This diagram shows how such an earthquake early warning system would operate. When an earthquake occurs, both compressional (P) waves and transverse (S) waves radiate outward from the epicenter. The P wave, which travels fastest, trips sensors placed in the landscape, transmitting data to a ShakeAlert processing center where the location, size, and estimated shaking of the earthquake are determined. If the earthquake meets certain criteria, a message is issued by the USGS, which is picked up by partner organizations that produce alerts. Credit: USGS image created by Erin Burkett (USGS) and Jeff Goertzen (Orange County Register) and updated by Robert de Groot (USGS), public domain