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Pacific Northwest Earthquake Liquefaction

Pacific Northwest Earthquake Liquefaction
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After the Oregon Coast suffered a 5.9 magnitude earthquake on Wednesday, April 11, 2012, 160 miles off its coastal shore, the PBS Newshour broadcast a story about the threat of liquefaction in the Pacific Northwest, which hosts two large cities: Portland and Seattle. It discussed the possibilities of liquefaction and what local engineers are doing to prevent or diminish its impact (Woodruff and Bearden 2012). The PBS Newshour video is linked at the base of this post.

The Pacific Northwest has suffered minor amounts of liquefaction in recent years, however. In the PBS Newshour account, they discussed a big event, one that occurs every 300 years or so (the last of which occurred 312 years ago – grade school was quite terrifying as the teachers kept reminding us of the fact that our time was up).

Nisqually Earthquake: February 28, 2001

On February 28, 2001, the Nisqually earthquake rattled the Pacific Northwest. The 6.8 magnitude earthquake caused damage throughout Olympia and Seattle, and even a little as far north as Vancouver, British Columbia (Wikipedia 2012). My boss and I spent several hours of quality time together at the Boise airport, due to flight delays (thank heavens for the french fry machine – but there is really only so much you can say about it). Later, we visited Olympia itself, where our hosts took us on a personal field trip to a then-closed off area. Road pavement was separated several feet from the ground. Sand boils (like those mentioned in the PBS Newshour video) left marks throughout the place. Beautiful homes were cracked, some slightly tilted.

That earthquake’s liquefaction scars continue to fill the area with stories and motivate our thoughts. Currently, at least two bridges are being torn down due to damage from the earthquake: the South Park (16th Street) and Alaskan Way Viaduct. It should be noted that their removal results from other issues as well, but you can see their bent supports and cracks formed during the earthquake. These bends and cracks formed by movement of the soil during liquefaction. While working in South Park on an archaeology project, we were in the yard of a family whose house’s chimney collapsed during ground liquefaction. They replaced it with a bay window.

Links

PBS Newshour video: Would a Major Earthquake Sink Portland or Seattle in Liquefied Soil? (Woodruff and Bearden 2012)

Wikipedia: 2001 Nisqually Earthquake: nice general summary of the earthquake.

University of Washington Nisqually Earthquake clearinghouse: reams of info on the earthquake.

References

Wikepedia

2012   2001 Nisqually Earthquake. Wikipedia (last updated April 20, 2012). Electronic document, http://en.wikipedia.org/wiki/2001_Nisqually_earthquake, accessed April 21, 2012.

Woodruff, Judy  and Tom Bearden

2012   Would a Major Earthquake Sink Portland or Seattle in Liquefied Soil? PBS Newshour (broadcast online April 12, 2012). Electronic document, http://www.pbs.org/newshour/bb/science/jan-june12/liquefaction_04-12.html, accessed April 21, 2012.

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Pacific Northwest Earthquake Liquefaction by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.


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