The magnitude 4.4 quake — centered near Highland Park on Monday — came with an early warning from California’s quake alert system.
It was not immediately clear how many people got the alert.
But it is the latest example of how the network is growing. Just last week, more than 5.4 million people got early warning alerts that went out for the magnitude 5.2 quake that struck Kern County about 18 miles southwest of Bakersfield.
Here is what you need to know about the system:
How does it work?
Shaking from a quake travels at the speed of sound through rock — slower than the speed of today’s communications systems. For example, it would take more than a minute for a magnitude 7.8 earthquake that starts at the Salton Sea, along the state’s longest fault, the San Andreas, 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 who have iPhones can get earthquake early warnings by downloading the free MyShake app, developed by UC Berkeley and provided in partnership with the California Governor’s Office of Emergency Services, which alerts users in California, Oregon and Washington. San Diego County also offers the 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’re set to trigger alerts if a quake is estimated at magnitude 4.5 or higher and the intensity of shaking at the phone’s location is expected to be “weak” — defined as Level 3 on the Modified Mercalli Intensity Scale.
Scientists urge California residents to download the early-warning apps, and say it’s not a bad idea to have more than one way of getting alerts on your phone. MyShake is available for both Apple’s 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 get quake alerts on their cellphones — but only for those in which a higher magnitude or higher level of shaking is projected at their location. Those alerts are sent through the Wireless Emergency Alert system, similar to Amber Alerts.