Our Northwest Energy
11:24 am
Wed April 21, 2010

"Sleeping Giant" Overdue, Seismologists Ponder "The Big One"

PORTLAND – There's a sleeping giant in the Pacific Northwest that could wake very soon and shake us all up. That giant is a major quake on par with the one that rattled Chile earlier this year. Some seismologists say it's overdue. More than 500 of the world's leading earthquake experts are in Portland this week for their annual conference. Correspondent Tom Banse dropped by to find out when the next “Big One” might shake the region.

It's a question seismologists get asked all the time. When is the next Big One going to unleash? Steve Malone, professor emeritus at the University of Washington.Steve Malone: “A specific prediction of an event? No, I don't see that occurring.”

The best Oregon State University researcher Chris Goldfinger can give you is probabilities. His new finding - presented in Portland - is that the risk from a huge offshore quake varies depending on how far north or south you live.

Chris Goldfinger: “People have been used to hearing that we have a probability of a great earthquake of around 10 to 14 percent in the next 50 years. But that really only applies to the northern part of the margin. It increases up to about 37 percent down south.”

Goldfinger studied undersea landslide debris to construct a 10,000 year record of major earthquakes along the Cascadia subduction zone. That's the tectonic plate boundary offshore, our biggest source of trouble. The geologic evidence now leads him and others to conclude the Cascadia fault has segments. They can break loose individually or all together. The southern end seems to be more active. It's where Goldfinger expects to see the next big temblor.

Chris Goldfinger: “Particularly for southern Cascadia, instead of a rather remote sounding risk of 10 to 15 percent chance that doesn't really quite rate as highly as driving on I-5 in a commute rush, the message is that the earthquake hazard is higher than previously thought.”

The last Cascadia earthquake was 310 years ago. If the past predicts the future, Goldfinger says we're overdue.

Chris Goldfinger: “We're sitting in a pre-earthquake time just like the week before Katrina. What are we going to do about it?”

Consulting seismologist Roland Laforge has reviewed the work of Goldfinger's team. Laforge gives slightly lower odds for catastrophe, but he would take steps to reinforce buildings regardless.

Roland Laforge: “It appears on the northern end that you don't get these magnitude eights – eight-and-a-half's. You just get the Big One.”

...the magnitude nine where the entire fault rips all at once from Canada to California.

Roland Laforge: “Up at the northern end – Seattle and Vancouver – it looks like you're sitting there for a long time and all of a sudden, blammo! You get a big one. At the southern end, you get hammered more frequently.”

Even before these latest scientific developments, Northwest states and coastal towns started some new projects to be better prepared. The town of Cannon Beach, Oregon is considering whether and how to build an evacuation tower for the tsunami that could follow "The Big One." A proposed building on earthquake resistant stilts would be large enough to provide refuge to more than 1,000 people.

Forty miles up the coast, residents living on Washington's Long Beach peninsula realize they too may not have enough time to flee inland to higher ground. The proposed solution there is to build artificial high ground by mounding dirt.

John Schelling:“The berm would be sort of circular in the front to dissipate the wave energy around it. People would access the site from a ramp in the back.”

John Schelling is the earthquake and tsunami program manager for Washington State Emergency Management.

John Schelling: “Berms may be a little more attractive than towers or buildings for a couple of reasons. One, after earthquakes people generally don't like to be in buildings.”

Schelling says a new federal grant will pay for planning and design of four berms on the Long Beach peninsula and more elsewhere in Pacific County. It's still unclear who would pay for the actual construction of mounds two to three stories tall.

The Big One. Are We Prepared? (OPB Think Out Loud):
http://www.opb.org/thinkoutloud/shows/big-one-cascadia-subduction-earthquake/