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ShakeAlertLA to Lower Alert Threshold After 6.4 Magnitude Quake Hits Mojave Desert, City Says

Data pix.

Los Angeles’ early earthquake warning system will lower its alert threshold after a 6.4 magnitude earthquake hit Southern California Thursday, city officials announced.

USGS officials hold a news conference about a 6.4 magnitude quake that struck the Mojave Desert on July 4, 2019. (Credit: KTLA)

USGS officials hold a news conference about a 6.4 magnitude quake that struck the Mojave Desert on July 4, 2019. (Credit: KTLA)

No alert was sent out before the temblor jolted Searles Valley in the Mojave Desert about 10:35 a.m. because ShakeAlertLA only issues a warning if a quake is a magnitude 5.0 or higher in Los Angeles County, officials said on Twitter.

It is also programed to send out alerts if there is “light shaking,” or Level 4 on the on the Modified Mercalli Intensity Scale, the Los Angeles Times reported, while the intensity in Los Angeles was at a 3.

The Caltech Seismological Laboratory in Pasadena did get an early warning about the quake just under 50 seconds before it hit, and predicted it would be a 6.2 earthquake, seismologist Dr. Lucy Jones said Thursday.

Interfaces of ShakeAlertLA app are seen in a screenshot taken from the Apple's App Store on Jan. 3, 2019.

Interfaces of ShakeAlertLA app are seen in a screenshot taken from the Apple's App Store on Jan. 3, 2019.

“The app performed as designed, it’s just that the intensity levels were below that threshold that had been set by the app," USGS seismologist Rob Graves said. "It’s something that we look into, though, as to whether that threshold should be adjusted for the future."

The public does not have access to information that is available to scientists, who also continue to refine the smart phone application, the Times reported.

ShakeAlert, which rolled out on the West Coast last fall, is run by the U.S. Geological Survey and is available in Oregon and Washington.

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