The Big One  

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Researching the Risks

In addition to solving the Big One mystery, lots of research is going on right in our own backyard.

Seattle’s Kingdome imploding.

When Seattle’s Kingdome was scheduled for implosion (the opposite of explosion), one study placed seismographs in backyards and schools around the Seattle area. The results are helping to create a detailed picture of which neighborhoods are most vulnerable to earthquake shaking.

Uncovering the Seattle Fault

The discovery that a Big One really had happened in the Pacific Northwest prompted new interest in our region’s geology. Within a few years, reseachers found evidence of another great earthquake, one that took place 1,100 years ago—right under Seattle.

Unlike the big subduction zone earthquake in 1700, this one was centered on a fault that lies close to the surface. That’s significant. Movement along a shallow fault can cause very intense shaking, and the Seattle Fault runs through one of the most heavily populated parts of Washington. There are shallow faults beneath Tacoma and Whidbey Island as well. The information we get from studying the Seattle Fault helps predict earthquakes throughout the Pacific Northwest.
In order to better understand the risks to communities, scientists today are making use of ingenious new approaches to map the geologic structures beneath Puget Sound.

LIDAR (Light Distance and Ranging) technology uses airplane-flown lasers to reveal surface features hidden by buildings and vegetation. This map traces part of the Seattle Fault.

Quakes in Eastern Washington

Although the risk is greater west of the Cascades, the Columbia Plateau also is geologically active. The ground shaking that took place in Spokane in the summer of 2001 was a reminder that Eastern Washington has earthquakes, too. In fact, a very large earthquake occurred near the southern tip of Lake Chelan in 1872, and a moderate earthquake damaged Walla Walla in 1936.
Just a few months after the 2001 Nisqually earthquake, Spokane experienced a series of small, shallow, closely spaced earthquakes that geologists call a “swarm.” More than 80 small earthquakes were recorded by the end of 2001. The largest quake of the swarm was a magnitude 3.9. Another notable swarm began in November of 1987 near Othello, Washington. That series of 200 quakes took place over nearly a year.
Aerial image of Latah Creek in Eastern Washington
Straight lines are rare in nature, and may be signs of an underlying fault. Some geologists believe a fault beneath Latah Creek is responsible for the recent earthquake swarm in Spokane.

Portland's Shallow Faults

It can be difficult to find surface faults in the tree-covered Northwest. Today, hidden shallow faults can be “seen” by a variety of new technologies, including those that use the natural magnetism of rocks. In the Portland-Vancouver area, studies revealed the almost-straight line of the Portland Hills fault zone. If this fault becomes active, it poses significant seismic hazard to the communities near Portland, Oregon, and Vancouver, Washington.

Red line shows the Portland Hills fault zone.

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© 2002 Burke Museum of Natural History & Culture
University of Washington, Seattle, WA 98195-3010

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