Fiber Optic Lines Could Give Humboldt County an Earthquake Early Warning Edge

A magnitude 5.6 earthquake rattled Mendocino County on the morning of June 24, centered about seven miles north of Redwood Valley near Willits. It knocked out power to about 10,000 PG&E customers at its peak and cracked walls and knocked pictures off shelves in Redwood Valley and Ukiah. Shaking was felt as far away as Sacramento and southern Oregon.

There’s no predicting an earthquake before it strikes. But the warning that comes after the first shock waves start moving, the kind that buzzes phones seconds before shaking arrives, depends on speed. It takes California’s earthquake alert system, ShakeAlert, about five seconds to process a signal from a seismometer, estimate the earthquake’s size, and send out an alert. For people near the epicenter, that’s often too slow. The shaking on June 24 hit Ukiah before any alert could go out. Farther away, in Humboldt County, phones buzzed with a few seconds of notice before the shaking reached here.

That five second lag is exactly what a team at Cal Poly Humboldt is trying to shrink. For years, researchers there have been testing whether fiber optic cables built for rural broadband, stretching across Humboldt County and into Trinity County, can also work as an earthquake detection network, one dense enough to pick up shaking faster and process it quicker, even for communities close to where a quake starts.

No technology can erase the head start an earthquake gets on the ground closest to it, said Dr. Eric Riggs, Dean of the College of Natural Resources and Sciences at Cal Poly Humboldt. But a denser, faster network could shave time off how long it takes to detect and confirm a quake is happening in the first place, potentially stretching the warning window even for people nearby. “We’re farther away, and so the speed of light that those network notifications can travel at is much faster than the speed of seismic waves,” Riggs said, describing why Humboldt got a few seconds of notice on June 24 while Ukiah got none.

“If you can increase warning time for a large earthquake, even just a handful of seconds, that does give you enough time to shut off power, gas and electricity if necessary to critical systems, and that saves lives,” Riggs said.

Turning internet lines into earthquake sensors

The fiber optic detection project is led by the U.S. Geological Survey, Cal Poly Humboldt, and Vero Fiber Network, with help from state and local partners. The cables themselves are part of California’s Middle Mile broadband expansion, a state program built to bring modern internet service to rural communities. Humboldt County ended up with a bonus: buried glass fiber that can double as a seismic sensor.

Riggs said the fiber lines were never meant to detect earthquakes. They were built to carry internet traffic. But hook a laser and a detector up to an unused strand of fiber, and scientists can measure the cable’s exact length using light. “The wonderful thing about that is lasers are quite sensitive to changes in distance,” Riggs said. As an earthquake wave passes through the ground, the cable stretches and flexes just enough to change that measurement, and scientists can use the shift to track the wave as it moves.

“You actually get to track the entire wave as it’s moving along through its course, and so you can tell an awful lot about the source of what moved to make the earthquake,” Riggs said.

Cal Poly Humboldt students spent an afternoon last August in Arcata testing if the system worked by taking turns swinging a sledgehammer against a steel plate bolted to the ground. They struck it every five seconds, spaced out so the signal would stand apart from passing cars and other noise. Half a mile away, in a campus lab, scientists watched a machine called a Distributed Acoustic Sensing interrogator to see if the taps showed up. That interrogator is sensitive enough to pick up earthquakes as small as magnitude 1.

The technology has already been tested on a larger scale, too. Three years ago, Cal Poly Humboldt and the USGS ran a pilot study on a short fiber line between Arcata and Eureka, laying traditional seismometers alongside it to compare results. Riggs said the approach has already proven itself during real earthquakes. “Early results with other earthquakes in the region, including the one that hit Rio Dell a couple years ago, generated very clear, amazing signals, and we learned a lot about the seismic response of this entire area,” Riggs said. The network has since grown, now stretching from the Samoa Peninsula to Willow Creek, with plans to reach Trinidad soon.

Cal Poly Humboldt isn’t working alone, and it isn’t the only place testing the idea. Riggs said similar fiber optic earthquake tests have already run in scientific settings in a handful of spots up and down the West Coast, and Cal Poly Humboldt is now coordinating with the University of Washington and other Cascadia focused institutions in Oregon and Washington to study the subduction zone as a whole.

What sets the Humboldt project apart, Riggs said, is scale. Rather than testing a short, isolated stretch of research fiber, the university is working to become a hub that links fiber lines from multiple partners into one connected testbed, pulling in data from real, working broadband infrastructure instead of a lab setup. Cal Poly Humboldt is also bringing in young scientists from Berkeley, Caltech and Stanford to help analyze what comes out of it.

The same glass fiber bringing Netflix, TikTok, and everyday internet service to rural households could, one day, also double as an early warning system for the ground shaking beneath them.

A complicated, active corner of California

Humboldt County sits near the Mendocino Triple Junction, where three tectonic plates meet, making it one of the most seismically active spots in the continental United States. Riggs described the underlying geology as “very complex,” with a lot of moving parts researchers can’t see because they’re underground. He pointed to the 2022 Rio Dell earthquake as an example of how that complexity plays out on the surface. “It really just threw a whole bunch of energy right up the river valley and into a very confined space with a soft sediment floor that the city is built on, and that is a much greater recipe for damage and disaster,” Riggs said.

That complexity was on full display again earlier this summer when a research team led by the California Geological Survey’s Jay Patton and Cal Poly Humboldt professor emeritus Mark Hemphill-Haley confirmed a previously unknown fault running through Shively south of Rio Dell, as Emeritus Professor of Geology and Times-Standard columnist Lori Dengler reported. The fault had gone unnoticed until researchers compared Caltrans road surveys taken 20 years apart and spotted an odd bump in the ground. A trench dug into the site turned up evidence of at least four past earthquakes.

Discoveries like that show how much is still unknown about the faults running beneath Humboldt County, and why researchers see value in a denser network of sensors. A fiber optic system that runs for miles, rather than sitting at a single point, can help track exactly how an earthquake’s energy moves through the ground and give scientists a clearer picture of which faults are active and which ones are static, building up stress.

Looking toward the ocean

The bigger long-term goal is extending the fiber network offshore, toward the Cascadia Subduction Zone, the fault capable of producing both a massive earthquake and a tsunami. Riggs said the university has a cable landing facility that could support that kind of expansion if funding comes through. “If the Cascadia Subduction Zone decides to start moving, we’ll know about it with some time to hunker down and lock down critical systems,” Riggs said.

Riggs also cautioned that better data could mean more precise warnings, not just louder ones. He pointed to a tsunami warning issued roughly a year ago that prompted a large evacuation for a threat that never fully materialized. “We had a tsunami warning that ended up trying to evacuate way too many people,” Riggs said.

The project is still considered experimental. Cal Poly Humboldt is partway through a three-year testing period with the USGS. “The earthquake science community in California is shockingly very mature, and as a regional center for this kind of science, it’s fantastic for us to be part of these partnerships,” Riggs said. He estimated it could take about a decade before the technology is reliable enough to become part of an operational warning system.

For Riggs, the value of the research goes beyond any single building or alert. What began as an internet upgrade for rural Humboldt County is turning into something closer to a listening device for the earth itself. “It’s almost an optical observing platform, a telescope of sorts,” Riggs said, “looking into the earth as earthquake signals travel.”

 

Earlier:

• [Update: 7400 Without Power] 5.6 Earthquake Rattles Mendocino County; Power Lines Down in Willits, CalFire Assessing Damage
• Geology Expert: Mendocino Quake No Surprise; Aftershocks Expected
• (Video) Broken Glass, Burst Water Heaters, Empty Shelves: Mendocino County Picks Up the Pieces After Morning Quake