Los Alamos National Laboratory (LANL) researchers have advanced a new Earthquake detection method after underwater fiber optic cables in Alaska detected detonations from a construction project on land.
The Alaskan port city of Cordova had scheduled controlled demolitions to make way for an oil spill response facility and a new road, relatively close to the submerged cables. A team of scientists led by Loïc Viens launched LANL’s Distributed Acoustic Sensing (DAS) project, attempting to detect the explosions using a 50-kilometer stretch of fiber optic cable owned by Cordova Telecom Cooperative, which runs between Cordova and Valdez.
Distributed Acoustic Sensing
The team applied the DAS technique, transforming existing fiber optic infrastructure into a dense network of seismic sensors. This method uses microscopic imperfections within the optical fiber as detection points. A device known as an “interrogator” emits laser pulses down the cable; when these pulses encounter flaws in the fiber, they scatter and return to the source.
Even faint seismic waves can subtly shift the way the fiber optic cable lies, affecting which imperfections the pulses strike before being reflected. These changes, recorded over time, reveal seismic activity through Rayleigh backscattering. Researchers analyze the reflected signals’ amplitude, frequency, and arrival time to determine the nature of the detected events.
“We applied deep-learning algorithms to detect earthquakes as well as approximately 50 blasts associated with the road construction project,” said Viens. “These explosions generated seismic wavefields distinct from typical earthquake signals recorded along the fiber.”
Wave Field Signal Detection
Acoustic and seismic energy from explosions travels through wave fields, offering clues about the origin and size of the blasts based on how they interact with imperfections in the cable. As scientists refine the technique, they’re becoming better able to distinguish between different types of seismic events by analyzing these unique backscattering signatures.
“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,” Viens added.
The research also provided insight into the precision limits of current DAS methods. Smaller explosions were more difficult to detect, registering only at the closest points along the fiber, roughly 5 to 10 kilometers away. In contrast, larger blasts were more easily resolved, registering along the entire 50-kilometer section of cable used in the project.
Finding New Sensors in Existing Technology
Despite the challenges of detecting lower-intensity signals, Viens emphasized the broad potential of DAS as a “powerful solution for monitoring offshore regions where deploying real-time seafloor seismometers is logistically challenging and prohibitively expensive.”
Traditional seismic sensors only cover single points and require dedicated infrastructure. DAS, by contrast, repurposes existing fiber optic cables to create long-distance, real-time monitoring systems. The technique can warn early about natural and man-made events, from earthquakes and volcanic eruptions to pipeline ruptures and gas leaks. With cables already in place and spanning vast distances, DAS enables wide-area, continuous monitoring at a fraction of the cost.
The new research was presented by Brent Delbridge at the Seismological Society of America’s annual meeting held April 14-18, 2024 in Baltimore, Maryland.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.
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