It sent the warning Tuesday because the initial
reading was magnitude 4.8.
The quake was centered in the rural Cholame
Valley. It was felt in the city of Paso Robles more
than 20 miles (32 kilometers) away but shaking
there was very mild.
The app is expected to be most effective for areas
some distance from the epicenter where the
warning can be received before strong shaking
arrives and protective actions can be taken.
A similar app called ShakeAlertLA was
developed for the city of Los Angeles and
released about a year ago.