Detecting strain with a fiber optic cable on the seafloor offshore Mount Etna, Southern Italy

A groundbreaking study successfully detected permanent strain at the seafloor for the first time using a 6-km-long fiber optic cable deployed offshore Mount Etna, Sicily. Over a 21-month period (October 2020 to July 2022), the cable experienced a total elongation of 2.5 cm, with significant strain (+25 to +40 microstrain) observed at two locations where it crossed an active strike-slip fault. The most pronounced changes occurred between November 19 and 21, 2020, suggesting potential fault slip or seabottom currents as causes. Brillouin Optical Time Domain Reflectometry (BOTDR) laser reflectometry demonstrated the cable's ability to detect strain in near real time, with strain amplitude increasing to +45 to +55 microstrain over subsequent months, affecting a longer portion of the cable. A sandbag experiment further validated the technique by showing how the cable deforms under applied load and how deformation signals partially dissipate due to elastic properties. These findings highlight the potential of fiber optic cables for seismological monitoring in deep-sea environments.

Gutscher, M.-A., Quetel, L., Murphy, S., Riccobene, G., Royer, J.-Y., Barreca, G., Aurnia, S., Klingelhoefer, F., Cappelli, G., Urlaub, M., Krastel, S., Gross, F., & Kopp, H. (2023). Detecting strain with a fiber optic cable on the seafloor offshore Mount Etna, Southern Italy. Earth and Planetary Science Letters, 616, 118230. https://doi.org/10.1016/j.epsl.2023.118230