Fiber-optic cables, which keep the internet running, may also help detect underground geohazards such as sinkholes, according to new research from Pennsylvania State University.
Researchers at the university's University Park campus tested a technique using existing communications cables buried only a few feet below ground.
By applying Distributed Acoustic Sensing, or DAS, they observed how the cables can map fractured zones, including sinkholes, stretching hundreds of feet beneath the surface. The findings were published in the Journal of Geophysical Research: Solid Earth.
The team built a DAS interrogator, a device that sends light pulses through fiber-optic cables and captures acoustic signals along the way. Attached to about four miles of existing cable, the tool recorded vibrations from its surroundings.
Researchers then applied computational models to filter out noise from cars, students, and construction, leaving behind signals linked to rock density.
"We geoscientists often think of inputs such as everyday traffic as noise in the data," said Tieyuan Zhu, associate professor of geophysics and co-author of the study. "However, our research shows that the so-called 'garbage noise' is very useful."
Ground density has long been measured with geophones, instruments that are costly, labor-intensive, and limited to single data points. The new method turns routine traffic vibrations into seismic surface waves using cross-correlation.
This creates a detailed picture of wave speeds beneath the cables and generates a web of measurements, instead of isolated readings.
The approach proved effective when researchers mapped a low-density zone beneath campus that could develop into a sinkhole. Acoustic models showed the area as a low-velocity structure, less dense than the surrounding ground at the same depth.
Zhu noted that the result was not surprising given Pennsylvania's Karst geology, which includes porous limestone and dolomite. These rocks gradually dissolve when exposed to acidic water, often leaving cavities that lead to sinkholes.
Penn State's Office of Physical Plant and its contractors reviewed the data and confirmed the void does not pose an immediate threat to campus structures. Still, Zhu said the technology could play a critical role in future planning.
The system is already being expanded in Pittsburgh through a Civic Innovation Challenge grant from the U.S. National Science Foundation. The project aims to reduce disaster risks by detecting underground weaknesses before they become dangerous.
"Sinkholes are widespread in Pennsylvania and beyond," Zhu said. "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."
The study was co-authored by Zhinong Wang, a postdoctoral scholar studying geoscience. It is part of the Fiber-Optic for Environmental Sensing (FORESEE) project, led by Zhu and supported by the National Science Foundation.
FORESEE gathers high-resolution vibration data from underground cables and has previously been used in energy extraction, severe weather forecasting, and even monitoring activity at Penn State's legendary Beaver Stadium, home of the Nittany Lions football team.