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The network of submarine cables that transmit data around the world could one day be used to track earthquakes and tsunamis, new research shows. In a test last year, one of Google’s fiber-optic cables was able to detect nearby earthquakes by detecting distortions in the light pulses sent along the cable. It’s a new take on an idea researchers have been working on for several years.
“Can we find a cheaper way to cover the ocean with geophysical sensors? This telecommunication cable infrastructure already exists. If you can turn them into sensors, that’s wonderful – and that’s what we’re doing now, ”says Zhongwen Zhan, assistant professor of geophysics at the California Institute of Technology and senior author of the research published today in the journal Science.
In addition to their primary mission of sending data all over the world, these cables could one day send early warnings to people ashore when a tsunami hits its way. They could also allow seismologists and geophysicists to take a closer look at earthquakes that occur underwater. Since almost all of the sensors currently used to detect earthquakes are on land, these cables could fill huge gaps in scientists’ ability to observe seismic activity. The new approach does not even require installing new equipment on the existing network of more than a million kilometers of fiber optic cables that cross the seabed.
The new approach capitalizes on what cables are already designed for. When a transmitter at one end of the cable sends out a light signal transmitting data, the light waves are directed in a particular direction. If an earthquake occurs, it can shake, bend, or twist the cable – and this changes the orientation of the light waves. On the other end of the cable, Google notices the distortions and fixes them. Now he wants to share his data, the changes in what is called the “state of polarization” of light, with seismologists like Zhan so they can study the earthquakes that caused the distortions.
Between December 2019 and September 2020, Zhan’s research team documented around 20 moderate to large earthquakes using Google’s 10,500-kilometer cable, Curie, which runs from Los Angeles, Calif., To Valparaíso. , in Chile. The cable was also able to pick up swells in the ocean caused by storms. This suggests that the technique can also be used to spot tsunamis, which earthquakes can trigger.
The ability to see tsunamis while they are still far from shore could save lives. In addition to having a better view of the ocean than the small number of existing sensors specifically designed to find tsunamis, fiber-optic cables can also send alerts ashore much faster – perhaps in milliseconds, depending Google.
“We are honored and excited about the opportunity to collaborate with the optical, underwater and seismic research communities to use all of our cable infrastructure for greater societal benefits,” Google wrote in a blog last July. , shortly after the company contacted Zhan to further develop the new approach to seismic detection on the seabed.
“We hope this new approach can really give people a better chance of catching these events early, so people have more time to react,” Zhan says.
In 2018, similar research was published that showed seabed cables had the potential to detect earthquakes and tsunamis – but this approach had some limitations. The cables had to be fitted with specialized equipment to fire lasers at the cable. In comparison, this new approach saves money because it does not require any new infrastructure. There were also concerns that adding equipment to cables could open the door to security holes, allowing malicious actors to gain access to data sent over the network. Zhan says that’s okay with the new approach; scientists cannot see information about transmitted content when studying the polarization of light.
“It’s a perfectly safe way to take advantage of pre-existing infrastructure to do something that’s good for society and science,” Zhan says.
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