Recent SoCal Earthquakes Spur Reassessment of Warning Systems

1 min
An employee works at the cash register at Eastridge Market, near broken bottles scattered on the floor, following a 7.1 magnitude earthquake that struck in the area, on July 6, 2019, in Ridgecrest, California. The earthquake, which occurred July 5, was the second large earthquake to hit the area in two days and the largest in Southern California in 20 years.  (Mario Tama/Getty Images)

When two major earthquakes rattled the Mojave Desert this past weekend, Los Angeles residents didn’t receive an alert — prompting a public outcry for local officials to reassess and update the county's local earthquake warning system.

The system currently in place, an app for L.A. County called "ShakeAlert," is programmed to send out notifications only when a 5.0 or higher magnitude earthquake is detected within the county, or if there’s intense shaking from a smaller tremor. Although at their epicenters, the magnitudes of the Ridgecrest and Trona earthquakes measured 6.4 and 7.1, respectively, the shaking detected within L.A. still fell below the system's threshold.

"We got warnings here in the lab," Dr. Lucy Jones, a research associate at Caltech's Seismological Laboratory, said on KQED's Forum on Monday. "But the decision had been made that the public version should be set at a higher threshold because they were concerned about false alarms at lower levels."

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County officials now plan to lower the magnitude threshold for when notifications are sent out.

"I think this change is probably going to make us be able to meet the needs of the community," said Leslie Luke, deputy director of L.A. County's Office of Emergency Management.

The plan to implement a lower threshold has been in the works for some time, according to a spokesperson for L.A. Mayor Eric Garcetti, who noted that more details are expected to be announced later this month.

On a statewide level, Jones said, there are two separate issues to tackle: expanding the network of seismometers to alert scientists when an earthquake is underway, and then actually delivering that information to people.

California is currently spending more than $16 million to install quake-detecting sensors throughout the state, and is aiming to spend $25 million more, with funding made available in Gov. Gavin Newsom's recently approved budget, Michael Cabanatuan, a staff writer at the San Francisco Chronicle, said on Forum.

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Still, a warning system like the one L.A. uses might not be as effective in the Bay Area, Cabanatuan said, noting that San Francisco and a number of East Bay cities are located directly on faults, and the closer a sensor is to an earthquake’s epicenter, the less warning time people there receive.

Nonetheless, scientists say last week’s quakes should serve as a wake-up call for Californians living on or near the San Andreas Fault to be prepared for the long-dreaded "Big One."

"This has been a very quiet time in California, especially Southern California," Jones said about the lack of significant earthquakes in California over the past few decades. "It's not that we can tell you when the next one is, but we can say that the last 20 years was abnormal. Don't expect that to be what the next 20 years looks like."

The Associated Press, KQED's Forum and The California Report's Benjamin Gottlieb contributed to this report.

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