Tsunami Issues for the Washington Coast

[poonchang]

Originally Posted by PNW-type-gal

The other thing to keep in mind is that it's possible you'd have a long warning lead time, in the case of a distant source at just the right angle, but it's also possible so that you'd have scant minutes.

Concerning the latter (in terms of minutes):

...The Cascadia subduction zone, a 680-mile fault that runs 50 miles off the coast of the Pacific Northwest -- from Cape Mendocino in California to Vancouver Island in southern British Columbia...Scientists say a rupture along the Cascadia fault would cause the sea floor to bounce 20 feet or more, setting off powerful ocean waves relatively close to shore. The first waves could hit coastal communities in 30 minutes or less -- too rapidly for the current warning systems to save lives.

The quote is pulled from this article (old article, first hit on a google search):
Tsunami-Generating Earthquake Near U.S. Possibly Imminent | LiveScience
Apparently, major earthquakes happen, on average, every 300 years. Guess when the last one was?

Wikipedia says major earthquake events have occurred every 300-900 years (590 year average) with the last one in 1700.
1700 Cascadia earthquake - Wikipedia, the free encyclopedia

Personally, I love the area and the thing that makes me hesitate moving there is difficulty making a decent living; not tsunamis.

[PNW-type-gal]

Thew new warning system can go off a lot faster than that. And a large off-shore subduction quake does not mean a massive tsunami is an inevitable consequence.

[LMB]

I've seen tsunami warning signs along the coast in Port Townsend, but we don't have any signs like that in Poulsbo along the Liberty Bay waterfront. When I asked my son-in-law (a Seattle native) about it, he laughed and said tsunami's don't turn corners--and that Poulsbo wouldn't need evacuation signs. Is that true? I'm too embarrassed to ask any of the locals here.

[PNW-type-gal]

Originally Posted by LMB

I've seen tsunami warning signs along the coast in Port Townsend, but we don't have any signs like that in Poulsbo along the Liberty Bay waterfront. When I asked my son-in-law (a Seattle native) about it, he laughed and said tsunami's don't turn corners--and that Poulsbo wouldn't need evacuation signs. Is that true? I'm too embarrassed to ask any of the locals here.

No, it's not true. Anywhere low near the water has a chance of tsunami - it just takes the right conditions, such as shallowing or a narrowing. There have been tsunamis caused by earthquake-induced landslides in places that hadn't been considered a direct risk.

If you are at the beach on the west coast, even if it's an inlet or protected bay, it's always a good idea to keep a way out or up in the back of your head. Not in panic or fear, just the way you watch your gas tank level to make sure it's not empty.

[Fat Freddy]

Originally Posted by PNW-type-gal

...a large off-shore subduction quake does not mean a massive tsunami is an inevitable consequence.

True, but it does mean that most of the structures and infrastructure in Western Washington will be destroyed.

[PNW-type-gal]

Originally Posted by Fat Freddy

True, but it does mean that most of the structures and infrastructure in Western Washington will be destroyed.

No, it doesn't. Destruction depends entirely on duration, type and direction of movement, what the subsurface conditions are underneath any building. Certainly there are higher risk structures - bridges, overpasses, anything built on dredge fill, buildings which haven't been retrofitted. Looking at other large earthquakes, damage can be severe in one place and almost non-existent in another, depending on a number of conditions.

Counting on being one of the undamaged places, though, is probably not a good idea. Certainly a homeowner can do a number of things to limit damage, and all of those are worth doing as a preventive measure.