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Earthquake sensors at Farallon Islands upgraded as part of ShakeAlert network improvements

Magnitude 4.1 earthquake in Delta triggers ShakeAlert warning
Magnitude 4.1 earthquake in Delta triggers ShakeAlert warning 01:05

A seismic sensor station on the remote Farallon Islands off the coast of San Francisco was upgraded with new sensors in January and February, according to an announcement from the University of California, Berkeley Seismological Laboratory.

The sensors are part of a greater network that is being upgraded with funding from the state and the U.S. Geological Survey and will help complete a seismic detection network covering the entire Pacific coast.

Known as "ShakeAlert," the network utilizes 1,675 sensors from UC Berkeley, USGS, the California Institute of Technology, the University of Washington, and the University of Oregon. The digital seismic network feeds data to the publicly available MyShake app, designed to be an early warning system for imminent earthquakes.

Berkeley Seismology Lab director Richard Allen said the station on Southeast Farallon Island, 28 miles off the coast, was among the first sensors the university deployed in 1994 as it built up the Berkeley Digital Seismic Network project.

The Farallon Islands station is one of only a few stations in Northern California that is west of the San Andreas Fault, making it a critical component to detecting and studying the area's seismology, Allen said.

"It's been upgraded a couple of times since, but this is our opportunity to really turn this into a state-of-the-art site where we have much lower noise levels and we can really detect all earthquakes that are occurring in the region," Allen said.

The mission to upgrade the sensor station involved seven round-trip flights from Half Moon Bay Airport to transport all the needed equipment, which cost about $90,000 more than replacing a station on the mainland, according to the university.

Seven engineers helicoptered onto the island for eight days to perform the work. They discovered that the outdated equipment was dusty, rusty, and damaged from wind, mice, and birds such as ashy storm petrels.

The team installed two types of devices called accelerometers, which measure the ground's acceleration. One is known as a strong motion sensor, which measures strong ground shaking, and the other is called a broadband seismometer which can detect smaller quakes.

Instead of being protected by wooden boards glued together, like the old sensors, the new ones were bolted to cement foundations and placed inside aluminum cylinders that were packed with glass beads for protection, then the entire sensor was placed in a stainless-steel box that was bolted to rocks.

The seismology lab's field operations manager Jonah Merritt said detailed planning helped make the mission a success, despite the challenges involved.

"Things went shockingly well," Merritt said. "This was the most involved project we have ever pulled off, honestly."  

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