A large network of undersea telecommunications cables crisscrosses the planet under the water and on land. The cables carry data all around the world, and many of them are owned by Amazon, Facebook, Google, and Microsoft. A team of researchers from UC Berkeley, Berkeley Lab, the Monterey Bay Aquarium, and Rice University has described an experiment that turned 20km of undersea fiber-optic cable into the equivalent of 10,000 seismic stations.
The experiment spanned four days in the Monterey Bay, and the team says that they recorded a 3.5 magnitude quake and seismic scattering from underwater fault zones. The team had previously tested the technique with fiber-optic cables on land. The hope is that the cables could be used to give much-needed data on quakes that occur under the seas where few seismic stations exist.
Researchers say that there is a huge need for seafloor seismology. They note that even if the instrumentation only covers the first 50km from the shore, the array would be beneficial. The team used 20km of the permanent cable that leads to the Monterey Accelerated Research Systems node that was laid in 2009 while it was offline for maintenance in March 2018.
The ultimate goal of the research is to be able to use the dense fiber-optic networks around the world on both land and sea to measure the Earth’s movement. This would allow earthquake monitoring in regions that don’t have expensive ground stations. The technique uses Distributed Acoustic Sensing.
It uses a photonic device to send short pulses of laser light down the cable and detects backscattering that is created by strain in the cable caused by stretching. The team can measure the backscatter every 6 feet turning the 20km cable into 10,000 motion sensors. One scientist says the beauty of the system is that “You just walk out to the site and connect the instrument to the end of the fiber,” turning the cable into seismometers.