Scientists discovered that thunder-generated seismic waves, referred to as “thunderquakes,” might help map Earth’s subsurface utilizing present fiber-optic cables. The approach might detect groundwater, sinkholes, fractures and contamination with out drilling, providing an economical technique for monitoring geological hazards and infrastructure
Revealed Date – 23 August 2026, 10:38 AM
Pennsylvania: When lightning strikes, it superheats the air round it and creates a shock wave that we hear as thunder. However thunder doesn’t simply journey by the environment to our ears.
When that vitality reaches the bottom, a few of it’s transformed into seismic waves that ripple by the soil and rock beneath. The ensuing vibrations are referred to as “thunderquakes.”
Till now, scientists haven’t understood these indicators effectively sufficient to make sensible use of them. Our group’s analysis exhibits that thunderquakes can be utilized to map the construction beneath the Earth’s subsurface – akin to groundwater motion, environmental contamination, sinkholes, or for evaluating constructing websites and foundations – identical to X-rays picture contained in the human physique.
We found this by listening to thunder with one thing present in communities around the globe however uncommon as a seismic measuring instrument: fiber-optic cable.
Turning fiber optics into vibration sensors
Utilizing a way referred to as distributed acoustic sensing, we turned an strange fiber-optic cable, the sort used for web or cellphone service, right into a string of 1000’s of vibration sensors.
A laser-pulsing laptop, referred to as an interrogator, sends gentle by the cable and measures tiny adjustments brought on by vibrations alongside its size. In our experiment, a part of the Penn State FORESEE mission, we used a cable that’s over 2 miles (greater than 4 kilometers) lengthy. That gave us greater than 2,100 sensors, spaced just a few ft aside, all listening to the bottom directly.
Over two years, we used an outdated telecom fiber to report and establish 458 clear, high-quality thunderquakes.
The large quantity of element captured by this course of has allowed us to see one thing that had been troublesome to look at earlier than: particular varieties of seismic waves produced when sound from the environment interacts with the bottom.
An important of those seismic waves are what we name air-coupled Rayleigh waves. They’re measurable on the floor however can be utilized to check the subsurface far beneath, even down 300 ft (round 100 meters).
How a thunderquake ‘X-rays’ the bottom beneath
The trick to this method is called seismic dispersion: Waves of various frequencies journey at totally different depths. By measuring how the thunderquake’s wave speeds modified with frequency, we might reconstruct the seismic wave velocity at totally different depths, which permits us to interpret the properties of the bottom beneath the fiber.
The end result was the equal of an X-ray of the subsurface extending roughly 300 ft underground, with out drilling a single gap.
Imaging the subsurface usually requires specialised gear, akin to truck-mounted vibration sources or arrays of sensors that need to be put in for surveys. These approaches might be costly and troublesome to deploy over massive areas.
Thunderstorms supply a naturally occurring supply of seismic vitality that’s already unfold throughout the panorama. And fiber-optic cables are buried beneath cities and cities around the globe.
As a substitute of bringing a seismic supply to the bottom, we are able to hearken to the storms passing overhead. That would finally make it doable to watch the shallow subsurface repeatedly, utilizing infrastructure that’s already within the floor and seismic vitality that’s already coming from the sky.
What we discovered at our check web site
In State Faculty, Pennsylvania, the place we carried out the assessments, the geology is usually limestone and dolomite, rocks that may slowly dissolve as groundwater strikes by them. Over time, this course of creates fractures, caves and sinkholes.
Our thunderquake research revealed 4 distinct areas the place seismic waves traveled rather more slowly than by the encompassing rock. These “weak zones” may very well be brought on by fractured or weathered rock or the presence of water or air. Two of them coincide with areas the place satellite tv for pc radar exhibits that the bottom is actively subsiding. The depths of all 4 are in line with fractures and voids documented at close by websites.
These outcomes matter as a result of karst landscapes just like the one beneath State Faculty are widespread. They cowl roughly 20% of the world’s continental land space and have an effect on practically 1 / 4 of the worldwide inhabitants. Sinkholes, groundwater contamination and different hazards related to these landscapes can threaten buildings, infrastructure and public security. Understanding the place these hazards are permits for higher development and planning.
Not only for thunder, and never simply on Earth
Our outcomes reveal a elementary course of: Sound waves within the environment might be transformed into helpful seismic waves within the stable Earth. However thunder is just one instance.
Sonic booms, volcanic eruptions and meteor airbursts can produce related atmospheric shock waves, doubtlessly creating different pure seismic sources.
The thought might even lengthen past Earth. Earth-like tectonic earthquakes will not be anticipated to be widespread on another planets and moons, however atmospheric disturbances should still be current.
Titan, Saturn’s largest moon and the vacation spot of NASA’s upcoming Dragonfly mission, is one intriguing chance. If lightning and thunder happen there as fashions predict, atmospheric vitality might doubtlessly present one other solution to examine its subsurface.
Again on Earth, the environment is continually interacting with the bottom beneath our ft. Our work means that this interplay may very well be a supply of details about the hidden world beneath us.
