17 April 2025—Researchers from Los Alamos National Laboratory have been collecting seismic data from a submarine telecommunications fiber optic cable in coastal Alaska, exploring how the cable could be used to detect signals from earthquakes, ocean currents and marine mammals.
Then the researchers learned about construction on an oil spill response facility and road in the nearby town of Cordova that would include a series of controlled explosions. Could the underwater cable detect those blasts as well?
At the Seismological Society of America’s Annual Meeting, LANL scientist Brent Delbridge described what the research team has learned during the distributed acoustic sensing project, which involves a 50-kilometer segment of telecommunications fiber optic cable that is owned by Cordova Telecom Cooperative and runs offshore between Cordova and Valdez.
Distributed acoustic sensing, or DAS, uses the tiny internal flaws in a long optical fiber as thousands of seismic sensors. An interrogator at one end of the fiber sends laser pulses down the cable that are reflected off the fiber flaws and bounced back to the instrument. When the fiber is disturbed by seismic activity, researchers can examine changes in the reflected pulses to learn more about the resulting seismic waves.
“We applied deep-learning algorithms to detect earthquakes as well as approximately 50 blasts associated with the road construction project,” said Loïc Viens, a LANL research scientist who leads the project. “These explosions generated seismic wavefields distinct from typical earthquake signals recorded along the fiber.”
The explosion wavefields include both seismic and acoustic energy. The researchers’ analysis allowed them to locate the blast sources and estimate the size of the explosions, said Viens. “We are collaborating with the blasting company to obtain ground-truth measurements, which will help us better understand how factors like firing mechanisms and burial depth influence the recorded signals.”
The smaller explosions were only detectable at the closest point on the fiber, about 5 to 10 kilometers away. But the researchers note that larger blasts were recorded across the entire section of fiber included in the project.
DAS could offer a “powerful solution for monitoring offshore regions where deploying real-time seafloor seismometers is logistically challenging and prohibitively expensive,” Viens said.
Using existing fiber optic cables, he noted, an offshore DAS system could detect underwater explosions from gas leaks and pipeline breaks, as well as detect signals from submarine earthquakes, volcanic eruptions and landslides.