Penn State researchers use 'thunderquakes' and fiber optics to map subsurface
By leveraging existing telecommunications infrastructure, scientists can now image the Earth's shallow crust using the acoustic pressure of thunderstorms.
Researchers at Penn State University have demonstrated that "thunderquakes"—seismic waves generated by the acoustic pressure of lightning—can be used to image the Earth's shallow subsurface. This discovery allows scientists to map underground structures by repurposing existing fiber-optic cabling as a massive seismic sensor array.
The team utilized Distributed Acoustic Sensing (DAS) technology to detect vibrations caused by thunderstorms. By sending laser pulses through a 4.9 km fiber-optic array on the Penn State campus, the researchers identified minute changes in the glass caused by ground movement. This passive imaging technique is capable of mapping subsurface structures down to a depth of approximately 100 meters.
The shift to passive sensing
Traditional seismic imaging typically relies on active sources to generate waves, such as controlled explosions or heavy vibrating trucks. While effective, these methods are often expensive, disruptive to local environments, and logistically challenging in urban areas. DAS technology transforms this paradigm by turning kilometers of standard telecommunications cable into thousands of individual sensors, removing the need for artificial triggers.
Implications for geological surveying
This approach enables the continuous, passive monitoring of both urban and rural subsurface structures using infrastructure already in place. By eliminating the cost and environmental impact associated with active seismic sources, the method could significantly streamline geological surveying and infrastructure monitoring. It provides a scalable way to gather data on shallow Earth structures without the need for specialized, invasive equipment.
Future outlook
As the technology matures, integrating seismic monitoring into existing city fiber networks could provide unprecedented data on urban geology. While the Penn State demonstration proves the viability of using thunderquakes for imaging, further research will likely focus on the consistency of these natural signals and the potential to expand the depth of the imaging capabilities. This shift toward opportunistic sensing suggests a future where the very cables powering our internet also serve as a planetary stethoscope, revealing the hidden architecture of the ground beneath our feet without disturbing the surface.