Earthquake News

Since the Nisqually earthquake in 2001, we've learnt a lot about dangerous ground.

Scientists understood a decade ago that Western Washington was vulnerable to considerably more powerful earthquakes than the magnitude 6.8 that shook Seattle on Feb. 28, 2001.

But it's what they've discovered in the ten years since the Nisqually earthquake that has some scientists concerned.

The fact that the Nisqually earthquake wasn't much worse was the biggest surprise.

Scientists realized the Northwest was vulnerable to earthquakes that were far more powerful than the magnitude 6.8 that struck Seattle ten years ago Monday.

Other researchers, on the other hand, are concerned about what they've learned during the last ten years.

Chris Goldfinger, a marine geologist at Oregon State University, remarked, "I never really thought about it before."

"Now I'm sitting in my earthquake-prone home, hoping it doesn't happen now."

Megaquakes of the type that wrecked Sumatra and triggered a fatal tsunami may shake the Northwest much more frequently than previously anticipated, according to Goldfinger's research. Scientists have discovered more than ten active faults in the Puget Sound region, up from two in 2001. Furthermore, fresh studies reveal that the earth beneath downtown Seattle isn't nearly as stable as previously thought. 

"The risk has obviously increased," said Brian Sherrod, a USGS scientist stationed at the University of Washington. "But it's a reflection of our better knowledge." 

A decade of astonishing discovery in the Northwest has been fueled by technologies that uncover hidden faults and measure the scrunching of the Earth's crust down to the millimeter.
Traditional fieldwork also played a role.
Sherrod and his colleagues excavated so many holes in their search for indications of prior earthquakes that he's lost count. 

"The new insights are beginning to inform building and emergency preparation," says Craig Weaver, the USGS' regional seismic-hazards chief.

"Ten years ago, we were in an exploratory period.

We now have a much better sense of what to anticipate." 

"The new insights are beginning to inform building and emergency preparation," says Craig Weaver, the USGS' regional seismic-hazards chief.

"Ten years ago, we were in an exploratory period.

We now have a much better sense of what to anticipate." 

"The quantity of major flaws we're dealing with astounds us," Weaver added.

The recent earthquake in New Zealand highlighted the dangers of shallow faults near cities.

When the shaking is not mitigated by distance or depth, even a very small quake can be fatal.

A magnitude 7+ earthquake on the Seattle Fault, the larger of the two faults that geologists had penciled in on their charts 10 years ago, is Seattle's worst-case scenario.

It runs from Bainbridge Island to Bellevue, passing beneath Safeco Field.

A repeat of the Seattle Fault's last big jolt 1,100 years ago would be among the most destructive in American history. And Sherrod and others now believe the Seattle Fault is dwarfed by a much larger fault zone called the Southern Whidbey Island Fault, which may have strands that extend from Vancouver Island to Richland.

The good news about the region's shallow faults is they don't pop very often, Sherrod said. Repeat times seem to range between 700 and several thousand years. The bad news is Sherrod and his colleagues keep finding more.

He stated, "Right now, I'm working on three more."

"We haven't even started looking southward of Olympia."

It's a big deal to change "everything."

LIDAR, an airborne laser scanner, proved critical in revealing the region's seismic history.

The process eliminates all vegetation from the area and produces topographic maps bare of it.

Potential faults appear on an X-ray as fractured bones.

"That truly impacted everything," Sherrod said. 

On the coast, Goldfinger is employing novel methods to gain a better understanding of the cocked gun known as the Cascadia Subduction Zone, which is responsible for some of the world's most powerful earthquakes.

The 600-mile-long offshore fault is where the continental plate is jammed under the ocean floor.

By the early 2000s, it was obvious that the fault might produce earthquakes and tsunamis of magnitude-9, comparable to Sumatra's 2004 disaster.

The most recent occurred in the year 1700.

Goldfinger stretched the record back to include 22 megaquakes during the last 10,000 years by looking for evidence of underwater landslides in sediment cores.

His contention that major quakes on the part of the fault off the Oregon coast strike every 240 years, rather than the 400 to 500 years now considered into risk assessments, is more contentious.

If this is correct, there's a 37% probability the region will be shaken in the next 50 years.

Another disturbing piece of research reveals that Cascadia's danger zone — the area of the fault that would shatter in an earthquake — could be closer to Seattle, Portland, and Vancouver, B.C. than previously anticipated.

The evidence comes from a study of "silent earthquakes", a recently discovered phenomenon. Seismologists "listening in" on the Olympic Peninsula have detected minuscule vibrations that they believe are caused by geologic plates sliding past each other in the subduction zone. The slip, as well as all the other tectonic twisting that makes the Northwest such rich earthquake ground, can be measured by a network of more than 400 GPS stations spread across the region. According to Central Washington University geologist Tim Melbourne, there were only about a dozen of the stations a decade ago.

According to Melbourne, the slip measurements and seismic signals allow scientists to pinpoint the region of the subduction zone that is slipping freely. They utilize this information to calculate the danger zone's position, the area where the fault is locked, and to build up tension before releasing it with a bang.

Some experts are skeptical that the danger zone is only 50 miles from the Interstate 5 corridor. "The jury is still out," Goldfinger added, "but if it's real, it has to be treated seriously because of the divisions."

Assessing the danger Another quake similar to Nisqually is the most likely to strike the Puget Sound region. Over the next 50 years, the USGS estimates that the probability will be greater than 80%. The Nisqually began more than 30 miles below the surface, when the Juan de Fuca plate bends dramatically as it dives beneath the continent, similar to earthquakes in 1949 and 1965.

According to USGS scientist Art Frankel, the 2001 quake revealed some unexpected insights into what's likely to happen the next time the ground starts moving.

The 30-second Nisqually quake shook Seattle twice as strongly as expected since it lies atop a basin.

The basin, according to Frankel and others, might trap and amplify vibrations in unanticipated ways, which Nisqually verified.

Frankel incorporated this knowledge into a cutting-edge computer model that he worked on for more than a decade. He ran more than 500 scenarios through the computer, taking into account what was known about the region's subsurface geology, newly discovered faults, and the conceivable spectrum of earthquake types. He compared simulated results to measurements from previous earthquakes to validate the model.

As a result, the most advanced seismic-hazard map in the country has been created. The map pinpoints sensitive places, such as the basins beneath Seattle, Tacoma, and Everett, and forecasts the magnitude of the tremors.

"We don't have to wait for a large earthquake to figure out where the dangerous spots are," Frankel explained.

Building codes haven't yet taken into account the modeling, but Frankel expects they will.

"It's right on the cusp of study and application."

Frankel has already started work on a new hazard map. He's also confronting the region's largest seismic conundrum: how long and how strongly will a magnitude-9 subduction-zone quake shock the ground? The answer is crucial to knowing how Seattle, Portland, and Vancouver, B.C.'s skyscrapers would fare during the voyage. Last year's magnitude-8.8 earthquake on an offshore fault comparable to Cascadia smashed several modern high-rises in Chile constructed to strict codes.

"A large subduction-zone quake would be disastrous," Frankel predicted. "We're determining how bad it is."

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