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The Really Big One - 75 years overdue, and counting...

bilby

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The US Pacific Northwest is a very stable region geologically - there hasn't been a major earthquake on the Cascadia fault since 1700. But that's not a good thing.

A magnitude 8.7 - 9.2 quake in the area is now 72 years overdue; The mean recurrence in the last 10,000 years is every 246 years, but the last was in 1700.

Screenshot_2018-10-04 10,000 years of Cascadia earthquakes.png
(source)

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

Such a quake will, of course, be hugely destructive; But the associated Tsunami will be even worse - devastating and with little warning for the US West Coast, and potentially devastating (albeit with several hours warning) in Japan, Hawaii, and perhaps even the Australian East Coast.

The first sign that the Cascadia earthquake has begun will be a compressional wave, radiating outward from the fault line. Compressional waves are fast-moving, high-frequency waves, audible to dogs and certain other animals but experienced by humans only as a sudden jolt. They are not very harmful, but they are potentially very useful, since they travel fast enough to be detected by sensors thirty to ninety seconds ahead of other seismic waves. That is enough time for earthquake early-warning systems, such as those in use throughout Japan, to automatically perform a variety of lifesaving functions: shutting down railways and power plants, opening elevators and firehouse doors, alerting hospitals to halt surgeries, and triggering alarms so that the general public can take cover. The Pacific Northwest has no early-warning system. When the Cascadia earthquake begins, there will be, instead, a cacophony of barking dogs and a long, suspended, what-was-that moment before the surface waves arrive. Surface waves are slower, lower-frequency waves that move the ground both up and down and side to side: the shaking, starting in earnest.

Soon after that shaking begins, the electrical grid will fail, likely everywhere west of the Cascades and possibly well beyond. If it happens at night, the ensuing catastrophe will unfold in darkness. In theory, those who are at home when it hits should be safest; it is easy and relatively inexpensive to seismically safeguard a private dwelling. But, lulled into nonchalance by their seemingly benign environment, most people in the Pacific Northwest have not done so. That nonchalance will shatter instantly. So will everything made of glass. Anything indoors and unsecured will lurch across the floor or come crashing down: bookshelves, lamps, computers, cannisters of flour in the pantry. Refrigerators will walk out of kitchens, unplugging themselves and toppling over. Water heaters will fall and smash interior gas lines. Houses that are not bolted to their foundations will slide off—or, rather, they will stay put, obeying inertia, while the foundations, together with the rest of the Northwest, jolt westward. Unmoored on the undulating ground, the homes will begin to collapse.

Across the region, other, larger structures will also start to fail. 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 buildings—more than three thousand of them schools—will collapse or be compromised in the earthquake. So will half of all highway bridges, fifteen of the seventeen bridges spanning Portland’s 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.

Certain disasters stem from many small problems conspiring to cause one very large problem. For want of a nail, the war was lost; for fifteen independently insignificant errors, the jetliner was lost. Subduction-zone earthquakes operate on the opposite principle: one enormous problem causes many other enormous problems. The shaking from the Cascadia quake will set off landslides throughout the region—up to thirty thousand of them in Seattle alone, the city’s emergency-management office estimates. It will also induce a process called liquefaction, whereby seemingly solid ground starts behaving like a liquid, to the detriment of anything on top of it. Fifteen per cent of Seattle is built on liquefiable land, including seventeen day-care centers and the homes of some thirty-four thousand five hundred people. So is Oregon’s critical energy-infrastructure hub, a six-mile stretch of Portland through which flows ninety per cent of the state’s liquid fuel and which houses everything from electrical substations to natural-gas terminals. Together, the sloshing, sliding, and shaking will trigger fires, flooding, pipe failures, dam breaches, and hazardous-material spills. Any one of these second-order disasters could swamp the original earthquake in terms of cost, damage, or casualties—and one of them definitely will. Four to six minutes after the dogs start barking, the shaking will subside. For another few minutes, the region, upended, will continue to fall apart on its own. Then the wave will arrive, and the real destruction will begin.

The article is from three years ago, but since then, little has changed - other than that the quake has steadily become even more overdue.

The odds of this happening in the next 50 years are about 1 in 10. It's a brave person who would stake their life, and that of their family, on such odds.
 

steve_bank

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It is not just the Cascadia fault, it is the entire Cascade Mountains range from California to Washington.

For the Puget Sound region it gets worse.

The Univ Wash in the 90s did a seismic charge survey of the floor of the sound. The conclusion was that a particular quake will excite a resonance the sound's bottom. It will be sustained and water will slosh back and forth up and down the sound like a tsunami. Low lying areas will be devastated.

Geologic evidence supports the analysis. Estimates of a big quake would be on the order of three muntes systained vibration in Seattle. It would destroy the city and area.

I remember the Nisqually quake. I was about 150 miles north of the epicenter at work. I was on the bottom floor built into a hill.

I heard what I first thought was something gone wrong with a vibration table nearby until the walls staring moving in and out sinusoidally.

The Oregon and Washington coast have disaster plans and evacuation drills. There are buoys that will warn of a tsunami.

Also back in the 90s evidence was found of periodic lahars from Mt Rainier triggered by smaller quakes. The mud-ice flow will today bury populated areas all the way down to coastal region. Ice sliding down the mountain melt creating a fast moving slush picking up rocks and debris.

We are on the Ring Of Fire. Up on Rainier od Hood on a clear day you can see how the nearby volcanoes line up.

Staring with Shasta in northern California there are a series of volcanoes leading up to Rainier. Some small some bug like Hood, Rabier, and St Helens.

I've been up to Crater Rock on Mt Hood, the plug from the last eruption. It is warm. You can smell sulphur. About 80 mils as the crow flies from Seattle is Glacier Peak which is considered more dangerous than others, but low population density. Last erupted late 1800s.

USGS current quakes. They occur all the time.

https://earthquake.usgs.gov/earthquakes/map/

There is a fault in the midwest. Just as dangerous as the California region. A big one in the 19th century changed the course of the Mississippi and was felt as far north as NY. Today affect millions. millions.

https://www.smithsonianmag.com/science-nature/the-great-midwest-earthquake-of-1811-46342/

https://en.wikipedia.org/wiki/New_Madrid_Seismic_Zone

Then there is the potential supervolcano eruption in Yellowstone.

https://en.wikipedia.org/wiki/Yellowstone_Caldera#Volcanoes
 

repoman

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Is there information on what is actually happening at the plate junction? How fast are the plates moving or how much pressure is built up?

I would think that when the plates can't move anymore that the quake would be imminent.



at 29 minutes shows the ChristChurch quake, at a 6.3. But how is that local 6.3 compared to a 9.0 from far off the coast going to be for the same building and ground is Seattle? What is the local intensity measured in? Thinking of something like magnitude per square kiliometer.
 

skepticalbip

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Is there information on what is actually happening at the plate junction? How fast are the plates moving or how much pressure is built up?
My understanding is that it is a "megathrust" fault like the fault that resulted in the Boxing day 2004 Indonesian quake and tsunami. The Juan de Fuca plate is being forced under the North American plate along a thousand miles. This has created the string of volcanoes of the Cascadia range.

ETA:
Never mind. I just started watching your linked video which describes the problem.
 

repoman

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Is there information on what is actually happening at the plate junction? How fast are the plates moving or how much pressure is built up?
My understanding is that it is a "megathrust" fault like the fault that resulted in the Boxing day 2004 Indonesian quake and tsunami. The Juan de Fuca plate is being forced under the North American plate along a thousand miles. This has created the string of volcanoes of the Cascadia range.

ETA:
Never mind. I just started watching your linked video which describes the problem.

I guess what I mean is this; have they anchored in sensors on the ocean floor on both the Juan de Fuca plate and the North American plate.

At any rate, money should be better spent of getting warning systems, like a tsunami text service instead of this dumb Presidential one.
 

Sarpedon

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The article is from three years ago, but since then, little has changed - other than that the quake has steadily become even more overdue.

The odds of this happening in the next 50 years are about 1 in 10. It's a brave person who would stake their life, and that of their family, on such odds

Not really. The odds of dying in a big earthquake are pretty low. If it were a 1/10 chance of death, that would be something.
 

bilby

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The article is from three years ago, but since then, little has changed - other than that the quake has steadily become even more overdue.

The odds of this happening in the next 50 years are about 1 in 10. It's a brave person who would stake their life, and that of their family, on such odds

Not really. The odds of dying in a big earthquake are pretty low. If it were a 1/10 chance of death, that would be something.

That's true, if you look at random members of a given large population. The chances of any particular resident of the Pacific Northwest dying in this event are fairly low. But it's not at all low for specific small communities that are on the coast and have no clear evacuation options. There are plenty of people who are almost certain to die if this happens while they are at home (or work, or school, or perhaps more than one of these places).

The fraction of people who are hit by the main impact of a large tsunami, and survive the experience, is very small indeed.
 

Worldtraveller

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With any luck, this will trigger the supervolcano under yellowstone and just take out most of the US, and a good chunk of the rest of the world. :D
 

steve_bank

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The Pacific Plate is moving to the northwest at 3 inches (8 centimeters) each year, and the North American Plate is heading south at about 1 inch (2.3 cm) per year. The San Andreas Fault was born about 30 million years ago in California, when the Pacific Plate and the North America plate first met.Mar 10, 2015

Plates are monitored with GPS. The big threat in a quake is something falling on you. The threat to the coast is a tsunami. Readiness on the coast and in Seattle is periodically on local news. Coastal communities have designated high spots to flee to.

In the region bridges have been reinforced on highways to ensure emergency supplies can get in to Seattle and elsewhere. There have been drills. The facility I am in has eminency food supplies along with a generator.

There has been an historical correlation with a Cascadia event and a tsunami recorded in Japanaround 600,

https://en.wikipedia.org/wiki/Cascadia_subduction_zone

It is old news. There have been local TV shows on the issue. The Unov Of Washington is active on all the seismic issues.

Back in the 90s it was reported an area in Oregon in the Cascades was rising indicating magma build up.
 
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