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New project aims to use undersea telecom cables to detect earthquakes

02/12/2019
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Lying at the bottom of the world’s oceans is a vast network of telecommunications cables linking countries thousands of miles apart with internet and telephony services. A team of researchers from the University of California-Berkeley has been testing another use for these cables – turning them into seismic sensors to help detect earthquakes.
New project aims to use undersea telecom cables to detect earthquakes
(The researchers used a 12-mile stretch of cable (highlighted in pink above) to test their new DAS technology. Image via UC Berkeley).

The project, involving researchers from UC Berkley, the Lawrence Berkeley National Laboratory, the Monterey Bay Aquarium Research Institute and Rice University, utilised a 12 mile stretch of cable that had been laid in 2009 along the bottom of California’s Monterey Bay.

So, what did the project involve?

The researchers managed to transform the underwater cables into seismic sensors by using something called Distributed Acoustic Sensing (DAS). DAS uses a photonic device to send short pulses of laser light down the cable to detect any backscattering created by strain in the cable (caused by stretching). By using interferometry, the researchers are then able to measure the backscatter every 2 metres, effectively turning the 12-mile cable into 10,000 individual seismic motion sensors.

By the end of the project, it was clear that the new technology works. During the underwater test, the researchers were able to measure a broad range of frequencies of seismic waves from a magnitude 3.4 earthquake that occurred 45 kilometres inland near Gilroy, California and map multiple known and previously unmapped submarine fault zones, part of the San Gregorio Fault system. The team were also able to detect steady-state ocean waves – so-called ocean microseisms – as well as storm waves, all of which matched buoy and land seismic measurements.

With such excellent results, hopes are high that the researchers’ findings will be applied to existing telecommunication cable networks across the world, greatly increasing the amount of seismic data that can be gathered – increasing the likelihood that major seismic events such as earthquakes can be predicted more accurately and earlier than previously.
Researchers used a 12-mile section of underwater cable to test their new seismic technology
(A section of the underwater cable which was used by the team for research purposes. Image via UC Berkeley).

“The beauty of fibre-optic seismology is that you can use existing telecommunications cables without having to put out 10,000 seismometers,” says Nate Lindsey, a UC Berkeley graduate student and lead author of the paper which contains the team’s findings. “You just walk out to the site and connect the instrument to the end of the fibre.”

It’s a development which could have a transformative impact upon seismology, as evidence by the words of Michael Manga, a UC Berkeley professor of earth and planetary science:

“We have huge knowledge gaps about processes on the ocean floor and the structure of the oceanic crust because it is challenging to put instruments like seismometers at the bottom of the sea. This research shows the promise of using existing fibre-optic cables as arrays of sensors to image in new ways. Here, they’ve identified previously hypothesized waves that had not been detected before.”

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Tags: Engineering, ICT
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New project aims to use undersea telecom cables to detect earthquakes - Time to read 3 min
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