Aftermath of huge Peninsula quake would inundate communities -- a town-by-town analysis

By Paul Gottlieb
Peninsula Daily News

What happened in Chile will happen here -- sooner or later



By Alicia Chang

The Associated Press


Just 50 miles off the Pacific Northwest coast is an earthquake hotspot that threatens to unleash on the North Olympic Peninsula, Seattle and Portland the kind of damage that has shattered Chile.

The fault has been dormant for more than 300 years, but when it awakens -- tomorrow or decades from now -- the consequences could be devastating.

Recent computer simulations of a hypothetical magnitude 9 quake found that shaking could last 2 to 5 minutes -- strong enough to potentially cause poorly constructed buildings from British Columbia to Northern California to collapse and severely damage highways and bridges.

Such a quake would also send powerful tsunami waves rushing to shore in minutes.

While big cities such as Portland and Seattle would be protected from severe flooding, low-lying seaside communities like Neah Bay and LaPush would not be as lucky.

The Pacific Northwest "has a long geological history of doing exactly what happened in Chile," said Brian Atwater, a geologist with the U.S. Geological Survey and University of Washington.

"It's not a matter of if but when the next one will happen."

The last one hit in 1700, a magnitude-9 that sent 30- to 40-foot-tall tsunami waves crashing onto the coast and racing across the Pacific, damaging Japanese coastal villages.


80 percent chance in 50 years

There's an 80 percent chance the southern end of the fault off southern Oregon and Northern California would break in the next 50 years and produce a mega-quake, according to Chris Goldfinger, who heads the Active Tectonics and Seafloor Mapping Laboratory at Oregon State University.

Research presented last year at a seismology conference found that Seattle high-rises built before 1994, when stricter building codes took effect, were at high risk of collapse during a super-quake.

Disaster managers in Washington state and Oregon are aware of the risks, and work is ongoing to shore up schools, hospitals and other buildings to withstand a seismic jolt.

"We're definitely being proactive in trying to get those fixed, but we have a long way to go," said Yumei Wang, geohazards team leader with the Oregon Department of Geology and Mineral Industries.

Oregon has 1,300 schools and public safety buildings that are at high risk of collapse during a major quake. The state recently doled out $15 million to two dozen schools and emergency facilities to start the retrofit process.

Seattle plans to retrofit its 34 fire stations. The city is also working on a plan to upgrade 600 buildings considered most at risk.

"We have been preparing aggressively," said Barb Graff, who heads the city's Office of Emergency Management.


Global hotspots

Chile and the Pacific Northwest are part of several seismic hotspots around the globe where plates of the Earth's crust grind and dive.

These so-called subduction zones give rise to mountain ranges, ocean trenches and volcanic arcs, but also spawn the largest quakes on the planet.

The magnitude-8.8 Chile quake occurred in an offshore region that was under increased stress caused by a 1960 magnitude-9.5 quake -- the largest recorded in history, according to geologist Jian Lin of the Woods Hole Oceanographic Institution.

The temblor destroyed or badly damaged 500,000 homes and killed more than 700 people.

Similar tectonic forces are at play off the Pacific Northwest, where the Juan de Fuca plate is diving beneath North America.

At some point, centuries of pent-up stress in the Cascadia subduction zone will cause the plates to slip.

Scientists cannot predict exactly when a quake will occur, only that one will happen.

The region is all too familiar with violent earthquakes.

In 2001, a 6.8-magnitude quake centered near Olympia, rattled a swath of the Pacific Northwest, but remarkably caused no deaths.

While it was not the type of quake that hit Chile, it was a reminder of how a big disaster could strike at any time.

To better understand mega-quakes, a group of scientists planned to travel to Chile in May for a conference on giant earthquakes and their tsunamis.
The near-record magnitude 8.8 earthquake that rocked Chile on Feb. 27 resonated here on the North Olympic Peninsula with tsunami advisories that resulted in mere inches of a splash.

But experts say the megathrust-temblor arising from the Cascadia Subduction Zone off the Washington state coast would be even greater, at 9.1.

They also say the huge quake -- the U.S. Geological Survey reports only four worldwide at 9.0 magnitude or greater since 1900 -- would create a giant wave that would race across the Pacific, aiming right for our coast.

The last such quake was in 1700. Experts say there's no doubt that another will happen; they just don't know when.

A minimum 10-foot tsunami would hit the Pacific coastline of the Peninsula in a Cascadia Subduction Zone earthquake, hitting coastal towns, then curling up the Strait of Juan de Fuca, said Tim Walsh, chief hazards geologist for the state Department of Natural Resources.

Areas in the immediate vicinity of shorelines would be flooded, he said, citing DNR earthquake models.

Residents should have three weeks of food and water on hand in preparation for a Cascadia earthquake, Clallam County Emergency Management Program Coordinator Jamye Wisecup said.

Below are brief assessments of the impact of such a tsunami on the Peninsula's coastal communities from interviews with Walsh and county, city and tribal officials.

Go to www.emd.wa.gov for more information.


LaPush

The Quileute tribal community of LaPush would see more devastation than any on the Peninsula, Walsh said.

The earthquake would generate an estimated 14-foot wave, he said.

"They've got a lot of infrastructure at very low elevations," he said.

Inundation areas include Rialto Beach and the Quileute River area, said John Schelling, earthquake-tsunami program manager for the state's Emergency Management Division.

"The lower village is pretty much within the inundation area, but there are portions of the upper part are outside," Schelling said.

The state emergency management office has worked with the tribe to develop evacuation routes with signs directing residents the fastest way to get to high ground.

The signage works in concert with evacuation brochures developed by the agency and available at www.emd.wa.gov.

The community also has All Hazard Alert Broadcast sirens.


Neah Bay

In Neah Bay, on the Makah reservation, an estimated 10-foot wave would probably inundate low-lying areas downtown, said Andrew Winck, Makah emergency management coordinator.

The Makah tribe has two of the 49 All Hazard Alert Broadcast sirens distributed by the state Emergency Management Division that would sound, and the population of 1,800 has evacuation areas to gather at above the flood zone.

Local roadways would be extensively damaged.

"The whole downtown is kind of sandy soil, so that would provide minimal protection," he said, adding few houses would survive without significant damage from the shock and water.

But the 200-slip Makah Marina would likely survive 10-foot waves, said Bob Buckingham, the tribe's port director and marina manager.

"It's enough for 10 foot of freeboard at high tide," he said.

There are no plans for evacuation towers or "breakaway" buildings, in which the first floors are built on concrete pilings.

In a strong tsunami, contents of the first floor fall away in onrushing water, but the contents of the second floor and above stay intact.


Clallam Bay-Sekiu

A tsunami would inundate areas north of Highway 112 including Kydaka Point, Sekiu Point and Slip Point, Front Street to Highway 112, Pysht River Road and surge up the Pysht, Sekiu and Clallam rivers, according to the state.

A warning siren for alerting residents of an impending tsunami is perched at the water treatment plant.

The siren, financed by the federal Department of Commerce, was installed earlier this year.

Other sirens are at LaPush, Neah Bay, the Lower Elwha Klallam reservation, Port Angeles, Sequim and Diamond Point.

The warning signal would be followed up by instructions for evacuation.


Lower Elwha Klallam reservation

A Cascadia Subuction Zone earthquake tsunami would cause some flooding of the Lower Elwha Klallam reservation from Angeles Point south to around Stratton Road.

"The lower part of the reservation would get extensive flooding," Walsh said.

Lower Elwha Road is outside the inundation area.

The tribe is part of the State-Local Tsunami Working Group.

Evacuation routes from the reservation west of Port Angeles have been developed with the state Emergency Management Division.

The tribe held an earthquake emergency evacuation drill last year that showed the All Hazard Alert Broadcast siren near the tribal center was not loud enough to notify Head Start children and other tribal members, so the tribe is exploring the acquisition of a second siren, tribal Chairwoman Frances Charles said.

"I would say we are a little over 50 percent prepared," Charles said. "We still have a few things to iron out."


Port Angeles

Ten-foot waves from an offshore undersea earthquake would flood the waterfront, damaging the downtown and businesses and some homes in low-lying areas, as well as likely flooding Ediz Hook, including Coast Guard Group/Air Station Port Angeles, Walsh said.

"I don't think anything would come up the hill," Walsh said.

"It stays pretty much down along Ediz Hook and the ferry terminal and along [Railroad Avenue], but I don't think it penetrates more than a block in."

The city expects a one-hour warning for an approaching offshore tsunami, giving time to get to the high ground. There would be less time to escape a wave produced in the Strait of Juan de Fuca.

The city and Clallam County are upgrading multilevel warning and notification systems that include All Hazard Alert Broadcast sirens, Wisecup said.

Hazard warning information is available by registering at www.nixle.com.

Citizens throughout Clallam county would be notified by phone, both on land lines and on some cell phones, through the Enhanced Telephone Notification System, which employs 9-1-1 system to notify at-risk areas, Wisecup said.

"We're not looking at anything in Port Angeles going above the bluffs and heading for City Hall or anything like that," Walsh said.

Of concern would be boats moored to marinas.

"You have to make a decision of whether or not to send boats to deeper water," Walsh said.

That would be water 100 to 200 feet deep "so there's not much of a wave," he said.

"The issue is a matter of time. If you're caught while you're trying to do that without having gotten very far off shore, it could be worse than you encountering high currents.

"If you only have an hour, that may not be enough time."


Sequim

A tsunami wave would probably inundate Dungeness Spit, affecting the keepers of the lighthouse, Walsh said.

John Wayne Marina, with 300 slips, may be compromised, he said.

"If you look at the pilings that floating docks are secured by, typically they don't have 10 feet of freeboard," Walsh said.

Floating docks are connected to pilings by rings that ride up and down with the waves, he said.

"In the event of a tsunami, they could just float off the top," break free, and the entire dock could float away, Walsh said.

"You could readily imagine in a worst-case scenario, a wave could float the docks off and there would be free-floating docks with boats going with them, so you would have many millions of dollars in damage," he said.

"You have boats with a 6-foot draft that don't have too much to spare."

A "simple fix," Walsh said, would be to extend the pilings higher so the connecting rings ride higher.


Port Townsend

Scientists predict a rapid tide, perhaps 10 feet high, would hit the downtown historic district and the marina area south of downtown, flooding both and damaging some of the city's old buildings.

Old building foundations "may give way," Port Townsend City Manager Dave Timmons has said.

North Beach, where as many as 500 city residents live, probably would have to be evacuated, and the city's sewage-treatment plant would likely flood.

There would be ample warning if the wave came from the Cascadia Fault, but less if a wave was created by a second fault near the south tip of Whidbey Island.

"One thing we learned from the Sumatran earthquake was that the currents are probably going to more lateral than onrushing coming down the Strait," Jefferson County Emergency Services Director Bob Hamlin said.

"Anything at the water line or below will be scoured out," he said, including old foundations along the waterfront downtown that would be compromised by the water surge.

The city's water treatment plant also probably would flood, Hamlin said.

Discovery Bay also likely would be flooded. There's already evidence of past tsunamis at the upper end of the bay.

"It's definitely in the 50-foot parameters, where we recommend everyone evacuate to at least 50 feet above sea level," Hamlin said.

People are urged to flee to higher ground but also should be prepared to last on their own with food, water and other essentials for three weeks, he added.


Hood Canal, including Brinnon, Quilcene

The impact from a tsunami probably would be minimal in Hoodsport and other towns along the canal, Hamlin and Walsh said.

By the time the 10-foot wave predicted for most of the Peninsula reached the Hood Canal, it would have diminished.

For that reason, no models have been established to predict wave height or impact, Walsh said.

"As [the wave] turns corners and interacts with islands and peninsulas and the like, it loses energy to friction," he said.

"As it got down to Admiralty Inlet and then into the canal, it would lose a lot of energy," he added.

"We don't think it's a specific hazard there."

Hamlin said there could be some sea-level changes down Hood Canal but nothing significant.

"Anything below the [Hood Canal] bridge and Marrowstone Island is pretty well out of the picture," he said.

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Senior Staff Writer Paul Gottlieb can be reached at 360-417-3536 or at paul.gottlieb@peninsuladailynews.com.

Last modified: March 14. 2010 1:05AM
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