Bill Adamec in Cupertino and Danny Blanco in Gilroy got earthquake alerts on their phones just as they started to feel Tuesday’s temblor east of San Jose. Up in Berkeley, Stefan Lasiewski said he got the alert five to 10 seconds before the shaking started. In Scotts Valley, Jerry Turin got it a minute after.
Around the Bay Area, the 5.1 magnitude earthquake lit up mobile phones thanks to ShakeAlert, the U.S. Geological Survey’s fledgling earthquake early warning system, putting it to the test regionally for the second time in as many months.
“I was a bit confused then realized it was an alert system,” Blanco wrote in a Twitter reply to the USGS seeking feedback on the system on social media.
Adamec told the USGS it was “wild how it could be so fast!”
The ShakeAlert system is finally a reality for over 50 million West Coast residents after more than a decade in development. With more than 903 buried sensors in California that can mobilize cellphone users who are at risk, it’s more than 80% complete. It is planned to have 1,115 California sensors and quicker transmission time, with additional sensors in Oregon and Washington. The goal is to give recipients a few critical seconds of warning before an earthquake’s most destructive phase — time that could save lives.
Several countries, including Japan, Mexico, China and Turkey, have long had such earthquake warning systems in place.
FEMA’s Wireless Emergency Alert system sent out the automatic ShakeAlerts on Tuesday’s quake, similar to an Amber Alert. But whether your phone started buzzing depended on the high-tech system’s predicted intensity of the shaking for wherever you happened to be at the moment.
The earthquake struck at 11:42 a.m., according to the USGS, with an epicenter 12 miles east of San Jose and at a depth of just over 4 miles, within the Calaveras fault zone where a magnitude 6.2 Morgan Hill earthquake struck in 1984.
Tuesday’s quake was widely felt with over 18,000 “Did You Feel It?” reports submitted to the USGS as of 1 p.m. Tuesday, extending from Central California north to Sacramento and Sonoma County.
USGS ShakeAlert systems authorized the initial alert five seconds after the earthquake was detected, initially estimating a magnitude 4.8. That estimate grew, USGS seismologist Annemarie Baltay said, as alerts were delivered.
The ShakeAlert system detects an earthquake’s initial waves of ground motion, which travel quickly and are weaker than the more damaging second set of waves. That triggers 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 ShakeAlert message, which is picked up and delivered by government and private partners.
It didn’t work for everyone. Iene Shi felt the quake in Fremont but didn’t get an alert, and USGS replied on Twitter with information about how to make sure your phone is set up to receive them.
In addition to the automatic alerts from USGS and FEMA, two different apps — MyShake, developed by UC Berkeley, and QuakeAlertUSA, by Early Warning Labs — issue alerts, even for lower magnitude quakes, to those who download them.
Early Warning Labs said Tuesday it sent alerts to 928 users on Android and iOS devices via the QuakeAlertUSA app. Those users, the company said, were forecast to experience shaking of a level 3 on the Modified Mercali Intensity scale, which measures an earthquake’s intensity.
Early Warning Labs said that under USGS rules, to receive an early warning, the earthquake must be over magnitude 4.5 and the forecasted intensity over MMI 3.
“If the quake is smaller or your MMI is under 3 you might still feel light shaking but not be issued an alert,” the company said.
The ShakeAlert system got its last big trial Sept. 13 when a magnitude 4.4 earthquake struck 2.4 miles north of Santa Rosa. As with Tuesday’s earthquake, some people got alerts without much shaking, some got shaking before the alerts, and for others, the alert came just as the earthquake was being felt.
Eric Nau who lives in downtown San Francisco some 42 miles away said he got Tuesday’s alert on his MyShake app one second before the shaking started, which he considered barely helpful.
“Based on USGS ShakeAlert data, I believe I should have gotten the alert about 10 seconds before,” Nau said. “So this was a disappointing result.”
Turin in Scotts Valley 21 miles away also got the alert a minute late, and said that “the message of drop!, cover!, hold on!, protect yourself! is meaningless and silly in context of a 5.1.”
“But I am not critical about that,” Turin added, “as they may improve it.”
Robert de Groot, the national coordinator of outreach and education for ShakeAlert at the USGS’ Pasadena Field Office, said the early warning system went out to at least 95,000 people and “performed as expected during this earthquake, similar to the Santa Rosa earthquake.”
“We learn something new from each earthquake,” de Groot said. “It did exactly what it’s supposed to. We are really happy with the way things are going, and with the public uptake as well. We want people to use it.”
How to get a USGS ShakeAlert message:
• Wireless Emergency Alerts, such as an AMBER Alert, are delivered by FEMA’s Integrated Public Alert and Warning System. It is not necessary to sign up for alerts but make sure you didn’t turn off the option. For questions, contact your cell phone service provider.
• The MyShake app is available for free in the Apple App and Google Play stores. Learn more: https://myshake.berkeley.edu/
• The QuakeAlertUSA app is available for free on the Apple App and Google Play stores. Learn more: https://earlywarninglabs.com/mobile-app/.
• Google provides a ShakeAlert-powered earthquake alert feature that is integrated into the Android Operating System. Go to Safety and emergency option in Settings on your phone and select “Earthquake alerts.”