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Telecom Fiber-Optic Cables Captured a Magnitude-7 Quake in Unprecedented Detail

04:50 AM, 12/06/2025
Telecom Fiber-Optic Cables Captured a Magnitude-7 Quake in Unprecedented Detail

Researchers used about 15 km of telecom fiber near Mendocino, California, to record a magnitude-7 earthquake on December 5, 2024, with exceptional spatial detail. By attaching an interrogator to an unused fiber, the cable acted like ~2,800 mini seismometers, mapping how the rupture slowed near a three-plate junction and then accelerated into a supershear phase. The result shows fiber sensing can augment early-warning systems and monitor remote or harsh environments such as Antarctica.

Telecom Fiber-Optic Cables Captured a Magnitude-7 Quake in Unprecedented Detail

The same fiber-optic lines that carry much of the world’s Internet traffic also make excellent sensors for the planet’s movements. In a recent Science paper, researchers used roughly 15 kilometers of telecom fiber near Mendocino, California, to record a magnitude-7 earthquake on December 5, 2024, with extraordinary resolution.

By connecting an "interrogator"—a device that sends laser pulses down an unused fiber—to a coastal telephone cable, the team turned tiny imperfections in the glass into a dense array of sensors. Each imperfection reflected light back every few meters, effectively transforming the cable into about 2,800 mini seismometers that measured ground motion along the line.

“What’s noise to telecommunications is data to us,” says Zhongwen Zhan, a geophysicist at Caltech who was not involved in the study.

The fiber data revealed a detailed portrait of the rupture: it propagated eastward, slowed near a complex junction where three tectonic plates meet, and then accelerated into a "supershear" phase—moving faster than the speed of sound in the surrounding rock and producing a sonic-boom–like signal. The authors call this one of the clearest demonstrations of how fault complexity can trigger supershear rupture.

Traditional seismometer networks would likely have needed a much larger earthquake occurring directly above the instruments to produce comparable spatial detail. Because fiber lines are long, commercially widespread, and already buried along coasts, this approach could meaningfully strengthen earthquake early-warning systems—especially for offshore ruptures and tsunami-prone regions.

Experts also highlight additional uses: specially installed or repurposed fibers could monitor glacial motion and changing terrain in remote environments such as Antarctica, where installing many traditional sensors is difficult.

Why This Matters

  • Fiber-optic sensing offers high spatial resolution along the cable length, filling gaps between conventional seismic stations.
  • The method leverages existing infrastructure and can be deployed on unused fibers or new cables.
  • Improved rupture imaging can refine models of earthquake dynamics and enhance early-warning capability for coastal communities.

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