Since 1967 the U.S. Geological Survey has operated the Northern California Seismic Network (NCSN) to provide earthquake data for a wide range of research topics and hazard-reduction activities. The NCSN is designed to detect all local earthquakes having signal strength above the background level of microseisms. The network configuration was motivated by the need to monitor active faults and volcanoes with a station density sufficient to determine the focal depth of shallow (0-15 km) crustal earthquakes. Depending on the concentration of stations in a region, the magnitude (M) level at which earthquake detection is complete varies from approximately 1.0 in parts of the central Coast Ranges to 2.6 in the Klamath Mountain range. However, earthquakes with M<1.0 are routinely detected throughout the network.
The NCSN operates 580 stations in northern and central California and records an additional 159 stations maintained by the Southern California Seismic Network, Pacific Gas & Electric, the University of Nevada Reno, the California Department of Water Resources, Calpine/LBNL, and the California Geological Survey. It records a total of 1850 channels of data using a mix of digital and analog systems. Nearly 60% of the stations in the network are now digital, and 24 of the digital stations have broadband sensors, 333 have strong-motion sensors, and 10 are borehole installations. The remainder of the stations are mostly comprised of short-period vertical-component sensors. The NCSN telemetry system utilizes local collection nodes which are linked to Menlo Park via a microwave system between Geyser Peak above Geyserville and Black Mountain near San Luis Obispo, satellite telemetry, and leased digital circuits. The network also utilizes direct radio telemetry to Menlo Park, cellular data services, and operates an extensive LAN that links urban stations located in the San Francisco Bay region.
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