Swiss researchers convert fiber optic network into earthquake sensor

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 track each wave of the earthquake in detail. Keystone / Carlo Reguzzi

Researchers at the Swiss Federal Institute of Technology ETH Zurich and the Swiss Federal Institute of Metrology (Metas) have discovered a fiber optic network that can be used to predict earthquakes and tsunamis.

This cost-effective method allows the precise measurement of earthquakes on the ocean floor or in countries that lack funding for a sufficiently dense measurement network, ETH Zurich announced on Thursday.

+ How Swiss researchers are predicting earthquakes

According to the university, they used the so-called Active Phase Noise Cancellation (PNC) of 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 almost 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 fibers being 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 slightly. This changes the frequency of the light signals by a tiny factor, which is then corrected by PNC.

Researchers can read earthquakes from this PNC data. According to ETH Zurich, the data only needs to be stored, which can be done without any additional equipment or 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 track each wave of the earthquake in detail, as can be seen from the data published in the journal Scientific Reports. A modeling of the earthquake corresponded almost precisely to the measurements of the Swiss Seismological Service.

According to ETH, this alignment 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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