Undersea fiber-optic cables can be used to detect earthquakes, say researchers

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Scientists in California have successfully conducted an experiment showing how networks of undersea fiber-optic cables can be used to detect seismic activity, including earthquakes.

In a paper published in the journal Science, the research team described how they were able to turn about 12 miles of undersea cable in California’s Monterey Bay into the equivalent of 10,000 seismic stations.

During their four-day experiment the cables detected a 3.5 magnitude quake and seismic scattering from underwater fault zones. The researchers hope that the experiment could lay the groundwork for the use of fiber-optic cables for seismic detection around the world.

There are estimated to be a network of more than 6 million miles of fiber-optic cables stretching throughout the world, many of them used for telecommunications. Researchers are especially interested in leveraging undersea cables since very little of the Earth’s oceans are covered by current seismic sensing technology.

“There is a huge need for sea floor seismology,” Nate Lindsey, a University of California graduate student and the lead author of the paper, told Science Daily. “Any instrumentation you get out into the ocean, even if it is only for the first 50km (30 miles) from shore, will be very useful.”

In order to turn the cables into seismic sensors the research team, which also compromised scientists from Rice University in Houston and the Monterey Bay Aquarium Research Institute, used a technique known as distributed acoustic sensing.

The technique involves sending short pulses of laser light down the cable and measuring the backscattering created by strain in the cable caused by stretching. From the stretching the team can infer the effect of seismic activity on the cable.

The next step for the researchers is demonstrating the technique does not interfere with the functionality of the cable. To do this they are conducting experiments now with lit fibers in a geothermal area in the Brawley seismic zone in Southern California.

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