An early-alert system designed to give people crucial seconds of warning before earthquakes lived up to its promise on Monday. It buzzed through a half a million phones ahead of a 6.2 magnitude earthquake that hit northwest California — the largest quake since the system, called ShakeAlert, rolled out across the entire state, The Guardian reported.

ShakeAlert pulls information from the United States Geological Survey’s (USGS) sensor network. If data from those sensors says there will be major shaking in an area, people living there get alerts through the MyShake app (if they’ve downloaded it), or through the wireless emergency alerts system on their phones. Alerts also go out to Android users through a partnership between Google, USGS, and the California Office of Emergency Services.

The epicenter of Monday’s earthquake was off the coast of a small town called Petrolia, and around 45 miles from the nearest population center, Eureka. People reported getting alerts around 10 seconds before shaking started, Robert de Groot, a ShakeAlert coordinator with the USGS, told The Guardian, making it a successful proof of concept for the first substantial earthquake handled by the system. The quake didn’t do major damage to the area, and there were no fatalities.

The ShakeAlert system was first introduced in Los Angeles in 2018, before expanding to all of California in 2019. The system was in place in LA when a 6.4 magnitude earthquake hit around 150 miles outside of the city, but didn’t set off an alert because the expected shaking in the city wasn’t strong enough to cross the app’s threshold. Users complained they didn’t get an alert even though they felt shaking, so the app’s developers lowered the threshold before the state-wide rollout.

Now, the scientists behind ShakeAlert can use the information from this most recent earthquake to again improve the system for next time. “We are really going to learn the most from real earthquakes,” de Groot told The Guardian. “It’s giving us the chance to use the system and learn how to do a better job of alerting people.”

https://www.theverge.com/2021/12/24/22852863/shakealert-earthquake-california-app-android-petrolia