Fibre sensing at regional scales on onshore-offshore telecom cables

Fibre sensing technology can provide seismic data at a variety of scales, but most studies sensing telecom infrastructure however focus on short (<50 km) cables, due to instrumentation range limitations, presence of line amplifiers and, importantly, difficulty in accessing commercially valuable fibres. This has so far hampered the use of fibre sensing to study low frequency signals—key for global seismic monitoring and deep Earth imaging—for which large inter-channel distances and spatial stacking are required.

In this study, we showcase results from a new project acquiring on- and offshore fibre sensing data on commercial telecom fibres in the North Atlantic Ocean, Irish Sea and across Ireland, using a combination of Distributed Strain Sensing (DSS, also known as DAS) across >400 km on land and near-shore, and new distributed Microwave Frequency Fiber Interferometer (MFFI) technology to sense the 1700 km on the IRIS submarine cable connecting Ireland to Iceland. All data were recorded using technology capable of sensing live, traffic-carrying fibres, and the onshore DSS data were recorded on fibres actively carrying the Irish National Research and Education Network traffic.

Our DSS results show that while having lower signal to noise ratios compared to nearby seismic stations, DSS on noisy telecom fibres can successfully record most Mw>6 teleseismic events worldwide, microseisms originating in the North Atlantic and Irish Sea as well as broadband seismic signal caused by localised rainfall on the cable. In order to sense the North Atlantic Ocean, we present the newly developed MFFI sensor, which uses fibre interferometry in conjunction with high-loss loop backs at line amplifiers, turning each section between amplifiers (50-100 km) of the cable into independent strain sensors. Since its installation in November 2025, we have sensed major teleseismic earthquakes (Mw 7.6 Hokkaido-Japan and Mw 7.4 Molucca Sea-Indonesia), secondary microseisms generated by Atlantic storms and local, ocean-bottom variations in ocean tides.

Our results show that we can leverage the existing telecom infrastructure to perform seismic and environmental sensing over large distances, filling the seismic instrumental gap in the oceans and provide key data for seismic and ocean monitoring and deep Earth imaging.