LOS ANGELES -- More than 500,000 people have downloaded Los Angeles County's new ShakeAlertLA app to warn them of impending earthquakes.
So when the two strongest earthquakes in almost two decades hit Southern California this month, those residents were surprised by what they saw on their smartphones: nothing.
Officials were quick to explain to outraged app users that the shaking in the county wasn't strong enough to trigger an alert.
But that rationale hasn't mollified the public.
And the program's inauspicious start has officials grappling with an existential question that quake-prone countries such as Japan and Mexico have faced before: Is it better to issue too many earthquake warning alerts or not enough?
"We've long treated citizens as people who need to be protected, rather than people we need to empower," said David Eisenman, the lead scientist on the Los Angeles County Community Disaster Resilience Project. "More information is always the way we need to go. It's undeniable."
Before the ShakeAlertLA app was rolled out on New Year's Eve, researchers spent a great deal of time debating the appropriate minimum threshold for alerts, U.S. Geological Survey seismologists said. They decided to send alerts for quakes in L.A. County with a magnitude of at least 5.0, or quakes that occur anywhere and produce "light" shaking in Los Angeles.
But after the blowback that followed the Ridgecrest quakes July 4 and 5, officials agreed to lower the mark. By the end of July, the app will send alerts for local quakes with a magnitude of at least 4.5 and for any quake that results in "weak" shaking locally despite officials' concern that too many warnings could lead to complacency.
"We want you to see the alert and immediately drop, cover and hold on," said Robert de Groot, the USGS' ShakeAlert national coordinator. "If you see 30 of those a day, you're either going to get incredible muscle tone and a core workout, or you're going to stop reacting altogether."
Striking a balance