Researchers Unlock Potential Of Fibre-Optic Networks As Earthquake Early Warning Systems
Researchers think fibre-optic networks could be useful as early warning systems for earthquakes. The inexpensive method enables accurate earthquake measurements even on the ocean floor.
"We¡¯re taking advantage of a function that existing fibre-?optic infrastructure already performs: we obtain the vibration data from the active noise suppression system, which has the job of increasing the accuracy of the signals in optical data communication," said geophysics professor Andreas Fichtner.
How was the system developed?
Scientists from the Institute of Geophysics at ETH Zurich, working together with the Swiss Federal Institute of Metrology (METAS) say all that's needed to achieve this is the storage of active noise suppression data and its evaluation, without additional devices or expensive infrastructure.
Active phase noise cancellation (PNC) can measure seismic tremors underwater akin to how noise cancelling headphones work by making ambient noise completely disappear.
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Such headphones have microphones designed to pick up internal noise that is inverted and fed into the audio signals in real-time. Similarly, PNC inverts signals and removes external noise one-to-one, which makes it inaudible.
"In the PNC of an optical data communication system, the ¡°ambient noise¡± in the optical fibre is determined by comparing the originally transmitted signal with a partial signal that is reflected by the receiver. The difference between the two signals then indicates the interference to which the light signal was exposed on its way through the optical fibre," ETH Zurich explained in a news release.
How would this fibre-optic technique work?
During optical data transmission, "noise" is produced because optical fibres are disturbed by mere micrometres. Deformations in the Earth's surface due to earthquakes, water waves, differences in air pressure, and human activity can cause this.
With each deformation, the fibre is slightly shortened or lengthened. In turn, it produces what's known as a photo-elastic effect that causes the speed of light in the fibre to fluctuate.
The change in fibre length and fluctuations in the speed of light are able to change the light signal's frequency by a small factor. This phenomenon is already employed to measure vibrations in various special instruments.
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Scientists, in this particular assessment, investigation the noise suppression system in the fibre-?optic communication of Switzerland¡¯s atomic clock infrastructure. "Using the PNC of the fibre-?optic link between Basel and the atomic clock site at METAS in Bern, we were able to track every single wave of a magnitude 3.9 earthquake in Alsace in detail," Fichtner said. "But even better, a model of the quake based on our data also corresponded extremely accurately to the measurements taken by the Swiss Seismological Service."
Essentially, PNC data may be used to figure out an earthquake's location, depth, and magnitude with a high degree of accuracy. "This is particularly interesting for comprehensive tsunami warnings or for measuring earthquakes in less developed regions of the world," Fichtner said.
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