How to turn underwater cables into earthquake detectors

How to turn underwater cables into earthquake detectors

In addition to transmitting large amounts of information between continents, transoceanic fiber-optic cables can act as environmental sensors for seismic movements and ocean currents. To this end, the new equipment uses replications carried out by this infrastructure and was able to detect earthquakes on the line connecting Peru and Indonesia to the United Kingdom with Canada.

View of the Tannat submarine cable access on the shores of Las Toninas Buenos Aires, Argentina's internet connection point
View of the Tannat submarine cable access on the shores of Las Toninas Buenos Aires, Argentina’s internet connection point

Various studies have already shown that great Underwater optical communication cablesWhich is currently used to transmit multiple data, can be used as sensors to monitor seismic activity and other disturbances on the seabed.

However, existing equipment often has limitations in terms of spatial resolution and sensitivity, as the entire length of the cable – which can extend thousands of kilometers – acts as One sensor.

Now an international group of scientists was leading National Physical Laboratory (NPL) The United Kingdom has developed a method that turns a long fiber optic cable into a multi-segment or Individual sensors Can register a mess around them. In this way, it is possible to better detect and characterize underwater seismic vibrations and ocean currents, says a study published in Science.

Using laser technology and performing interferometric measurements at the bottom of the cable, the method incorporates numerous of its data. Repetitions – Used to amplify optical signals – and special fibers that connect them.

View of some of the underwater cables that cross oceans and seas across the planet to carry telecommunications
View of some of the underwater cables that cross oceans and seas across the planet to carry telecommunications

“The speed of light propagation in a fiber optic is greatly affected by environmental factors such as vibrations, variability in pressure and temperature, and Ultrastable interferometry“We can detect these extremely small changes, as shown in the previous 2018 Earthquake Survey,” explains the lead author. Giuseppe Mara NPL, which emphasizes: “And there is no need to change the underwater telecommunications infrastructure.”

Use the repeat return path

“But at a time when the cable was acting as a single detector, in this new study we show that it can act as a set of detectors,” he continues. We did this using modern cable architecture that includes a Way back In their repeaters, allowing us to “cut” the cable into smaller pieces, each of which acts as a sensor.

The researchers tested their technique on the submarine cable that connects the UK and Canada.  The actual number of repetitions (128) is reduced in the figure for illustrative purposes only
The researchers tested their technique on the submarine cable that connects the UK and Canada. The actual number of repetitions (128) is reduced in the figure for illustrative purposes only

Operators of these long transoceanic connections use return paths to periodically monitor the status of their optical amplifiers. Checks are usually performed on a scheduled basis or in case of failure, so in most cases these channels are unusable and can be used for the function suggested by the authors.

“If this new technology were used on a large number of cables around the world, the existing global network could become a giant set of thousands of environmental sensors for earthquakes, but also, as shown in this paper, for marine currents and tides.” Emphasizes Mara.

The researchers tested their method on an underwater fiber-optic link 5860 km In the length that runs between UK and Canada, With repetitions approximately every 46 km. They tested some of them and were able to detect various seismic movements and ocean currents along the cable.

In particular, they detected a magnitude 7.5 earthquake that struck the north. Peru Thousands of miles away – on November 28, 2021 and another 7.3 magnitude Sea of ​​flowers (Indonesia) next month, December 14th.

Underwater cable, fiber-optic in the middle and protection from moisture and shock;  Measures 2 to 7 cm in diameter, depending on its location
Underwater cable, fiber-optic in the middle and protection from moisture and shock; Measures 2 to 7 cm in diameter, depending on its location

“Earthquakes and currents are the main use at the moment,” confirms the NPL scientist. Tsunami warning And maybe on a map Temperature variations On the seabed, which is affected by global warming.

The authors acknowledge that other methods, e.g. Distributed Acoustic Sensing (DAS)Which has recently been used in the Canary Islands also offers high sensitivity and spatial resolution as environmental sensors, but this is a limited approach to coastal zones. Up to 100 km Due to signal attenuation from the coast.

“DAS works a bit like radar: laser pulses are emitted into the fiber and small reflections (due to fiber imperfections) are analyzed, but the reflected signal is extremely low and usually operates at 50-80 km,” Mara explains.

“In our technology, we use light that travels forward and backward through the return path inside the repeater, and this – he concludes – makes the return signal one order of magnitude larger than the DAS, allowing you to reach Over long distances And has a high signal-to-noise ratio for ultra-accurate measurements.

Agency SINC

Source: La Nacion

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