undersea cable internet traffic

Underwater earthquake monitoring system bolted on to existing fibre network

Underwater earthquakes could be detected using pre-existing cross-continent fibre cables that form the basis of the global communications infrastructure.

Scientists at the National Physical Laboratory (NPL) and Istituto Nazionale di Ricerca Metrologica (INRiM) detected earthquakes using land-based and underwater fibre-optic links of lengths up to 535km and ranging from 25 to 18,500km from the earthquake’s epicentre.

Optical fibre has previously been used to transmit data between earthquake-detecting devices, but in the new method the fibre itself is used for detection.

Whilst approximately 70 per cent of the surface of the Earth is covered by water, the large majority of earthquake monitoring stations are on land because it is too costly to install them on the sea bottom.

A network of seafloor stations large enough to cover most of the Earth’s waters is estimated to cost between $700m and $1bn. A large fraction of underwater earthquakes go undetected, limiting our ability to investigate the Earth’s interior.

The researchers used the land-based and undersea cables as ‘acoustic sensors’ – detecting earthquake-induced vibrations along the length of the cable.

By using this technique on the existing undersea telecommunications network, a global network for underwater earthquake monitoring could be implemented, without the need to install additional devices on the seafloor.

The undersea cable network, which currently accounts for over one million km of optical fibre, already spans the Atlantic and Pacific oceans, and is rapidly expanding due to an exponential rise in mobile services and the Internet.

Taking advantage of this vast network could enable the detection of huge numbers of underwater earthquakes that are currently missed as well as furthering our understanding of the Earth’s interior.

By integrating this approach with the current seismometer-based networks, the global earthquake monitoring infrastructure could be significantly expanded and strengthened, on both land and sea. Utilising the existing cable infrastructure means that the associated costs will be substantially lower than installing new sensors on the seafloor.

In the future, the technique could potentially even be used to ensure precious life-saving warning time in the event of tsunamis caused by underwater earthquakes, or even changes in volcanic structure.

Giuseppe Marra, Senior Research Scientist at NPL and lead author on the paper, said: “Detecting underwater earthquakes is crucial to understanding how our planet works, but installing a large array of ocean bottom sensors is a very challenging and expensive task.

“We have now discovered there is a solution at hand, which relies on existing infrastructure rather than on new installations. A great new tool for research in geophysics and other areas of science. 

“We made the first detection of seismic events whilst running frequency metrology experiments not designed to detect earthquakes. I am delighted to see two scientific areas, frequency metrology and seismology, meeting in such an unexpected way.”

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