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The Really Big One


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The Really Big One

 

New Yorker article, and very well written. Apparently that Cascadia subduction zone has the potential for a huge earthquake, and is past its average time between quakes. We didn't know about it until recently, because the last quake happened in 1700, before the area had a written history (and most of the people with an oral history died in the quake and its aftermath)

 

Thanks to that work, 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.

 

 

The quake will cause a tsunami

 

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.”

 

 

Re-thinking my idea of moving back to Oregon when I retire.

 

Also of interest: I did not know that geologists had determined the maximum strength a San Andreas quake can have is about an 8.2, and that was what many also thought the max was for Japan quakes.

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That was an enjoyable read. So to speak. Dreadfully fascinating.

 

Edit: Actually I am also quite impressed how well the author conveyed info. I am in no position to judge the veracity (though nothing struck me as obviously wrong) but it seems to be one of the better popular science articles that I have read. Maybe a few references would be nice but other than that, very well written.

Edited by CharonY
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I didn't see any mention of how far inland the eastbound tidal wave will travel, just that it will be 700 miles wide.

 

Not to be too doom and gloom here, but could a major quake in the Pacific Northwest like this trigger the Yellowstone supervolano?

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I didn't see any mention of how far inland the eastbound tidal wave will travel, just that it will be 700 miles wide.

 

Not to be too doom and gloom here, but could a major quake in the Pacific Northwest like this trigger the Yellowstone supervolano?

 

 

Its about 1000 km from the coast - that's a lot of dampening space. And there is a lot of high land just East of I5 ( and thus far far west of Yellowstone) - Yosemite at one end and Mount Ranier at the Northern end for a start. I presume it is the plains between the coastal reach and this inland range which they fear will be inundated

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Not to be too doom and gloom here, but could a major quake in the Pacific Northwest like this trigger the Yellowstone supervolano?
The article mentions the "craton" - the big and old and rigid and "immovable" central mass of the NA plate, described as backstopping the more elastic and lighter fringe. The Yellowstone supervolcano is more in there - not on the Ring of Fire. Unlikely it would feel a thing.

 

There are a lot of active, dangerous volcanos much closer to the fault - if one or more of them is by chance right on the edge of something, this little nudge (on their scale) might push them over; so the pros say, anyhow.

 

On a mountain-buiding scale, these quakes and tsunamis are quite small. Pebbles in a pond.

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I live across the Columbia from Portland, roughly 70 miles from the coast and about 50 miles from the volcanoes Mt. Hood, Mt. St. Helens, and Mt. Adams. Since these are subduction volcanoes I would think the released stresses of the 'big one' would make their eruptions, in the short term, less likely.

 

As to Phi's question about how far inland the tsunami will reach I think it will vary depending on specifics of terrain and the angle of the wave front(s). I don't recall seeing projections for how far up the Columbia it will go, but I imagine it will surely reach Bonneville dam by some degree.

 

Forewarned is for-armed. >> Earthquake Readiness

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I didn't see any mention of how far inland the eastbound tidal wave will travel, just that it will be 700 miles wide.

 

 

They said it will be 60 feet high, so the coastal range mountains should limit the tsunami damage to the coast. Inland I was assuming it was all earthquake damage, because not much is built to code. I recall one that was <6.0 when I lived in Corvallis, OR (I think it was Scotts Mills, rather than the 6.0 Klamath Falls quake, in 1993, that we felt). It was a big deal in terms of damage

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They said it will be 60 feet high, so the coastal range mountains should limit the tsunami damage to the coast. Inland I was assuming it was all earthquake damage, because not much is built to code. I recall one that was <6.0 when I lived in Corvallis, OR (I think it was Scotts Mills, rather than the 6.0 Klamath Falls quake, in 1993, that we felt). It was a big deal in terms of damage

Actually the OP article said:

... Its height will vary with the contours of the coast, from twenty feet to more than a hundred feet. ...

Here's a set of inundation maps for Oregon. YRMV >>DOGAMI Tsunami Inundation Map (TIM) Series

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TV news stations out of Portland all covered the New Yorker article last night. A local geologist acknowledged most of the facts given in the article but contended the shaking inland would not be as severe as stated and that it would be felt but insufficient to knock a person down. The news here has been doing stories periodically on the Cascadia danger for years so any 'revelation' is more for you outlanders. ;)

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Well, I live in Oregon. Therefore, if this happens suddenly...

I doubt it is going to happen slowly ...

 

While I suspect Unity+ is unaware of slow quakes and that you meant to be facetious Strange, there is indeed a slow quake element to the Cascadia fault system.

 

Full article: >> Pacific Northwest Geodetic Array: Central Washington University

Slow Earthquakes, ETS, and Cascadia

 

In 2001, CWU researchers with the continuous GPS network Pacific Northwest Geodetic Array discovered periodic slow-slip across the Cascadia Subduction Zone. Previously undetected by seismic networks, these slip events exhibit regular recurrence intervals thus changing current understanding of earthquake behavior. Since this time, definitions for this newly discovered phenomenon have evolved. At first, the term "silent-earthquake" was employed to illustrate the absence of a seismic signature. Subsequent investigations and recent discoveries have led to a change in characterization. Now these slow-slip events are defined as eposodic tremor and slip (ETS).

 

In short, an ETS is a discreet time interval (episode) of relative tectonic plate movement (slip) coupled with high frequency seismic energy bursts (tremor). ETS usually last for around a few weeks duration as opposed to regular earthquakes where energy is released within seconds to minutes. ...

Only slightly off topic, the potential for a devastating 'really big one' occurring nowhere near a plate boundary also exists in the United States. I suspect the folks there are even less prepared than usins in the Pacific Northwest. Duck & cover!! :o

New Madrid Seismic Zone

...

Potential for future earthquakes

 

In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kansas, Kentucky, Mississippi, Missouri, Oklahoma, Texas, and particularly Tennessee, where a 7.7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.[20] The earthquake is expected to also result in many thousands of fatalities, with more than 4,000 of the fatalities expected in Memphis alone.

 

The potential for the recurrence of large earthquakes and their impact today on densely populated cities in and around the seismic zone has generated much research devoted to understanding in the New Madrid Seismic Zone. By studying evidence of past quakes and closely monitoring ground motion and current earthquake activity, scientists attempt to understand their causes and recurrence intervals.

 

In October 2009, a team composed of University of Illinois and Virginia Tech researchers headed by Amr S. Elnashai, funded by the Federal Emergency Management Agency (FEMA), considered a scenario where all three segments of the New Madrid fault ruptured simultaneously with a total earthquake magnitude of 7.7. The report found that there would be significant damage in the eight states studied Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee with the probability of additional damage in states farther from the NMSZ. Tennessee, Arkansas, and Missouri would be most severely impacted, and the cities of Memphis, Tennessee and St. Louis, Missouri would be severely damaged. The report estimated 86,000 casualties, including 3,500 fatalities; 715,000 damaged buildings; and 7.2 million people displaced, with 2 million of those seeking shelter, primarily due to the lack of utility services. Direct economic losses, according to the report, would be at least $300 billion.[21]

...

Here's some history and more data on the faults from USGS: >> New Madrid 1811-1812 Earthquakes

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Won't these slow quakes release energy that would otherwise be released with "the big one" ?

Possibly. However we must presume the slow quakes have been going on all along even though they are a recent discovery, and yet the Cascadia mega-quakes do occur with [more-or-less] regularity. The article I quoted goes on to say:

...

In contrast, the subtle motion caused by ETS is so "slow" it's difficult to record at the surface. One might say "quiet" or possibly "silent" in nature, but definitely important since these events affect lithospheric plate interactions that are responsible for damaging "fast" earthquakes. Will the size of future large-scale megathrust earthquakes be reduced or will the time interval between these earthquakes increase with an ETS? A process with such imposing consequences is hardly "silent" in terms of relevance. ...

So the exact correlation of slow to fast quakes of Cascadia is an open question.
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Won't these slow quakes release energy that would otherwise be released with "the big one" ?

 

To echo what Acme said, the article points out that small quakes possibly relieving stress doesn't eliminate big quakes. Presumably that would apply here as well — big quakes still happen.

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...

Not to be too doom and gloom here, but could a major quake in the Pacific Northwest like this trigger the Yellowstone supervolano?

Maybe. :o A new study has allowed researchers to make the most detailed map to date of the plumbing and they find there is magma o'plenty for a super eruption.

> Study: Yellowstone magma much bigger than thought (Update)

 

Here's a couple pertinent FAQs rom USGS. (I'm having to refresh these pages a couple times to get them to display.)

> Are earthquakes at Yellowstone related to volcanism?

> Is there a relationship between large earthquakes (>M6) that occur along major fault zones and nearby volcanic eruptions?

Edited by Acme
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  • 1 month later...

Update:

Seems the story Swansont posted has got some traction.

One note, this story I'm posting says I-5 runs along the coast, which it does not. It runs between the coast range and the Cascade range on average 100 miles from the coast. Not that it's bridges get an all clear, just that I feel compelled to pick a nit. :)

 

Will talk of the 'Big One' shake the US into quake prep?

...

The real-time, deep ocean alert system DeFazio wants would give people on the coast more time to move inland to safety.

 

And it would provide Portland a warning of three to five minutes -- enough time to stop trains and close its precarious bridges. Estimates on such a system are hard to come by, but some go as high as $250 million.

 

"The New Yorker article has certainly hit a nerve in the Pacific Northwest. It was written in such a way -- it even raised the hair on the back of my neck. But in Congress, it is a different situation," he said.

 

"The technology is known, we just lack the will to fund it. It is kind of pathetic."

 

DeFazio says he is concerned about the national security and economic impact that such a disaster would have on the country.

 

"It would be a huge blow to not just the Western economy, to the US economy. Look at what is based in Portland and Seattle: Intel, Microsoft. Their headquarters would be decimated."

...

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  • 2 weeks later...

wow this is very interesting normally i am not interested in earthquakes because i am not by the coast but its amazing how they were able to find out that there was an earthquake in the 1700, when you say it was found out because of an oral history how was it recorded? someone said it to someone else it got passed down until a certain century and then it got recorded is that what they mean? I read the article on the new yorker and i cant really understand where the big cascadia was i think they said it started near the coast of California but it kept on going west until it reached japan. am i understanding right?

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wow this is very interesting normally i am not interested in earthquakes because i am not by the coast but its amazing how they were able to find out that there was an earthquake in the 1700, when you say it was found out because of an oral history how was it recorded? someone said it to someone else it got passed down until a certain century and then it got recorded is that what they mean?

Yes, native Americans kept the oral history and eventually passed it on to researchers. From Wikipedia:

... Oral history

 

At the time of the 1700 earthquake, there were no written records of the event in Cascadia. Orally-transmitted legends from the Olympic Peninsula area talk of an epic battle between a thunderbird and a whale. Therefore, in a 2005 study, seismologist Ruth Ludwin set out to collect and analyze anecdotes from various First Nations groups. Reports from the Huu-ay-aht,[4] Makah,[4] Hoh,[5] Quileute,[2][5] Yurok,[2] and Duwamish[2] peoples referred to earthquakes and saltwater floods. This collection of data allowed her team to come up with an estimated date range for the event, whose midpoint fell in the year 1701.[4] ...

Further field research of submerged forests and debris fields has revealed the details of much earlier mega-quakes & tsunamis from the Cascadia fault.

 

I read the article on the new yorker and i cant really understand where the big cascadia was i think they said it started near the coast of California but it kept on going west until it reached japan. am i understanding right?

The subduction zone does not run to Japan, rather it's the Pacific [tectonic] plate they refer to as reaching Japan. Here's a map of the subduction zone from Wiki and a link to their article:

Cascadia subduction zone @Wiki

800px-Cascadia_Subduction_Zone.jpg

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