The real-time continuous ground motion measurements 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 many partner organizations also contribute to the system.
To maximize the system’s effectiveness the goal is to build and 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.
This optimal distribution of sensors has not yet been achieved and more stations are needed. Data from approximately 710 seismic stations are currently contributing to the ShakeAlert. About 530 of the current stations are in California (CISN) and 180 are in the Pacific Northwest (PNSN). The planned density of 1,675 stations will be accomplished, as funding allows, by updating older existing stations and adding new stations. In addition, some currently contributing stations need to be upgraded to reduce data latency or relocated to reduce spurious signals due to cultural noise.
ShakeAlert seismic stations (9/2016).