California's new earthquake early warning cellphone app issued its first public alert when a modest tremor occurred this week in a rural area of the state.
The Los Angeles Times says the MyShake app was triggered by a 4.3 quake Tuesday in mountains between the central coast and the San Joaquin Valley.
MyShake app project manager Jennifer Strauss says more than 40 people received the warning.
The app was developed by the University of California, Berkeley, and released in October.
One of its thresholds is magnitude 4.5. The earthquake initially registered 4.8 before being calculated at a lower magnitude.