Thunder and Fiber-Optic Cables Offer New Way to Map What Lies Beneath Earth’s Surface
Scientists at Penn State have demonstrated that thunderstorms can provide more than dramatic flashes and booming sound. The seismic energy produced by thunder can penetrate the Earth’s upper crust, potentially giving researchers a new way to study underground structures without waiting for earthquakes or deliberately generating seismic waves.
The phenomenon, known as a “thunderquake,” has long been difficult to analyze because of the complexity of the signals involved. Researchers have now developed a modeling approach that allowed them to interpret those signals and reconstruct features beneath the Penn State campus.
Thunderquakes Could Provide a New Source of Seismic Data
Much of scientists’ understanding of Earth’s interior comes from seismic waves. These waves travel at different speeds depending on the materials they encounter, including solid rock, fractured formations, water-rich areas and partially molten material.
Earthquakes naturally generate seismic waves, while researchers can also create them using controlled sources such as explosives. Thunderstorms could provide an alternative source that occurs naturally but far more frequently than significant earthquakes in many regions.
Lightning generates thunder by producing intensely heated plasma along its irregular path. This creates a chain of rapidly expanding regions that generate acoustic shock waves.
Why Thunder Creates Complicated Seismic Signals
Those shock waves spread through the atmosphere and eventually strike the ground. Because lightning does not follow a straight path, the resulting acoustic waves originate from different locations and elevations and can interfere with one another.
The situation becomes even more complicated once the energy reaches the surface.
Shock waves may encounter soil, bedrock, buildings, roads and other infrastructure. Some energy becomes Rayleigh waves, which travel along the Earth’s surface, while other seismic energy penetrates deeper underground.
To extract useful geological information, researchers need to determine what a thunder-generated seismic signal should normally look like before identifying changes caused by underground structures.
Researchers Build a Model for Thunder-Generated Seismic Waves
The Penn State researchers used SPECFEM3D Cartesian, software designed to simulate three-dimensional seismic-wave propagation.
The modeling process required several approximations. For example, the atmosphere was represented as a homogeneous layer about 2.2 miles thick, even though atmospheric conditions surrounding an actual thunderstorm are far more complicated.
Researchers also had to compensate for differences between the model’s timing resolution and the rapid movement of waves across the air-ground boundary. To address this limitation, they effectively stretched the upper 20 meters, or roughly 66 feet, of Earth in the model to represent 200 meters, or about 656 feet.
Despite those compromises, the team tested whether the approach could produce useful results using real thunderstorms over the Penn State campus.
Fiber-Optic Cable Turns Into a Large Seismic Sensor
The experiment benefited from another emerging technology: using fiber-optic cables as seismic sensors.
Penn State has roughly 4 kilometers, or 2.5 miles, of fiber-optic cable beneath its campus dedicated to seismic sensing. Such cables can detect extremely small physical disturbances along their length, effectively transforming existing telecommunications infrastructure into a dense network of seismic sensors.
Summer thunderstorms are also common in the region, giving researchers a steady supply of natural events to study.
Over two years, scientists recorded 458 well-resolved thunderquakes. The events were independently verified using data from the U.S. National Lightning Detection Network.
Researchers observed multiple seismic signals arriving from different elevations, consistent with shock waves being generated along a lightning channel extending between the clouds and the surface.
“The impingement of each bubble onto the ground or environment generates a high-energy impulsive wavelet followed by a decaying wave train dominated by surface-wave content lasting one to two seconds.”
Thunder Reveals Weak Zones Beneath Penn State Campus
After reaching the surface, the thunder-generated seismic waves interacted with underground geological features.
Researchers identified four “weak zones” where the waves slowed as they passed through less rigid materials. Such areas can contain sediments, fractured rock or elevated concentrations of groundwater.
That finding is particularly relevant at Penn State because the campus sits above karst geology. Karst landscapes form as water gradually dissolves soluble rocks such as limestone, potentially creating fractures, cavities and other underground weak points.
Independent Tests Confirm Underground Features
Researchers compared the four identified zones with information gathered through several other methods, including radar measurements of surface deformation, engineering surveys, boreholes and independent seismic observations.
Those comparisons indicated that unusual underground conditions were indeed present at the locations highlighted by the thunderquake analysis.
The results suggest that the model can extract meaningful information despite the approximations required to simulate the complicated interaction among lightning, atmospheric shock waves and underground geology.
Thunderstorms Could Help Map Areas Near the Surface
Thunderquakes could be particularly useful for studying shallow geological structures. That is important because roads, buildings, pipelines, utilities and other critical infrastructure are concentrated close to the surface.
Thunderstorms also occur regularly across large parts of the United States and many other regions worldwide, potentially providing researchers with repeated natural seismic sources at no additional environmental cost.
Combined with fiber-optic sensing networks, thunder-generated seismic waves could eventually complement traditional geological surveys, earthquakes and deliberately generated seismic signals.
The Penn State research shows that an everyday weather event may provide scientists with an unexpectedly valuable tool. By turning thunder into seismic data and fiber-optic cables into underground sensors, researchers could gain a new way to identify fractures, water-rich zones and other hidden structures beneath developed areas.
Jacob Whitman is a contributor at Prudent Press Agency, covering a wide range of topics including news, politics, business, technology, sports, entertainment, and lifestyle. He focuses on delivering clear, balanced reporting that helps readers stay informed about current events and emerging developments. With an emphasis on accuracy, relevance, and accessibility, Jacob aims to provide useful insights and timely stories that matter to everyday readers and the communities they follow.
