Reviewed by Frances BriggsSep 30 2025
The same fiber optic cables that carry internet traffic could help detect underground hazards like sinkholes, according to a new study by researchers at Penn State, published in the Journal of Geophysical Research: Solid Earth.
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Using the communication cables buried beneath Penn State's University Park campus, the researchers demonstrated how existing acoustic sensing technology can map fractured areas extending hundreds of feet below the surface.
Having previously designed a distributed acoustic sensing (DAS) interrogator, the team connected the tool to a four-mile stretch of campus telecommunications cable. The DAS interrogator sent beams of light through the cable and captured the returning signals.
Given the extent of activity on campus, the researchers devised a set of computational methods to isolate sound waves associated with rock density while filtering out noises produced by vehicles, students, or construction activities.
We geoscientists often think of inputs such as everyday traffic as noise in the data. However, our research shows that the so-called ‘garbage noise’ is very useful. We can rely on these signals to spot geohazards in a way that’s much more affordable and effective than traditional methods.
Tieyuan Zhu, Study Corresponding Co-Author and Associate Professor, Geophysics, The Pennsylvania State University
Geophones are typically used to measure ground density, but these instruments are expensive, labor-intensive, and can only generate single-point readings. In contrast, the DAS interrogator turned common traffic sounds into seismic surface waves through cross-correlation to provide a comprehensive view of the surface wave velocity beneath the cable, yielding an array of data points.
Zhu compared the concept to shouting into the Grand Canyon: the time it takes for one’s voice to echo back can reveal important clues about the canyon’s depth and distance. Similarly, sound propagates through the ground. The greater the density of the rock, the more sluggishly the sound wave traverses through it.
In this proof-of-concept study, the new technique found a low-density zone deep beneath the campus. The team created a model of the data points, finding that the feature could potentially evolve into a sinkhole.
The region's Karst geology, which is characterized by caves, low-density rocks, springs, and other typical landscape features found throughout Pennsylvania, is recognized for its soluble rocks, mainly limestone and dolomite, which are eroded by acidic water. As a result of this geology, the low density area is not particularly surprising.
Contractors and others at Penn State's Office of Physical Plant examined the researchers' findings and concluded that the possible underground void does not immediately threaten campus structures.
The DAS technology is currently being implemented on a broader scale to assist in disaster prevention in Pittsburgh, supported by a Civic Innovation Challenge grant from the U.S. National Science Foundation.
Sinkholes are widespread in Pennsylvania and beyond. What makes this research especially powerful is that it turns everyday traffic noise, something completely free, into a tool for locating geohazards. By using the existing fiber optic cables already in place as sensors, we can provide an affordable and scalable way to assess risks and help prevent future threats for Pennsylvanians.
Tieyuan Zhu, Study Corresponding Co-Author and Associate Professor, Geophysics, The Pennsylvania State University
Journal Reference:
Wang, Z. and Zhu, T. (2025) Characterizing Fractured Zones in Urban Karst Geology Using Leaky Surface Waves From Distributed Acoustic Sensing. Journal of Geophysical Research: Solid Earth.doi.org/10.1029/2025JB031477