It’s been building up pressure for 316 years, but scientists only discovered the earthquake potential of the Cascadia Subduction Zone roughly 30 years ago.
What they found is alarming.
This June, a consortium of emergency management agencies from four Pacific Northwest states and Canada will coordinate a four-day emergency management exercise called Cascadia Rising 2016. Federal agencies will join state and local agencies — including some in North Idaho — to prepare for the aftermath of “perhaps one of the most complex disaster scenarios” that will eventually impact the Pacific Northwest.
“The threat of an M9 (magnitude-9) Cascadia Subduction Zone earthquake is very real,” said Bill Steele, seismology lab coordinator at the University of Washington. “These earthquakes have re-occurred every 200 to 1,000 years over the past 10,000 years with an average re-occurrence rate of one every 500 years.”
Steele, who is also part of the Pacific Northwest Seismic Network, said now the Pacific Northwest finds itself in that megathrust-earthquake window again.
He said the last great M9 earthquake in the Cascadia Subduction Zone occurred on Jan. 26, 1700, which was recorded by the Japanese coastal communities that suffered inundation from the Cascadia Tsunami on the morning of Jan. 27.
The Cascadia Subduction Zone, or CSZ, stretches 700 miles along the west coast from Mendocino, Calif., to Vancouver Island, British Columbia. A subduction zone is where two tectonic plates meet. In this case, the Juan De Fuca tectonic plate that lies beneath the Pacific Ocean is pushing itself under (subduction) the North America plate just off the coast of California, Oregon, Washington and British Columbia.
The subduction has been “locked” for more than 300 years and when — not if — it slips, scientists believe it could result in another M9 earthquake and tsunami that will cause massive destruction to coastal communities along the subduction zone.
“At depths shallower than (18 feet) or so, the CSZ is locked by friction while strain slowly builds up as the subduction forces act until the fault's frictional strength is exceeded and the rocks slip past each other along the fault in a ‘megathrust’ earthquake,” the PNSN explained on its website.
Scientists expect the severity of shaking caused by an M9 earthquake will be strong enough to cause slight damage to specially designed structures and considerable damage in ordinary substantial buildings with partial collapse.
There will also be severe damage to poorly built structures, toppling chimneys, factory stacks, columns, monuments and walls. The shaking will be strong enough to overturn heavy furniture. In certain areas the shaking will cause the ground to liquify.
According to the Cascadia Rising Exercise Scenario Document published by the Washington and Oregon Whole Community Exercise Design Committee in January of 2015, liquefaction is one of the most damaging effects of ground shaking.
“Certain soils, such as water-saturated silt and sand, can become dangerously unstable during an earthquake. The shaking increases water pressure, forcing the water to move in between the individual grains of soil, and as the grains lose contact with each other, the soil begins to act like a liquid,” the report states. “Overlying layers of sediment can slump and spread laterally. Structures built on such soils may shift position or sink, while buried pipes and tanks become buoyant and float to the surface.”
Transportation, energy and water infrastructures will be devastated.
Once the devastating earthquake occurs, a massive tsunami is going to follow. Scientists say in the case of the CSZ, it would hit different areas of the coast between 15 and 30 minutes after the shaking starts. According to the Cascadia Rising document, a tsunami can travel across the deep ocean at nearly 500 mph.
“In deep water, the amplitude or height of the tsunami is low relative to its length, so the slope of the waves is very low, and they may pass unnoticed under ships,” the report states. “Upon entering shallower water, however, they slow down and gain in height as water piles up behind the wave front. Once it hits shore, a single tsunami wave can take as much as an hour to finish flowing in.”
The height of the wave and how far inland it travels varies with location, the report said. In places along Cascadia’s coast, the tsunami may be as high as 30 to 40 feet. Much depends on the local topography — the lay of the land — both underwater and along the shore.
Steele said the coastal residents of Washington and Oregon will be hit the worst. They will be subjected to very strong shaking as the fault ruptures directly below them.
“Along the Washington Coast we expect the land to thrust to the west and drop between three to eight feet, flooding low lying areas at high tide,” he said. “The sea floor, where the toe of North America plate has been pushed down by the slow subduction of the Juan de Fuca plate since 1700, will pop up, generating a tsunami that will hit the coast between 20 and 30 minutes after the onset of strong shaking.”
Although this series of water waves will be devastating to low lying coastal areas, Steele said only a small amount of the tsunami energy will enter inlets, such as the Strait of Juan de Fuca. Much of that energy will be dissipated by flooding along the strait and dispersal when the straight opens to the Puget Sound. Although maximum wave heights in the Seattle area are likely to be between 3 and 6 feet high, very strong currents will wreak havoc with navigation and marinas for hours, he said.
“We will have hours to prepare for this disruption, however,” he said, adding that the coast could see tsunami heights 30 to 40 feet high, and sadly, hundreds to thousands of people will be in towns and communities that have no access to high ground in the time available for evacuation.
The Cascadia Rising document says timing of an earthquake cannot be forecast very precisely, but great subduction zone earthquakes are inevitable — they are a fundamental consequence of plate tectonics.
“Whether this type of earthquake is considered alone or in combination with other earthquake sources, the odds that a large, damaging earthquake will occur in the near future in the Cascadia region are very high,” the report said.
Steele said the probability of a reoccurrence in the next 50 years is about 15 percent, but some areas of the subduction zone could experience quakes sooner than a full-margin rupture.
“It is higher in Southern Oregon as the fault breaks on southern sections of the 700-mile-long fault, occasionally in between the ‘full rip’ M9 earthquakes,” Steele said. “Still, looking at the probable impacts of the next M9 is sobering.”
According to the Cascadia report, more than 86,000 residents live in the tsunami inundation zone that is likely to result from an M9 Cascadia Subduction Zone earthquake.
“Some survivors may try to evacuate by car but will likely be stopped by impassable roads or bridges,” the report predicts. “With limited passable driving routes away from the coast, the movement of people fleeing the coastline will likely result in gridlock. Thus, most survivors will be forced to walk or run to higher ground.”
Assuming these 86,000 residents are present at the time of the initial earthquake and evacuate the inundation zone at a slow walk, the report said more than 20,000 residents will likely be unable to make it to high ground.
“When the wave hits, as many as 15,000 of these residents could potentially be swept out to sea or crushed in debris entrenched in the tsunami water,” according to the report. “The remaining survivors may suffer from crushing, puncture, abrasion, exposure, and other injuries.”
Survivors in many coastal communities may be stranded for weeks due to damaged ground transportation networks.
Early detection of the quake and the ensuing tsunami is critical in those situations.
Steele said The Pacific Northwest Seismic Network, along with several other emergency management agencies, has been working to develop an early detection system that could give inland cities time to prepare for an earthquake.
The University of Washington, Caltech, and the University of California, Berkeley, with support from the U.S. Geological Survey and the Gordon and Betty Moore Foundation, have begun development of an earthquake early warning system.
According to the Cascadia Rising document, detecting the smaller seismic waves that precede the earthquake’s destructive waves, experts can develop an early warning system that might provide a few seconds to a few minutes of warning to cities that are some distance from the Cascadia subduction zone.
“This would give people time to drop, cover, and hold, and it could be enough time to shut off gas mains, open fire station doors, slow freeway traffic, and clear cars away from potentially dangerous structures such as bridges and viaducts,” the report said.
“Caltech just turned the key on their system last week,” Steele said. “They have it up and running in California.”
Oregon and Washington are not far behind.
Steele said the system uses the initial shock wave from an earthquake to predict the more destructive waves that will follow. Basically, he said, detectors will pick up a “P-wave,” which occurs at the moment the the subduction zone ruptures.
“A P-wave is like a sound wave that can travel through rock faster than it can through the air,” he said, adding that it travels at a speed of 6 miles per second.
The P-wave is followed by a series of “shear” waves, or “S” waves, which are the more destructive waves. S-waves travel at about 3.7 miles per second, Steele said.
“So as a rupture occurs, it sends out a P-wave and when it hits four of our monitors, we can identify where it occurred.”
Then they communicate that on an international alert system so people can prepare for the onslaught of S-waves.
Using that system, Steele said scientists can determine the intensity and time of the event.
Other programs like UW’s Project Safe Haven are also under way to improve the situation by identifying and planning for vertical evacuation structures to avoid tsunamis where no natural high ground is available.
“The Ocasta Elementary School in Grays Harbor County will open this year as the first vertical evacuation structure in the United States,” Steele said, adding that more structures will follow.
“Here at UW and in the broader community there are many initiatives to increase our understanding of and resilience to earthquake hazards,” he said. “Some day Washington state will be rocked harder by an earthquake than we have in historic times. Hopefully by then, we will all be better prepared for the event and will be able to mount a rapid recovery.”
And that is what the Cascadia Rising 2016 exercise is designed to do. Planning is under way as far inland as Idaho.
Steele said he was glad to hear that Idaho is taking the initiative seriously.
“We are depending on you guys to come riding in on white horses and save us all,” he said.
Cascadia Rising: North Idaho
While much of the physical destruction and death will occur along the Interstate 5 crridor, inland states are expected to experience the crisis in the aftermath.
Kootenai County Sheriff’s Lt. Stu Miller is working with the Kootenai County Office of Emergency Management to prepare for the Cascadia Rising 2016 exercise June 7-10. They will join other agencies from all over the Pacific Northwest in a series of now secret scenarios that are likely to occur when the Cascadia quake occurs.
Miller said Kootenai County has established an exercise design team to develop possible local scenarios. He said in this case, the exercise will focus on a natural event that will be forcing people out of their communities, so Idaho is likely to see an influx of people who will have to be fed and cared for.
Miller said state law requires the sheriff to be the incident commander in all disasters. He also said Kootenai County has been using a multi-agency incident command system for several years.
While Sheriff Ben Wolfinger is the incident commander, his department is focused primarily on public safety issues and delegates other aspects of the disaster to the multi-agency partnership.
For instance, Miller said if there’s a wildland fire, wildland firefighters are called in to lead the efforts to suppress it. To train for the earthquake, he said there will be a series of scenarios emergency workers will be tested on.
“Really in any exercise you are testing certain aspects of your ability,” Miller said, adding that members of the exercise design team are the only ones who know what those scenarios will entail at this point.
“They are not telling us anything. I ask for them every so often, but they won’t give them to me,” he said. “That would kinda be like opening your presents before Christmas.”
Sandy Von Behren, director of the Kootenai County Office of Emergency Management, said her agency is coordinating with the Idaho Division of Homeland Security, FEMA and the nine northernmost counties of Idaho to prepare for the Cascadia Rising exercise in June. She said several scenarios are being developed and each of the participating counties will have different roles in the exercise. The exercise is designed to test existing procedures and plans that each of the players already have in place. Von Behren said Kootenai County is going to test its evacuation and reception plans. That plan, Von Behren said, was updated in 2009 after Hurricane Katrina struck New Orleans. By testing the existing plans they can see if they have all their bases covered before the real disaster strikes. “The plans are not perfect and these exercises help us evaluate changes that may need to be made,” she said. “We know that there is a possibility that this (earthquake) could happen.” By running the exercise based on the potential problems the earthquake will cause, they will know if their plans are sufficient. “If you think about it, we are a gas tank away from where this is going to happen,” Von Behren said. “So they will be stopping here to fill up with gas — some will stay and some won’t.” A steady stream of displaced survivors will start flowing east on Interstate 90 and many of them will be needing supplies. “How does something like that impact our gasoline supplies, our grocery stores, our banks, our hotels?” she asked. “Are we going to have to open shelters, do these people have pets, and if so, how do we deal with those pets? We have procedures for that as well.” Von Behren said the general public should be aware of the potential aftermath of such a large disaster. “Everyone at the home level should be prepared with at least three days worth of supplies like food, money and a full tank of gas,” she said, adding that she fills her tank when it reaches half full. “Always treat a half tank like you are out of gas, especially in the winter months.” Von Behren said people should also remember to check on family, friends and neighbors during a disaster to ensure they are properly taken care of. “We have been planning this for over a year now,” Von Behren said. “We are looking forward to testing our plans.”
Like Kootenai County, Bonner County agencies and groups will be a part of the Cascadia Rising training. Everyone from law enforcement to fire crews to the hospital have been invited to participate in the exercise, and Bonner County Emergency Management Services will have its emergency operations center in action, Bob Howard, Bonner County’s director of Emergency Management.
The agency will coordinate local resources and exercise that portion of the county’s emergency plan, Howard said.
“We’ll deal with the injection of all the different requests and scenarios that come in from the event,” he added.
And with several minor earthquakes recently, including a 4.1 temblor centered in the middle of Lake Pend Oreille in April 2015, and several others of smaller size a few months later, it’s important to prepare for such a scenario.
The lessons learned during a training could prove critical if a real earthquake-related disaster were to occur, Howard said. If the county did see large numbers of evacuees, it could strain available resources.
“It would be a stress on the entire economy for Bonner County and everybody in reality,” he said.
A training exercise allows local officials to get a feel for possible outcomes and to better plan on how to respond so they are better prepared, Howard added.
“Real life situations never textbook so always have lessons learned and things will come up that we may or may not have thought about,” he said.
Staff writer Caroline Lobsinger of the Bonner County Daily Bee contributed to this story.