Science
Related: About this forumFull Margin Rupture
There's a great description of how they dated the last 9.0 quake in the Cascadia subduction zone (~9pm, January 26, 1700), by corroborating tree ring data with written Japanese records of the resulting tsunami. Read the whole thing.
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.
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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 backstopthe craton, that ancient unbudgeable mass at the center of the continentand, sooner or later, North America will rebound like a spring. If, on that occasion, only the southern part of the Cascadia subduction zone gives wayyour first two fingers, saythe 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. Thats the very 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 westlosing, 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 FEMAs 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.
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Until 1974, the state of Oregon had no seismic code, and few places in the Pacific Northwest had one appropriate to a magnitude-9.0 earthquake until 1994. The vast majority of buildings in the region were constructed before then. Ian Madin, who directs the Oregon Department of Geology and Mineral Industries (DOGAMI), estimates that seventy-five per cent of all structures in the state are not designed to withstand a major Cascadia quake. FEMA calculates that, across the region, something on the order of a million buildingsmore than three thousand of them schoolswill collapse or be compromised in the earthquake. So will half of all highway bridges, fifteen of the seventeen bridges spanning Portlands two rivers, and two-thirds of railways and airports; also, one-third of all fire stations, half of all police stations, and two-thirds of all hospitals.
http://www.newyorker.com/magazine/2015/07/20/the-really-big-one
Trajan
(19,089 posts)I love it so much here ... I cannot live in fear, but I can be better prepared ....
phantom power
(25,966 posts)Most people can do that. I assume it's a lot harder to quake-proof a structure after the fact.
They really should build an early-warning system like Japan has. That could save a lot of lives.
Lordquinton
(7,886 posts)When it comes from new york...
phantom power
(25,966 posts)Cleita
(75,480 posts)Go to Anchorage Alaska and see what a 9+ earthquake did there in 1964. Go see part of the land that dropped eight feet into the sound. I saw it myself five years later. You can't deny what has happened.
https://en.wikipedia.org/wiki/1964_Alaska_earthquake
It can happen here. I find many deniers though who would rather not think that a Fukushima event or worse could happen to us.
Warpy
(112,810 posts)and I read an article not to long ago that showed coastal cabins sunk in marshland up to the old roof lines. The pre FEMA government had done a great job of evacuating many people from the coast before the tsunami struck but even at that, there were deaths.
The problem with this is that there is no way to predict it. Oh, we know it's going to happen, but not when. It could be happening while I type this or it could wait for another hundred years. We do know that the longer the time interval, the stronger the quake is likely to be.
Cleita
(75,480 posts)drilling and keeping nuclear power plants operating that are past the age the were built to last, fracking and now attempts by the oil companies to bring in Alberta tar sands on oil bomb trains through the western states. One good earthquake in a land that is known for earthquakes could ruin this land worse than just what ma nature alone would do.
Lordquinton
(7,886 posts)People on the east coast, and the south are always talking like the west coast will just fall into the ocean any day now.
I have lived in the SF bay area for my whole life, and lived through the loma prieta earthquake, which was only 6.9, but still caused a massive amount of damage that I saw first hand. There are still scars from it, if you know where to look.
I actually watched that on TV. Devastating. I was living in LA then.
Lordquinton
(7,886 posts)I thought,"Well I went through a quake, and it was only 7 or so, not that bad, but let me google it to see it's actual number" and of course google brought up a bunch of images of the devastation. It's hard to comprehend that our freeway system had collapsed.
Were you in LA for the northridge quake? I don't recall it being quite as bad as loma prieta, but still caused some damage.
Cleita
(75,480 posts)It did force the County to speed up their retrofit program on buildings and freeways for earthquakes.
shenmue
(38,529 posts)Boy, was it embarrassing.
nilram
(2,940 posts)Fortunately, I was at home.
Now, home is in Oregon, and I hope it doesn't happen again in my lifetime.