What to Know
The ShakeAlert is designed to provide at least a few seconds of warning before the shaking starts.
The alert includes a sound and message that indicates the anticipated intensity level.
After Wednesday, ShakeAlert warnings will be issued for all quakes, including aftershocks, of magnitude-4.5 or greater.
You may recall that after a major Fourth of July earthquake, and subsequent temblors in the following days, that many criticized the ShakeAlertLA app for not notifying residents that a large one was coming.
It was the strongest quake the region had felt in 20 years.
After the criticism, Mayor Eric Garcetti and the U.S. Geological Survey announced changes, lowering the threshold, so more quakes at a lower magnitude will be detected.
It wasn't that the app didn't detect the earthquakes — the app was set to detect quakes at a magnitude of 5.0 or greater.
Wednesday, city officials announced along with the U.S.G.S. that the number would be lowered to 4.5-magnitude.
The ShakeAlertLA app is the nation's first publicly available early warning mobile app.
"There were no glitches," said USGS seismologist Robert Graves at the time of the earthquake. He also said the ShakeAlert system provided 48 seconds of warning to the seismology lab well before the shaking arrived at Caltech in Pasadena, just northeast of Los Angeles.
Garcetti took to Twitter to publicly announce that day that the ShakeALert app would be changing, and that change came Wednesday.
At its epicenter in Kern County, the temblor registered as a 6.4-magnitude quake. The shaking in Los Angeles was below 4.5, the U.S.G.S. confirmed.
Here's how the app works.
Once the app is downloaded, users are asked to enable notifications. ShakeAlert warnings are issued for all quakes, including aftershocks, of magnitude-4.5 or greater. The alert includes a sound and message that indicates the anticipated intensity level.
The early warning function only works in Los Angeles County. The app does not need to be open, but users must set the phone's location services to "Always On."
ShakeAlert LA also has resources to help prepare for an earthquake.
It's part of the early warning system being built for California, Oregon and Washington, which detects that an earthquake is occurring, quickly analyzes the data and sends out alerts that may give warnings of several seconds to a minute before strong shaking arrives at locations away from the epicenter. A few seconds is enough time to scramble for protection, slow trains, halt industrial processes, trigger backup power generators and pause surgeries at hospitals.
Pilot programs involving select users have been underway for several years.
A new generation of ShakeAlert software was deployed in September, including improvements in reducing false and missed alerts. False alerts typically have occurred when a large quake elsewhere in the world is detected by a sensor and is mistaken for a local earthquake.
There's still work to do. The sensor network is only about 50 percent of the target size. Funding has been secured to complete the network in California in the next two years.