at 2:14 am NPR Residents living on the West Coast don't know when the next earthquake will hit. But a new expansion of the U.S. earthquake early warning system gives 50 million people in California, Oregon â and now Washington â seconds to quickly get to safety whenever the next one hits. As of 8 a.m. Tuesday, cellphone users in California, Oregon and Washington should receive a mobile alert from the ShakeAlert earthquake early warning system when tremors are detected. Alerts are sent from the Federal Emergency Management Agency's Wireless Emergency Alert system, third-party phone apps and other technologies. The West Coast, the most earthquake-prone region in the U.S., is home to major fault lines that put the area at risk of devastating earthquakes.