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PhuckSJWs t1_j8lieiu wrote

  1. Nisqually quake was deep (35 miles) and relatively "far away" from dense population centers.

  2. Seattle and Tacoma both have a lot of loose soils on top from when the cities were created (in Seattle's case when the hills were flattened), which luckily helped cushion the blow

  3. Even though many buildings were not earthquake ready, it is fair to say the majority here were likely more earthquake ready than most in Turkey

  4. Even for only being 20 years ago, we now have about an extra million in the metro area that were not here in 2001.

  5. Some luck

  6. Our big quake that we are overdue for will hit eventually. The Seattle fault is the one that will fuck us up if/wen it slips.

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normalabby t1_j8lqhqu wrote

Loose soil is typically bad for earthquakes, from what I've read. Is number 2 a guess? Or did you read something that said that?

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PhuckSJWs t1_j8lrncx wrote

we were far enough away, and across several fault areas, that the soils did dampen the shock wave somewhat in places by the time it got here.

that said, a strong quake near to Seattle (e.g., one on the Seattle fault) will likely trigger liquefaction locally in places due to strength AND proximity. that was not an issue with the nisqually quake. by the time the waves got here we got lots of shaking and damage to old infrastructure, but the skyscrapers handled it like they were designed, and for the most part we mostly suffered cosmetic damage and not a HUGE amount of infrastructure damage.

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normalabby t1_j8lsk2q wrote

But important to note there was liquefaction in SODO. It's a bit amusing to read this and think someone was surprised to find evidence of liquefaction in an area like SODO that is loose fill. It's a given, today. https://www.washington.edu/news/2001/04/17/damaged-chimneys-and-unexpected-liquefaction-from-nisqually-temblor-yield-earthquake-insights-uw-scientists-say/

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PhuckSJWs t1_j8lt7kl wrote

For sure, there WAS liquefaction, but it was very limited and low impact and almost entirely in the industrial areas south of downtown where it is mostly just garbage till soil on top of old tidal flats.

given the widescale "terraforming" the settlers did to the original Seattle hills to level out the city, it (liquefaction) was extremely limited in location and impact. we will not be so lucky with a closer and shallower quake.

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normalabby t1_j8lu7ng wrote

No disagreement on a differently located quake, just want to make sure we're not telling folks all the glacial till this region is built on is cushioning us. It didn't make the Nisqually less intense, the distance did. Someone would've felt the Nisqually more anywhere in the Puget Sound region that's on top of glacial till more than riding it out on bedrock, in the few places that exists.

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normalabby t1_j8lssc3 wrote

For how long the Earth has existed it's amazing how much our understanding has grown in just 70 years. Tectonic plates are a relatively recent discovery, thanks to ocean exploration.

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reroboto t1_j93u8vk wrote

I was at work in a building built on fill and it bounced rolled and cracked and we couldn’t go back for a month. Buildings in same area not on fill we’re fine

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SCROTOCTUS t1_j8odkgq wrote

The 9.0+ where it's like the whole region gets stuck inside a Shake Weight is not going to be a good time.

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iamlucky13 t1_j8prghz wrote

Because of the distance of the Cascadia Subduction Zone from Seattle, the local shaking will be more comparable to a magnitude 7 quake directly beneath Seattle. The biggest concerns for this quake scenario are the regional scale of the effects, and especially the dangers on the coast of the tsunami that will likely accompany it.

Here are the USGS predicted intensity maps showing this, as well as the 2001 Nisqually quake and the 2023 Turkey quake for comparison:

Magnitude 9.3 Cascadia Subduction Zone - Predicted - Modified Mercalli Intensity in Seattle 7 to 7.5

Magnitude 7.2 Seattle Fault Zone - Predicted - Modified Mercalli Intensity in Seattle 8 to 8.5

Magnitude 6.8 2001 Nisqually Quake - Modified Mercalli Intensity in Olympia: 6.5 to 6.8

Magnitude 7.8 Turkey 2003 Quake - Modified Mercalli Intensity: Over 9 in the worst affected areas

With that said, construction methods and quality matter a lot. The shaking in the Gaziantep, where a historically significant castle received major damage that has been shown widely in the news, the Mercalli Intensity is estimated at 6.7 - similar to what Olympia experienced in 2001.

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