A 10,000-kilometre-long fibre-optic cable owned by Google that is at the bottom of the Pacific Ocean can be used to detect deep-sea seismic activity and ocean waves.
Zhongwen Zhan at the California Institute of Technology in Pasadena, California, and his colleagues, including researchers at Google, used traffic data from one of the tech giant’s optical fibres to measure changes in pressure and strain in the cable. Using this data, they could detect earthquakes and ocean waves called swells generated by storms.
During a test run last year, one of Google’s fiber-optic cables was able to successfully pick up on nearby earthquakes by detecting distortions in light pulses sent along the cable. It’s a new approach to an idea that researchers have been working on for the past several years.
“Can we find a less expensive way to cover the ocean with geophysical sensors? There’s already this telecommunication cable infrastructure out there. If you can turn them into sensors, that’s wonderful and that’s what we’re doing now,” says Zhongwen Zhan, an assistant professor of geophysics at the California Institute of Technology and lead author of the research published today in the journal Science.
On top of their main job of sending data all over the world, these cables could one day send early warnings to people on shore when a tsunami is barreling their way. They could also give seismologists and geophysicists a closer look at earthquakes that occur underwater. Since nearly all the sensors currently used to detect earthquakes are on land, these cables could fill in huge gaps in scientists’ ability to observe seismic activity. The novel approach doesn’t even require installing any new equipment to the existing web of more than a million kilometers of fiber optic cables that cut across the seafloor.
The new approach capitalizes on what the cables are already designed to do. When a transmitter at one end of the cable sends out a light signal transmitting data, light waves are oriented in a particular direction. If an earthquake hits, it might shake, bend, or twist the cable and that changes the orientation of the light waves. At the other end of the cable, Google notices distortions and corrects them. Now, it wants to share its data, changes to what’s called the “state of polarization” of light, with seismologists like Zhan so they can study the earthquakes that caused the distortions.
Zhan says his team’s approach of using an existing traffic fibre is more flexible and scalable as it doesn’t need new infrastructure. “This is exciting as if only a fraction of the million kilometres of submarine fibre-optic networks could be used as sensors, there would be vast improvements in the amount and coverage of seismic data.”