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Unread 08-07-2012, 10:27 PM
wcc wcc started this thread
 
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Question Seismically safest areas in Seattle area?

Hi! I recently discovered that Seattle sits on top of some horrendous seismic faults which can generate scale 9 earthquakes. Since I am seriously considering moving to the Seattle area with my family, I would appreciate some expert opinions on what the safest areas are. I would be working in downtown Seattle, Redmond, or Bellevue (tech firms) and I could commute up to an hour if need be. Thoughts?

Interestingly, I actually used to live in Seattle long ago, and never knew that there was any seismic danger. Then I moved to the Bay Area, where quakes (small ones) are much more common. The Bay Area also has a lot more resources to help you figure out which areas are endangered by what faults etc. I have not been able to find the same level of detail about the Seattle area, so any help would be appreciated.

Some reference: http://geomaps.wr.usgs.gov/pacnw/lif...eqhazards.html
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Unread 08-08-2012, 06:25 AM
 
Location: East of Seattle, originally from SF Bay Area
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After 40 years in the SF bay area and many quakes including some big ones, we find that here it's very rare in comparison. Potential is there, though, and I wouldn't want to be in the downtown Seattle area in older (especially brick) buildings built on fill long ago when such an event happens. Other than the soon-to-be-demolished highway 99 viaduct most elevated roads are newer and built to standards. On the eastside, people do not worry about it much and unlike us, most don't even have earthquake insurance. The biggest worry is probably the path from Mt. Rainier to the Sound if it were to blow and send molten lava through Puyallup and Tacoma.
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Unread 08-08-2012, 09:30 AM
Status: "Nullius in verba" (set 27 days ago)
 
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Rainier isn't the kind of volcano that would send molten lava through Puyallup and Tacoma. It is a stratovolcano, and the biggest risk you have from those are pyroclastic flows, lahars and mud flows. Mudflows from Mount Rainier have reached as far as Puget Sound in Tacoma and even Elliott Bay. The biggest one that we know about happened about 5000 years ago and was the result of the top 2000 feet of Mount Rainier sloughing off the mountain. These mudflows can move at very high speeds, accelerated by the narrow river valleys that lead off the mountain. (CVO Website - Mount Rainier - Osceola Mudflow)

Mount Rainier and the other volcanoes in our region are very geologically unstable. The gases and water percolate through what seems like solid rock, weakening it. Huge amounts of weight from a thousand inches of snow a year compress the rock and the thaw decompresses it, working like a giant fist squeezing and releasing it. Sit for even an hour looking out over one of Rainier's glaciers and you'll see and hear rocks tumbling off the mountain. If you camp in the backcountry at Rainier you'll hear rock and ice fall all night long.

All of the volcanoes in our state are stratovolcanoes. If you live in a river valley and that river flows from a glacier on one of our volcanoes, you're at risk. The volcanoes that send out massive fields of flowing lava are shield volcanoes like the ones in Hawaii. They don't explode like stratovolcanoes like Mt. St. Helens or Mount Aetna or Krakatoa, but their lava flows can go quite far but usually at no more than a walking pace.

So, you don't want to live in a river valley downstream from a volcano. You also don't want to live on top of a cliff overlooking Puget Sound unless you have bedrock beneath you instead of loose dirt. Glacial till does not make for a stable hillside. Just find a place away from the edge of a steep slope or on bedrock. Don't live on fill.
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Unread 08-08-2012, 11:59 AM
wcc wcc started this thread
 
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Thank you! I had not thought about the volcanoes recently. My understanding was that mostly the cement-like dust in the air is dangerous, but looks like there is more.

In SF for example the hills are supposed to be seismically strong areas, e.g. Potrero Hill, Pacific Heights, etc. I was surprised for example that in Seattle Queen Anne is not supposed to be seismically strong - are hills in the Seattle area not made of solid rock?

Are there specific towns or parts of towns in the Seattle area that you think are safer, and which are say up to an hour away from Bellevue?
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Unread 08-08-2012, 01:52 PM
 
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Quote:
Originally Posted by wcc View Post
In SF for example the hills are supposed to be seismically strong areas, e.g. Potrero Hill, Pacific Heights, etc. I was surprised for example that in Seattle Queen Anne is not supposed to be seismically strong - are hills in the Seattle area not made of solid rock?
Well, when you look at the history of Seattle, you'll see we're actually suppose to have more hills... but a lot of its been "lopped" off. And you'll see that a lot of times, they were using high pressure water to do so. It's oddly fascinating to go through it. Especially when you see that some people wouldn't move out, so they "went around" the house and the house is on being supported by stacks because there isn't that much land left. Fascinating stuff, really.

One area that I can think of that is especially ok in terms of being "strong"... because of it being solid rock is the Sammamish Plateau.

Quote:
Originally Posted by wcc View Post
Are there specific towns or parts of towns in the Seattle area that you think are safer, and which are say up to an hour away from Bellevue?
You'll have to realize if the hour thing from Bellevue is the necessary aspect-- it gives you a very short radius to operate from. 405 is rush hour hell... I'd say even worse than i5 a lot of times. Which would make it better if you're already looking towards the East (Issaquah, North Bend, Snoqualmie, Sammamish, et. al) anyway.

You're going to deal with some sort of natural disaster potential wherever you go... like flooding in the low valleys and river areas.
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Unread 08-10-2012, 12:56 AM
 
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Good thing is, volcanoes start shifting and a shaking before they blow. Rainier has all kinds of sensors attached to GPS that are monitored all the time so that when she starts a shimmying we'll get a heads up before it blows.

As for earthquakes...if you're on the viaduct, it was nice knowing you. Other than that VERY unlikely event happening I would say as long as you don't live near the water, you'll be okay. The earthquake wont be as bad as the tsunami...

Forecasting Kitsap Blog Archive Could a Tsunami Someday Hit Seattle?
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Unread 08-10-2012, 01:26 AM
 
Location: West Coast Wanderer
11,437 posts, read 8,674,069 times
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Quote:
Originally Posted by wcc View Post
Hi! I recently discovered that Seattle sits on top of some horrendous seismic faults which can generate scale 9 earthquakes. Since I am seriously considering moving to the Seattle area with my family, I would appreciate some expert opinions on what the safest areas are. I would be working in downtown Seattle, Redmond, or Bellevue (tech firms) and I could commute up to an hour if need be. Thoughts?

Interestingly, I actually used to live in Seattle long ago, and never knew that there was any seismic danger. Then I moved to the Bay Area, where quakes (small ones) are much more common. The Bay Area also has a lot more resources to help you figure out which areas are endangered by what faults etc. I have not been able to find the same level of detail about the Seattle area, so any help would be appreciated.

Some reference: Pacific Northwest Geologic Mapping and Urban Hazards
If a quake of 9 hits, it won't matter if you're near a seismic zone. If you are within 800 miles, you will be effected.
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Unread 08-10-2012, 09:40 AM
 
Location: the Beaver State
6,434 posts, read 4,881,860 times
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Quote:
Originally Posted by wcc View Post
Since I am seriously considering moving to the Seattle area with my family, I would appreciate some expert opinions on what the safest areas are. I would be working in downtown Seattle, Redmond, or Bellevue (tech firms) and I could commute up to an hour if need be. Thoughts?
You might want to look further east. Like Spokane or Boise.

Not being facetious, at all:

SHIPS - Regional Map

SHIPS - Seattle and Tacoma Model

Seattle Fault - Wikipedia, the free encyclopedia
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Unread 08-10-2012, 03:10 PM
 
Location: Issaquah, WA
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Quote:
Originally Posted by Inkpoe View Post
One area that I can think of that is especially ok in terms of being "strong"... because of it being solid rock is the Sammamish Plateau.
I think the Seattle Fault line (West->East) runs down the I-90 and supposedly through Beaver Lake?

I also read that is why there is a Sammamish Plateau as it has been forced up along the fault line.

In the end, we have no control whatsoever over natural events like that. We could have stayed nice and safe in geologically boring England, but the opportunities and experiences of the PNW were too tempting.

Geological time frames are huge and the chances of them happening modulo a human lifespan are low. But we do try and keep earthquake supplies ready.
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