Underground telecom fiber-optic cables can be repurposed as geohazard sensors according to research

Researchers at Penn State University have shown that fiber-optic cables,  already installed underground for telecommunications,  can be repurposed as an early warning system for geohazards such as sinkholes. The study, led by geophysicist Tieyuan Zhu, used a four-mile stretch of fiber running beneath the University Park campus.

The team connected a distributed acoustic sensing (DAS) interrogator to the fiber. This device sends laser pulses through the cable and reads the backscattered signals caused by ground vibrations. In their trial, the researchers detected a low-density zone beneath the campus—an anomaly that could indicate a developing sinkhole. Campus geologic maps confirmed the area sits on karst terrain (limestone and dolomite). Facilities staff concluded the site was stable, but the test validated that the method could highlight anomalies of concern.

Unlike traditional geophones, which measure vibrations only at discrete points, DAS can transform long lengths of fiber into continuous sensing arrays. This gives engineers thousands of “virtual sensors” for near-real-time monitoring without installing new equipment underground.

The approach is part of a Penn State initiative called FORESEE (Fiber-Optic for Environmental SEnsEing). The project also involves testing the method in Pittsburgh, where dark fiber is being used to look for signs of failing pipes, soil shifts, and other underground risks in urban settings.

Researchers caution that the method has limitations. Fiber is most sensitive to strain along its axis, meaning vertical or cross-axis motions may not be captured as effectively. Signal quality also depends on how well the fiber couples with surrounding soils, and advanced filtering is required to distinguish geohazard signals from background noise.

Still, the test demonstrates how existing fiber-optic networks could be a low-cost surveillance tool against subsurface threats.