The 4.4 magnitude earthquake, centered near Highland Park on Monday, was accompanied by an early warning from California's seismic alert system.
It was not immediately clear how many people received the alert.
But it is the latest example of how the network is growing. Last week, more than 5.4 million people received early warning alerts that were sent 5.2 magnitude earthquake which affected Kern County about 18 miles southwest of Bakersfield.
Here's what you need to know about the system:
How does it work?
Earthquake vibrations travel at the speed of sound through rock, slower than the speed of today's communications systems. For example, a magnitude 7.8 earthquake originating in the Salton Sea along the state's longest fault, the San Andreas, would take more than a minute to be felt 150 miles away in Los Angeles.
How do I get it?
While Google's Android operating system comes with a built-in app, Apple's iOS system for iPhones does not.
Those with iPhones can get early earthquake alerts by downloading the free app My smoothie app, developed by UC Berkeley and provided in collaboration with the California Governor's Office of Emergency Services, alerts users in California, Oregon and Washington. San Diego County also offers the app for free SD Emergency app, which includes the ShakeReadySD earthquake early warning tool.
Android phones and those with the MyShake or ShakeReadySD apps installed have the lowest threshold for earthquake early warnings: they are set to trigger alerts if an earthquake is estimated to be magnitude 4.5 or higher and the shaking intensity at the phone's location is expected to be “weak” — defined as Level 3 on the Modified Mercalli Intensity Scale.
Scientists are urging California residents to download early warning apps and say it's not a bad idea to have more than one way to receive alerts on your phone. My smoothie It is available for both Apple iOS and Android.
What if I don't have a smartphone?
People who don't have smartphones or haven't installed early warning apps can still receive earthquake alerts on their cellphones, but only for those where a higher magnitude or level of shaking is projected at their location. Those alerts are sent through the wireless emergency alert system, similar to Amber Alerts.
