4 ms·

It's a weird statement to make, because the route of I5 is fairly arbitrary, geologically speaking. Lower parts of downtown Seattle may be at risk, but is upper

by Exmoor 5y ago

It's a weird statement to make, because the route of I5 is fairly arbitrary, geologically speaking. Lower parts of downtown Seattle may be at risk, but is upper Queen Anne hill? Ballard may be partially screwed, but Crown Hill is hundreds of feet higher in elevation. That assumes that Puget Sound even generates a large Tsunami based on an offshore quake. If we're talking about Oregon it gets even weirder since the population centers have a coastal range in between them and seawater. I don't know enough about the various fields involved to know if the Columbia river's level would raise catastrophically in such a scenario.

anonuser123456 5y ago
Lots of unreinforced masonry buildings are in these regions. The shaking from such a large quake will go on for minutes and make them crumble.
KirillPanov 5y ago
> because the route of I5 is fairly arbitrary, geologically speaking You sure about that? From Olympia to the Oregon border I-5 sits on the lowest, flattest stretch of land between the coastal range and the cascades. That's why it keeps getting flooded out by the Chehailis river. To the north, through Whatcom County the route is anything but geologically arbitrary: it's the unique route that required the minimum amount of blasting into Chuckanut rock. Parent post seems like a pretty city-centric view of the world. The dozen or so miles that pass through Seattle might be arbitrary to within a Seattle-diameter, but that's an irrelevantly small part of the freeway.
jandrewrogers 5y ago
There is not a significant tsunami risk from a Cascadia subduction zone earthquake in Seattle, due to its topography and distance from the fault. The biggest risk in that regard is from the Seattle fault, a thrust fault, that runs through the middle of Elliott Bay, which can both generate large water displacements and can cause large subsidence of the land (i.e. it can literally sink a dozen feet during an earthquake). Seattle is geographically very vertical, and heavily shielded from the open ocean, which limits the tsunami effects. The real risk is civil engineering in nature. While the fault is some distance away, it will shake hard and for a long time. Unreinforced masonry will probably be destroyed, and Seattle has a lot of old masonry in some neighborhoods. Some older structures not up to the current seismic code will likely fare poorly. Seattle has had enough local 7+ earthquakes that a distant offshore 8-9 won’t feel too much different, but the shaking time will be much longer. Landslides are undoubtedly a risk. Portland will likely fare much worse than Seattle. A modern steel or wood-framed building constructed in the last 20 years will very likely survive almost anything, they are built for it. Older steel and wood buildings that are still standing have already been through some earthquakes; not as large but they won’t immediately collapse. The real problem will be restoring infrastructure in the aftermath.
jvolkman 5y ago
Not sure if this is what they're referring to, but in the downtown area I-5 traces the original shoreline. Everything to the west is fill from Seattle's many regrades. https://youtu.be/oSSxdogrv1s?t=519 https://youtu.be/oSSxdogrv1s?t=519
irrational 5y ago
The danger zone in Western Oregon is places like the Tualatin Basin (which is all West of I-5). This is the location of things like all of the Intel Fabrication plants in Oregon, Nike World Headquarters, etc. The entire basin will liquefy in the event of a giant earthquake.

by Exmoor 5y ago

anonuser123456 5y ago

Lots of unreinforced masonry buildings are in these regions. The shaking from such a large quake will go on for minutes and make them crumble.

KirillPanov 5y ago

> because the route of I5 is fairly arbitrary, geologically speaking You sure about that? From Olympia to the Oregon border I-5 sits on the lowest, flattest stretch of land between the coastal range and the cascades. That's why it keeps getting flooded out by the Chehailis river. To the north, through Whatcom County the route is anything but geologically arbitrary: it's the unique route that required the minimum amount of blasting into Chuckanut rock. Parent post seems like a pretty city-centric view of the world. The dozen or so miles that pass through Seattle might be arbitrary to within a Seattle-diameter, but that's an irrelevantly small part of the freeway.

jandrewrogers 5y ago

There is not a significant tsunami risk from a Cascadia subduction zone earthquake in Seattle, due to its topography and distance from the fault. The biggest risk in that regard is from the Seattle fault, a thrust fault, that runs through the middle of Elliott Bay, which can both generate large water displacements and can cause large subsidence of the land (i.e. it can literally sink a dozen feet during an earthquake). Seattle is geographically very vertical, and heavily shielded from the open ocean, which limits the tsunami effects. The real risk is civil engineering in nature. While the fault is some distance away, it will shake hard and for a long time. Unreinforced masonry will probably be destroyed, and Seattle has a lot of old masonry in some neighborhoods. Some older structures not up to the current seismic code will likely fare poorly. Seattle has had enough local 7+ earthquakes that a distant offshore 8-9 won’t feel too much different, but the shaking time will be much longer. Landslides are undoubtedly a risk. Portland will likely fare much worse than Seattle. A modern steel or wood-framed building constructed in the last 20 years will very likely survive almost anything, they are built for it. Older steel and wood buildings that are still standing have already been through some earthquakes; not as large but they won’t immediately collapse. The real problem will be restoring infrastructure in the aftermath.

jvolkman 5y ago

Not sure if this is what they're referring to, but in the downtown area I-5 traces the original shoreline. Everything to the west is fill from Seattle's many regrades. https://youtu.be/oSSxdogrv1s?t=519 https://youtu.be/oSSxdogrv1s?t=519

irrational 5y ago

The danger zone in Western Oregon is places like the Tualatin Basin (which is all West of I-5). This is the location of things like all of the Intel Fabrication plants in Oregon, Nike World Headquarters, etc. The entire basin will liquefy in the event of a giant earthquake.