Will Snohomish County be ready when a quake strikes?

Published 11:02 pm Monday, February 15, 2010

SNOHOMISH — If you live here, you may have felt the ground tremble early Feb. 8.

At least six people in the area felt the magnitude 2.2 earthquake about 2 a.m. that day and reported it to scientists, said Bill Steele with the Pacific Northwest Seismic Network.

Hundreds of minor earthquakes are recorded in the Pacific Northwest each year. But experts say the forces beneath the surface have enough destructive potential to deal the region a powerful blow.

With the Haiti earthquake still so fresh in mind, it’s a frightening reality.

Several faults run through the ground in or near Snohomish County and can potentially unleash a damaging earthquake at any time, Steele said.

Newer structures have been built to withstand moderate earthquakes. But structures predating World War II, mostly built of bricks with mortar in between, likely will turn to rubble in a major quake, Steele said.

“You’re really looking at buildings that are essentially a stack of bricks,” he said. “In older parts of Everett or (Seattle’s) Pioneer Square, it may look a lot like Haiti.”

The South Whidbey Island Fault, stretching from west of Whidbey Island through Mukilteo and south Everett and relatively unknown until recently, is active and capable of creating an earthquake.

Then there is the Cascadia subduction zone, a giant fault running off the Pacific Northwest coast where the Juan de Fuca plate slides under the North American Plate.

Research shows that big earthquakes in the subduction zone happen, on average, every 550 years. Steele said that means roughly a 15 percent chance of a world-class earthquake in the next 50 years. The last big earthquake here happened more than 300 years ago.

“In the world of probability, that’s pretty high,” he said. “There is no doubt that this earthquake can occur tomorrow.”

Still, the odds of someone in Snohomish County dying in an earthquake are far smaller than, say, the odds of being hit by a bus, Steele said.

In a major quake, Snohomish County will be affected differently depending on which fault moves and other factors. Under any scenario, though, the county “will rattle pretty hard,” said John Pennington, the director of the county Department of Emergency Management.

Bridges and highways running through the county could come down. Lives may be lost. Dams could collapse and buildings may crumble.

Under what the experts say is an unlikely, nightmare scenario, the Culmback Dam on the Sultan River, which holds a major water reservoir, could collapse, causing flash flooding downstream. Bad news for Sultan.

Sultan officials practice emergency evacuations regularly and do a great job, Pennington said.

If a quake comes from the subduction zone, it may unleash a tsunami, he said. In that case, sirens will go off and tell those near shorelines to move to higher ground.

Even though a tsunami is a legitimate concern for the county, natural geography helps: The county is buffered from ocean tsunamis by Whidbey and Camano islands, Pennington said.

Another thing to worry about would be soil liquefaction, when certain unstable types of soil shake, turning into pools of mud, Pennington said. Buildings standing in those areas would collapse.

The good news is, the county is well equipped to deal with a disaster such as an earthquake. Having weathered six federally declared disasters, including floods and snowstorms in the past three years, many people here are prepared, Pennington said.

Under some scenarios, Snohomish County would play a critical role in supporting the Seattle area. The seismically stable Paine Field may well become a focal point for delivery of federal resources, Pennington said.

Officials meticulously planned what steps they will take if disaster strikes here. They are educating families, training first responders and stocking up on advanced equipment to rescue people from collapsed buildings.

“We are much better prepared than most communities, not just for earthquakes, but for any major disaster,” Pennington said.

Katya Yefimova: 425-339-3452, kyefimova@heraldnet.com