Undersea internet cables can detect earthquakes and may soon warn of a tsunami

Science fiction novelist Neil Stephenson wrote in wired 1996. “Once the cable is in place, it is treated not as a technological artifact but almost as if it were a naturally occurring mineral formation that could be exploited in any number of different ways.”

Each cable is roughly the thickness of a garden hose, but it’s mostly a protective sheathing around dozens of thin strands of glass, so pure that a kilometer thick block looks as pure as a freshly washed windshield. Today, about three hundred cables carry ninety-nine percent of all ocean traffic.

Bruce Howe, an oceanographer at the University of Hawaii, has been adding scientific instruments to seafloor cables since the early 1990s. Telecom companies lay new cables about once every quarter of a century to anticipate disruptions and incorporate more advanced materials. “When a company decided to turn off their cabling system, rather than just abandon it in place, as it used to be in those days, we thought science could use it,” Lee told me.

In the late twentieth century, Howe led the years-long installation process for part of Aloha Cabled Observatory, built on an old AT&T cable located one hundred kilometers north of Oahu. He and his colleagues later wrote that the team struggled to connect their devices to the cable, and that the facility struggled to reach its full potential, in part due to “very common cable and connector issues.”

Similar attempts to win over stuck cables have also faltered. In 1998, scientists added a seismometer, a microphone, two barometers, and other instruments to an old cable connecting Hawaii and California, but the system failed only five years later. One system near Hawaii developed a short circuit six months after its deployment, and another system was damaged by fishing activity off the coast of Japan. Commercial craftsmanship was not the way forward.

Howe began to wonder if scientific equipment could be incorporated into operational communications cables, which are meticulously maintained by the companies that benefit from them. He and his colleagues designed temperature, pressure, and seismic sensors that would fit snugly into cable repeaters. “The communications staff were adamant that they didn’t want anything to do with us,” Li Hao said. And while telling the story, they answered: “Impossible, because that would affect the reliability of communications.” This response disappointed the scientists, who later estimated that using the cabling infrastructure would give researchers data at a tenth of the cost of building their own system from scratch.

It takes two to three years to install a transatlantic cable and about two hundred million dollars, according to Nigel Bailev, CEO of Aquacoms Cable Operations. One repair can cost two million dollars. Any change to a working system—even a modest science package added at no cost to the cable company—could become a liability. “It’s a bit like asking for a different toilet on the space station,” Bailev told me. “It’s like, ‘Really you guys? Do you really want to risk the entire space station to change the toilet? “

“The only commercial reason for having these cables, as far as we’re concerned, is for data connectivity,” Bikash Kohli, vice president of global networks at Google, which has laid long distances of cable in partnership with carriers, told me. He said the company had no plans to add tools to its cables.

There are legal hurdles, too. Because seafloor communication cables are treated as an essential public service, they enjoy some freedoms under the United Nations Convention on the Law of the Sea, but the vague category of “marine scientific research” does not necessarily get the same privileges. Bayliff worries about what would happen to communications projects if they contributed to science.

“Is 90 percent of communications, 10 percent of science now science cable?” Bailf asked. We may not know until the first mover tests the legal waters. But he added that governments may be able to solve this problem by forcing cooperation between companies and researchers. “Once this becomes the norm, it will happen all the time and no one will worry, because the risks will be the same for everyone,” he said.

Howe and his team eventually teamed up with the government of Portugal, which was planning to replace the aging cable system – which knows something about offshore earthquakes. In 1755, a massive earthquake southwest of Lisbon triggered a tsunami and destroyed the capital. Tens of thousands died.

“They are excited,” Li Hao said. “They see it not only in terms of telecom operating costs, but in terms of human costs, and it may require governments to really balance these kinds of considerations. Companies are not going to do that.” The Portuguese government has approved the project, and Howe expects to allocate at least one hundred and twenty million euros sometime this year. The cable will connect Lisbon, the Azores and Madeira; Once operational, in 2025 the motion, pressure and temperature sensors in the cable repeaters will serve as a seafloor science platform and a tsunami warning system.

In order for scientists to break the deadlock with the cable industry, they needed ways to use data that already existed, without modifying cables or subsea repeaters. Mara’s coincidental discovery proved that this was possible.

Then, in 2020, Google agreed to share measurements of light polarization from its fiber-optic network with a science team that included Zhan and other researchers from the California Institute of Technology and the University of L’Aquila in Italy. Cooley told me that the Google scientists were happy to collaborate — as long as they didn’t need to add tools to their cables. “This was a bunch of data that you would actually have gotten rid of otherwise,” Cooley said. “There is no other benefit to us.”

The researchers identified shifts in polarization that occur as cables bend, twist and stretch, and compared the changes to dozens of earthquakes detected by seismographs over a nine-month period. This approach is not as sensitive as the Marra or DAS method, but it does require sophisticated technology in the form of an advanced laser. “Because the method is so easy to implement, we now have six or seven cables on board, providing the data,” Zahn said.

Last year, Google gave Mara and his team access to a cable landing station in Southport, England, where the company used a cable that runs to Dublin, and then to Halifax, Canada. The company was willing to give researchers temporary access to certain channels when they are not being used. The researchers drove for five hours from their lab in Teddington and installed custom lasers and detectors, as well as computers that they could access remotely. They now have the ability to detect phase transitions under the Irish Sea and the Atlantic Ocean.

But they still need a way to determine where the phase shifts occur in order to know the exact location of seafloor movements. To solve this problem, the researchers took advantage of small mirrors built into optical fiber repeaters, which usually help technicians diagnose problems along certain stretches of cable. One hundred and twenty-eight mirrors between Southport and Halifax allowed the specific portion of the cable to be identified where the phase shift first occurred. Their approach had the potential to turn the cable into one hundred and twenty-nine positional seismic detectors.

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