Two large earthquakes rattle LA—but where was the early warning?

No alert from the city’s new early warning app for the 6.4 or 7.1 quakes

A long, rolling earthquake that splashed water out of swimming pools and rippled through social media rocked the Los Angeles region on Fourth of July morning. The next evening, an even stronger, longer earthquake was felt across Southern California.

Although millions of people throughout the LA area—and all the way to Las Vegas—reported feeling both quakes, which were strong enough locally to disrupt live newscasts, shake cameras filming the Dodger game, and sway chandeliers, there were no alerts from the city’s early warning app, which became available at the end of 2018.

The 6.4 and 7.1 quakes (Friday’s magnitude 7.1 was downgraded to 6.9, then revised back to 7.1)—were both epicentered near Ridgecrest, California, in a remote part of Kern County about 100 miles from LA. The earthquakes are among the largest to hit Southern California since the Northridge earthquake of 1994. Some fires, rockslides, and damage to buildings and roads were reported near the epicenter.

But the ShakeAlertLA app did not send alerts before the earthquakes. On Thursday, the app did not even show the 6.4 event on the “recent earthquakes” screens.

At a January press conference for the early warning app, city representatives said the app 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 on Thursday, 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 on Thursday that the system was designed to send an alert only for events when the LA-area shaking intensity is 5.0 on the Modified Mercalli Intensity (MMI) scale 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.”

AP Photo/John Antczak

The shaking intensity in LA County for the Fourth of July event was below 4.5, and for most areas was only an intensity of 2 or 3, USGS confirmed. USGS has not yet confirmed the shaking intensity for Friday’s event.

A subsequent tweet from the City of Los Angeles’s account said that the city will lower the alert threshold with USGS. On Friday, before the 7.1 quake struck, LA’s chief technology officer Jeanne Holm told the Los Angeles Times that the city was already planning to lower the threshold to 4.5, and that the app will be updated by the end of the month.

On Friday, before the 7.1 quake, Robert-Michael de Groot, who manages the USGS ShakeAlert account, confirmed to The Verge that the threshold would be reduced.

“Yes, thresholds are going to come down. Absolutely,” he said. “But there’s also our need to make sure that the system is stable and it’s working as it should. Our threshold at the moment is to maximize public safety and minimize over-alerting.”

In the same interview, de Groot also said that the LA app developers were “on the verge of doing a speed test” to practice sending a message all the app’s users at once.

On Friday, the ShakeAlertLA app pushed an update for iPhone users that added all earthquakes of magnitude 3.0 and above for the past 30 days to the “recent earthquakes” screens. There was no update for Android users.

USGS posted a tweet late Friday night confirming that the organization had been working with the city to improve alerts when the second earthquake hit.

Although the city’s app did not send alerts, a different app named Quake Alert, which is in use by some commercial organizations and will be launched statewide this summer, gave LA beta testers an average of 45 seconds of warning, according to their post-event report.

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.”

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, 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, some of which could be felt in the LA area. After Friday’s 7.1 earthquake, Thursday’s 6.4 earthquake was now considered to be a foreshock. The chance of another earthquake occurring as part of this same sequence that’s larger than those two earthquakes is now 11 percent.

This story was originally published at 11:19 a.m. on July 4, 2019 and has been updated with new information.

Source: Curbed LA – All – Alissa Walker