PNW People and the Cascadia Subduction Zone?

[MommyLiberty5013]

All this has been really helpful and interesting.

 

For my own clarification, the actual fault line in the Cascadia Subduction Zone is in the seafloor, off the coast, correct? So when it shifts (earthquake), that is what sends out the tsunami?

 

I read in some of the information that they estimate the tsunami in 1700 was 100 feet high. If there were a repeat of this and another tsunami came that was of similar height, how far inland would the wave's momentum reach? And where do they say it would crest and break? After it breaks, how much further inland will the wave surge (not sure if that's the proper name) go?

 

Sister, BIL, and his whole family are in the Tacoma area (just moved there from Seattle). But, I know they all have homes that are up higher at like 370 feet elevation. Is that a safe zone? I know they are west of I5; that is a drawback.

[YaelAldrich]

The Seattle area is pretty much impossible to evacuate if there is an earthquake. We don't get the warnings like you do with hurricanes, and while earthquakes are less frequent than other major disasters, the devastation is worse. And the land transit is already at a dead standstill in rush hour.

 

Seattle is linked with bridges, not just across the major bodies of water but even through parts of town. We have done earthquake planning in the past and where we used to live, if an earthquake hit, we pretty much expected to become island dwellers because the land-links (no water) would be so broken.

 

Seattle is also an area not known for preparing its citizenry for disaster prep. There is actually a law on the books that prohibits the city council from preparing for nuclear attack aftermath. It was passed during the Cold War in an effort to keep the citizenry from freaking out about nuclear danger. (Part of the school of Stick Your Fingers in Your Ears and Say Lalalalala and It Will Be OK". )

 

In this area, there are land masses that are known to be unstable--but people still build there. They have to sign closing papers that say they know they live on a latent landslide.

 

Same thing happened when we lived in Boulder. There are significant parts of town known to be on the flood plain. People buy property on the food plain, and at closing they have to sign document saying they know it is on the flood plain. They can't get flood insurance. And then when the 100 year flood hits, it's a big shock ... "we had no idea we could be flooded." And the government assistance does more for them than a lot of insurance companies would so people don't even care about the lack of insurance.

 

It's the same all over. People bear different amounts and kinds of risk. I know things will stink if the Big One hits. But it gives me the same stomach-clench that the tornado warnings gave me in Colorado. It's always something.

 

And...I will say that a couple of months after we sold our beach house in Oregon, there was a tsunami warning for that area...and my response made me realize that I had endured a certain amount of I acknowledged stress for a long time.

 

So who knows how much stress affects me, living here. Day to day, the thought of earthquake never occurs to me. But I AM jumpy, driving across bridges.

FYI Boulder has an NGO called BoCo who are working on creating and strengthening ties between people specifically to deal with the disasters that have happened and will happen again.  My husband has been working with them over the last year or two.  He's also working with San Francisco and Christchurch NZ.  Gov'ts know they have problems and (I think) are trying to ameliorate them.

[Seasider]

FYI Boulder has an NGO called BoCo who are working on creating and strengthening ties between people specifically to deal with the disasters that have happened and will happen again. My husband has been working with them over the last year or two. He's also working with San Francisco and Christchurch NZ. Gov'ts know they have problems and (I think) are trying to ameliorate them.

Your dh's job sounds very interesting!

[gardenmom5]

All this has been really helpful and interesting.

 

For my own clarification, the actual fault line in the Cascadia Subduction Zone is in the seafloor, off the coast, correct? So when it shifts (earthquake), that is what sends out the tsunami?

 

I read in some of the information that they estimate the tsunami in 1700 was 100 feet high. If there were a repeat of this and another tsunami came that was of similar height, how far inland would the wave's momentum reach? And where do they say it would crest and break? After it breaks, how much further inland will the wave surge (not sure if that's the proper name) go?

 

Sister, BIL, and his whole family are in the Tacoma area (just moved there from Seattle). But, I know they all have homes that are up higher at like 370 feet elevation. Is that a safe zone? I know they are west of I5; that is a drawback.

 

correct - the cascadia fault is off the coast, so when it shifts it displaces water and that is what causes the tsunami.  how it shifts affects how the water is displaced, and how large the tsunami.    the farther away from the epicenter - the lower the wave.  (and the more time you have to get to higher ground)  there have been undersea quakes - even fairly large ones - that only produced small and localized tsunamis.

 

I don't know how high the tsunami was - that can be affected by tides at the time of the quake.   like a storm surge ahead of a hurricane - if it lands at high tide - it will be higher than if it landed at low tide.  and high tides vary in height.

tacoma is getting fairly far south in puget sound.  there will be tsunami action in the sound just from the shaking - it shouldn't be as large as on the coast near the epicenter.   they have found evidence of tsunami along the shores of lake washington - so it got sloshed around too.

 

as in japan - how far inland or uphill it goes it affected by topography.  if there are water outlets - the wave can push up river.  it did that in one area that was removed from the coast - and they had notable devastation.   in japan - it was early spring and the rivers would have been higher due to melt.  late summer, water levels are much lower.

 

tbh - i'd be more concerned about liquefaction.  that can cause a lot of damage.  tends to be areas on fill.  e.g. the marina district in SF - downtown seattle waterfront.  (which is where they put the top of first hill 100 years ago with the "denny regrade".)  or areas prone to sliding.  (which can get a homeowner in a high rain year.)

 

generally, at 370' - I'd consider it safe from tsunami.   I'm lower - but there are hills between me and the water.

[YaelAldrich]

Your dh's job sounds very interesting!

It is very interesting.  He originally was studying (and still does) NIMBY (not in my backyard) politics and how gov'ts convince communities to take NIMBY projects(like airports, nuclear facilities, dams).  Then he got his first job and we moved to New Orleans.  Six weeks later Hurricane Katrina made us evacuees to Houston.  As the global Jewish community contacted us to offer housing, schools, whatever we needed, Daniel started to wonder what made some people/communities bounce back faster than others after a disaster.  He theorized that it was social capital - the ties between people; not government, not charities.  So he pivoted and life changed for us and his academic career.  He is very proud to help people, NGOs, and government agencies understand how important social capital is to communal stability and resilience.  It also has interesting spin-offs like him using his research to teach US elite forces about counter-terrorism in Africa and the American response to the Ebola virus!

Edited June 21, 2017 by YaelAldrich

[MotherGoose]

I don't Iive there, but I found it fascinating, and scary, that every elevator I took in Seattle had a seismic warning light. We don't have those on the east coast :)