Sunday, January 22, 2012

It's a Branch, It's a Pothole - no, it's an Earthquake!

For December’s Accretionary Wedge, (#41!) Ron Schott has asked us to describe the most significant or memorable geologic event we have personally experienced. The first thing that sprang to my mind was the 2001 Nisqually Earthquake.
This is the seismograph from Wupatki, Arizona. There weren't many closer, and I quite liked how clearly the P-wave and S-wave showed up in this one.
In February of 2001, I was 13 years old. At that time, I was half-homeschooled – I took a couple classes at the junior high in the morning, and then my mum picked me up for some homeschooling. (Reality: I’d wait until she left on some lawyer-ly errand, and then make grilled cheese and watch Wheel of Fortune. What a rebel.)
On February 28, at 10:54 am, I had just been picked up from school, and we were driving in my mother’s 1870s powder-blue Camaro towards The Big Swoopy Hill. All of a sudden, the car swayed back and forth, the dashboard tilting up and down. It looked like that One Time My Dad Took the Car on the Potholed Forest Service Road Where People Go Mudding.

“Mum, do we have a flat?” I asked.
“No, I don’t think so. We might have run over a downed branch.” My mum looked in the rearview mirror. “Although I don’t see anything behind us…”
“Mum, look at the lady parked on the side of the road!”
“She’s getting back in her car, she’s ok.”

After we got back home, my mother worked on some legal briefs, and I worked on my report on deciduous trees. After an hour or so, the phone rang.
My mum picked it up. “Hello?”
“Are you ok? Is the house ok?” my dad asked, frantically.
“We’re fine… Are you?”
“There was an earthquake!”

We walked around the house, and, sure enough, some of the vases on top of the piano had shifted a little. The dishes had moved.

The next day at school, my classmates regaled me with tales of crawling under their plastic-topped desks, all the while imagining the back half of the portable buildings sinking into the ground. One girl even declared that she’d thought it was the Rapture.
This is from a school near Nisqually. Our school only had a couple lights fall down, and was otherwise fine.
I tried to explain our harrowing tale to them, but even my best retelling didn’t convince them it was cooler than the Rapture.
Well, I tried.
The 2001 Nisqually earthquake only rated a 6.8, with a depth of about 52km, and is an example of normal faulting in a subduction zone – the Juan de Fuca plate was bending (and stretching) as it was forced under the North American plate. This is possibly due to increased warmth near the mantle heating up the subducting plate, dehydrating it and making it more brittle - kind of like baked potato chips.
A fault plane solution for the Nisqually earthquake. The little circles are dilatations, and the little stars are compression - so you can see how part of the plate extended, compressing the material to either side.
A path near the State Capitol. One fellow looks depressed at the thought of all the work he's going to have to do. The other fellow looks like this is the coolest thing to ever happen - definitely a geologist.
Luckily, only one person died (as the result of a heart-attack) and 407 people were injured. It did cause significant damage to roadways near the epicenter (in the Olympia and Nisqually area.)
Highway 101 - nobody really uses the right lane, do they?
Additionally, it caused significant damage to buildings both in Olympia and Seattle – including causing a large crack in the dome of the Washington State Capitol in Olympia.
The exterior of the State Capitol. You can see that some of the bricks are separating from the facade. The building was shut down for quite some time as it was examined for structural stability.
Looters run rampant in downtown Seattle.
These fellows actually just found a co-worker's purse amidst the wreckage of their van.

 "Pssh, I've got nine lives, I ain't scared."
It also damaged the Alaska Way Viaduct in Seattle, which led to a decade of plans, negotiations, and general strum und drang about replacing it, as well as this terrifying simulation. Apparently, they’ve now begun construction on a replacement. The earthquake resulted in $3.5 million in repairs to the viaduct, and construction of a replacement/refurbishment/tunnel/etc. is projected to cost $3.1 billion. It’s money well spent, I think, because that sucker looks like a car-sandwich just waiting to happen.
Some fellows braving aftershocks to repair the Viaduct so people can tempt fate.
There were also spots of liquefaction and sand boils in both Olympia and Seattle. Liquefaction is pretty nifty, and luckily didn’t cause much damage in this earthquake. (Many portions of Seattle’s waterfront are built on fill – liquefaction could be a huge problem for those areas.)
A sand boil in Olympia.
While much of the liquefaction seems to have been little sand boils, it also invaded basements. Additionally, there was a large mudslide in the Renton area, which also did significant property damage.
Worst sweeping job ever.
I’m really glad that I was able to experience a medium-sized earthquake, without my family suffering any damages, and without the region suffering many deaths. I do still kind of wish we had realized it was an earthquake when it was occurring – that would have been so much more terrifying and exciting! But it was still a very memorable experience.

In addition to the websites linked through the above photos, here are some websites with information on the Nisqually earthquake:
Some Observations of Geotechnical Aspects of the February 28, 2001, Nisqually Earthquake in Olympia, South Seattle, and Tacoma, Washington
Geodetic Information from Central Washington University
The Nisqually Earthquake Information Clearinghouse, housed by the University of Washington
GPS Analysis of Olympia Quake from Rensselaer Polytechnic Institute
The Pacific Seismic Network's Nisqually Earthquake Page
USGS's Preliminary Earthquake Report
Washington State Department of Natural Resource's Nisqually Earthquake Page
Identifying the Rupture Plane of the 2001 Nisqually, Washington, Earthquake
A Video Taken Inside Microsoft During the Earthquake
KOMO News Broadcast from February 28, 2001
Car image:

This video made me laugh so hard I cried. It's ridiculous!


Pam and Wayne said...

If only they made geology this cool for kids in school! Great post, thanks for the education. I've never been in an earthquake. Even though I've lived in the midwest for 35 years I've never had a brush with a tornado either!

Gaelyn said...

This is a great post. Now I want to see liquefaction. Guess that's what can happen when cities like Olympia and Seattle are built on old Rainier mudflows.

My only felt earthquake was in the 90s while living in a bus in Yucca Valley and it felt like I was on a boat.

Hope you are doing well.