Mata Flores D. auteur aut IRD Mercerat E.D. auteur aut IRD Ampuero Jean Paul auteur aut IRD Rivet D. auteur aut IRD Sladen A. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Distributed acoustic sensing (DAS) enables data acquisition for underwater Earth Science with unprecedented spatial resolution. Submarine fibre optic cables traverse sea bottom features that can lead to suspended or decoupled cable portions, and are exposed to the ocean dynamics and to high rates of marine erosion or sediment deposition, which may induce temporal variations of the cable's mechanical coupling to the ocean floor. Although these spatio-temporal fluctuations of the mechanical coupling affect the quality of the data recorded by DAS,and determine whether a cable section is useful or not for geophysical purposes, the detection of unsuitable cable portions has not been investigated in detail. Here, we report on DAS observations of two distinct vibration regimes of seafloor fibre optic cables: a high-frequency (>2 Hz) regime we associate to cable segments pinned between seafloor features, and a low-frequency (<1 Hz) regime we associate to suspended cable sections. While the low-frequency oscillations are driven by deep ocean currents, the high-frequency oscillations are triggered by the passage of earthquake seismic waves. Using Proper Orthogonal Decomposition, we demonstrate that high-frequency oscillations excite normal modes comparable to those of a finite 1-D wave propagation structure. We further identify trapped waves propagating along cable portions featuring high-frequency oscillations. Their wave speed is consistent with that of longitudinal waves propagating across the steel armouring of the cable. The DAS data on cable sections featuring such cable waves are dominated by highly monochromatic noise. Our results suggest that the spatio-temporal evolution of the mechanical coupling between fibre optic cables exposed to the ocean dynamics and the seafloor can be monitored through the combined analysis of the two vibration regimes presented here, which provides a DAS-based method to identify underwater cable sections unsuitable for the analysis of seismic waves. specialized MEDITERRANEE FRANCE GRECE 066GPHMAR 234 2 1389-1400 2023 0956-540X https://www.documentation.ird.fr/hor/fdi:010089971 10.1093/gji/ggad139 0956-540X [F B010089971] https://www.documentation.ird.fr/hor/fdi:010089971 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2024-07/010089971.pdf IRD - Base Horizon / Pleins textes 2024-05-06 2025-02-24 fdi:010089971 fre