Closing the Ocean Data Gap: near-coast fibre-optics sensing to monitor tectonic and volcanic events

Scientific infrastructures cover areas worldwide to monitor Earth system processes. Most of these are installed on land, but land masses make up only about 30% of the Earth's surface. The oceans and particularly the ocean floor are difficult to access, and thus are not adequately instrumented and monitored. Since they play a critical role in regulating climate as a heat and carbon store, and are the site of deadly natural disasters including strong earthquakes, tsunamis, and volcanic eruptions, we are faced with a substantial gap in the monitoring of critical physical parameters in the near-coast and offshore domains. For seismology and geohazard assessment the global coverage is as essential as for oceanography and climate studies. Using a combination of established and novel technologies implemented in telecommunication infrastructure on the sea-floor and coastal areas will, without a doubt, prove to be a game changer in geosciences and Earth system understanding. In recent years, three different and complementary fiber-optics-based technologies have gained at-tention as valuable tools for investigating Earth system processes: Distributed Fiber-Optic Sensing (DFOS), State of Polarization (SoP), and Science Monitoring and Reliable Telecommunications (SMART) cable systems. The first two technologies use the fiber-optic cable as the sensing element, while in the third technology type (SMART cable systems), independent sensors are integrated into fiber-optic cable repeaters, and the cable is used for power and data transmission. These technologies and their application to geoscientific problems are at different levels of maturity, and combining them with a FAIR data infrastructure into a demonstrator is the vision of the planned infrastructure project SAFAtor (see presentation by Cotton et al., this meeting). We want to present and discuss in the framework of our planned SAFAtor initiative (SMART Cables And Fiber-optic Sensing Amphibious Demonstrator) the first experiments we performed in the testbeds foreseen at Mt. Etna, in the Marmara Sea, and in Chile. While Etnas volcano-tectonic setting is complex (Jousset et al., Currenti et al.) and origin and spatial-temporal evolution of the volcanism and its relationship with the tectonic dynamics are still a matter of debate, its unstable eastern flank stretches far into the Ionian Sea with an average flank movement of 2-3 cm/yr. In the Marmara Sea, critical data on offshore fault structure and seismicity will enable efficient investigation of structure and seismic hazard underneath densely populated areas along the coast, especially in Istanbul where the major earthquake is overdue. This also holds for Chile, where ongoing subduction erosion and mature seismic gaps should be complemented by new monitoring efforts. Developing our SAFAtor activities in terms of adapted fibre-optics sensing and monitoring will thus help areas exposed to hazard at active plate boundaries and volcanic systems in coastal zones.