Lab seismologist Gene Ichinose examines an interrogator, a device that transforms buried fiber-optic cables into thousands of virtual seismometers capable of detecting ground motion in Earth and nearby structures. [Photo by Blaise Douros]
Using an “interrogator” device to activate 50 miles of dormant fiber-optic cable, Lawrence Livermore National Laboratory seismologists created a network of 8,000 virtual sensors, recording March’s 3.9 magnitude Dublin earthquake with unprecedented detail, achieving 1,000 times the observational density of current seismic networks.
“The detail of the seismic wave field was unprecedented,” said Lab seismologist Gene Ichinose.
This high-resolution monitoring was possible because each meter of the glass fiber essentially acted as a tiny sensor, a strain gauge detecting minute stretches and compressions in the ground. The team could then sample ground motion every 10 meters at sub-millisecond intervals, allowing them to distinguish even the faintest vibrations, ranging from even passing traffic to the types of shockwaves (known as P- and S-waves) that the earthquake generated. Ichinose added that the technology enabled the researchers to track the seismic wave from the earthquake “propagating across the whole Bay Area.”
The shoebox-sized interrogator unit, costing around $160,000 (comparable to just eight to sixteen traditional seismometers), collected a full month of this street-level data.
Next up, LLNL scientists are analyzing this information to improve Bay Area earthquake hazard maps and to assess if such dense fiber networks could provide real-time earthquake warnings.
Distributed acoustic sensing is not new. Oil-and-gas outfits first field-tested the technology roughly 15 years ago, using it to monitor drilling and fracking operations. But Ichinose says urban telecom corridors may prove the sweeter spot: “People are excited about this research opportunity because there is plenty of fiber-optic cable laid all over the Bay Area and everywhere,” he said.
The technology’s applications expand beyond traditional seismology. In September 2023, researchers from Los Alamos National Laboratory demonstrated DAS’s versatility when they used 12 kilometers of fiber-optic cables to detect acoustic waves from NASA’s OSIRIS-REx spacecraft as it streaked through Earth’s atmosphere. That marked the first time the technology found use to record a space capsule reentry. The team managed to capture the spacecraft’s sonic boom as it propagated across the Nevada desert. That research, described in IEEE Spectrum, suggests that researchers could repurpose existing telecom networks to study meteors and other atmospheric phenomena.
Meanwhile, ocean scientists are taking DAS underwater: in January 2025, researchers at the Monterey Bay Aquarium Research Institute deployed their “Geo-Sense” system on the floor of Monterey Canyon, using a one-kilometer fiber-optic cable to monitor sediment transport, underwater landslides, and fluid seepage.
