13 ms·

Cascadia Subduction Zone[1] is why I never considered living in Seattle/Portland once I found out about it. Funny, cause I live in the SF Bay Area, where the ea

Cascadia Subduction Zone[1] is why I never considered living in Seattle/Portland once I found out about it. Funny, cause I live in the SF Bay Area, where the earthquakes are frequent, but they can never reach the magnitude of what's possible by the Cascadia Subduction Zone. [1] https://en.wikipedia.org/wiki/Cascadia_subduction_zone https://en.wikipedia.org/wiki/Cascadia_subduction_zone

dataflow 3y ago
> Funny, cause I live in the SF Bay Area, where the earthquakes are frequent, but they can never reach the magnitude of what's possible by the Cascadia Subduction Zone. What makes you think a big one ("The Big One") isn't going to hit the Bay Area?
- xattt 3y ago
  I’m wondering how far the big one will be felt. As egocentric as my question is, will I feel it on the East coast?
  - ksenzee 3y ago
    It won’t be _that_ big. They’ll feel it as far as Idaho maybe.
  - finite_depth 3y ago
    No, but you would feel it well inland throughout the Mountain West. See this simulated USGS map for a 9.0 quake: https://upload.wikimedia.org/wikipedia/commons/8/80/9.0_Cascadia_scenario_%28median%29.pdf https://upload.wikimedia.org/wikipedia/commons/8/80/9.0_Casc... - for scale, the light blues are about the edge of where you'd clearly go "oh, yep, that's an earthquake", although you might notice such a large one at lower ground acceleration because the shaking would be quite prolonged (~minutes, rather than the ~10-20 seconds of a typical minor quake).
- asveikau 3y ago
  I don't think they're saying that. But from what I recall reading, the big one that hits Seattle will exceed the big one that hits the Bay. Seattle's big ones are higher magnitude but less frequent. Iirc it's also likely the 9.0 that hits Seattle won't be in most of our lifetimes. The last really big one was before Europeans arrived.
  - rapind 3y ago
    Rainier will erupt first and the mudslide will wipe out all those houses built on the last mudslide.
    - seanmcdirmid 3y ago
      Rainier erupting would devastate slot of small communities between it and Tacoma. Like Helen’s blowing it’s glacial too (liquifying into a muddy huge river) but worse since the area around is more populated.
      - rapind 3y ago
        Yes and a lot of these suburbs are built upon the mudslides from previous (recent) eruptions (few million people). Last I heard it was a 1 in 7 chance in my lifetime. It's incredibly stupid and dangerous. Mudslides can travel up to 50 mph or more, and it doesn't even need to be an eruption that kicks it off.
- dkasper 3y ago
  From what I’ve read the faults in the Bay Area can’t really generate above an 8.0, whereas the cascadia zone can produce much larger events (remember a 9.0 is 10x the intensity of 8.0). It has to do with the size and type of the faults.
  - carbocation 3y ago
    Yes: a 7.8 is thought to be the max in the Bay Area, as far as I understand. E.g., https://www.sfchronicle.com/bayarea/article/only-one-bay-area-fault-is-capable-of-producing-a-17767684.php https://www.sfchronicle.com/bayarea/article/only-one-bay-are...
  - zamfi 3y ago
    > remember a 9.0 is 10x the intensity of 8.0 10x the ground movement amplitude — 32x the total energy release, though!
ianburrell 3y ago
The Cascadia quake will be about same damage to Seattle and Portland as Bay Area quake. It could be up to magnitude 9 but the fault is 60 mi away from the cities. The big difference is that it will affect the whole area. And that PNW is way behind in infrastructure.
- diogenes4 3y ago
  According to https://www.sfchronicle.com/projects/2023/bay-area-earthquake/ https://www.sfchronicle.com/projects/2023/bay-area-earthquak... vs https://www.newyorker.com/magazine/2015/07/20/the-really-big-one https://www.newyorker.com/magazine/2015/07/20/the-really-big... you're looking at two orders of magnitude difference in terms of the estimate of people affected. I'm not sure what led to the difference but that's striking.
  - adrianpike 3y ago
    That New Yorker article goes viral every few years - it's a well written piece and spins a great yarn, but there's some significant hyperbole and it's sources don't quite back up the claims. Yes, a 9.x will be devastating. No, everything west of i-5 will not be toast.
    - diogenes4 3y ago
      > it's sources don't quite back up the claims. I'll admit that FEMA isn't exactly cited in a way that's possible to corroborate, but presumably they're estimating a worst-case scenario and not a median- or average-case scenario. That might explain some of the large divorce in figures.
      - adrianpike 3y ago
        I'd love to find any actual FEMA publications that back up some of the numbers and claims - so far to the best I can tell is it's mostly from interviews with the regional director, which, while valuable, isn't quite at the level of citation I'd like. If anyone's got a PDF I'd love to retract all my critiques though. :)
ksenzee 3y ago
On the other hand, Seattle is one of the best places in the world to ride out climate change, which is 100% happening, and happening already. It’s all a numbers game.
- Axsuul 3y ago
  And SF isn't?
  - mvdtnz 3y ago
    I'm no expert on the region but aren't people in California forever whining about heat waves and water shortages?
    - akkartik 3y ago
      California != SF.
    - iancmceachern 3y ago
      Water shortages are largely in the central valley and Southern California. Sf gets its water from Hetch Hetche, clean hydro power too. SF is a very different place in a lot of ways from the rest of California, and the US in general.
      - callalex 3y ago
        Yes but that aqueduct is hundreds of miles long and goes through the Central Valley. Once the water wars begin, that situation could change rapidly.
        iancmceachern 3y ago
        They'd need to change some pretty old laws... https://www.archives.gov/legislative/features/hetch-hetchy/hr7207.html#:~:text=Introduced%20by%20Congressman%20John%20Raker,the%20bill%20with%20little%20debate https://www.archives.gov/legislative/features/hetch-hetchy/h....
Stratoscope 3y ago
My mom was a Red Cross nurse who worked in the relief effort after the 1964 Good Friday earthquake and tsunami that devastated Anchorage and areas as far south as Crescent City, California. It was magnitude 9.2, the second largest in recorded history. The photos she brought back were quite something. I may still have them somewhere, but in the meantime there are plenty online. LIFE.com has a remarkable collection: https://www.life.com/history/the-great-alaska-earthquake-of-1964-rare-photos-from-an-epic-disaster/ https://www.life.com/history/the-great-alaska-earthquake-of-... https://ready.alaska.gov/_64Quake/History https://ready.alaska.gov/_64Quake/History https://earthquake.usgs.gov/earthquakes/events/alaska1964/ https://earthquake.usgs.gov/earthquakes/events/alaska1964/ https://en.wikipedia.org/wiki/1964_Alaska_earthquake https://en.wikipedia.org/wiki/1964_Alaska_earthquake From Wikipedia: > As a result of the earthquake, 131 people are believed to have died: Nine died as a result of the earthquake itself and another 122 died from the subsequent tsunamis all over the world. Five died from the tsunami in Oregon, and 12 died from the tsunami in Crescent City, California.
- shostack 3y ago
  Those numbers, while sad, are surprisingly low compared to other causes of death.
  - Retric 3y ago
    Anchorage was 78 miles from the earthquake and still saw mass building collapses. The death toll was low due to the low population in the area. 128,026 in 1970 presumably less in 1964.
    - interloxia 3y ago
      About 290,000 in 2022. https://www.census.gov/quickfacts/fact/table/anchoragemunicipalityalaska https://www.census.gov/quickfacts/fact/table/anchoragemunici...
- seanmcdirmid 3y ago
  My mom was a schoolgirl in anchorage during the earthquake. We have a picture of my grandma and her trailer being 20 feet down from the rest of the ground. Haven’t digitized it yet.
jandrewrogers 3y ago
The fault is at least 150 miles from Seattle proper, the city will not receive the full brunt of the earthquake. Tsunamis are strongly mitigated by the geography of Puget Sound — the biggest tsunami threat is actually the Seattle fault. By contrast, the San Andreas fault literally runs through the middle of the Bay Area.
- btilly 3y ago
  Let's see. The Cascadia quake is 100x as big. I'm at 1/3 the distance from the San Andreas fault. Guess who gets the larger earthquake? Add to that the fact that I grew up in Victoria. All of Vancouver Island is a subduction zone during a Cascadia earthquake. Sadly, that means that a good chunk of what I knew growing up winds up under water. Seattle may fare better, but my home town does not.
  - seabrookmx 3y ago
    It's not like the island will just drop into the earth. Unless you were referring the tsunami risk, which is my big fear as a fellow Victorian.
    - btilly 3y ago
      The island does subside in these earthquakes. Reading up now, it looks like it is 1-2 meters, mostly on the west coast of the island. But my memory of the early research when I still lived there in the early 1990s was that it was about a 3 meter drop. Between how low much of Victoria is, widespread poorly build older houses, and lots of housing built on unstable landfill in places like James Bay, my belief was that it was going to be pretty devastating to a lot of parts that I knew. However recent articles like https://www.mdpi.com/2624-795X/4/3/13 https://www.mdpi.com/2624-795X/4/3/13 suggest a much milder risk than I had thought.
  - djmips 3y ago
    Can you back that up with some references? Very curious, I've never heard any claims that Victoria will end up under water in a big Cascadia earthquake.
mannykannot 3y ago
Your experience depends quite a bit on where you live and/or work, or, more specifically, what's underneath it. If one has nothing to do with the Millennium Tower, that is probably a plus.

dataflow 3y ago

> Funny, cause I live in the SF Bay Area, where the earthquakes are frequent, but they can never reach the magnitude of what's possible by the Cascadia Subduction Zone. What makes you think a big one ("The Big One") isn't going to hit the Bay Area?

xattt 3y ago
I’m wondering how far the big one will be felt. As egocentric as my question is, will I feel it on the East coast?
- ksenzee 3y ago
  It won’t be _that_ big. They’ll feel it as far as Idaho maybe.
- finite_depth 3y ago
  No, but you would feel it well inland throughout the Mountain West. See this simulated USGS map for a 9.0 quake: https://upload.wikimedia.org/wikipedia/commons/8/80/9.0_Cascadia_scenario_%28median%29.pdf https://upload.wikimedia.org/wikipedia/commons/8/80/9.0_Casc... - for scale, the light blues are about the edge of where you'd clearly go "oh, yep, that's an earthquake", although you might notice such a large one at lower ground acceleration because the shaking would be quite prolonged (~minutes, rather than the ~10-20 seconds of a typical minor quake).
asveikau 3y ago
I don't think they're saying that. But from what I recall reading, the big one that hits Seattle will exceed the big one that hits the Bay. Seattle's big ones are higher magnitude but less frequent. Iirc it's also likely the 9.0 that hits Seattle won't be in most of our lifetimes. The last really big one was before Europeans arrived.
- rapind 3y ago
  Rainier will erupt first and the mudslide will wipe out all those houses built on the last mudslide.
  - seanmcdirmid 3y ago
    Rainier erupting would devastate slot of small communities between it and Tacoma. Like Helen’s blowing it’s glacial too (liquifying into a muddy huge river) but worse since the area around is more populated.
    - rapind 3y ago
      Yes and a lot of these suburbs are built upon the mudslides from previous (recent) eruptions (few million people). Last I heard it was a 1 in 7 chance in my lifetime. It's incredibly stupid and dangerous. Mudslides can travel up to 50 mph or more, and it doesn't even need to be an eruption that kicks it off.
dkasper 3y ago
From what I’ve read the faults in the Bay Area can’t really generate above an 8.0, whereas the cascadia zone can produce much larger events (remember a 9.0 is 10x the intensity of 8.0). It has to do with the size and type of the faults.
- carbocation 3y ago
  Yes: a 7.8 is thought to be the max in the Bay Area, as far as I understand. E.g., https://www.sfchronicle.com/bayarea/article/only-one-bay-area-fault-is-capable-of-producing-a-17767684.php https://www.sfchronicle.com/bayarea/article/only-one-bay-are...
- zamfi 3y ago
  > remember a 9.0 is 10x the intensity of 8.0 10x the ground movement amplitude — 32x the total energy release, though!

ianburrell 3y ago

The Cascadia quake will be about same damage to Seattle and Portland as Bay Area quake. It could be up to magnitude 9 but the fault is 60 mi away from the cities. The big difference is that it will affect the whole area. And that PNW is way behind in infrastructure.

diogenes4 3y ago
According to https://www.sfchronicle.com/projects/2023/bay-area-earthquake/ https://www.sfchronicle.com/projects/2023/bay-area-earthquak... vs https://www.newyorker.com/magazine/2015/07/20/the-really-big-one https://www.newyorker.com/magazine/2015/07/20/the-really-big... you're looking at two orders of magnitude difference in terms of the estimate of people affected. I'm not sure what led to the difference but that's striking.
- adrianpike 3y ago
  That New Yorker article goes viral every few years - it's a well written piece and spins a great yarn, but there's some significant hyperbole and it's sources don't quite back up the claims. Yes, a 9.x will be devastating. No, everything west of i-5 will not be toast.
  - diogenes4 3y ago
    > it's sources don't quite back up the claims. I'll admit that FEMA isn't exactly cited in a way that's possible to corroborate, but presumably they're estimating a worst-case scenario and not a median- or average-case scenario. That might explain some of the large divorce in figures.
    - adrianpike 3y ago
      I'd love to find any actual FEMA publications that back up some of the numbers and claims - so far to the best I can tell is it's mostly from interviews with the regional director, which, while valuable, isn't quite at the level of citation I'd like. If anyone's got a PDF I'd love to retract all my critiques though. :)

ksenzee 3y ago

On the other hand, Seattle is one of the best places in the world to ride out climate change, which is 100% happening, and happening already. It’s all a numbers game.

Axsuul 3y ago
And SF isn't?
- mvdtnz 3y ago
  I'm no expert on the region but aren't people in California forever whining about heat waves and water shortages?
  - akkartik 3y ago
    California != SF.
  - iancmceachern 3y ago
    Water shortages are largely in the central valley and Southern California. Sf gets its water from Hetch Hetche, clean hydro power too. SF is a very different place in a lot of ways from the rest of California, and the US in general.
    - callalex 3y ago
      Yes but that aqueduct is hundreds of miles long and goes through the Central Valley. Once the water wars begin, that situation could change rapidly.
      - iancmceachern 3y ago
        They'd need to change some pretty old laws... https://www.archives.gov/legislative/features/hetch-hetchy/hr7207.html#:~:text=Introduced%20by%20Congressman%20John%20Raker,the%20bill%20with%20little%20debate https://www.archives.gov/legislative/features/hetch-hetchy/h....

Stratoscope 3y ago

My mom was a Red Cross nurse who worked in the relief effort after the 1964 Good Friday earthquake and tsunami that devastated Anchorage and areas as far south as Crescent City, California. It was magnitude 9.2, the second largest in recorded history. The photos she brought back were quite something. I may still have them somewhere, but in the meantime there are plenty online. LIFE.com has a remarkable collection: https://www.life.com/history/the-great-alaska-earthquake-of-1964-rare-photos-from-an-epic-disaster/ https://www.life.com/history/the-great-alaska-earthquake-of-... https://ready.alaska.gov/_64Quake/History https://ready.alaska.gov/_64Quake/History https://earthquake.usgs.gov/earthquakes/events/alaska1964/ https://earthquake.usgs.gov/earthquakes/events/alaska1964/ https://en.wikipedia.org/wiki/1964_Alaska_earthquake https://en.wikipedia.org/wiki/1964_Alaska_earthquake From Wikipedia: > As a result of the earthquake, 131 people are believed to have died: Nine died as a result of the earthquake itself and another 122 died from the subsequent tsunamis all over the world. Five died from the tsunami in Oregon, and 12 died from the tsunami in Crescent City, California.

shostack 3y ago
Those numbers, while sad, are surprisingly low compared to other causes of death.
- Retric 3y ago
  Anchorage was 78 miles from the earthquake and still saw mass building collapses. The death toll was low due to the low population in the area. 128,026 in 1970 presumably less in 1964.
  - interloxia 3y ago
    About 290,000 in 2022. https://www.census.gov/quickfacts/fact/table/anchoragemunicipalityalaska https://www.census.gov/quickfacts/fact/table/anchoragemunici...
seanmcdirmid 3y ago
My mom was a schoolgirl in anchorage during the earthquake. We have a picture of my grandma and her trailer being 20 feet down from the rest of the ground. Haven’t digitized it yet.

jandrewrogers 3y ago

The fault is at least 150 miles from Seattle proper, the city will not receive the full brunt of the earthquake. Tsunamis are strongly mitigated by the geography of Puget Sound — the biggest tsunami threat is actually the Seattle fault. By contrast, the San Andreas fault literally runs through the middle of the Bay Area.

btilly 3y ago
Let's see. The Cascadia quake is 100x as big. I'm at 1/3 the distance from the San Andreas fault. Guess who gets the larger earthquake? Add to that the fact that I grew up in Victoria. All of Vancouver Island is a subduction zone during a Cascadia earthquake. Sadly, that means that a good chunk of what I knew growing up winds up under water. Seattle may fare better, but my home town does not.
- seabrookmx 3y ago
  It's not like the island will just drop into the earth. Unless you were referring the tsunami risk, which is my big fear as a fellow Victorian.
  - btilly 3y ago
    The island does subside in these earthquakes. Reading up now, it looks like it is 1-2 meters, mostly on the west coast of the island. But my memory of the early research when I still lived there in the early 1990s was that it was about a 3 meter drop. Between how low much of Victoria is, widespread poorly build older houses, and lots of housing built on unstable landfill in places like James Bay, my belief was that it was going to be pretty devastating to a lot of parts that I knew. However recent articles like https://www.mdpi.com/2624-795X/4/3/13 https://www.mdpi.com/2624-795X/4/3/13 suggest a much milder risk than I had thought.
- djmips 3y ago
  Can you back that up with some references? Very curious, I've never heard any claims that Victoria will end up under water in a big Cascadia earthquake.

mannykannot 3y ago

Your experience depends quite a bit on where you live and/or work, or, more specifically, what's underneath it. If one has nothing to do with the Millennium Tower, that is probably a plus.