- A 6.4-magnitude earthquake shook Southern California on July 4, affecting its epicenter in Ridgecrest, CA and surrounding cities including Los Angeles.
- ShakeAlertLA, the earthquake alert app released by the city of Los Angeles in the beginning of 2019, did not alert residents of the quake, according to reports on Twitter and other social media. This earthquake was the area's first since the release of the app.
- Doug Given with the U.S. Geological Survey (USGS), which developed the app, told the Los Angeles Times that the shaking in Los Angeles wasn't significant enough to trigger the warnings — despite many residents having felt the tremors.
ShakeAlertLA was designed with resiliency in mind, outlined in Mayor Eric Garcetti's Resilient Los Angeles plan released in March 2018. Despite excitement and awareness of the app, its first true test proved underwhelming.
The 6.4-magnitude earthquake sent a number of aftershocks throughout the area, including a 7.1-magnitude quake on the evening of July 5. Though the ShakeAlert app only works if shaking is considered a level 4 intensity or higher on the Modified Mercalli Intensity Scale, which was not the case for the shocks that reached Los Angeles.
So it seems the only one who *didn't* feel the earthquake was that Shake Alert LA app I installed to my phone for just this one and only purpose. Cool.— Alan Denton (@AlanTheWriter) July 4, 2019
Some Twitter users also mistakenly assumed the app was intended to send an alert before an earthquake started, however the city and USGS have made it clear that ShakeAlertLA is not a predictive application; it's designed to send an alert after an earthquake has already started. Once alerts are received, users are encouraged to take immediate action.
This test of ShakeAlertLA indicates more user education and preparedness is necessary before the next earthquake. USGS told The Verge that the confused response to the lack of ShakeAlert notifications is "excellent feedback" for future improvements of the app. In a tweet on July 4, the City of Los Angeles responded to concerns and said the alert threshold will be lowered.
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