A magnitude 9.0 earthquake hitting the Pacific Northwest can be hard to imagine. What will it be like? How will the region be affected? This page provides some answers to those questions.
Each section below begins with a title that tells if the expectations listed are for Oregon, Washington, or the entire region. Below it, the subtitle (in italics) is a hyperlink and tells what report the information in the section comes from.
All reports come from data that explores the impacts of a 9.0 scenario, but it’s important to remember, not all Cascadia Subduction Zone earthquakes are 9.0s. Some are smaller… and some are larger. Visit Surviving Cascadia’s How Massive Will the Next CSZ Earthquake Be? page for more info.
Expectations for Washington
Understanding Earthquake Hazards in Washington State
Modeling a Magnitude 9.0 Earthquake on the Cascadia Subduction Zone off the Pacific Coast
Table 1. Summary of significant losses in the M9.0 Cascadia subduction zone earthquake scenario.
Expectations for the CSZ Impact Area
Cascadia Rising’s Exercise Scenario Document-January 2015
The report states: “The highest number of tsunami-related injuries and deaths will likely be in Grays Harbor County, with as many as 5,000 casualties in Ocean Shores alone. The city of Long Beach in Pacific County may also have a high number of tsunami casualties. It is likely that most residents in these communities will not reach high ground before the tsunami wave hits.” Increased planning is advised if you live in this area.
Nighttime vs Daytime Earthquake
If you ask the person next to you if they would prefer the earthquake to happen during the day or at night, chances are, they’ll say daytime. People don’t like the idea of the world crumbling around them… in complete darkness. Turns out though, a nighttime earthquake is the better option.
Expectations for Oregon
Oregon Public Broadcasting (OPB) Unprepared Series
Oregon Public Broadcasting (OPB) has an incredible amount of information pertaining to Cascadia Subduction Zone earthquakes. I highly recommend watching the OPB Unprepared documentary.
One of my favorite items is their Aftershock Widget. Normally, you can use the widget to enter your city (or even exact coordinates) & the page will return information about what to expect in the aftermath of a 9.0 earthquake. The widget is currently not working well and I have just learned OPB plans to retire the widget. Here are screenshots from their page comparing expectations for Neskowin (coastal city), Salem (valley city), and Bend (city east of the Cascades).
Below, check to see what intensity level a city has. Then scroll through the slides to read about that level’s expectations. There are two slides for level 5: one for coastal locations and one for inland locations.
Expectations for Oregon
Oregon Health Authority’s 2021 Cascadia Tsunami Casualty Estimates
“*Estimates were developed assuming that all persons quickly evacuate by foot for a DOGAMI Large tsunami scenario. Does not include earthquake casualties.”
More in-depth data on tsunami-related injury and fatality estimates can be found on Surviving Cascadia’s Tsunami page.
“Casualty estimates are assumed to occur within hours of the earthquake (as opposed to days after the earthquake). Estimates, which include permanent residents and visitor populations, are for a summer “night” (i.e., 2 AM) when visitor populations are high. It is important to note the modeling assumes that all persons quickly evacuate by foot using the most optimal tsunami evacuation route; these estimates are not a worst-case scenario.”
Expectations for Oregon
The Oregon Resilience Plan – Cascadia: Oregon’s Greatest Natural Threat – February 2013
24,000 buildings completely destroyed
85,000 buildings with extensive damage
$32 billion in economic losses
27,600 displaced households
10 million tons of debris (1 million dump truck loads)
650 to 5,000 fatalities resulting from the earthquake
600 to 5,000 due to the tsunami
The shaking will cause an immediate and permanent drop in elevation along the western edge of the North American Plate—a phenomenon known as co-seismic subsidence
Expectations for Oregon
Oregon Department of Geology and Mineral Industries (DOGAMI) Open-File Report Series
If you click the hyperlink above, you’ll be able to view and download detailed maps of Oregon with overlays for Peak Ground Velocity, Probability of Liquefaction, Peak Ground Deformation, tsunami inundation, and more. Some categories are shown here to provide an example of what you can learn about your area.
Expectations for Oregon
Oregon State University O-Help
Check out this website for an address-specific report like the one shown here.
Expectations for Oregon
Cascadia Playbook: Developing a Quick Reference Guide for the first 14 days – August 2014
Ground shaking for 4-6 minutes
Tsunami as soon as 15 minutes after shaking
10,000+ damaged structures
10,000+ people in need of shelter
$50+ billion in economic losses
25,000 fatalities from earthquake and tsunami
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Cascadia Subduction Zone 