Sensing ground motion using telecom fibres: from Earthquakes to urban traffic

Fibre sensing technology allows to use optical fibre cables as sensors for ground vibrations. Modern fibre-optic sensing technologies employ lasers to “interrogate” optical fibres, effectively converting them into arrays of ground-motion sensors by analysing the phase changes of backscattered or reflected light along the cable. Originally developed to monitor the structural health and security of telecommunication infrastructures, these systems have since been adapted for a range of geophysical and environmental applications, including the detection of earthquakes, typhoons, vehicular traffic, and even whalesong.

The most widely used form of this technology, Distributed Acoustic Sensing (DAS), mostly utilizes lasers with wavelengths that overlap telecommunication network traffic, prompting telecommunications operators to limit its deployment to spare, unlit ("dark") fibres. The scarcity and limited accessibility of dark fibres have so far constrained efforts to exploit the global telecommunications network for environmental applications. The spatial resolution of DAS is however of particular interest to both researchers and cable operators, as it gives the detail needed for effective environmental-, and perimeter and infrastructure monitoring.

We deployed DAS on over 100 km of telecommunication fibre cables in Ireland, sensing a wide array of signals ranging from distant, strong Earthquakes to vibrations related to urban traffic in Ireland’s cities and even signal possibly originated by the water flow in rivers. Our records show that telecommunication fibre cables can be successfully used for environmental and urban monitoring across large distances, filling the gap left by traditional ground vibration sensors—which are difficult and costly to deploy in large numbers. By collaborating with HEAnet, we also explored fibre sensing on data-carrying network fibres—as opposed to dark fibres—recording the destructive Myanmar Earthquake over 9000 km away from its source on cables between Galway and Athlone.

Commercial fibres span regions of significant seismic hazard, including hundreds of thousands of kilometres crossing submarine subduction zones and the world’s largest cities. By enabling high-resolution sensing on hundreds of kilometres of telecom fibres, we aim to open a pathway to transforming global telecom infrastructure into a distributed platform for geoscience observation and early warning.