How Cal Poly Humboldt researchers are turning internet cables into earthquake sensors

Cal Poly Humboldt geology students conduct a “tap test” using a sledgehammer to create ground vibrations that travel through the buried fiber-optic cable beneath. The vibrations are captured by a nearby seismometer-like sensor. (Cal Poly Humboldt ) Every day, thousands of miles of fiber-optic cable carry internet traffic beneath California's roads. Researchers say those same cables could also become one of the state's newest tools for detecting earthquakes. Scientists at Cal Poly Humboldt are helping develop a system that turns unused strands inside existing fiber-optic cables into a network of earthquake sensors. The project, a collaboration with the U.S. Geological Survey and Vero Networks, aims to improve earthquake monitoring along one of the most active seismic regions in North America while creating new research opportunities for students. Humboldt County sits atop what Eric Riggs, dean of the College of Natural Resources and Sciences at Cal Poly Humboldt, calls a natural earthquake laboratory. The region lies just north of where the San Andreas Fault and the Cascadia Subduction Zone meet. Riggs is co-leading a research project that uses fiber-optic internet cables to monitor earthquakes. Researchers use unused, or "dark," strands within existing fiber-optic cables. Laser-based instruments send light through the fibers and detect tiny vibrations created as earthquake waves stretch and compress the glass. Unlike traditional seismometers, which measure shaking at a single location, the cables measure movement along their entire length. "They become essentially a line kind of sensor rather than a traditional seismic monitoring station seismometer," Riggs said. Riggs said that allows scientists to track earthquake signals along the length of a cable, giving researchers new information about how the ground responds during earthquakes and helping them better understand the shape and structure of faults. The project also uses fiber installed through California's middle-mile broadband expansion. Riggs said the work creates new research opportunities for Cal Poly Humboldt students through the university's participation in California's Statewide Earthquake Coalition. "Being formally involved in this network is exciting because it will continue to open additional opportunities, especially on the geophysical side of things for our students," Riggs said. The project is entering its second year. Researchers are working to improve data processing with the long-term goal of supporting operational earthquake warning systems. Riggs said communities have shown strong interest in the approach because fiber-optic infrastructure is already widely installed. "It’s been recognized by the community as one of the higher priorities, especially as this infrastructure is installed virtually everywhere." Guest • Eric Riggs, Ph.D., Dean, College of Natural Resources and Sciences at Cal Poly Humboldt University