A local resident inspects a crack in the earth after a 6.4 magnitude earthquake struck the area on July 4, 2019 near Ridgecrest, California.
Mario Tama | Getty Images
The nation’s first publicly available earthquake early warning mobile app was launched earlier this year as part of a pilot program designed to give Los Angeles County residents a few seconds of warning before the shaking.
So, why didn’t users receive a notification from the ShakeAlert LA app when a magnitude-6.4 earthquake — the region’s strongest in 20 years — rattled a widespread part of Southern California on Independence Day?
ShakeAlert warnings are issued for all quakes, including aftershocks, of magnitude-5.0 or greater in Los Angeles County. Thursday’s earthquake was centered to the north in the Mojave Desert in Kern County and did not reach the shaking threshold in Los Angeles County.
“There were no glitches,” said USGS seismologist Robert Graves.
Graves said the ShakeAlert system provided 48 seconds of warning…