Ground motions readings used by ShakeAlert come from broadband and strong-motion seismic sensors operated by the California Integrated Seismic Network (CISN) in California and the Pacific Northwest Seismic Network (PNSN) in Washington and Oregon. Additional stations operated by partner organizations also contribute to the system.
The optimal number and distribution of sensors needed to maximize warning time has not yet been achieved, and more stations are needed. The goal is to operate a network of seismic stations that are spaced 20 km apart in high-risk areas and within 5 km of all mapped fault traces. Even denser station spacing of about 10 km is planned to maximize the warning time in more densely populated areas.
Real-time, continuous data from approximately 760 seismic stations are currently contributing to the ShakeAlert. About 540 of the current stations are in California (CISN) and 220 are in the Pacific Northwest (PNSN). The final density of 1,675 stations will be accomplished by updating older existing stations and adding new stations.
West Coast ANSS stations contributing to ShakeAlert as of Aug. 2016.