Mere seconds before a 5.1 magnitude earthquake struck the San Jose area Oct. 25, 2.2 million Californians received an early emergency notification.

The state government first launched the Earthquake Early Warning system in October 2019; the system pulls data from the U.S. Geological Survey’s ShakeAlert program and uses the information to send notifications to those in at-risk areas. The earthquake was a major test in determining how the early warning system would fare in delivering messages to large numbers of people with limited time.

“(The) single biggest threat we face to life and property in our state is a sizeable earthquake in one of our major population centers,” said California Office of Emergency Services director Mark Ghilarducci in a press release. “Tuesday was another important step in testing our technology but work still remains to prepare for the next big one.”

Though the state has offered an earthquake alert app from the early conception of the Early Warning program, only about 95,000 people were notified that way — the other 2.1 million benefitted from a partnership between Google and the state government.

In 2020, California Gov. Gavin Newsom announced that earthquake alerts would be implemented on all Android phones. These default alerts have since been the primary means of notification for Californians in the moments before a quake.

“These advanced notifications provided up to 19 seconds (of early warning), in many locations, for Californians to take protective action to ‘drop, cover, and hold on’ and stay safe during the earthquake,” according to a press release from the governor’s office.

Though those few seconds may seem negligible, they may provide recipients with enough time to take cover, thus mitigating risk of injury, according to the press release.

The ShakeAlert system, which detects potential earthquakes from seismic networks in fault lines across the state, was integrated into protective systems by BART prior to being used in the statewide Earthquake Early Warning system. The extra few seconds of warning allows trains to brake automatically before operators can feel the ground shake.

BART actually extended its partnership with the United States Geological Survey in December 2020 in order to continue using their ShakeAlert system; it has been doing so since August 2012.

“BART uses earthquake information from ShakeAlert to protect our riders, workers and infrastructure by triggering automated actions, like slowing trains to prevent potential derailment,” said BART director John McPartland in a press release.

In the most recent earthquake, this was fortunately not an issue as there were no reports of “significant” damage or injury following the quake, according to the press release from the governor’s office.

Even so, the earthquake did allow system operators to test the relatively new software in real-world conditions.

The software’s success and widespread publication also encouraged 108,000 people to download the MyShake app in a single day — a record for the app. This wave of downloads has the potential to more than double the number of alerts received via Myshake, though these will still be only a small fraction of the total alerts received.