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Google claims it has developed a way to use subsea fibre optic cables to detect earthquakes and tsunamis. While such systems already exist, the company claims its technique uses existing fibre optic cables and works ‘over tens of thousands of kilometres’ as opposed to the ‘up to 100 km’ limit that current sensing techniques have. The company is using the same cables that are instrumental in sharing, searching, sending and receiving information around the world. ‘Our technique relies on equipment that is present on the vast majority of the world’s existing fibre optic systems, so it is broadly applicable,’ the company said in a blog post. ‘Fiber optic cables connect far-flung continents along the ocean floor, and much of the Internet’s international traffic travels over these cables,’ the post adds.
Fibre optic cables carry data in the form of light, which is what makes them incredibly fast and averse to certain challenges copper wires suffer from, like the weather. ‘One of the properties of light that is tracked as part of the optical transmission is the state of polarization (SOP). The SOP changes in response to mechanical disturbances along the cable and tracking these disturbances enables us to detect seismic activity,’ the company explained in the post.
The company began monitoring the SOP on its cables in late 2019 and found that it was ‘remarkably stable’ even after travelling for 10,500km. After a period of no activity, the company detected an earthquake with 7.7 magnitudes off Jamaica, 1500km away from ‘the closest point’ of one of its cables. The detection happened ‘approximately five minutes’ after the earthquake happened, which correlates to the travel time of the seismic wave from Jamaica to the cable, claimed Google.
The company shared its findings with Zhongwen Zhan, assistant professor of Geophysics, Seismological Laboratory at the California Institute of Technology. Zhan confirmed the observations and added his own insights. Google says it has detected ‘multiple moderate-sized earthquakes, both shorter and longer distances’ since the Jamaican earthquake. This includes a 6.1 magnitude earthquake on the East Pacific Rise on March 22 and a 4.5 magnitude earthquake on March 28.
