Thunderstorms may do more than shake windows and rattle the air. The acoustic waves produced by thunder can also transfer energy into the ground strongly enough to create seismic signals that researchers can use to image shallow structures beneath Earth’s surface.
Researchers at Penn State demonstrated this approach using a technology called distributed acoustic sensing, or DAS. Instead of installing a conventional network of seismic instruments, they used an existing fiber-optic telecommunications cable buried beneath the University Park campus.
The 2.5-mile (4-kilometer) cable was buried just a few feet underground. A laser sent through the fiber allowed the researchers to detect tiny changes in the cable caused by seismic waves moving through the ground.
Those measurements captured what happened when thunder-generated acoustic waves reached the surface and transferred energy into the ground. The researchers call the resulting seismic signals “thunderquakes.”
The study provides what the researchers describe as the first successful seismic imaging using thunderquakes. It also demonstrates how DAS can record the transition from an atmospheric acoustic wave to a seismic signal at high resolution.
Using thunder instead of conventional seismic sources
Seismic tomography is used to create images of the subsurface from waves recorded at the surface. Traditionally, those waves can come from earthquakes or from equipment that actively generates seismic energy.
For this study, the researchers instead used acoustic waves generated by thunder.
That matters for areas where earthquakes are less common. Passive seismic imaging often depends on a strong monitoring array and naturally occurring seismic sources. Thunderquakes provide another possible source for near-surface imaging, according to the researchers.
The approach also relies on fiber-optic cables that are already in place. That could make it possible to conduct measurements in locations where installing conventional equipment is difficult, including highly regulated urban areas and less accessible environments such as the Arctic.
The fiber captured the moment thunder reached the ground
Using thunder for seismic imaging has been attempted before, but the transition from an atmospheric sound wave to a seismic signal is difficult to observe in detail.
DAS gave the Penn State team a much denser set of measurements along the fiber. The system recorded hundreds of samples every second at intervals of a few meters along the cable.
That resolution allowed the researchers to examine how the acoustic energy from thunder coupled into the ground and produced seismic signals.
The result was both an imaging method and a way to study the interaction between the atmosphere and solid Earth.
The work could lead to more studies of atmosphere and ground interactions
The researchers said that a better understanding of this coupling could support research spanning geoscience and meteorology.
They also pointed to a possible application beyond Earth. Seismic activity on other planets and moons is not well understood, and the researchers said that a different source of seismic energy could eventually be useful for seismic imaging there.
For now, the team plans to expand the work beyond the Penn State campus and investigate whether thunderquakes can be used more broadly, particularly in regions with limited access to traditional seismic sources.
The study was published in Science Advances.
