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Dangers still lurk 20 years after Washington's last big earthquake
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Dangers still lurk 20 years after Washington's last big earthquake

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Today marks the 20th anniversary of the Washington’s last big earthquake, and there’s no forgetting it.

On the morning of February 28, 2001, one of the earth’s tectonic plates cracked 35 miles below the Nisqually River delta, sending shock waves over a broad area of Western Washington for about 30 seconds. It caused more than $1 billion in damages, nearly toppled the state Capitol Dome, rumpled roads and runways and peeled brick facades off buildings in downtown Seattle.

Miraculously, no one died, and damage in Southwest Washington was relatively minor.

Nevertheless, the 6.8 magnitude Nisqually temblor was a reminder that an earthquake more than 1,000 times more powerful lurks in the Pacific Northwest’s future — perhaps its near future. Scientists and engineers say there’s still a lot of work to do to prepare for that great quake, but the region today is more ready than it was 20 years ago.

The state of readiness for the big one is a list of dueling realities, of plusses and minuses.

A new earthquake warning system set to come on line in Oregon and Washington this spring is a potential preparedness “game changer,” but it had a rough start in a test run Thursday, Feb. 25.

Many state bridges have been retrofitted to withstand greater shaking, but many more need work. Newer buildings have been constructed to withstand violent tremors, but there are still thousands out there that could be death traps.

Better understanding

Lastly, seismologists and planners better understand the hazards. Yet they’ve also learned that the region’s major cities — and perhaps the Kelso-Longview area — will tremble more violently in a big quake than had been projected 20 years ago, and that coastal communities will be hit by tsunami sea waves even bigger than they had at first estimated.

Seismologists have known for about 30 years that “great” earthquakes up to magnitude 9 have occurred along the Cascade Subduction Zone off the Pacific Northwest Coast.

That’s an 800-mile long undersea fault line where two colliding continental land masses are locked in a planetary wrestling hold that some day will break. When that happens it will trigger an earthquake equal to the 9.0 magnitude Tohoku quake in Japan on March 11, 2011. That subduction zone quake killed 20,000 people, rendered 140,000 homeless and caused reactor meltdowns at the Fukushima Daiichi nuclear power plant.

When the next Cascade subduction earthquake occurs, collapsing buildings and structures and tsunamis could kill 30,000 people in Washington, Oregon and Northern California, and damage and economic loss could exceed $70 billion, according to the Cascadia Region Earthquake Workgroup (CREW), a non-profit coalition of business people, emergency managers, scientists, engineers, civic leaders and government officials.

“While this is not as high as Japan’s staggering $309 billion in estimated losses (from the Tohoku quake), the potential consequences of a great Cascadia quake are sobering,” according to an online CREW briefing paper.

Magnitude 9 quake

A magnitude 9 earthquake will shake the Interstate 5 corridor as violently as the Nisqually quake jolted the Olympia area, where the tremors were stronger even then those in Seattle. But they will also last two to three minutes, not just 30 seconds, so structures that withstood the 2001 quake may fail in a magnitude 9, said Art Frankel, a Seattle-based USGS seismologist.

But there’s even more concerning news.

Frankel led a team of seismologists that in 2018 produced 30 “shake maps” estimating how much shaking a Cascade Subduction Zone earthquake will cause in western Oregon and Washington. Significantly, they show that Seattle, Portland and Tualatin (a Portland suburb) are more vulnerable to violent, damaging shaking than previously estimated.

Using a supercomputer to process billions of bits of data, the seismologists discovered that the deep layers of sedimentary soils beneath those communities will amplify, or increase, a great earthquake’s shock waves.

These findings raise additional concern for the Longview and Kelso lowlands, which rest atop several hundred feet of river sediment. The one possible saving grace is that these communities don’t have many tall buildings, which are the most vulnerable unless they were designed to withstand great earthquakes.

Nevertheless, “I would not say in general that Longview would have less hazard than Seattle or Portland,” Frankel said.

Frankel said many factors can affect how the great earthquake will rumble through western Washington and Oregon, such as where and how deep it begins and the type of soils that a community is founded on. So the shake maps show a wide range of shaking and potential damage across the region and are important for planning and engineering.

No good scenario

But there is no good scenario, Frankel said.

“I would not want to give anyone a feeling of safety about this at all.”

Long and tall structures — such as bridges and skyscrapers — are the most vulnerable because of the nature of the shock waves from a subduction zone earthquake. Old, unreinforced masonry buildings also are vulnerable.

State building codes continue to change to take into account the shaking from subduction zone earthquakes.

“In the last 20 years there has been a lot of construction in urban areas. These new buildings are built to modern code standards and are resistant to earthquake shaking much better than 20 years ago,” said Bill Steele, seismology lab coordinator for the Seattle-based Pacific Northwest Seismic Network.

“But we still have a lot of unreinforced masonry buildings that will be death traps, not just to the people inside but to people outside in the streets. We’re better off than we used to be, but we still have a long ways to go.”

When, not if

By digging in marshes and sampling sea sediments, researchers have determined that magnitude 9 quakes occur on the Cascade Subduction Zone on average every 500 years or so. The last one struck on January 27, 1700. But they occur irregularly, separated by as many as 1,000 years and as few as 200 years.

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Given that irregularity, seismologists estimate there is about a 15% chance that the next magnitude 9 Cascadia earthquake will occur in the next 50 years, Steele said.

Recent work by Oregon State University researcher Chris Goldfinger suggests magnitude 8 quakes might be a bit more common off the coast of Oregon. So the probability for one occurring along that segment of the subduction zone is about 25% to 30% in the next 50 years.

Scientists are no closer to predicting the big one or any other earthquake than they were two decades ago, even though they are far better equipped to predict its impacts, Steele said.

“We are getting better at predicting the level of shaking that a building is going to experience,” he said. “We’ve come a long way and we’re pretty good at that. But as far as (predicting earthquakes), we have never been able do that anywhere in the world.”

Early warning system

Seismologists and emergency officials are about to launch a “shake alert” system to give the public some advance notice of earthquakes that have already begun and are radiating shock waves outward.

The U.S. Geological Survey is coordinating creation of an shake alert warning system with help from the University of Washington, Caltech, and University of California, Berkeley and the Betty Moore Foundation.

It is slated to go live to the public in Oregon on March 11 — the anniversary of the 2011 Japan earthquake — and in Washington some time in May. The public mainly will be able to get alerts through cell phones, much like its gets Amber Alerts.

The goal is to get warnings out within 10 seconds of the beginning of an earthquake. A test run in the Puget Sound area on Thursday fell well short of that standard. Some participants waited as much as a minute, Steele reported, saying the exercise had “mixed results.”

There’s work still to be done, but the system will be “a game changer” for Pacific Northwest earthquake preparedness, Steele said.

“You will be able to alert people far away from the source of the earthquake that strong ground motion is coming.”

The shake alert system is based on simple physics: Electrical and radio and microwave signals travel far faster than earthquake shock waves, so alerts can arrive before the onset of shock waves. The farther a community is from the quake epicenter, the more advance warning it can get.

Seconds count

Depending on the location of an earthquake, a community can get a few seconds to a few minutes alert before the ground actually starts trembling. Seattle would have had about 10 seconds’ advance notice of the Nisqually earthquake had the system been operational in 2001, according to a state estimate.

Communities in the Interstate 5 corridor could get two to three minutes of advance warning of a Cascade Subduction Zone earthquake, but that will depend on where in the subduction zone the earthquake starts, and no one knows that.

Alerts will be sent out only to areas expected to get significant shaking — those of magnitude 4 or stronger. This could include more deep earthquakes like the 2001 Nisqually event, which affect a broad area and take time to spread. The system will have less value for more localized shallow earthquakes, such the magnitude 5.5 along the Mount St. Helens seismic zone that jolted Cowlitz County on Valentine’s Day 1981. In such cases the shaking may start before the alerts arrive, Steele said.

A few seconds or a minute or two of advance warning may not sound like much, but its enough time to alert school children to “drop, cover and hold” and for firefighters to open garage doors to make sure their vehicles are not trapped inside if the power grid fails, Steele said.

Eventually, the warning system will automatically shut down utilities such as water, gas and sewer systems; close traffic into bridges and tunnels; and slow down or stop passenger trains and cars to avoid derailments and accidents. San Francisco’s BART commuter trains use such a system, and Japan’s shake alert system functioned well during the 2011 Tohoku subduction zone earthquake, Steele said.

There is no timeline yet for these steps, but a few utilities in the region already have adopted the technology, Steele said.

Tsunami impact

Timely warning is critical to protecting people, particularly in coastal communities. Tsunami sea waves will slosh ashore within 15 to 20 minutes of the subduction zone earthquake, and many coastal communities have few or no places to escape on foot. Roads likely will be impassible due to earthquake damage or will be jammed with fleeing vehicles.

A 2018 state re-evaluation of coastal tsunami hazards found that the waves will inundate broader areas than estimated in 2005. It also confirmed that they will swamp most of the Long Beach Peninsula, Ocean Shores and downtown Aberdeen and Hoquiam. Parts of Washington’s south coast could be covered by up to 20 to 60 feet of seawater in successive waves that occur over 12 hours.

Corina Forson, chief hazard geologist for the state Department of Natural Resources, told the Chinook Observer.: “It is quite shocking. That’s on the outer coast if you’re standing on the shoreline.”

The tsunami will surge into the Columbia River, raising the water level 13 feet just inside the river’s mouth (assuming the highest tides of the year), according to Oregon State University engineers. The 2015 analysis showed communities near the mouth of the river will have some flooding, but tsunami impacts on the river would dissipate quickly and be undetectable at Longview.

A joint state/local effort called Project Safe Haven is seeking to help coastal communities construct earthen berms or structures to give people nearby refuge from tsunamis. But there have been problems.

The town of Long Beach planned to build a 32-foot tall, flat-topped earth and concrete berm on an acre of land near the town’s elementary school. It would have offered refuge for townspeople and visitors who couldn’t get to the distant high ground in time to escape the surges of seawater. And the Ocean Park fire district wanted to build a new training tower that could also offer tsunami refuge.

Both efforts have been scuttled because of the new tsunami projections. As originally planned, they would not be high enough to protect people, said Scott McDougall, deputy emergency management director for Pacific County. Building even taller structures proved too costly, even with a75% federal grant, McDougall said. Long Beach, with a population of about 1,500, would have had to shell out as much as $2 million, he said.

“We have had a number of entities try to delve into the planning process, and in almost every case the (financial) burden becomes so unwieldy they are not able to take on the project.”

After a year’s delay due to the pandemic and other factors, the Shoalwater Indian tribe is moving forward with a 60-foot steel tsunami evacuation tower at its reservation near Tokeland. The $2.5 million tower will have room for at least 400 people, said Mark Romero, the tribe’s projector leader. The tribe plans to call for bids on there project in two weeks.

McDougall said he wished that some of the millions of dollars (precise figures are unavailable) put into the shake alert system could have been used to build more tsunami-safe structures on the coast. They’re more valuable than the few seconds or minutes that the warning system will provide, he said.

The absence of such structures is frustrating to him — just one indication that the region still has a long way to go to address the earthquake hazards that it was jolted into heeding 20 years ago today.

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