California’s early warning system didn't send out an alert before Thursday or Friday’s quake because it's still under development in San Diego.
ShakeAlert officials have developed an earthquake early warning mobile app but its only available in Los Angeles.
ShakeAlert has been in development since 2006 and uses 400 ground motion sensors to gather the data.
The ShakeAlert system has deployed its Phase 1 in California, Oregon and Washington. But it will not become fully functional until their mass alerting technologies are able to deliver effectively and early. Plus, they need to educate the public on how to respond to the alerts when they're delivered, according to their website.
On June 27 at 11 a.m. the California Governor’s Office of Emergency Services and the San Diego County Office of Emergency Services sent a test signal.
"The ShakeAlert system is still under development. The test we did two weeks ago was really important to help scientists and public safety officials determine the best ways to notify the public with an earthquake early warning," said Alex Bell, communications officer for City of San Diego. "We were looking to see how quickly alerts were received by the public if we used the Wireless Emergency Alert (WEA) system. We haven’t rolled out an earthquake early warning program in San Diego at this time, but California is actively working on a statewide system."
ShakeAlert warnings are issued for earthquakes of a 5.0 magnitude or greater, but because it registered below that magnitude in Los Angeles the alert was not sent out.
The earthquake was detected by the state's ShakeAlert system and gave 48 seconds of warning to the United States Geological Survey (USGS) Seismology lab at Caltech in Pasadena, confirmed USGS seismologist Robert Graves.
ShakeAlert officials are developing a mobile phone app to help alert people of major earthquakes and will be active in San Diego in the future.