this morning's earthquake? >> most come without very much warning. at least with the currents understanding of how they work. even the largest ones will often come out of really nowhere in terms of a short-term precursor. we know which areas of faults are active. we know that they have probabilities of earthquakes occurring. but we don't always know when the earthquakes are imminent. >> there's a shake alert l.a. app. apparently some people in los angeles residents are wondering if the app actually failed. we're going to listen now and go back to dr. lucy jones with cal tech. let's listen. >> we're just getting an update about this morning's earthquake. searles valley earthquake, near ridgecrest.