happen?

 we now know that the Pacific Northwest has experienced forty-one subduction-zone earthquakes in the past ten thousand years. If you divide ten thousand by forty-one, you get two hundred and forty-three, which is Cascadia’s recurrence interval: the average amount of time that elapses between earthquakes. That timespan is dangerous both because it is too long—long enough for us to unwittingly build an entire civilization on top of our continent’s worst fault line—and because it is not long enough. Counting from the earthquake of 1700, we are now three hundred and fifteen years into a two-hundred-and-forty-three-year cycle.

Any day now, in geologic time. Time to be thinking about how to survive it with civilization intact.

Come to think of it; summers aren't that bad on the east coast. . .