ShakeAlert warning system gets first test with Santa Rosa earthquake

Santa Rosa’s earthquake gave the Bay Area its first real test of the nation’s new ShakeAlert system, and it was a qualified success, warning thousands of residents on Tuesday night with a loud alarm and instructions to seek cover.

“The moment the wave hit the house, my watch and phone went off. It’s a miraculous technology — a definite win,” said Robert Stephens, who was sitting at a table at his home on Sonoma Mountain, about five miles from the quake’s epicenter.

In downtown Sonoma, the alarm sent journalist Sarah Stierch diving under her dining room table for protection. “Very impressed with the alert — it’s my first experience with it,” she wrote on Twitter.

But many residents at greatest risk did not receive an alert until after the shaking started because they were so close to the epicenter. The system gives longer warnings to those who are farther away from the rupture.

After more than a decade in development, the ShakeAlert system is finally a reality for over 50 million West Coast residents. Created by the U.S. Geological Survey, it is 81% complete, with more than 903 buried sensors in California that can mobilize cellphone users who are at risk. When complete, it will have 1,115 sensors and quicker transmission time.

FILE - In this Jan. 3, 2019 file photo a mobile phone customer looks at an earthquake warning application on their phone in Los Angeles. The warnings produced by the ShakeAlert system will be pushed through two delivery systems: a cellphone app called MyShake and the same wireless notification system that issues Amber Alerts, meaning people may receive both notifications. (AP Photo/Richard Vogel, File)
In this Jan. 3, 2019 file photo a mobile phone customer looks at an earthquake warning application on their phone in Los Angeles. The warnings produced by the ShakeAlert system will be pushed through two delivery systems: a cellphone app called MyShake and the same wireless notification system that issues Amber Alerts, meaning people may receive both notifications. (AP Photo/Richard Vogel, File) 

“The good news is that we’re going in the right direction,” said USGS’s Robert de Groot, the national coordinator of outreach and education for ShakeAlert.

“The ShakeAlert system behaved as we expected it would last night,” he said, “and it shows that we’re continuing to improve earthquake early warning on the West Coast.”

The system initially overestimated the earthquake’s magnitude, calling it a 4.9; later, the quake was downgraded to a magnitude 4.4. But it identified the site of the quake’s rupture with extreme accuracy, pinpointing the epicenter 2.4 miles north of Santa Rosa.

In some spots, it was overenthusiastic, puncturing the serenity of a seismically uneventful evening. “The alert scared me to death,” wrote Anna Boucher, of San Rafael, who said she did not experience any shaking.

In other places, it worked just as planned. At a youth soccer game in Rohnert Park, “everyone’s phones went off with emergency alerts — and then we felt the quake about 20 seconds later,” tweeted Matthew Valkovic. “It was pretty wild!”

Sometimes it came too late. By the time Santa Rosa resident Kathy McMorrow got the alarm, she and her dog had already felt the temblor and were down the porch stairs. Spectators at the town’s Montgomery High School basketball game heard the alert after the main shock but before the aftershock.

A map showing the range and response time of ShakeAlert an earthquake early warning system to an earthquake that occurred in Santa Rosa on Tuesday, Sept. 13, 2022.Alexa Chipman heard the clamor after the earth finally stood still. “I was like ‘so helpful…I noticed, thanks!’” she joked on Twitter.

While there were few reports of damage or injury, the city has dispatched public works employees to assess possible damage to essential services and city infrastructure.

ShakeAlert’s performance has been a disappointment in some previous earthquakes, especially in rural regions where there are few sensors. While fast, it wasn’t accurate.

But Santa Rosa’s 4.4-magnitude shaker and a 4.3-magnitude aftershock — which struck about two miles northeast of downtown, causing some bottles and other items to topple off store shelves — triggered a near-perfect alert for residents of densely populated communities in Sonoma County, as well as some adjacent towns in Napa, Marin, Contra Costa, Alameda and Mendocino counties, even San Francisco’s Presidio.

At least 20,000 people got the apps’ messages, with more getting notice from FEMA and Google, said de Groot.

USGS has prioritized high-population areas, especially those located near major faults, in its ‘build up’ strategy. Businesses and public agencies such as BART are already acting on alerts from the system.

Communities on the distant edge of Tuesday’s “shake zone” received an alarm well in advance, up 30 seconds before the shaking.

ShakeAlert relies on cell phones — so residents who weren’t near their phones, or who hadn’t downloaded the app, missed the message.

For the system to send an alert, the earthquake must be recorded as having a magnitude of 4.5 or more. Although the final magnitude was lower, the quake initially registered at 4.9.

Shake Alert does not predict earthquakes, but it detects an earthquake’s initial waves. These waves, which travel quickly, are weaker than the more damaging second set of waves.

When the system’s sensors detect these first waves, it enlists high-speed telemetry to send that ground motion information to processing centers in Seattle, Menlo Park and Pasadena. Within about five seconds, computer algorithms analyze the data to rapidly identify the epicenter and strength of the earthquake and publish a data package, called a ShakeAlert message.

The ShakeAlert message is picked up by government and private partners. FEMA may issue a Wireless Emergency Alert, like an AMBER Alert.

ShakeAlert’s big test in Santa Rosa earthquake