Swiss researchers convert fiber optic network into earthquake sensor
Published: Thursday, Nov 23rd 2023, 10:00
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The fiber optic network can be used to predict earthquakes and tsunamis. This was discovered by researchers at the Swiss Federal Institute of Technology in Zurich (ETH Zurich) and the Swiss Federal Institute of Metrology (Metas).
ETH Zurich announced on Thursday that this cost-effective method enables the precise measurement of earthquakes on the ocean floor or in countries that lack the funds for a sufficiently dense measuring network.
According to the university, they used the so-called Active Phase Noise Cancellation (PNC) of the fiber optic cables. This works in a largely similar way to noise canceling in headphones. Microphones pick up external noise and feed in a counter-signal practically in real time. This makes the noise from outside inaudible.
In the case of optical fibers that transmit light signals, the "noise" is caused by the fact that the fibers are slightly deformed by movements of the earth's surface. This in turn leads to a so-called photoelastic effect, which causes the speed of light in the fiber to fluctuate minimally. This changes the frequency of the light signals by a tiny factor, which is then corrected by PNC.
Tested between Basel and Bern
Researchers can read earthquakes from this PNC data. According to ETH Zurich, the data only needs to be stored. According to the university, this requires neither additional equipment nor expensive infrastructure.
The researchers tested the method on the 123-kilometre-long fiber optic cable between Basel and Bern during a magnitude 3.9 earthquake, where they were able to reproduce every wave of the earthquake in detail, as the data published in the journal "Scientific Reports" shows. A model of the earthquake corresponded extremely accurately to the measurements taken by the Swiss Seismological Service.
According to the ETH, this exact match shows that the PNC data can be used to determine the location, depth and strength of an earthquake with a high degree of accuracy.
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