Fibre sensing at regional scales with telecom cables: the IMAGFib project

Fibre sensing technology can provide seismic data at a variety of scales, but, currently, the difficulty in accessing long telecom fibres, together with the novelty of the instruments, their range limitations and massive data output, mostly constrain its applications to fibre <100 km long.

In this study, we showcase the first results from the new project IMAGFib (multiscale seismic IMAGing with optical FlBre telecom cables), acquiring on-/offshore fibre sensing data on commercial telecom fibres in the North Atlantic Ocean, Irish Sea and across Ireland. This project combines utilising Distributed Strain Sensing (DSS, also known as DAS) on >400 km with 10 m spatial sampling with a new, distributed Microwave Frequency Fiber Interferometer (MFFI) capable sensing over 1700 km of submarine cables connecting Ireland to Iceland, albeit with a coarser 50-100 km spatial sampling. We use the acquired data to assess the performance of fibre sensing as a regional-to-continental scale seismic and ocean monitoring, and a future imaging tool, with a focus on low frequencies (<1 Hz).

By forging research collaborations with multiple telecom operators, we are able to perform DSS on multiple cable sections across the region, aiming to cover a continuous linear profile from Wales to the North Atlantic through different experiments (to be completed early 2026), part of which is performed on live, traffic-carrying telecom fibres. 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, as well as microseisms originating in the North Atlantic and/or Irish Sea on all sections of the cable.

In order to extend fibre sensing far into the North Atlantic Ocean, we present the newly developed MFFI sensor, which uses optical interferometry in conjunction with high-loss loop backs at line amplifiers, turning each section of the cable between amplifiers (50-100 km) into independent strain sensors. For our experiment on the Ireland-Iceland cable, this yields 17 traces along the fibre. Ongoing recording in late 2025-early 2026 allows us to evaluate its capability to sense seismic signals, marine storms, currents and possibly ocean-bottom temperature variations across seasons.

With a strong focus on long-range and low-frequency sensing and integration with live telecom infrastructure, IMAGFib is centred on the establishment of fibre sensing as a global geo-sensing tool. Our successful results using DSS on live telecom fibres, and developing MFFI technology using affordable off-the-shelf components represent a key step in advancing the efforts to broaden trusted research utilising existing, commercial telecom cables.