7 October, 2025
fiber-optic-cables-a-new-frontier-in-geohazard-detection

Simple fiber-optic cables, essential for powering the internet, may soon serve a dual purpose as an early warning system for geohazards like sinkholes. This groundbreaking potential is highlighted in a new study led by researchers at Penn State University.

Utilizing existing communications cables buried just beneath the surface at Penn State’s University Park campus, the research team has developed an innovative method to employ acoustic sensing technology. Detailed in the Journal of Geophysical Research: Solid Earth, this approach can map fractured zones, such as sinkholes, at depths reaching hundreds of feet below the Earth’s surface.

Revolutionary Acoustic Sensing Technology

The researchers’ method involves a tool they developed called the distributed acoustic sensing (DAS) interrogator. This device was attached to preexisting telecommunications fiber optic cable stretching approximately four miles across University Park. By sending a beam of light through the cable, the DAS interrogator captures acoustic signals throughout.

Given the bustling activity on campus, the researchers devised computational methods to isolate sound waves correlating to rock density, filtering out noise from cars, students, and construction. “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,” said Tieyuan Zhu, associate professor of geophysics and corresponding co-author of the paper.

Advantages Over Traditional Methods

Traditionally, geophones are used to measure ground density. These instruments are costly, require manual deployment, and provide limited data points. The new approach, which converts everyday traffic noises into seismic surface waves through cross-correlation, offers a comprehensive view of the surface wave speed below the cable, creating a dense mesh of data points.

To illustrate, imagine shouting into the Grand Canyon. The distance your voice travels before echoing back reveals much about the canyon’s depth and distance. Similarly, sound travels through the ground, with denser rocks slowing the sound waves.

Real-world Applications and Implications

The proof-of-concept work was validated when researchers identified a low-density area with the potential to form a sinkhole deep below the surface. Modeling of the acoustic signals showed this area as a low-velocity structure, less dense than the surrounding ground at the same depth.

Penn State’s region, characterized by Karst geology with caves, low-density rocks, and springs, is known for its soluble rocks like limestone and dolomite, weakened by acidic water. Thus, spotting a low-density area was not entirely unexpected, Zhu noted.

Professionals at Penn State’s Office of Physical Plant, along with their contractors, reviewed the data and concluded there is no immediate threat to campus structures from the potential underground void.

Future Potential and Broader Impact

Zhu emphasized that the technique could be instrumental in future planning. DAS technology is already being deployed on a larger scale to prevent disasters 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.”

Zhinong Wang, a postdoctoral scholar in geosciences, co-authored the research funded by the U.S. National Science Foundation. This study is part of the Fiber-Optic foR Environmental SEnsEing (FORESEE) project, led by Zhu, which collects high-resolution acoustic vibration data using underground telecommunication fiber-optic cables. Previous research has demonstrated the technology’s ability to aid in energy extraction, severe weather forecasting, and even tracking the score of a Penn State football game at Beaver Stadium.

The announcement comes as geohazard detection becomes increasingly critical in areas prone to such natural phenomena. The innovative use of existing infrastructure not only highlights the potential for cost-effective solutions but also underscores the importance of interdisciplinary research in addressing real-world challenges.