The ShakeAlert earthquake early warning system has been rapidly expanding since its launch in 2021. Now, researchers at University of Washington affiliated Pacific Northwest Seismic Network (PNSN) have finished all planned installations, bringing the two-state total to 569 seismic monitoring stations spread across Washington and Oregon.
ShakeAlert detects ground motion from earthquakes before it is felt, giving people precious time to drop, cover and hold on. An earthquake exceeding magnitude 5 will trigger an automated cell phone alert from the Wireless Emergency Alerts program, or WEA, which also sends AMBER alerts. Millions of people benefit from the network as is, but the researchers are still exploring ways to improve it.
“When we launched ShakeAlert, we felt confident that we had enough seismic stations to do a good job with early warning, but that wasn’t the optimal number. Now, with the buildout complete, we have coverage where it was lacking at launch,” said Harold Tobin, director of PNSN and a UW professor in Earth and space sciences.
However, expanding the network to include sensors on the ocean floor could help Pacific Northwest residents contend with the area’s greatest hazard — the Cascadia Subduction Zone.
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.
Just over a year ago, a midsized earthquake under Orcas Island offered ShakeAlert its first test in Washington. Multiple seismometers in the area picked up the signal and ran it back to headquarters for verification. The earthquake wasn’t quite big enough to trigger a WEA automated alert, or cause major damage, but in the affected region it did notify people with early warning apps such as MyShake, as well as all Android mobile devices.
PNSN has been adding seismic monitoring stations for decades, although the system went live in 2021, the planned installations weren’t finished until 2026. New stations are represented by red dots in the graphic. PNSN
“The system detected the earthquake rapidly, accurately assessed its magnitude and automatically sent out a warning — all in a handful of seconds,” said Tobin. “It was the first event that met all the criteria in Washington and it worked really well.”
During a larger earthquake, warnings will be automatic no matter the app or operating system. Warnings will also trigger certain public safety measures: Schools can connect PA systems to ShakeAlert for rapid updates, public transit may slow trains to avoid derailment and fire station doors will go up to allow firetrucks out even if electricity is lost.
Right now, the system is most effective for land-based earthquakes because the sensors are on land. Expanding the sensor network to include offshore, ocean bottom seismometers could improve detection and warning time for offshore earthquakes, namely a much-anticipated megathrust earthquake at the Cascadia Subduction Zone.
“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.”
Seismometers can be placed on the ocean floor, but they must be connected to cables for early warning, which is expensive. Japan installed an impressive network of offshore seismic stations that cost $120 million following the devastating 2011 earthquake. The country now has more than 200 seismometers covering its subduction zones.
The Cascadia Subduction Zone has a handful of existing offshore sensors — five near Vancouver Island and two off the coast of Oregon. A UW-led project this summer will add four new sensors to the Oregon cable, which spans hundreds of seafloor miles, crossing the subduction zone twice. None of the offshore sensors are in the ShakeAlert network, but adding them could be impactful.
Zoe Krauss, a UW postdoctoral researcher in Earth and space science, recently presented new research at the Seismological Society of America’s annual meeting detailing the potential benefits of adding offshore seismic monitoring.
Krauss found with modeling that incorporating just a few ocean bottom sensors improved detection time for offshore earthquakes and warning time for millions of people. In hypothetical earthquake scenarios, the sensors picked up ground motion faster and improved magnitude estimates because they were closer to the fault.
“ShakeAlert is all about figuring out that an earthquake is happening as fast as possible, so having sensors nearby is essential,” Krauss said. “But in these magnitude 8 or 9 scenarios, it’s not just about detecting it, but realizing how big it is, and fast.”
The researchers also explored incorporating telecommunications cables into the sensor network using a method called distributed acoustic sensing (DAS), which records ground motion based on cable stretch. Incorporating DAS could extend the reach of existing cables even further than sensors, translating to “huge warning time improvements,” Krauss said.
Different combinations produced varying improvements in both detection and warning time, depending on where the hypothetical earthquake occurred. Regardless, having sensors always beat not having them. While there are several hurdles to clear before ocean bottom sensors can be brought into ShakeAlert, Krauss said none are insurmountable.
“Although we’ve marked this milestone of completing our station buildout, that doesn’t mean we’re not continuously improving the ShakeAlert system,” Tobin said. “We’re working to make it faster, better and more reliable.”
For more information, contact Tobin at htobin@uw.edu and Krauss at zkrauss@uw.edu.