Researchers use underwater telecoms cables to detect earthquakes

Cables carrying telephone calls and internet messages deep beneath the world’s biggest oceans could also give early warning of devastating tsunamis after a “serendipitous” combination of techniques.

Researchers at the UK’s National Physical Laboratory and the National Institute of Metrological Research in Italy combined their knowledge of metrology with seismology to successfully detect underwater earthquakes.

The technique, which involves sending lasers down existing fibre-optic cables, could one day save lives by giving advanced warning of tsunamis.

Despite the high proportion of Earth covered by water, most earthquake monitoring stations are on land because it is too expensive to install them on the seafloor. As a result, many underwater seismic movements are not detected, limiting scientists’ ability to study the globe’s interior.

“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,” said Giuseppe Marra, senior research scientist at the NPL.

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

Collaborating with the British Geological Survey and the University of Malta, the researchers used telecommunications cables as acoustic sensors. Earthquake vibrations cause “infinitesimal changes” in the cables’ length, allowing the team to monitor them in real time.  

“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,” said Davide Calonico, principal research scientist for the Italian group.

The technique could create a global network for earthquake monitoring without any extra underwater infrastructure, said the researchers. The undersea cable network already accounts for more than one million kilometres of optical fibre spanning oceans including the Atlantic and Pacific, and it is rapidly expanding owing to the massive increase in mobile services and the internet.

The research was published in Science.