The Washington State Dept. of Natural Resources has released its findings from a 2,500 year old Cascadia Subduction Zone (CSZ) Earthquake scenario. The results have given state and local agencies a better picture as to what could possibly be expected if there were to be a large earthquake in the CSZ.
Findings
Over the last few decades numerous state and federal agencies have conducted studies on the west coast from Washington to Southern California to understand what has previously happened and what could potentially happen again on the Cascadia Subduction Zone. A study completed by Atwater and Hemphill-Haley uncovered at least six events in Willapa Bay over the last 3,500 years.
In the study the scientist excavated a bank on the Niawiakum River to analyze the build up of sediment. "By doing so they can look at the record of previous events," Pacific County Department of Emergency Management Director Scott McDougall said. "For example, they can look at a layer and tell us that it resulted from a tsunami and provide a time frame by analyzing contents within the layer. It's absolutely fascinating."
The studies suggest that a 9.0 earthquake happens as frequently as every 500-540 years, but possibly every 100-1000 years. The most recent CSZ quake was anticipated to have happened around 1700 A.D which would put the current time frame at the 318 year mark.
Biggest risk to local communities
One of the bigger threats to local communities from a CSZ quake will not be a tsunami, but the quake itself, water indundance, and soil liquefaction. Water indundance is the level of water on what is normally classified as dry ground. "The Riverdale area would potentially see several feet of water near Lions Park," Director McDougall stated. "Downtown Raymond would also see several feet of water."
Soil liquefaction is the other risk and is a phenomenon where a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid. Videos surfaced from the Japanese quake showing water rising through the soil and city streets as a result of soil liquefaction.
While speaking with Director McDougall it was expressed that local areas Raymond, South Bend, Bay Center, and Tokeland would see little to no direct impact from a major tsunami. The Washington State Dept. of Natural Resources findings also support that, such as if a 60-ft tsunami were to hit the Long Beach area by the time it hit Willapa Bay it would diminish to around 10-ft and steadily diminish further in land.
Vertical High Ground?
According to Director McDougall there is still no immediate concern for vertical high ground for the nearby areas of South Bend, Raymond, Tokeland, and Baycenter. "We're never going to have to worry about vertical evacuations here locally," he stated. "And quite frankly a lot of places on the coast don't have to worry about vertical evacuation, but we do have the Long Beach peninsula where that is a concern."
Vertical high ground is a structure that is built for residents to evacuate to such as what Westport has done with the Ocosta Elementary School. "There is no natural high ground around those places," McDougall said. "So vertical evacuation becomes very critical."
He continued, "I will say this though, I would still love to see a lot more structures be built in the area that are tsunami safe."
Preparedness still key
With the risk of a CSZ earthquake still always a possibility it's emphasized that residents need to always be prepared. The entire area of Washington lies on multiple active fault lines. It wouldn't take just a CSZ quake to debilitate the area if one of the other fault lines struck a major quake. "Residents need to always be prepared not just for an earthquake," Director McDougall said. "They also need to be prepared for any natural disaster that could happen."
Residents are encouraged to have supplies at the go to sustain themselves for up to two weeks and possibly longer. Food and water are among the necessities along with a NOAA radio that is hand crankable or a good supply of batteries.
"Residents should always have a plan in place," McDougall said. "They need to know where the nearest high ground is incase of any risk of an aftermath from a coastal tsunami or quickly rising water. They also need to be prepared to move at a moment's notice. Which means having their emergency supplies fully stocked and packed and ready to go quickly."
No new changes to plans; As of now
According to Director McDougall much of what has been provided in Washington Department of Natural Resources findings has been expected. "We knew from the beginning that probably the biggest risk to residents would be water indundance, rising water, and liquefaction," he stated. "A lot of residents have been rather angry that the 2000 line has been gated, but they would actually have to go through safe areas to get there. And by that time liquefaction will have taken place."
During the Alaskan quake and tsunami scare on January 23 the Pacific County Emergency Operations Center was operational within 20 minutes and had all staff on deck within one hour. The incident happened late at night and many officials were asleep and had to respond quickly from home.
Unfortunately, a large number of residents who were signed up for the emergency alert system didn't sign up for non-weather alerts. "We have automatically signed up currents residents who are in the system to receive the non-weather alerts also," McDougall previously stated. "We've removed to the choice. This will limit the chance residents aren't warned in the future."
There were numerous reports of residents waking up in the early AM hours in a panic. Due to finding out late in the series of alerts that a tsunami watch had been issued for the Washington coast. Little to no additional information was provided to local officials from the National Tsunami Center until the watch was cancelled adding to the panic and frustration.
"What I want to leave behind when I'm done"
The likelihood of any event occuring in the near future is still hypothetical of when, but both state and federal officials are highly confident one day it will. McDougall suggests that the likelihood of any such event happening in the next 50 years is around 18-20%.
Still regardless of the odds McDougall hopes to have Pacific County far more prepared then current times. "I want to make sure we get everyone taken care of during any such event. It is very survivable," Director McDougall stated. "The japanese prepared for, but didn't prepare enough and we aren't prepared at all. Our level of preparedness is nowhere near where it should be."
He continued, "If the event happens tomorrow we're going to be in trouble. But my job and the legacy I want to leave behind as the Director of PCEMA is years ago no one thought this was possible. That there was a threat off the coast and now we know there is and we've started to get prepared. When I walk away from this job I want people to look back on what I accomplished and say, 'Wow we made a lot of progress during that period of time'."
The road to being sufficiently prepared is a ways away, but McDougall believes it is possible and has made it his personal mission to see it through. "50 years from now I want us to be at a point where vertical evacuation structures are common, part of the public and private sectors. So when something happens everyone knows where they're gonna go. I want us far more prepared then we are right now."
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