The Trembling Earth

now at blogs.agu.org/tremblingearth

Seattle’s “Big One”… almost

Instrumentally recorded shaking intensity throughout Washington state, interpolated among the network of local seismometers that recorded this earthquake..

February 28 marks the anniversary of Washington state’s most recent large quake, the M6.8 Nisqually earthquake of 2001. The epicenter was at the southern end of Puget Sound, and the 10:54am quake heavily rocked Washington’s most populous region, including the capitol Olympia, Tacoma, and Seattle.

This quake was a relatively “small” quake for the region, considering the Pacific Northwest is periodically rocked by massive subduction zone “megaquakes” like the recent ones in Japan, Indonesia, and Chile, but at a respectable 6.8 and located so close to metropolitan areas, it was a violent and destructive quake nonetheless. It represents a different kind of quake risk to the Pacific Northwest from that posed by the much-publicized Cascadia subduction zone. This quake occurred in the crunching and crumpling upper plate as it grinds over the diving Pacific ocean slab.

There are a couple of decent videos of it occurring, including one from an unstable webcam in a Seattle Microsoft office:

(in that video note the distinct P- and S-wave arrivals: the rumbling Primary waves herald the quake’s onset at this location, giving ample warning for the office occupants to head to shelter before the Secondary and Surface waves arrive with significant lateral forces. Also keep an eye out for the continuing long-period motion and two severe vertical jolts that keep rocking the office as the quake subsides. You’ll notice this especially in the the swinging telephone cords, whose oscillation doesn’t simply dampen, but responds to renewed accelerations during continuing low-frequency shaking.)

Microsoft execs including Bill Gates were giving a press conference on new Microsoft products in a Westin Hotel conference room when the quake struck, so two news crews captured it on film. The quality of these is poor, so turn down your speakers:

 

The quake also interrupts a meeting of Seattle’s City Council:

 

In addition, there are a couple of radio recordings of the quake happening, as documented in this article.

 

This was a significant event for Washington state, so lots of money and research has been dedicated to studying it. Much of this research is highlighted through the University of Washington’s Nisqually Earthquake Information Clearinghouse, a great site for more detailed information about the quake and its effects. There’s also an excellent blog dedicated to chronicling the experiences of Washingtonians during and after the earthquake, at http://isquallyquake.wordpress.com.

The Southern California Earthquake Center has also put together an info page comparing the 2001 Nisqually quake to L.A.’s similarly sized 1994 Northridge Earthquake, at http://www.scec.org/news/01news/feature010313.html.

 

As always, mark this anniversary by considering your own preparedness were an earthquake like this to strike your hometown. Every time it happens we learn more, so we should fare better after each new earthquake.

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