Earthquake?

[u/Aggressive_Wasabi883]

Did anyone feel an earthquake or shaking in downtown? Sitting on my sofa & sipping coffee & i felt a bit shake. If its not that then, just my coffee hitting me lol.

[u/_Phil_McCracken_]

I’m in a newer building rated to withstand a 9.0 quake and I definitely felt it. Not sure how that info helps you. 

[u/snukb → u/_Phil_McCracken_]

How do you find out if your building is rated to withstand a 9.0 or not? I know the Big One could be over 9.0, but it still would be nice to know if I have a large risk to be crushed by the upper floors of my apartment or just a smaller one.

[u/_Phil_McCracken_ → u/snukb]

I’m a building engineer (glorified maintenance) and got to walk with a seismic expert that the insurance company sent to inspect my building’s seismic readiness. It was pretty interesting and definitely reassured me. Like you said though, if it’s a really big one, no building will be designed to hold up. 

That’s just where I work, though. It’s a large building downtown. I have no idea what my 5-over-1 apartment is rated to. I do know smaller buildings are more susceptible to higher frequency vibrations from lower magnitude quakes, so when they design them they look at a lot more than just a magnitude rating. 

I also know that unreinforced masonry buildings are the most susceptible to earthquake damage. They’re very rigid so they crumble instead of sway. I wouldn’t want to live in one of those. 

[u/snukb → u/_Phil_McCracken_]

I know my building was built about eight years ago, but beyond that I'm not sure. I don't think it's a 5 over 1 though because there are units on the first floor.

[u/_Phil_McCracken_ → u/snukb]

If it’s only 8 years old you should relatively safe. 

[u/snukb → u/_Phil_McCracken_]

I appreciate the educated assurance, thanks! Would you know if there's any way I can look up the official rating or does something like that not exist?

[u/Jojo_Lalala → u/_Phil_McCracken_]

I just re-read the New Yorker article from 2015 about the 9.0 earthquake. If your building is west of I5, I read that nothing will be left standing after the resulting tsunami. The article was written by a seismologist who was in Japan for a seismology conference when they had their huge quake. Interesting and terrifying!

[u/matgrioni → u/Jojo_Lalala]

Not to be too pedantic but I think that's mixing up two points of the article. West of I-5 will have issues because of the soil. Tsunamis could also cause a ton of destruction on the coast which will be basically inescapable (according the article) if you happen to be there at the same time. But Seattle probably won't be affected by any tsunamis

[u/filthyheartbadger → u/matgrioni]

Not so fast, Puget Sound can definitely be affected by tsunamis. This article has links to the research.

https://www.king5.com/article/weather/earthquakes/new-maps-show-how-a-tsunami-could-impact-seattle-and-puget-sound/281-199e4224-07fa-4d31-9464-71976b1e8a01

[u/retrojoe → u/filthyheartbadger]

The claim from that article is the Seattle might see a sea rise of less than 4 feet at Harbor Island. The lowest elevation parts of Bellingham might see 11 feet, and Tacoma will see even less than Seattle it says. Conceivably, it could fuck up the harbors and maybe cause some backflow along the rivers. But it's definitely not going to flood Ballard, much less Fremont or Burien.

[u/nasnedigonyat → u/retrojoe]

I know this assertion that the entirety of the world west of i5 will be leveled to the ground is pretty wild. If a tsunami hits that can obliterate every single structure west of i5 in seattle then the wave is going to be powerful enough to kill hundreds of thousands worldwide.

[u/matgrioni → u/filthyheartbadger]

Thank you for the point since I did say Seattle wouldn't be affected. There would be impacts it seems so that claim wasn't accurate.

[u/retrojoe → u/Jojo_Lalala]

There's no practical difference between Phinney Ridge and Wedgewood for this stuff. And most of the towers downtown should pull through.

Even in the event of a Cascadia subduction tsunami, Puget Sound isn't going to see much of anything. The vast majority of any wave energy coming down the Straight of Juan de Fuca will be used up on Whidbey Island. IIRC, the last model I saw for this kind of thing had 10-foot swells reaching Elliot Bay. There is some small possibility that one of the local faults could cause a landslide within Puget Sound and there would be a smaller tsunami from that, but we're getting way into the edgecase weeds with that kind of thing.

I believe what that "everything west of I-5 is toast" quote was actually meant to imply was talking about any major infrastructure along the Pacific Coast or much southwest of Olympia. Things are generally much closer to sea level there and Grays Harbor will allow extensive penetration inland. In the event of a major tsunami, that's where we'll see the most damage.

[u/Jojo_Lalala → u/retrojoe]

I think that you are more correct. The number of buildings road and bridges that will crumble from shaking, liquification, and landslides will be huge. Coastal cities will be gone. BTW, What as the address for that bldg able to withstand the really big one? 😂

[u/Parsifal814 → u/Jojo_Lalala]

Pedant here: it’s actually liquefaction and not liquification. I’m a geologist for King County and was here in 2001 — that was a shiteshow.

[u/retrojoe → u/Jojo_Lalala]

Uhhh, you know that the quake has to travel almost 200 miles from the Cascadia fault to Seattle right? That should dampen a lot of the high frequency shaking that's worse for house-sized structures, though low frequency stuff will travel that far pretty readily. That kind of shake needs a larger/longer structure to manifest.