Did ShakeAlertLA Fall Short During the Recent Quake?

The app was only designed to alert users physically located in Los Angeles County. What was felt Thursday, while seemingly scary, was actually not that bad — either level 2 or level 3 shaking, or “weak shaking.”

by Rong-Gong Lin II, Los Angeles Times / July 5, 2019

(TNS) — Did Los Angeles’ ShakeAlertLA smartphone app fail to provide an earthquake early warning?

Los Angeles residents were asking that question after Thursday’s earthquake that was felt through Southern California, when they didn’t get an early warning from the much-anticipated ShakeAlertLA app, released by the city of Los Angeles earlier this year.

Did it fail? Not quite. The ShakeAlertLA app was only designed to alert users of cellphones physically located in Los Angeles County if there was at least “light shaking,” or level 4 on the Modified Mercalli Intensity Scale, expected for Los Angeles County.

What was actually felt Thursday in Los Angeles County, while seemingly scary, was actually not that bad — either level 2 or level 3 shaking, or “weak shaking.”

“It didn’t meet the threshold for the L.A. area,” said Doug Given, the U.S. Geological Survey’s earthquake early warning coordinator. “ShakeAlertLA is not designed to detect earthquakes that far away,” said California Institute of Technology seismologist Egill Hauksson.

ShakeAlertLA is a mobile phone app developed by the city that transmits earthquake early warnings based off a separate, but similarly named, system called ShakeAlert and run by the U.S. Geological Survey.

The USGS’ system relies on hundreds of earthquake sensors scattered throughout the West Coast. There is no public smartphone app yet available that sends earthquake early warnings throughout all of California.

However, scientists are continuing to test, refine and perfect the USGS’ ShakeAlert system that does aim to provide earthquake early warnings throughout California, and eventually Oregon and Washington.

That ShakeAlert system worked — it’s just that the public does not yet have access to that information as scientists continue to refine its public delivery system. The USGS’ ShakeAlert system issued an alert about 6.9 seconds after the shaking began, Given said.

Had there been a public warning system in place for Kern County, the USGS ShakeAlert system would not have been fast enough to issue an early warning for Ridgecrest — at 10 miles away from the epicenter too close to get a warning, but enough to give some warning to California City, about 50 miles southwest of the epicenter.

The intensity of shaking was obviously worse closer to the epicenter, maxing out at intensity level 7, or very strong shaking, but that occurred in a much more remote area.

The city of Ridgecrest, population 29,000, endured intensity level 6 or “very strong” shaking, in which damage that might occur could result in broken chimneys, considerable damage in poorly built or badly designed buildings, but negligible damage in buildings of good design and construction.

©2019 Los Angeles Times. Distributed by Tribune Content Agency, LLC.

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