NPL research demonstrates how submarine fibre cables could be used to detect earthquakes

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The undersea cables used for communications could be used to detect underwater earthquakes according to scientists at the National Physical Laboratory (NPL) and Istituto Nazionale di Ricerca Metrologica (INRiM, Italy), who have developed a new method of using the cables as ‘acoustic sensors.’

Research from the two organisations, in collaboration with the British Geological Survey, and University of Malta, 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. Using the new method, the fibre itself is used for detection where it had previously been used to transmit data between earthquake-detecting devices. The researchers used the land-based and undersea cables as acoustic sensors to detect earthquake-induced vibrations along the length of the cable.

In its announcement, which was distributed via a press release, NPL said that the undersea cable network used currently accounts for more than a million kilometres of optical fibre, spanning the Atlantic and Pacific oceans and is rapidly expanding. Taking advantage of it, said the institute, 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 expanded and strengthened, on both land and sea. In addition, using the existing cable infrastructure means that the associated costs would be lower than installing new sensors on the seafloor.

Other work has been undertaken on using submarine cables for this purpose over the years, and in Japan, earthquake and tsunami seismometers had been installed on NEC’s submarine cables in 10 locations since 1979 (see Can ocean cables go green?). In the future, said NPL, the new technique could potentially be used to ensure warning time in the event of tsunamis caused by underwater earthquakes, or even changes in volcanic structure. Although the innovation has not been tested in this area, the ability to detect underwater earthquakes close to the epicentre, rather than after they are picked up by on-land seismometers, presents an opportunity for the future.

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.’

Davide Calonico, principal research scientist at INRiM and coordinator of the research, added: ‘It is always a serendipity when techniques used in one branch of science can be so useful in another area. Here, established techniques for time and frequency metrology achieve new interesting results when applied to underwater seismology and sensing. Our capability to measure the infinitesimal change in the length of the fibre using an ultra-stable laser almost in real-time has been crucial to exploit the underwater infrastructure of optical fibres used for telecommunications.’

Commented Dr Richard Luckett, seismologist at the British Geological Survey: ‘The potential of this method is huge. By using existing infrastructure, we can produce a wealth of new and important data.  The ocean floor is currently poorly monitored seismically but is home to some of the most interesting geological processes on earth.’

Dr Andrè Xuereb, senior lecturer in physics at the University of Malta concluded: ‘This exciting collaboration with our colleagues in the UK and Italy gave rise to some exceptional results and solves a problem of global relevance. It shows the power of international collaborations and fundamental science research to overcome challenges and create new technologies.’

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