01:26 - Source: CNN
Witness experiences aftershock during CNN interview
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People in Los Angeles are once again wondering why their phones didn’t warn them before the ground started shaking.

An earthquake quake detection app released by the city of Los Angeles earlier this year did not alert its users when two large earthquakes struck near the desert town of Ridgecrest this week.

The ShakeAlertLA app, which is connected to the US Geological Survey’s network of early warning sensors, is set to alert cellphone users when the system senses an earthquake of magnitude 5.0 or greater, or with potentially damaging shaking, within Los Angeles County.

While both quakes were greater than magnitude 5 in Kern County, it appears that the shaking in Los Angeles was below 4.5.

Following the Fourth of July quake, officials pledged to make changes to the app but noted that it was not a failure.

“The system actually worked as designed,” Rob Graves, a seismologist at the US Geological Survey, told reporters.

After receiving questions from residents about the lack of push alerts from the app, the city of Los Angeles said officials will be making adjustments.

“We hear you and will lower the alert threshold with @USGS_ShakeAlert,” the city tweeted Thursday.

On Friday, the Los Angeles City Emergency Management Department tweeted a reference to the city’s previous tweet.

“If you’re wondering why your Shake Alert app didn’t go off… #ShakeAlertLA #WeHearYouLA,” the agency wrote.

Jeanne Holm, senior technology adviser to Mayor Eric Garcetti, told the Los Angeles Times that officials expect the app will be updated by the end of the month.

Earlier this year, residents downloaded the app hoping it would give them a heads-up before a big quake hits. USGS said the warnings could go out seconds, or even tens of seconds, before people start to feel the shaking.

The alert would read “Earthquake! Earthquake! Expect strong shaking. Drop, cover and hold on. Protect yourself now!”

Los Angeles was the first US city to make the app available to the public, but the US Geological Survey has said it plans to deliver it to the entire West Coast once the pilot project is completed.

The app is a collaboration between Los Angeles, the US Geological Survey, the Annenberg Foundation and AT&T, CNN’s parent company. It’s available in English and Spanish in the Apple and Google Play stores.

CNN’s David Williams contributed to this report.