I'm not trying to burst your bubble but a 3.2 is really not much. Washington State actually experiences around 1,000 earthquakes a year. The majority of those are in the west but they have had some real big ones on the eastern side of the Cascades.
There have been three or four intraplate quakes since the 1940's in Washington (your CSZ event) the biggest of which was a 7 or so, while there have been thousands and thousands of Crustal quakes in the same time period.
Thanks for your post, Westwall; and for your kind visitor message on my profile.
You may be a geologist, but you are no seismologist. I can guarantee you that I am MUCH more familiar with West Coast earthquake patterns than you are.
Yes, there are "thousands and thousands of crustal quakes" -- but there are not thousands of quakes stronger than 3 in either Washington or Oregon. That's the CSZ trade-off, you see: in the hundreds of years between mega-thrust earthquakes, we have very few earthquakes of any size at all. I've lived in the Pacific Northwest all of my life, and I remember only three earthquakes that were big enough to feel (but the one year I lived elsewhere, 2001, we had our "big" Nisqually quake). Two of the three were just larger than a 3 in magnitude; the third was a 4.5. Those were pretty big quakes for this part of the world.
An "intra-plate" quake is NOT the same thing as a Cascadia Subduction Zone event. The Nisqually quake to which you refer was intra-plate along the Nisqually fault that runs east-west just south of Tacoma; the Cascadia Subduction Zone runs north-south between the 600-mile-long Juan de Fuca plate and the North American plate under which it subducts. The rate of subduction is 3-4 centimeters per year; but because the plates lock together, it doesn't subduct gradually, but all at once, in a mega-quake that occurs when the plates suddenly break free.
It has been nearly 313 years since the last CSZ event. In that time, the plates have built up 10-12 meters of un-realized subduction between them. The stress has pushed the N. American plate up, causing it to bow upwards on the coast; consequently, when the stress is finally released, the coast will drop by six to ten feet in elevation, permanently flooding existing coastal communities.
Really, I don't explain it as well as the experts do. However, I've posted some great links to information on the Cascadia Subduction Zone, especially in my first post:
Wikipedia: Cascadia Subduction Zone
(Note: the oft-quoted time-spacing of 500 years in between events is out-dated. It has since been found that the CSZ often breaks only on the north or south half. Essentially, earlier researchers were missing approximately half the data.)
Oregon Department of Geology publication Cascadia Winter 2010 Pay particular attention to the timeline at the bottom of page 8 -- 313 years is WAY longer than the normal time between events. We haven't gone this long without an event since before the invention of the wheel!
Also,
the BBC documentary linked in post #33 is excellent. The UK isn't as afraid to discuss our impending disasters as our own government is; they tell it like it is. It's important to remember that they are not exaggerating the danger; if anything, it's actually worse than they show.
As a Nevada resident, both you and Geezer (who lives in Utah) should stay abreast of developments. Although it's possible that either or both of you may feel the earthquake when it happens, the greater threat is to our power generation systems.
You may think that in Nevada you are wholly dependent on the Hoover Dam for your electricity, but that is not how it works. Although there are many power generation facilities across the US, there are only three electrical distribution regions ("grids") that are completely independent of one another -- the West Coast, the East Coast, and Texas. (Don't ask me why Texans have to have their own isolated power grid; they just do.) Within a region, all generation facilities and all consumers are tied into the same grid; so if the grid itself collapses, all its consumers will be without power until it can be stabilized and brought back online -- a complicated process that has historically taken days, and can take much, much longer if the grid has experienced significant losses.
When the CSZ event finally occurs (and as a West Coast dweller myself, I hope against hope that it doesn't occur for many decades) it will bring down the entire West Coast grid. It will do this through the widespread destruction of both transmission and generation facilities.
It will most certainly destroy Boundary Dam, which provides half the power the city of Seattle consumes; but Boundary is just a tiny drop in the bucket.
It will also destroy all the dams on the Columbia, from the Grand Coulee to the Bonneville, and a dozen other dams in between those great ones.
The dams that will cause this disaster are not in the US, but in Canada. There are three Canadian dams that pose the greatest danger to the Columbia valley: Mica Dam, Keenleyside Dam, and Corra Linn Dam. All three dams are now used for both power generation and flood control, although one, Keenleyside, was originally built only for flood control according to the terms of the Columbia River Treaty between our countries.
In addition to being used to generate power and control the floodwaters into the Columbia River, the three dams have two more commonalities: all three are earth-fill construction -- the most vulnerable to breaching in an earthquake -- and all three hold back extremely large reservoirs of water. The Keenleyside and the Corra Linn reservoirs hold more than 7 million acre-feet each, and Mica holds back more than 20 million acre-feet of water!
These dams are between 300 and 400 miles from the coast, but that is not far enough to protect them from a magnitude 9+ subduction zone event. They will experience severe shaking for a period of 3-6 minutes, which will cause settling of their earth-fill barriers and subsequent loss of structural integrity.
If any one of these three dams are breached, the waters released will quickly scour away the remaining dam material, dissolving it into mud. The billions of cubic feet of water will scour the riverside of trees, which will become battering rams against any obstacle in their path. Debris-filled flood-waters that can achieve speeds above 40 miles an hour will rush down the Columbia River valley, removing everything that stands in their way.
Even the Grand Coulee cannot stand against such a force; and when it falls, another 9 million acre-feet of water will be added to the torrent.
By the time the flood reaches the ocean, it will have scoured the Columbia River valley clean of civilization as we know it. The town of Mason City will disappear as soon as Lake Roosevelt overtops Grand Coulee Dam; then the torrent will overtop and destroy Chief Joseph Dam, Wells Dam, and Rocky Reach Dam before inundating the city of Wenatchee. The next dams to fall will be Rock Island, Wanapum, and Priest Rapids; and then the deluge will arrive at the Hanford Reservation.
Hanford remains the single most radioactively polluted site in all of North America, in spite of billions of dollars already spent on the clean up. There are still over 170 huge underground single-walled storage tanks (of the size used to hold our nation's oil reserves) that have been leaking radioactive waste into the groundwater, and thence into the Columbia River. An aerial view of Hanford reveals patchy white areas; if you zoom in, these become visible as massive areas of leaching salts that are slowly flowing downhill, into the Columbia River...
... And then the deluge arrives.
Hanford disappears. The town disappears, the last remaining active nuclear plant disappears, and the poisoned, radioactive soil disappears. It is swept away with the river, to be deposited all along the downstream riverbanks and in the river delta... turning the most heavily polluted radioactive site in America into an environmental disaster of previously unimagined proportions.
More cities: Richland, Kennewick, and Pasco; then the McNary Dam, the John Day Dam, the Dalles Dam... and the city of The Dalles. After passing through and destroying the towns of Hood River and Stevenson, the torrent of mud and debris blasts its way through and over Bonneville Dam, and heads for the really populated areas: Portland, Vancouver, and Longview.
By the time the deluge has reached Portland, it will be over 22 million acre-feet of water -- that's over 7 TRILLION gallons of water -- plus millions of tons of debris from the dams, forests, and towns the deluge destroyed on its way there.
The loss to our generation capacity will catastrophic. Including Boundary dam on the Pend Oreille, the Western region will have lost total generation capacity of more than 21,000 mega-watts -- enough to power ten cities the size of Seattle -- representing trillions of dollars over a century of infrastructure investment.
That infrastructure will not be replaced quickly or easily. It may be a long, long time before the lights go back on again in any western state.
-- Paravani
