Pinpointing devastation if Seattle Fault ruptures
Seattle Times staff reporter
Why an earthquake scenario?
The Seattle Fault earthquake scenario is the brainchild of Dave Swanson, a structural engineer with Reid Middleton in Everett. Inspired by a less-detailed scenario for an earthquake on the Hayward Fault in the San Francisco area, he began trying to assemble a team to take an in-depth look at a Seattle Fault earthquake.
The Earthquake Engineering Research Institute, a nonprofit society that works to reduce earthquake risks, offered $50,000 for administrative expenses. The state kicked in $30,000 to publish the report, and the U.S. Geological Survey is helping pay for a Feb. 28 meeting where it will be unveiled. But expert volunteers did most of the work. The meeting is not open to the public, but the group hopes to offer public sessions on the scenario later this year.
Create a state seismic safety board, reporting directly to the governor, to recommend policies and programs to reduce the earthquake risk in Washington.
Identify critical public facilities — hospitals, schools, police and fire stations — at high seismic risk and establish long-range plans to improve their safety.
Develop local and state funding and legislation that requires upgrades to high-risk buildings, such as unreinforced masonry and concrete tilt-up structures.
Quicken the pace of upgrades to highways and freeways vulnerable to earthquake damage.
The most damaging earthquake in state history strikes on a weekday, shortly before noon.
In downtown Seattle, the violent lurching knocks pedestrians off their feet. Drivers struggle to hold their cars on the road. A 14-mile rupture splits the ground from Elliott Bay to Issaquah, with one side thrusting six feet into the air.
By the time the shaking stops — 30 sickening seconds later — 1,600 people are dead or dying. More than 24,000 are injured as brick buildings crumble, freeway bridges buckle, ferry terminals slump into the water and the Alaskan Way Viaduct collapses.
More than 45,000 families are forced out of their shattered homes, and nearly 10,000 commercial buildings and houses are destroyed. Another 183,500 buildings are moderately to severely damaged.
The toll on the state's economy is a staggering $33 billion in property damage and lost income, on a par with the country's most costly natural disaster to date: the 1994 Northridge earthquake in Southern California.
The Seattle quake is still fictional, of course. But if it does occur, it will take years for the region to recover, according to a new report based on the most comprehensive earthquake scenario ever devised in the United States. The report urges state and local governments to accelerate the pace of upgrades to highways, buildings and other structures vulnerable to an earthquake."When you start talking about numbers like this, you realize the impacts are huge and we're not ready for it," said Craig Weaver, a U.S. Geological Survey seismologist. The scenario, which will be unveiled in a daylong workshop in Bellevue on Feb. 28, uses a sophisticated computer model and the collective expertise of dozens of local engineers, scientists and emergency managers to forecast the devastation that would be wrought by a magnitude 6.7 earthquake on the Seattle Fault.
The 30-mile-long fault runs through the heart of Seattle and Bellevue. In the past 3,000 years, it has violently rearranged the local landscape as many as four times — or every 750 years, on average. The last of those quakes came 1,100 years ago, and geologists estimate there's at least a 5 percent chance the fault will let loose again within the next 50 years.
The scenario group invested three years and almost 4,000 hours of volunteer labor in the project. It recommends the state establish an independent seismic safety board that would report directly to the governor and would push for more highway retrofits and tougher building codes.
The group also is calling for upgrades to facilities such as hospitals, schools and fire stations. And it wants rules that would mandate improvements for the most vulnerable buildings — those made of unreinforced brick or concrete.
"We've been plodding along in Washington," said Don Ballantyne, a Seattle civil engineer who specializes in earthquake-resistant designs and was a leading organizer of the project. "This makes it clear we're at significant risk, and we should be working hard to manage those risks."
Much worse than NisquallyA magnitude 6.7 earthquake on the Seattle Fault would be up to eight times more destructive than the magnitude 6.8 Nisqually earthquake that caused about $2 billion worth of damage four years ago this month, Weaver said.
Like most quakes in Washington's modern history, including large ones in 1949 and 1965, the Nisqually quake originated deep underground, which dampens effects on the surface.
But the Seattle Fault is much shallower, and distance would not mute the fury of a quake there.
For the Puget Sound area, a quake along the Seattle Fault would even be worse than the other type of seismic hazard hanging over the region: A quake on the Cascadia subduction zone off the coast, where one tectonic plate dives beneath another. While that zone has unleashed massive earthquakes and tsunamis in the past, the shaking would be diminished by the time it reached the state's most populated urban corridor.
"With the Seattle Fault, the strongest shaking will be right in the middle of where we live and work," said Weaver, whose office is at the University of Washington.
A magnitude 6.7 quake isn't even the worst-case scenario for the Seattle Fault.
The quake 1,100 years ago was a magnitude 7.3 behemoth that uplifted the bluffs that ring Alki Beach and parts of Bainbridge Island.
"This scenario is not the big one," Weaver said. "We chose it because earthquakes of that size occur more frequently."
The new report has an important message for people who might feel complacent after the Nisqually quake, said Ines Pearce, a program manager with Seattle's emergency-management department.
"I think a lot of people who went through Nisqually are thinking: My house made it through in 2001 — maybe '65 and '49, too — so I don't have to worry," she said. "This report shows that's not true."
"It's pretty ugly"The scenario takes data from the census and other sources on the region's buildings, population, business districts, utilities and transportation networks and overlays it onto maps that estimate how hard the ground would shake in different areas.
A computer model called HAZUS, developed by the Federal Emergency Management Agency, spits out estimates of fatalities, injuries and the number of buildings destroyed or damaged.
"It's pretty ugly," said Mark Stewart, a hazards specialist with the Washington State Emergency Management Division.
The Seattle seawall would probably crumble, taking out ferry terminals and docks. Thousands of landslides would roar down the area's steepest slopes and slop into Puget Sound, triggering local tsunamis that could swamp waterfront homes and buildings.
Brick buildings in Pioneer Square and the Chinatown International District would tumble. Also at high risk are the scores of concrete warehouse-type buildings in the Sodo district and further south that house megastores, light industry and other businesses.
In river valleys and low-lying areas built on fill, the shaking would turn loose soils to mush, destroying foundations and breaking buried water pipes and utility lines. The Olympic Pipeline, which carries gasoline and jet fuel from northern refineries, crosses the Seattle Fault in Bellevue and passes through unstable soils in the Renton and Kent valleys.
A big chunk of Harbor Island, in the heart of the Port of Seattle, could slide into Elliott Bay, taking with it container terminals, cranes and docks.
Up to 40 percent of schools could be unusable as a result of the earthquake, and damage to hospitals could slash the number of available patient beds by 75 percent in the first days after the quake.
One of the biggest blows to the economy would be traffic snarls that could take years to unravel.
The day after the 2001 Nisqually quake shut down the Alaskan Way Viaduct, a five-mile commute from West Seattle took two hours. In a quake on the Seattle Fault, portions of Interstate 5, I-90, I-405 and all other major highways would be closed, and repairs could take a year or more. If the Alaskan Way Viaduct is destroyed, it will take up to six years to replace and cost more than $4 billion — an amount that isn't included in the scenario's $33 billion economic-impact estimate.
With ports and ferries crippled and highways impassible, many businesses might be forced to leave the area. To understand the impact, scenario writers looked to Kobe, Japan, where a magnitude 6.9 earthquake on a similar fault in 1995 drove business to other cities.
The Port of Kobe saw its ranking among world container ports drop from No. 6 to No. 17 after the quake, and manufacturing operations suffered for years.
Informed estimatesAside from the rickety viaduct, which already is scheduled for replacement if the money can be found, the scenario doesn't include enough detail to single out specific buildings or bridges, said Gregory MacRae, professor of civil engineering at the UW.
And the numbers the model generates should be viewed as estimates — not absolutes.
"This is a very rough tool, but it's better than anything we've ever had before," he said.
Despite the uncertainty, the scenario makes clear the need for more aggressive preparations, said Ballantyne, the civil engineer.
The region's preparedness has improved over the past several decades, with cities, businesses and the state upgrading older buildings and bridges, and stricter building codes being phased in.
But efforts have been piecemeal and spotty, the report says.
The Washington Department of Transportation estimates it will take until 2070 to complete ongoing bridge upgrades at a rate of about $5 million a year.
After the Nisqually earthquake, the city of Seattle considered requiring retrofits to brick buildings and other unreinforced masonry structures, but backed off for lack of money.
The Transportation Department's top priority for its limited budget is maintaining the state's aging highway system, rather than retrofitting for earthquakes that may not occur for decades or centuries, said agency spokeswoman Linda Mullen.
That conflict between immediate needs and future disasters sums up the basic challenge in earthquake preparedness, and the reason the state needs an independent seismic safety board, the report concludes. In California, Oregon, Utah and Alaska, such boards have kept quake initiatives from stalling and have pressed for better funding and stricter building codes, said Mark Pierepiekarz, president of the Structural Engineers Association of Washington.
In Oregon, where earthquake hazards are much lower than in Washington, the commission developed bond issues approved by the public to upgrade schools, hospitals and other critical facilities.
"Without that kind of leadership here," Pierepiekarz said, "I don't think we're going to be addressing these problems."
Sandi Doughton: 206-464-2491
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