Anyone who resides in the Pacific Northwest has heard — and likely worries — about when the “big one” will happen. Experts estimate that in the Pacific Northwest, the greatest likelihood of a damaging earthquake is from a magnitude 7 Nisqually-type deep earthquake, with about an 84% chance to occur in any 50-year period. The region’s greatest potential impact threat is posed by a magnitude 9 rupture of the “megathrust” plate-boundary Cascadia fault and accompanying tsunami, with about a 14% probability in any 50-year period.
While there is plenty of scientific research to back this up, that doesn’t mean we can predict earthquakes, and this makes it easier for people to forget about the threat of an earthquake.
“People become comfortable and begin to ignore or ‘live with’ this threat,” Elyssa Tappero, tsunami program coordinator for the Washington Emergency Management Division says. “It can be seemingly easy to brush it off as it’s hard to predict earthquakes and, like climate change, there’s not a lot of political agreement on how to address earthquake preparedness.”
Tappero and Dr. Paul Bodin, research professor at the University of Washington with the Pacific Northwest Seismic Network, discussed Washington’s earthquake readiness during a recent webinar facilitated by M.J. Murdock Charitable Trust and led by Seattle Times science reporter Sandi Doughton.
3 classes of earthquakes in the PNW
Education can be key to understanding what can happen during an earthquake and tsunami — and how you can best prepare for one. One place to start is to understand the different types of earthquakes that are present in the region.
Bodin outlines the three classes of earthquakes in the region.
- Subduction: Occurring along the Cascadia subduction zone, this is the kind of earthquake that would lead to the “big one.” This is the largest earthquake source in our area and can cause an earthquake up to magnitude 9.
- Intraslab: The most common earthquake in the area; the notable recent quake of this type was the 2001 Nisqually earthquake (magnitude 6.8). These tend to be smaller in magnitude but are very deep. People in the area are most likely to experience this type of earthquake.
- Crustal: This is a shallower and more difficult type of earthquake to define as these faults move slowly. If they occur, they can cause a lot of damage, even if the magnitude of the quake is smaller, because these faults are closer to the surface and create a great deal of ground motion.
How earthquakes trigger tsunamis
“When it comes to the Cascadia subduction zone — that big one we talk about so much — how that generates a tsunami is when plates slip, it moves a column of water above it,” Tappero says. “As water is lifted, it comes down and causes ripples and those are the tsunamis that hit our coast very quickly. Once those waves reach the coast they slow down and become big tsunamis. That’s why Cascadia is our biggest tsunami worry, because it can hit us very quickly and cause a lot of damage.”
Tappero adds that a tsunami from a subduction zone quake does provide more lead time to warn people — from 2 to 2 ½ hours — on the inner coast but that high currents could affect the area for more than 24 hours. Crustal faults can hit the inner coast area faster while distant tsunamis, those that happen in other parts of the world, can also provide a wider warning window.
She adds that with the amount of coastline in the state, coastal towns would see the brunt of the damage from a tsunami that would be similar to the 2011 Tohoku earthquake and tsunami in Japan.
Across the West Coast, Shake Alert is a system in place to notify people of earthquakes. Every regional seismic network in California, Oregon and Washington contributes data to it, Bodin says. But he cautions, “to be clear, its current manifestation is that it’s set up to provide warning for ground shaking, not necessarily a tsunami.” The system detects shaking, locates the earthquake, how big it is, and notifies people.
“Instead of taking minutes, the process now takes seconds. We can give people a few seconds, maybe a minute to take action to protect themselves,” he says.
In the event of a tsunami, the first course of action is to find higher ground, Tappero says. She warns that people should not wait for an alert or a tsunami siren but begin to move to higher ground “the minute” shaking from a quake ends.
Drop, cover, hold on
Maybe you’ve seen the drop, cover and hold posters posted in schools or other public buildings, but both Tappero and Bodin say it’s the most important thing you can do.
“Here in the United States, and especially in Washington, we have very good building codes. There’s a very good chance that when an earthquake strikes, no matter what kind of earthquake it is, you’ll be in a building that will hold up,” Tappero says. “Your biggest risk in an earthquake is stuff falling from the ceiling or windows shattering, that kind of thing. And getting under a sturdy piece of furniture, or if you can’t do that, get against an interior wall” will best protect you.
The reason to drop is that it lowers your center of gravity, which helps prevent you from moving around during a quake. Covering your head and neck is also important. And it’s important to hold on so that you’re not moving and running the risk of stepping on broken glass or having something fall on you.
How to prepare
Tappero and Bodin noted that since predicting earthquakes is difficult, they can happen anywhere — and at any time. This means that you want to be prepared, and here’s what you should do:
- Make sure you have a go pack. Tappero advises to have multiple packs: one for your home, one for work and a lightweight pack you can take with you if you’re hiking or camping on the coast. “Over and over what we see is people are prepared in other ways, they have things in the garage, but we see people losing time trying to find things. If an earthquake is 5 minutes long and the waves are coming in 15 minutes, that’s not a lot of time to gather things.”
- In the event of a tsunami, know the evacuation route and where the nearest high ground is.
- Stay calm — know that you can survive this.
- Sign up for alerts.
- Have a communication plan in place. Bodin recommends having a contact that is not in the area but in the east side of the state, for example.
- Have a plan for your pets.
- Check with your place of work, school or other location where you spend a great deal to time to find out:
- Where do we assemble after an earthquake?
- Where are the nearest exits?
- Have structural and nonstructural (heavy objects, overhead shelving) hazards been identified?
- Is there a stockpile of emergency supplies available?
- Ask schools about family notification and reunification plans.
- Ask employers about their emergency response plans and your role in them.
- Ask if your employer, school or other organization takes part in the Great Washington Shakeout as it’s the best opportunity for people to practice earthquake and tsunami safety skills, and to test their emergency response plans.
Lastly, is it safe to live here?
“Yes,” Tappero says. “Every place on earth has its unique hazards — earthquakes, blizzards, hurricanes, monsoons, droughts — there’s no escaping the might of nature. However, many of our biggest hazards are low-probability events, meaning they occur infrequently.”
“It’s a trade-off, of course — you get more practice with an event that happens every year versus one that happens once every couple of decades, but the longer periods of ‘peace’ are also precious. Western Washington is relatively safe in that sense because emergency managers, first responders, local and tribal governments, and their volunteers are very aware of potential dangers and dedicated to preparing for them. When the next ‘big one’ hits, whatever it ends up being, a whole host of folks will jump into action.”
Since 1975, the M.J. Murdock Charitable Trust has invested more than $1.2 billion in a diverse array of individuals and nonprofits serving the social, cultural, educational and spiritual fabric of the Pacific Northwest in innovative and sustainable ways.