Underground fiber-optic cables help scientists record thunderquakes

Dec. 11 (UPI) — Loud thunderclaps can cause the ground to shake. The quakes are too subtle for humans to feel, but new research showed fiber optic cables can detect the thunderquakes.

A new study, published Wednesday in the Journal of Geophysical Research: Atmospheres, suggests underground fiber-optic cables could be used to track thunderstorms.

“Severe weather has strong interactions with the ground, but we haven’t had the capability to study the coupling between the atmosphere and the solid Earth,” Tieyuan Zhu, lead study author and an assistant professor of geophysics at Pennsylvania State University, said in a news release. “With this new technology, we can utilize existing fiber-optics networks to clearly see how thunderstorm energy passed through campus.”

To track the tiny seismic events caused by thunder, scientists deployed a new technology called a distributed acoustic sensing array, or DAS array, which fires a laser down one of the glass fibers in fiber-optic cables. The laser registers tiny changes in pressure, recording measurements every six feet. A few miles of underground cables create a network featuring thousands of sensors.

“If there is any change in the external energy on the ground above, even walking steps, you will have a very small change that’s going to stretch or compress the fiber,” Zhu said. “The laser is very sensitive and can detect these small changes.”

When the thunder-generated acoustic pressure wave hits the ground, it travels outward like a wave in a pond. The DAS records the location and movements of these pressure waves.

When scientists compared the measurements recorded by the newly deployed array, the thunderquake data matched the distribution of lightning recorded by the U.S. National Lightning Detection Network.

In addition, to help scientists track extreme weather, the new technology could be used to study Earth’s interior and model earthquake risks. Seismic events are relatively rare on the East Cast, but researchers could potentially use fiber optic cables to measure the movement of pressure waves through Earth’s mantle and crust.

“This research is an example of taking an existing technology and using it to serve another purpose,” said study co-author David Stensrud, head of the department of meteorology and atmospheric science at Penn State. “Having technologies that are multifunction maximizes the benefits to society.”

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