ShakeAlert—Earthquake Early Warning. How does it work?

ShakeAlert (www.shakealert.org) is an experimental earthquake early warning system (EEW) for the West Coast of the United States and the Pacific Northwest. ShakeAlert is a product of the US Geological Survey and its partners including the California Institute of Technology, University of California, Berkeley, University of Oregon, University of Washington, Eidgenössische Technische Hochschule Zürich (ETH), California Office of Emergency Services, and California Geological Survey.

This animation, produced by IRIS in collaboration with University of California, Berkeley, describes how the system uses sensors to detect P and S waves to determine earthquake location and magnitude, and how that information can be sent to ShakeAlert users to give time to Drop, Cover and Hold On.
For more earth-science animations:
http://www.iris.edu/hq/inclass/search/animation