10 years later, what has science learned about quakes?



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Posted on February 28, 2011 at 7:54 PM

SEATTLE -  Ten years ago, the ground under western Washington shook with the Nisqually earthquake, registering a 6.8 in magnitude. 

In some places, the damage was bad. Seattle's Pioneer Square and downtown Olympia were two of the most damaged urban areas.  

The quake struck just before 11:00 a.m., and Nisqually became a seismic wake up call in the middle of the day.

Depending on where you were, Nisqually was either a nightmare or a non event.

"I don't remember feeling much of anything," said Jack Snell of Lake City, who was in his home at the time. But he is aware that the next quake might be a lot bigger.

"I'm sure this area here is not very good for an earthquake," he said.

Snell is volunteering to host an earthquake seismometer in his garage, part of a University of Washington project called Netquakes that will help scientists record shaking.

"I thought, by golly, if I can do something to help science I'll do that," Snell said.  
Netquakes helps scientists beef up their network of seismometers around Washington, particularly in the especially earthquake-vulnerable western half.  It will all be piped in to the Pacific Northwest Seismic Network. These strong motion sensors will paint a detailed picture of what the ground under our feet looks like. That information helps predict which parts of the state are going to shake more and which will shake less.

There are three basic types of quakes under Washington. Nisqually, the 1965 and 1949 quakes were deep, happening about 30 miles below the surface, likely cracking of the ocean floor near the mantle of the earth. Their depth minimizes their damage. 

But further up that boundary between the ocean floor and the North American continent is the real danger -- that is the site of the megathrust earthquakes, which can top a magnitude 9.0. 

Alaska's 9.2 in 1964 was a megathrust or subduction quake. So was the giant quake that hit Indonesia in 2004 that sent a Tsunami around the world devastating coastal communities around the Indian Ocean.

Science is busy pulling back the veil that shrouds our earthquake risks. Everyday the picture gets a little clearer, and the news a little more disconcerting. That's where the third type of quake comes into play -- faults near or at the surface.

Just last week one of those quakes played out in Christchurch, New Zealand. It was a shallow fault, responsible for a 6.3 magnitude earthquake that killed at least 145 people. 

In Washington, geologist Brian Sherrod with the U.S. Geological Survey is looking for faults just like it. Sherrod is a shallow fault hunter. 

From exposed evidence of the Seattle Fault he spotted under I-5 near Downtown Seattle while stuck in traffic, to new frightening evidence found in 2009 that suggests the South Whidbey Island fault extends east of the Cascade mountains to near Yakima. By following aerial surveys, Sherrod digs trenches across suspected faults looking for evidence and exposing the danger.

In the ten years since Nisqually, Sherrod has found 10 previously undiscovered faults in our state. 

"Are they active? How big are the earthquakes they produce? I call that first order of problems," said Sherrod. "And we're just getting some of those questions answered now."

In 2005, the potential devastation from one of these faults was addressed in a study looking at a 6.7 magnitude quake on the Seattle Fault.

While the quake would technically be smaller than Nisqually, it's damage far, far greater because it's a lot closer. That study in part prepared by Washington's Emergency Management Division estimated it would kill 1,600 people, injure 24,000 others and destroy 9,700 buildings.  

In the six years since the report, Sherrod's research thinks the quake potential is even higher and there are still unanswered questions.

"Where does the Seattle Fault go to the west? Where does it go to the east?" asked Sherrod. 

Those are answers he is trying to find.