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thunder over a city

Pre-existing fibre-optic networks could be adapted to detect thunderquakes

Image credit: Photo by lee junda on Unsplash

The network of underground fibre-optic cables that is used to for internet and phone calls could also function as a warning system for severe weather events.

Penn State University researchers were able to detect thunder-induced seismic events, or thunderquakes, using the kind of fibre-optic network buried under most major cities.

During storms, thunder creates acoustic pressure miles above the Earth that travels down, hits the ground and spreads like waves in a pond. Humans cannot hear or feel these thunderquakes, but the slight movements can be captured by the fibre-optic cables.

They used technology called a distributed acoustic sensing (DAS) array to track the direction of the storm based on the intensity of the thunderquake events

Their findings tallied with the location of lightning recorded by the US National Lightning Detection Network.

“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,” said assistant professor Tieyuan Zhu, lead author on the study. “With this new technology, we can utilise existing fibre-optics networks to clearly see how thunderstorm energy passed through campus.”

The DAS array sends a laser down one of the hair-thin glass fibres contained inside the cables and can detect small changes caused by pressure as slight as a human walking, the scientists said.

The array takes measurements every six-and-a-half feet, meaning the several miles of continuous cable under the University Park campus acts like a network of 2,000 sensors.

“The ability to use fibre-optic cables to detect the source of thunder provides yet another way to track thunderstorms and help with public safety and emergency response, especially in urban areas,” said David Stensrud who co-authored the study. “Every new data source helps to improve our storm-tracking ability.”

Zhu added: “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 fibre.

“The laser is very sensitive and can detect these small changes.”

The method has the potential to be used more broadly for other natural hazards like earthquakes, hurricanes and flooding, as pre-existing fibre-optic cable networks exist in urban areas throughout the country, according to the scientists.

“This research is an example of taking an existing technology and using it to serve another purpose,” Stensrud said.

In 2017 E&T looked at the technologies cities around the world are using to detect earthquakes early in order to send early warning signals to citizens.

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