After months of rain and gray skies, it’s time to pack up swimsuits and sunscreen and head to the Northwest coast. But beach visitors in our region need to prepare for more than sunshine. The Pacific coastline from northern California to British Columbia is at risk from a powerful offshore earthquake and resulting tsunami, events that are likely to cause many injuries, deaths and widespread property damage.
Coastal residents and visitors can reduce their risk from a tsunami simply by knowing when to get out of its path and how to reach safety.
What is the threat?
Tsunamis triggered by nearby earthquakes offshore, as well as distant tsunamis caused by earthquakes across the Pacific Ocean, have struck the Northwest coast. The source of the nearby quakes is the Cascadia subduction zone, which lies offshore from northern California to British Columbia. In this zone, two tectonic plates -- the North America plate and the Juan de Fuca plate -- come together to form an 800-mile long earthquake fault.
Scientists believe the most recent Cascadia subduction zone earthquake, a magnitude 9 event, occurred in January 1700. The best available evidence indicates that these earthquakes occur, on average, every 500 to 600 years. However, the years between these events have been as few as 100 to 300 years -- meaning, all Cascadia residents, especially coastal residents and visitors, should prepare to experience a powerful and potentially damaging subduction zone earthquake in their lifetimes.
After a Cascadia subduction zone earthquake, a tsunami could arrive within 15 to 20 minutes, sending a series of massive waves crashing into the shoreline and flooding entire coastal communities.
How can beachgoers prepare?
Before you head to the coast, find out if your lodging and the places you will visit are in a tsunami evacuation zone. (Oregon and Washington residents can search for an address with this tsunami evacuation zone map viewer.) Once there, look for street signs or seek out evacuation maps that show local tsunami hazard zones and routes. It’s also a good idea to prepare personal disaster supply kits to take with you on any trip.
Signs of a tsunami
You may feel that a tsunami is on its way from the ground shaking that precedes it. Other signs include a sudden rise or fall in sea level or a loud roar like a jet aircraft. Once the shaking stops, move to higher ground or farther inland as quickly as possible. Do not wait for an official warning; a tsunami may arrive within minutes. Wait for emergency officials to issue the “All Clear” signal before returning to low-lying areas. Never try to watch a tsunami or surf a tsunami wave. Tsunamis travel faster than a person can run.
Should Northwest residents be worried about visiting the coast?
Be prepared, not worried. By knowing when and how to respond to a tsunami, residents can significantly reduce the risk to their loved ones and themselves.
More tsunami resources
Oregon Tsunami Clearinghouse (evacuation maps and other resources)
Surviving a Tsunami: Lessons from Chile, Hawaii and Japan (U.S. Geological Survey)