How to ensure you know about the next big California earthquake

The U.S. Geological Survey’s ShakeAlert system activated Tuesday morning when a magnitude 6.4 earthquake struck just off the coast of Northern California near Ferndale, with hundreds of thousands of residents receiving messages on their smartphones telling them to “drop, cover, hold on” and prepare for shaking.

The quake struck at 2:34 a.m. about 9 miles west of Ferndale, and more than 270,000 people received alerts through the MyShake app, one of a few tools that deliver the information, Robert de Groot, the USGS ShakeAlert coordinator, told SFGATE.

ShakeAlert does not predict earthquakes; rather, it’s the USGS warning system that gathers information when an earthquake begins and then sends it out to third parties that deliver the alerts.

“It takes some time, several seconds, to gather the information,” de Groot told SFGATE on the phone. “Then we hand it off to MyShake and Google, they have to do quick processing on it, that takes maybe a second, then they deliver the alerts to the phones.”

On Tuesday morning, the system gathered information about the quake 5.5 seconds after the temblor first reached the surface, and the first messages went out at 7.5 seconds, according to the USGS. People who were located less than 17 miles from the epicenter, such as in the towns of Fortuna and Ferndale, received an alert after the shaking began. Those living 17 miles or more away from the epicenter, such as in the towns of Eureka and Fort Bragg, got a few seconds of warning. 

“There’s a little bit of buffer time before people onshore feel it,” said Stephen DeLong, a supervisory research geologist with the USGS. “Eureka received the alert about 4 seconds before there was shaking, Fort Bragg 29 seconds.”

People located 200 miles to the north of the epicenter in Medford, Oregon, received alerts — so did people living as far away as 300 miles south in San Jose. It may seem unnecessary for areas where shaking was felt minimally or not at all to receive alerts, but de Groot said this is part of the system that’s continuously being perfected.

“Our goal is human safety. It’s not to be too concerned with where people get alerts, because if we limit that we might jeopardize human safety,” he told SFGATE on the phone. 

How to sign up for ShakeAlert earthquake messages
Several apps deliver ShakeAlert messages, and they are easy and free to download on a mobile phone.

UC Berkeley’s MyShake, which was first launched in 2019, is available on the Apple App Store and Google Play store and operates in California, Oregon and Washington. Early Warning Labs’ QuakeAlertUSA app, available in California and Oregon only, can also be downloaded through the Apple App Store and Google Play store.

Google Android phones come with the feature pre-installed, and it’s available in California, Oregon and Washington. You can enable the feature by going to the “Safety & emergency” tab in Settings and turning on the earthquake alerts. 

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