Large-scale monitoring of Earth’s tidal response on the deep seafloor using fiber-optic sensing

The understanding of the seafloor tidal response in deep-sea environments remains sparse due to the logistical challenges associated with long-term deployment of sensors in such extreme environments. Here, we demonstrate the capability of Distributed Acoustic Sensing technology to monitor tidal deformation in the deep sea. Leveraging the thermal stability of the deep Mediterranean Sea and a signal processing approach for low-frequency noise suppression, we achieve a sensitivity on the order of picostrain per second. Although common-mode noise removal, a pivotal stage in data preprocessing, attenuates part of the tidal deformation signals, it effectively enhances the continuous monitoring of part of the Earth tides over tens of kilometers with kilometer-scale spatial resolution. This result is supported by agreement with theoretical predictions. These findings support the use of Distributed Acoustic Sensing for extracting sub-nanostrain signals at periods exceeding several hours, with potential applications to constraining the elastic and mechanical properties of the upper crust in offshore regions and calibrating ocean tide models. Distributed Acoustic Sensing enables sensitive, continuous monitoring of Earth tides in the deep sea, with potential applications to constraining the elastic and mechanical properties of the upper crust in offshore regions and calibrating ocean tide models, according to an analysis of a 53-km offshore telecom fiber-optic cable near Toulon, southern France.