Seattle and the Big One

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beej

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http://www.newyorker.com/magazine/2015/07/20/the-really-big-one

Just north of the San Andreas, however, lies another fault line. Known as the Cascadia subduction zone, it runs for seven hundred miles off the coast of the Pacific Northwest, beginning near Cape Mendocino, California, continuing along Oregon and Washington, and terminating around Vancouver Island, Canada. The “Cascadia” part of its name comes from the Cascade Range, a chain of volcanic mountains that follow the same course a hundred or so miles inland. The “subduction zone” part refers to a region of the planet where one tectonic plate is sliding underneath (subducting) another. Tectonic plates are those slabs of mantle and crust that, in their epochs-long drift, rearrange the earth’s continents and oceans. Most of the time, their movement is slow, harmless, and all but undetectable. Occasionally, at the borders where they meet, it is not.

Take your hands and hold them palms down, middle fingertips touching. Your right hand represents the North American tectonic plate, which bears on its back, among other things, our entire continent, from One World Trade Center to the Space Needle, in Seattle. Your left hand represents an oceanic plate called Juan de Fuca, ninety thousand square miles in size. The place where they meet is the Cascadia subduction zone. Now slide your left hand under your right one. That is what the Juan de Fuca plate is doing: slipping steadily beneath North America. When you try it, your right hand will slide up your left arm, as if you were pushing up your sleeve. That is what North America is not doing. It is stuck, wedged tight against the surface of the other plate.

Without moving your hands, curl your right knuckles up, so that they point toward the ceiling. Under pressure from Juan de Fuca, the stuck edge of North America is bulging upward and compressing eastward, at the rate of, respectively, three to four millimetres and thirty to forty millimetres a year. It can do so for quite some time, because, as continent stuff goes, it is young, made of rock that is still relatively elastic. (Rocks, like us, get stiffer as they age.) But it cannot do so indefinitely. There is a backstop—the craton, that ancient unbudgeable mass at the center of the continent—and, sooner or later, North America will rebound like a spring. If, on that occasion, only the southern part of the Cascadia subduction zone gives way—your first two fingers, say—the magnitude of the resulting quake will be somewhere between 8.0 and 8.6.Thats the big one. If the entire zone gives way at once, an event that seismologists call a full-margin rupture, the magnitude will be somewhere between 8.7 and 9.2. That’s the very big one.

Flick your right fingers outward, forcefully, so that your hand flattens back down again. 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. Roughly three thousand people died in San Francisco’s 1906 earthquake. Almost two thousand died in Hurricane Katrina. Almost three hundred died in Hurricane Sandy. FEMA projects that nearly thirteen thousand people will die in the Cascadia earthquake and tsunami. Another twenty-seven thousand will be injured, and the agency expects that it will need to provide shelter for a million displaced people, and food and water for another two and a half million. “This is one time that I’m hoping all the science is wrong, and it won’t happen for another thousand years,” Murphy says.

In fact, the science is robust, and one of the chief scientists behind it is Chris Goldfinger. Thanks to work done by him and his colleagues, we now know that the odds of the big Cascadia earthquake happening in the next fifty years are roughly one in three. The odds of the very big one are roughly one in ten. Even those numbers do not fully reflect the danger—or, more to the point, how unprepared the Pacific Northwest is to face it. The truly worrisome figures in this story are these: Thirty years ago, no one knew that the Cascadia subduction zone had ever produced a major earthquake. Forty-five years ago, no one even knew it existed.



theres a lot more to the story on the link...too long to post the whole thing. Interesting how they tracked down the last major earth quake up there in Jan, 1700
 

Mackeyser

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I don't like that Seahawks, but I wouldn't wish a 9.2 on anyone...
 

CGI_Ram

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I don't like that Seahawks, but I wouldn't wish a 9.2 on anyone...

I wanted to say something like I hope they float off into the ocean... Then your post reminded me the Seabags hardly amount to squat in a disaster like this.
 

beej

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I don't like that Seahawks, but I wouldn't wish a 9.2 on anyone...
we can take comfort, though, in knowing that if the sea rises 20-30 feet in the next little bit, most of them will be washed away or inland anyway.
 

DaveFan'51

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I don't like that Seahawks, but I wouldn't wish a 9.2 on anyone...
I live in California, and I been through all of the BIG ONES since the mid 1940's and they are terrifying! I couldn't agree with you more!!
 

JonRam99

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If you have time, read the entire article. I read it from a link earlier this week; terrifying. They said that essentially, everything west of Interstate 5 from Vancouver down to northern California will be toast. Literally. And, it's overdue by about 60 years--it should have happened about 1940.
 

beej

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It is pretty scary. I don't usually buy in to the dooms day predictions but that article whether right or wrong was convincing.
 

Elmgrovegnome

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Well. Scratch the upper West Coast off of my list of places that I would like to live. Vancouver B.C. is such a beautiful city too. Damn.
 

Greg Stone

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I checked this thoroughly before moving here. It's unlikely that it will happen in my lifetime but it is one reason I live atop a 500 foot hill overlooking the Strait of San Juan de Fuca. Even in the rural area I live there are tsunami evacuation signs all over and a system of sirens. I do think the "west of I-5" destruction estimate is overblown. The tsnami will enter the west end of the Strait that is perhaps 10 miles wide and traverse 100 miles of the vast and sprawling Salish Sea. The Seattle water front is a steep hill. Some places will be devastated and others will be much less affected.
 

Rams Until I Die

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Funny that this article is all of sudden going around like wildfire. Living here in the Seattle area the "big one" has been talked about since I was elementary school. That being I'm totally unprepared lol and this is s good reminder to fix that.
 

RAMSinLA

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I hate earthquakes, the aftershocks wear out nerves and go on for weeks after a large quake. I lived in Sylmar CA at the time of the Sylmar/San Fernando earthquake in the 70's. I was just a kid and it scared the hell out of me. The sewer system was out for months, we had to stand in line at dump stations with our neighbors to take a dump in the morning. Not fun! When we finally fled our home right after the shaking stopped we looked up to see flames everywhere from exploding gas lines so we ran back in the house. As we passed the pool I noticed it was almost empty. I figured it must of cracked and leaked but it didn't...the water was bounced right out of the pool!
I've been in three other quakes as an adult. Glendale, Northridge (that was a bad one) and a small but damaging one in Hemit CA.
https://en.wikipedia.org/wiki/1971_San_Fernando_earthquake


:oops: Check out where the next big one could be...
http://www.livescience.com/42802-new-madrid-earthquakes-aftershocks-risk.html
 

jrry32

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I was going to say poor Seahawks fans but then I remembered that 80% of their fan-base would be unaffected by an earthquake and tsunami in the Pacific Northwest. ;)