On the ocean floor there are over one million kilometres of fibre optic cables used for telecommunications. In the past, many scientists have looked for an effective method to monitor seismicity through those cables and today, the California Institute of Technology (Caltech), together with some optics experts at Google, have created a way to detect earthquakes thanks to cables in optic fibre. 

The study published by the institute has shown that submarine fibre optic cables are sensitive to wave pressure and temperature variations that can be linked to external events and therefore are useful for the study of earthquakes and for analysing the ocean floor. 

This new technique can really convert the majority of submarine cables into geophysical sensors that are thousands of kilometers long to detect earthquakes and possibly tsunamis in the futureWe believe this is the first solution for monitoring seismicity on the ocean floor that could feasibly be implemented around the world. It could complement the existing network of ground-based seismometers and tsunami-monitoring buoys to make the detection of submarine earthquakes and tsunamis much faster in many cases, said Zhongwen Zhan, assistant professor of geophysics at Caltech. 

The study was mainly based on the monitoring of Google’s Curie submarine cable, about 10,000 kilometres long, that connects the Californian city of Los Angeles to Valparaíso in Chile. The cable, with a diameter of two centimetres, is located at a depth between four and six kilometres and contains four optical fibres. The monitoring lasted nine months (from December 2019 to September 2020) during which the team of experts recorded about twenty earthquakes, including the one of magnitude 7.7 that took place off the coast of Jamaica on January 28, 2020. 

The researchers are now studying the development of a machine learning algorithm that will allow to understand whether the changes in polarization (of the light running through the fibre optic cables) can be linked to earthquakes or ocean waves, or to other causes such as ships or animals close to the cable.