Monitoring earthquake-induced changes in fiber optic cables on the ocean floor represents a new way to detect quakes, researchers say. Their approach - which would make it possible to sense temblors without installing new seafloor equipment - could permit detection of earthquakes in regions where seismic monitoring has otherwise been difficult, including in subduction zones or in remote ocean regions lacking seismometers. Even though 70% of the Earth's surface is covered with water, almost all seismic stations are on land. As a result, underwater earthquakes remain largely undetected, limiting scientists' ability to identify the source mechanisms of underwater seismic events. To date, scientists have recognized that existing optical fire cable networks - a backbone of international and intercontinental telecommunication - could help expand quake detection capabilities if the fibers therein were used as the sensing element. Now, Giuseppe Marra and colleagues report an approach by which to gauge quake-generated "disturbance" signals in oceanic fiber optic cables. The approach involves measuring so-called optical phase changes triggered in the fibers by seismic waves. It not only allows for earthquake wave detection, but for estimating quake magnitude and epicentral location, the authors say. In several evaluations of this approach involving earthquakes with epicenters in Italy, New Zealand, Japan and Mexico in recent years, Marra and colleagues demonstrated that their approach could effectively detect quake activity and parameters as well as local seismometers.
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Science