UCB had installed sensors in LA area. When Earthquake occurs these sensors reports datacollection center and based on sufficient data, algorithm predicts that whether this is earthquake or not based on result sends information to app.
There is another app which is local to each mobile and do second level of algorithm run based on initial Algorithm run and tells approx rector info.
Univ of Santa Cruz is also doing similar type based on their set of installed sensor.
Results are promising, they are still tuning algorithm.
Basically, it gives few secs advanced warning, sufficient to avoid lift or come out of car.