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Abstract

Hundreds of submarine communication cables cross the world's oceans. Today, these cables are unaware of their environment. However, repeaters spaced at ~50 km intervals along them offer access to power and bandwidth, providing the opportunity to add sensor capability to future SMART cables (Science Monitoring And Reliable Telecommunications), a concept advanced by a Joint Task Force of the International Telecommunication Union, the World Meteorological Organization and the Intergovernmental Oceanographic Commission of UNESCO1. Two NASA workshops focused on applications in climate research and oceanography2. In the workshop described here, research scientists, practitioners from earthquake observatories and tsunami warning centers, and engineers discussed potential applications of SMART cables for earthquake and tsunami early warning and reviewed existing approaches and how they can benefit from SMART cables. They also considered what possibilities exist in research on Earth structure, the physics of earthquakes, and tsunami excitation and propagation. According to current planning, a first generation of SMART cables will be equipped with a simple instrumentation package containing accelerometers, pressure gauges and temperature sensors in order to make the sensor package simple and able to withstand the rough deployment conditions in standard cable-laying operations. Most destructive tsunamis are triggered by great earthquakes along the plate boundary faults in subduction zones. Their offshore location makes quick detection and assessment of their tsunamigenic potential a real challenge using land-based networks. The DART system of ocean bottom pressure detectors can detect ocean-crossing tsunamis but sensors are too sparse and too far from shore to be much help in local warning. Dedicated submarine cables present another real-time solution but come with a hefty price tag. Thus a comprehensive coverage of all endangered subduction zones is out of reach, particularly in the developing world. Already a few cables crossing the Pacific can reduce the time-to-detection of potentially tsunamigenic earthquakes along the Ring of Fire by ~20%, and the detection of the actual tsunami wave would be reduced by a similar fraction. With trench-parallel cables even larger improvements are possible. The continuous high sampling rates possible in a cable allow separation of tsunami and seismic wavefields, allowing reliable tsunami measurements in the near field. Wide science benefits are expected from the faithful recordings of offshore earthquakes as well as from the vastly improved coverage of the ocean basins from even a small number of SMART cables.