Last week, about 60 miles off the coast near Ferndale, California, the tectonic plates shifted under the Pacific Ocean, sending seismic waves through the ocean floor that radiated onto land and were felt from Santa Cruz to Medford.
Within seconds, cellphones buzzed with alerts about the earthquake throughout California cities and towns and up into Oregon, reaching Ashland, Bandon, Lincoln City and Corvallis.
Shortly afterward, a tsunami warning was issued for coastal areas in California and Oregon. Beaches and low-lying areas were evacuated, though some people were drawn to the water, hoping to see big waves. Schoolkids ducked under desks or left buildings en masse and moved to higher ground.
That earthquake, the 2024 Offshore Cape Mendocino, California Earthquake, registered a magnitude of 7.0.
The Cape Mendocino earthquake was felt in parts of Oregon, but caused little damage and no known injuries. And the possible tsunami never materialized.
But for some, the quake was a reminder, and even a dry run, for a much bigger event that could cause catastrophic damage to the Pacific Northwest, a Cascadia subduction zone earthquake registering in the high 8 and even 9 range, referred to frequently, chillingly, as “the really big one.”
The Cape Mendocino earthquake sent a message, said Peter Ruggiero, an Oregon State University professor who works on earthquake preparedness: “We live in earthquake country.”
Big earthquakes present a unique problem for scientists, citizens and officials thinking about how to better survive them – they barely ever happen.
“The major disaster hazard that our region experiences is something that most people that live here, certainly anyone alive, has never experienced,” Ruggiero said. “In Oregon and Washington, we don’t have much of an earthquake culture.”
While Oregonians don’t have first-hand experience, big earthquakes have happened in living memory. There was the 6.9-magnitude Loma Prieta earthquake that shook San Francisco during the World Series in 1989, killing 63 people, causing extensive damage and thousands of injuries.
More comparable though, and more recent, was the 2011 Tohoku Earthquake and Tsunami in Japan, which killed around 20,000 people.
That event was triggered by a 9.1 subduction zone earthquake, which caused widespread destruction, fires and a tsunami with a maximum height of 130 feet. As bad as the earthquake was, that wave was worse, causing the majority of the deaths and a nuclear accident.
Like the Tohoku Earthquake, “the really big one” would be a subduction zone event.
In a subduction zone earthquake, one plate slides under another, lifting the top plate up. In the case of “the really big one,” that would mean the Juan de Fuca plate subducting under North America, pushing North America up and creating a killer wave.
The Cape Mendocino earthquake was a different type of earthquake, a strike-slip event, which caused horizontal motion. Water was displaced, said Andrew Meigs, an earthquake expert from OSU, but it was measured in centimeters, not meters.
The Cape Mendocino earthquake was not on the Cascadia subduction zone, but it was on part of the same system of plate boundaries, Meigs said.
And that subduction zone earthquake is coming.
Scientists know that the last major Cascadia subduction zone quake happened on Jan. 26, 1700 – an estimated 9.0 earthquake that caused the coastline to drop several feet and sent a tsunami to Japan.
“Earthquakes do not occur periodically,” said Meigs.
Instead, he said, pressure builds and builds until it is released.
“The longest interval of time between earthquakes is something like 1,050 years,” Meigs said, “and the shortest period of time is about 150.”
The average for the Cascadia subduction zone, he said, is between 500 and 600 years. Currently, the Pacific Northwest has gone 325 years without a massive earthquake.
The next one could happen at any time.
“It could happen on this call,” Meigs said, “or it could happen in 700 years.”
It’s impossible to know when “the really big one” will happen or even how big it will be, but the consensus, among experts working on studying earthquakes and preparing the region for shaking and its aftermath is this: A Cascadia subduction zone earthquake is survivable. But everyone should be ready for it to happen today.
“This is so overwhelming,” said Jenna Tilt, a social scientist working on earthquake resilience along the coast. “But the thing that we say a lot is, those that think about this and prepare are the ones that are able to weather the storm.”
An event like The Cape Mendocino earthquake was a chance for everyone, from researchers to citizens, to prepare.
For some scientists, said Erin Wirth, a research geophysicist with the USGS, it was a chance to test the tools they are using, the instruments that record the earthquakes and the speed at which they are able to get more instruments out into the field to test for aftershocks.
“Another thing that we can learn from this event is how sites around the earthquake may respond to future earthquake shaking based on how they responded during this earthquake,” she said. “So, for instance, did some areas shake more or less than we expected? Were did we observe shaking-induced landslides?”
Researchers are also looking at the human side of earthquake preparedness and are interested in how the response to The Cape Mendocino earthquake can inform their work.
Take, for example, ShakeAlert. It’s a relatively new system from USGS that sent out early warnings to at least half a million people last week.
It sends messages to people in areas that could be impacted as soon as an earthquake is detected, giving people extra seconds to “drop, cover and hold on,” the recommended steps to stay safe in an earthquake.
These alerts are sent through the same process as Amber alerts, so any phone that receives those alerts will also receive ShakeAlerts.
“ShakeAlert is in a constant state of improvement,” said Robert de Groot, ShakeAlert operations coordinator, adding, “These earthquakes teach us something new.”
Last Thursday, he said, “The system performed as designed and did exactly what we expected it would do.”
The Cape Mendocino earthquake was only the second earthquake where the system was activated in both Oregon and California. It didn’t just send notices to phones, but some institutional alarms were set off.
In Medford, de Groot said, alerts were delivered in the Medford School District and at Providence Medford Medical Center, instructing people to drop, cover and hold on.
Still, he said, they are always looking for ways to improve the system.
“Every bit of data that we get from the earthquakes and how the system performs gives us clues into how to improve our earthquake detection algorithms,” de Groot said.
ShakeAlert is part of a much wider system being built to prepare for the actual earthquake and tsunami and what comes after. Across the Pacific Northwest, researchers are looking for ways to improve the chances that as many people as possible will survive the inevitable Cascadia subduction zone earthquake.
The Oregon Department of Geology and Mineral Industries has spent years creating maps of what inundation would look like in cases of different types of earthquakes and tsunamis. They have a tool that allows anyone to put in an address on the coast of Oregon or Washington and see exactly how they should evacuate on foot, noting where bridges may fail and whether they need to run or jog to safety.
“The geography of the Oregon coast is such that our tsunami zones are relatively narrow,” said Laura Gabel, a coastal field geologist for the Oregon Department of Geology and Mineral Industries. “There’s accessible high ground for a lot of people on the Oregon coast.”
But, much like checking a theater for the fire exits before a movie or knowing where to go in an emergency plane landing, people need to know their routes before a disaster happens.
So social scientist Tilt and others are working with the department on ways to make those maps more accessible, especially to people on the coast who don’t speak English and people who may just be visiting.
The Cascadia Coastlines and Peoples Hazards Research Hub, which Tilt and Ruggiero work for, is also looking for ways to help people survive earthquakes and tsunamis while improving infrastructure and responses to more predictable events like flooding, erosion and climate change.
In 2020, construction was completed on the Gladys Valley Marine Studies Building, an Oregon State University building created to not only withstand a 9 or higher earthquake but also as a vertical tsunami evacuation route, accessible 24 hours a day and open to the public.
Seaside moved some schools out of the tsunami inundation zone in 2021.
“There is progress,” said Tilt.
None of these systems or solutions are perfect.
For some people, it was unclear when the alert came through last week just how serious the danger was. For some, it was an invitation to go down to the beach and try to spot big waves.
The evacuation maps are hard to find and require knowing your address. In an emergency, you might not know where to look.
Not everyone has a cellphone, or a phone that can handle a lot of text, or speaks English, or reads, or sees, or hears.
The most vulnerable people are also the most at risk in any disaster. During the earthquake and tsunami in Japan in 2011, nearly 60% of those who died were over 65. What happens if you can’t receive the alerts? What happens if you can’t run or walk to safety?
These are the questions officials are working on, helped by the data that smaller earthquakes like The Cape Mendocino earthquake provide.
But individuals and families need to work on them too.
Last week’s earthquake should be a reminder to everyone: Even in the most severe earthquake, the biggest version of “the really big one,” many people will live. Officials agree on that point, that a Cascadia subduction zone earthquake is survivable. But you need to be ready.
Get an emergency kit ready. Make sure you have a plan, wherever you are, for what to do in a disaster and make sure your phone gets alerts. If you’re on the coast, know your evacuation route.
“We don’t want people to panic,” research geophysicist Wirth said. “We just want people to be prepared.”
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