Fiber-optic seismology

Fibre-optic deformation sensing provides new opportunities for seismic data acquisition with high spatio-temporal resolution. The relative ease of deploying fibre-optic cables, or the possibility to piggyback on existing telecom infrastructure make this technology particularly attractive for environments where large numbers of conventional seismic instruments may be difficult to install. These include active volcanoes, glaciers or densely populated urban centres. In the first, more observational part of this talk, we will present a series of case studies where Distributed Acoustic Sensing (DAS) greatly improved the location of glacial icequakes and our knowledge of ice sheet structure, enabled the observation of previously unknown volcanic tremor and resonance phenomena, and increased the number of detected seismic events by two orders of magnitude – all relative to data from existing seismometer networks. In the second, more theoretical part, we will report on the development of two novel fibre-optic sensing systems based on the transmission of laser pulses that enable interrogation distances of thousands of kilometres. While the first system exploits microwave-frequency signals, the second system co-uses the active noise cancellation in metrological frequency dissemination. For these kinds of transmission systems, we show that different segments of the fibre can have different sensitivities for deformation sensing, largely depending on fibre curvature. Data from a large-scale experiment support this theory and demonstrate that transmission-based systems can constrain earthquake source mechanisms using only a single time series.