A new seismic monitoring station in Nicasio received approval from the county last week, part of an effort by the United States Geological Survey to fill the gaps in its expanding earthquake early warning system. Once the station is built later this summer, West Marin residents will be alerted more quickly if a quake hits the area. 

The station will be part of ShakeAlert, a warning system developed by U.S.G.S. and a coalition of institutions and agencies. The system, which came online in 2019 and is still being built out, can deliver smartphone alerts to those nearby a few seconds before they feel the shaking from an earthquake. 

“This new station is one of literally hundreds of new stations that we’re building across the state,” said Richard Allen, the director of the University of California, Berkeley Seismology Lab, one of the primary institutions involved in the project. “We’re completing the network.” 

To generate reliable and quick alerts, the seismologists behind the early warning system want to create a web of seismic monitoring across urban areas in California with roughly 10-kilometer spacing between instruments. Currently there are still a few holes in the web, and Nicasio is one of them. 

For an earthquake to generate an alert in the system, four separate stations need to detect the shaking. Seismologists say it’s particularly important to have an even distribution of these stations because there are unknown and unmapped faults around Northern California. When multiple sensors detect an earthquake deep underground, the system can send out an alert within seconds, giving people a short but vital window of time to respond. 

“The Bay Area is crisscrossed with faults, and Nicasio is only about 9 or 10 kilometers off the San Andreas fault,” said Dave Croker, a U.S.G.S. seismologist with the Northern California Seismic Network. “If we get nice, even coverage of our stations, we’re covered no matter what fault an earthquake might happen on.” 

Last Tuesday, the Board of Supervisors signed off on a site access agreement between the county and U.S.G.S. for the county’s Department of Public Works Corporation Yard in Nicasio. On Friday, the county issued a permit. 

Though many seismic monitoring stations exist on private land, Mr. Croker said it’s helpful that the Nicasio station will be on a county-owned property, because it’s unlikely to change hands in the future. 

The station’s footprint is relatively small, at roughly 5 feet by 35 feet. One partially buried box holds two seismic sensors, each of which is designed to register different intensities. A second box holds batteries and radio equipment, and sits under a 9-foot mast with a solar panel and antenna for transmitting data 24/7 to a U.S.G.S. office in Menlo Park. 

Similar sensors exist at the Bear Valley Visitor Center and the Point Reyes Lighthouse, at the Marconi Conference Center in Marshall, and on private properties in Hicks Valley and Bolinas. The U.S.G.S. is preparing to build another station at the historic KPH Maritime Radio Receiving Station in Point Reyes National Seashore next month, and has identified the Tomales Elementary School campus as another potential site to fill a gap in the network. 

“It’s a big push to get a bit more coverage,” Mr. Croker said, “and it’s really needed for somewhere like the Bay Area.” 


You can download the free MyShake app on the App Store and Google Play to receive earthquake early warning alerts from the ShakeAlert system. Android phones automatically deliver earthquake alerts.