On Tuesday, Sept. 26, 2026, around 2:00 p.m., a magnitude 4.2 earthquake struck near Wauna, Washington.
Some people felt weak shaking in Seattle, Tacoma, Olympia and Bremerton. Many others felt nothing at all.
And most phones stayed quiet. That was by design.
The earthquake was automatically detected by ShakeAlert, the West Coast earthquake early warning system operated by the U.S. Geological Survey in partnership with university seismic networks, including the Pacific Northwest Seismic Network (PNSN) headquartered at the University of Washington.
ShakeAlert uses a network of seismic sensors to detect an earthquake as it begins, rapidly estimate how strong it is and where damaging shaking may be headed. When expected shaking reaches certain thresholds, the system can send warnings to phones and trigger automated safety actions, sometimes giving people precious seconds to prepare before the strongest shaking arrives.
ShakeAlert correctly determined that the Wauna earthquake was too small to warrant cellphone alerts. It was a real-world test of a system built to make decisions in seconds.
The science behind the alert
ShakeAlert depends on a network of seismic instruments that can detect the first signs of an earthquake, rapidly estimate its location and strength, and determine where damaging shaking may be headed.
PNSN Researchers at the University of Washington and their partners have spent decades building and improving that network, and the ShakeAlert station buildout in Washington and Oregon is now complete, with 569 seismic monitoring stations across the two states.
Building that system has required researchers and engineers to install and maintain equipment across some of the region’s most remote terrain. Near Mount Rainier, for example, a UW PNSN team recently installed new monitoring equipment as part of the network that helps scientists detect earthquakes and volcanic activity throughout the Pacific Northwest.
Every station adds another stream of information. Together, they allow scientists and automated systems to understand what is happening underground almost the moment things begin to change.
When seconds matter
Earthquake early warning is possible because information can travel faster than damaging seismic waves.
When an earthquake begins, nearby sensors detect the first waves and send data into the ShakeAlert system. Computers rapidly determine the earthquake’s location and magnitude and estimate where significant shaking is expected.
If that shaking crosses alerting thresholds, warnings can reach people before the strongest waves arrive.
Those seconds can give someone time to drop, cover and hold on. They can also allow automated systems to take protective actions, such as slowing trains, stopping elevators or opening firehouse doors. The United States Geological Survey says ShakeAlert is designed to warn people when strong shaking is expected, rather than sending an alert for every earthquake detected by the network.
In March 2025, a magnitude 4.2 earthquake near Orcas Island put the system into action, sending ShakeAlert warnings to tens of thousands of people across the San Juan Islands, Bellingham and surrounding communities.
“This was the first earthquake in Washington that has triggered a live warning since ShakeAlert became available in 2021, and it worked very well,” said Pacific Northwest Seismic Network Director Harold Tobin.
Together, these two recent earthquakes illustrate what the system is designed to do: detect earthquakes quickly, estimate the shaking they may produce and send a warning when that warning is likely to be useful.
Not only does the MyShake app alert people to imminent shaking, but it also collects location and motion data to share with scientists, which can help improve earthquake research. Through the app, users can also share their own experiences — like their location, how much shaking is felt and where there’s any damage to buildings and roads nearby.
If the earthquake had been magnitude 5.0 or larger, ShakeAlert warnings would also have gone out to area mobile devices that receive Wireless Emergency Alert messages, like Amber Alerts and severe weather warnings. (The MyShake app and Android have a lower alerting threshold of magnitude 4.5.)
“Just a few seconds of advance warning may not sound like much, but it’s just enough time to stop and think, ‘What am I supposed to do in a quake?’ and take action. There’s clear evidence from other countries that smartphone earthquake warnings have saved lives and prevented injuries.”
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An advance warning of even a few seconds can have a huge impact — people can move to safer locations away from windows and structures that may topple over, and critical processes like surgeries or the movement of trains can be halted or adjusted.
The West Coast is a hotbed for seismic activity. Nestled in the Ring of Fire, an array of volcanoes circling the Pacific Ocean where 90% of Earth’s quakes occur, the region’s volatile geology clashes with its growing population. Early warning systems can give people seconds to minutes of time to prepare for shaking, and a sense of how strong it will be.
ShakeAlert and the deployed sensors make the nation’s only public Earthquake Early Warning (EEW) System, today serving 50+ million people in California, Oregon, and Washington.
The next challenge is offshore
With the planned ShakeAlert station buildout now complete in Washington and Oregon, researchers are turning their attention to one of the system’s biggest remaining challenges: the Pacific Ocean.
“The fundamental problem we have is that our seismic network — hundreds and hundreds of stations — is on land, but the biggest earthquake hazard comes from off our coast,” Tobin said. “Earthquake detection works much better when the earthquake is in the area of your network, not off to one side.”
That hazard is the Cascadia Subduction Zone, which stretches offshore from Northern California to British Columbia and is capable of producing a magnitude 9 earthquake.
Today, only a handful of seismic sensors sit offshore along Cascadia, and none are currently part of the ShakeAlert network. Installing more could make a meaningful difference. UW researchers are studying how ocean-floor sensors could help detect a major offshore earthquake sooner, potentially providing additional warning time before strong shaking reaches populated areas.
A UW-led project is also expanding the region’s offshore observing capacity by adding new sensors to an existing cabled observatory off the Oregon coast. Researchers are exploring other possibilities as well, including whether telecommunications cables already running across the ocean floor could one day help detect earthquakes.
While this recent earthquake proved to be minor, the ability to test the early warning system is invaluable. “Fortunately this was only a mild earthquake that didn’t injure people, but it provided a real-world test of the warning system and it worked as intended,” said Tobin. “This really bolsters our confidence in the ShakeAlert system for future larger quakes.”
A few actions you can take now to be prepared for the next earthquake:
- iPhone and Android users can download the MyShake app, which delivers alerts and information from ShakeAlert. For Android users, ShakeAlert warnings are also built into the operating system.
- All cellphone users should check to make sure Wireless Emergency Alerts are enabled. ShakeAlert notifications will automatically push to all phones with this enabled (similar to an Amber Alert).
- In your home, make sure large furniture is strapped down or secured, and remove any frames or other items from above sleeping areas that could fall during an earthquake.
- Check out these safety videos on how to protect yourself in various settings during an earthquake.
Research Makes America
This story is part of Research Makes America — an ongoing effort by the University of Washington to demonstrate how research supported by federal funding drives innovation, opportunity, and national progress.
