An international team of geoscientists led by Caltech has used fiber optic communications cables stationed at the bottom of the North Sea as a giant seismic network, tracking both earthquakes and ocean waves.
The project was, in part, a proof of concept. Oceans cover two-thirds of the earth's surface, but placing permanent seismometers under the sea is prohibitively expensive. The fact that the fiber network was able to detect and record a magnitude-8.2 earthquake near Fiji in August 2018 proves the ability of the technology to fill in some of the massive blind spots in the global seismic network, says Caltech graduate student Ethan Williams (MS '19). Williams is the lead author of a study on the project that was published by Nature Communications on Dec. 18.
"Fiber optic communications cables are growing more and more common on the sea floor. Rather than place a whole new device, we can tap into some of this fiber and start observing seismicity immediately," Williams says.
The project relies on a technology called distributing acoustic sensing, or DAS. DAS was developed for energy exploration but has been repurposed for seismology. DAS sensors shoot a beam of light down a fiber optic cable. Tiny imperfections in the cable reflect back miniscule amounts of the light, allowing the imperfections to act as "waypoints." As a seismic wave jostles the fiber cable, the waypoints shift minutely in location, changing the travel time of the reflected light waves and thus allowing scientists to track the progression of the wave. The DAS instrument used in this study was built and operated by a team from Spain's University of Alcalá, led by study co-author Miguel Gonzalez-Herraez.
Read more at California Institute of Technology
Image: Researchers used fiber optic cable that connects a wind farm in the North Sea to detect an earthquake. (Credit: Marlinks)