Fourth of July earthquake rattles LA—where was the early warning?

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A long, rolling earthquake that splashed water out of swimming pools and rippled through social media rocked the LA region on Fourth of July morning.

Although people across Southern California—and all the way to Las Vegas—reported feeling the quake, which was strong enough to sway chandeliers and make national headlines, there was no alert from the city’s early warning app, which became available at the end of 2018.

The 6.4 quake was epicentered near Ridgecrest, California, in a remote part of Kern County about 100 miles from LA, and was among the largest to hit Southern California since the Northridge earthquake of 1994.

But the app did not send an alert before the earthquake and did not even show the event on the apps “recent earthquakes” screens. On the city’s website, the recent earthquake page showed today’s earthquake, in addition to other smaller ones.

Yeah @LACity. Like, it *still* hasn’t updated. pic.twitter.com/X787kTXQur

— Rico Gagliano (@RicoGagliano) July 4, 2019

At a January press conference for the early warning app, city representatives said the app, named ShakeAlertLA, was intended to send an alert to local residents for earthquakes of magnitude 5.0 and above when shaking is felt in Los Angeles County.

But Angelenos who had downloaded the alert system posted screengrabs of their apps, wondering why those parameters wouldn’t have included a 6.4 earthquake that was felt across the county.

Los Angeles deputy mayor Jeff Gorell said in a tweet that the system was designed to send an alert only for events when the LA-area shaking intensity is 5.0 or higher, regardless of the earthquake’s magnitude. “You will not get a warning every time there is shaking,” he said in a separate tweet. “Only if it’s dangerous.”

The shaking intensity in LA County was below 4.5, and for most areas was only an intensity of 2 or 3, USGS confirmed.

A subsequent tweet from the City of Los Angeles’s account said that the city will lower the alert threshold with USGS.

The #ShakeAlertLA app only sends alerts if shaking is 5.0+ in LA County. Epicenter was 6.4 in Kern County, @USGS confirms LA’s shaking was below 4.5. We hear you and will lower the alert threshold with @USGS_ShakeAlert

— City of Los Angeles (@LACity) July 4, 2019

Although the city’s app did not send an alert, a different app named Quake Alert, which is in use by some commercial organizations and will be launched statewide this summer, gave some LA beta testers up to a minute’s warning today.

Josh Bashioum of Early Warning Labs, the Santa Monica-based company that’s developing the QuakeAlert app, says the city’s warning system should have sent an alert to Angelenos who have the app on their phone.

“It should have worked,” Bashioum tells Curbed. “The app says they will only alert people in Los Angeles County, but they need to alert them for earthquakes that happen anywhere outside of LA County, too. The San Andreas Fault isn’t in LA County.”


Screengrabs from the Quake Alert app.

One major difference between ShakeAlertLA and QuakeAlert is that Early Warning Labs uses raw USGS data to calculate customized alerts based on the user’s location, says Bashioum. “This is expensive, to create ‘intensity’-based alerts but we believe it’s the best method when lives are on the line,” he says. “We hope our consumer app will be ready soon; our commercial platform already protects over 100,000 California residents.”

QuakeAlert users can also set their own thresholds for what alerts to get for any quakes—as long as they’re above magnitude 3.5. But the app will only give an estimate of shaking intensity if the quake is expected to be felt by the user.

LA’s app was made publicly available over six months ago, but the city has still not released video or sound showing what users will see and hear in the moments before a quake. In a USGS and Caltech press conference today, seismologist Lucy Jones was asked what the ShakeAlertLA alert sounded like and she said she didn’t know.

Jones also said to expect more aftershocks.

The @LACity#ShakeAlertLA app sends USGS ShakeAlerts to people in @CountyofLA at M5.0+ for areas that could experience potentially damaging shaking. Estimated shaking for @CountyofLA was non-damaging and #ShakeAlertLA performed as designed during today’s M6.4 earthquake.

— USGS ShakeAlert (@USGS_ShakeAlert) July 4, 2019

By the time the damaging p-waves got to LA, the earthquake was less than a mag 5.0 which is the minimum set for the app to send an alert to LA residents. The #ShakeAlertLA App is working as designed. You will not get a warning every time there is shaking. Only if it’s dangerous. https://t.co/X9bfyMzpbc

— eff orell (@JeffGorell) July 4, 2019

It’s fine and good to set a threshold at which #ShakeAlertLA sends alerts to the public, but does the average layperson understand what that means in practice? And was the threshold communicated at app launch? Because right now, I think a lot of people think it just doesn’t work. https://t.co/2P3NrERP3Z

— Andrea Gutierrez (@AndreaGtrrz) July 4, 2019

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