Cal OES works collaboratively with all system partners and uses the workgroup as a forum to exchange ideas, coordinate resources, set system priorities, inform decision-making, integrate new innovations, and expand and strengthen California Integrated Seismic Network (CISN) capabilities to support a full public alert and warning system rollout. The CISN collects ground motion data from seismic stations throughout California to rapidly and automatically process this data and produce information about earthquakes occurring. CISN provides this information to the State of California, emergency managers and responders, and to the public and the organization archives the data for use in event review and by scientists and engineers. To learn more about CISN, visit the California Integrated Seismic Network website.
Seismic sensor set-ups may vary based on the landscape, geological features, telemetry capabilities, and contracted partners’ equipment experience.
Seismic Sensor – all cases in accelerometers (that measure larger ground motion) and some cases include a seismometer (that are more sensitive but cut off larger ground motion).
Data logging collector and storage unit.
Power system (which may include solar panels).
Telemetry equipment to transmit data to the CISN processing centers.
The current capability of EEW, which includes 536 stations, is primarily limited to the Los Angeles and San Francisco Bay areas. To complete the EEW network, 579 seismic stations need to be installed or upgraded to ensure as many people as possible are alerted prior to strong shaking. Of the remaining stations, 434 will be installed in Northern California and 145 in Southern California.
The vision for the earthquake early warning system in California was articulated in the May 2016 California Earthquake Early Warning System Project Implementation Framework (the Framework). The framework set a target of 1,115 seismic sensors state wide to achieve the optimum sensor density spacing for earthquake early warning. To maximize warning time and minimize the “delayed notification zone” (the area close to the earthquake epicenter that will likely receive a notification after shaking occurred), stations must be located near active faults. The current goal is to operate a network of seismic stations that are spaced no more than 20-km apart and within 5-km of all mapped fault traces. However, experience tells us that damaging earthquakes can occur even where faults have not been mapped (e.g., 1994 Northridge earthquake); therefore, 20-km spacing or closer is also needed throughout all high-risk areas. A denser station spacing of about 10-km is needed to minimize the delayed notification zone in more densely populated areas.