Shake Alert app: The reason why some didn't receive the alert

Did you receive a shake alert notification this morning about the 6.4 earthquake? If not then you're not alone.

According to the City of L.A. those in the Los Angeles area didn't receive a notification because the shaking was below 4.5. The app only sends alerts if shaking is over 5.0 in L.A County.

Related: L.A. County earthquake early warning mobile app available for download

Following the quake several people took to Twitter to express their frustration and concern about not getting a notification. In a post online the City said "we hear you and will lower the alert threshold".

Seismologist Lucy Jones of Caltech says the shake alert computer system at Caltech's seismic facility registered a 48-second warning that shaking had begun.

Several aftershocks in the magnitude-3 range were reported by the USGS, as expected following a substantial quake. Jones said there was a better than 50-percent chance of a larger aftershock in the magnitude-5 area sometime this afternoon.