Collaborative Research: Meshed GNSS-Acoustic Array Design for Lower-Cost Dense Observation Fields

Precise observations of seafloor deformation is important for assessing ongoing geologic processes and the hazards they pose, including the largest earthquakes, tsunamis, submarine volcanism, hydrocarbon changes, and submarine landslides. Making observations of the centimeter-scale deformation that occurs over a year or longer using a combination of sea surface and seafloor instrumentation is currently expensive, particularly when using a large research vessel as a part of the measurement design. In this project, the team will use a rather new but previously tested autonomous, green-powered vessel that replaces the ship-based measurement design, reducing measurement costs by more than an order of magnitude over prior methods. To further reduce instrumentation costs and enable more broad use, the project will test new design geometries that have the potential to significantly increase capabilities where dense observations are needed. During this project, a postdoctoral scholar will be trained as a next-generation scientist and educator. The data collected will be contributed to a community data archive, and methods will be incorporated into community software for research. Following the project, the instrumentation will become a part of an existing NSF-funded instrument pool, doubling the capabilities for deep-water observations from 3000 to 6000 meters. The surface vessel for these operations, a commercially available Wave Glider, will be outfitted with antennas for positioning itself using Global Navigational Satellite Systems (GNSS). The vessel will interrogate a mesh-network of seafloor transponders during the summers of 2024 and 2025 using a lower frequency acoustic signal than currently available with the US instrument pool to allow for the extended ranging needed for deeper water operation. The 10-transponder array will be deployed between 4 and 6 km depth along a segment of the Aleutian trench in 2024, combining ship-activities with an existing community geodetic experiment, that can only extend to 3 km depth. The dense mesh-network design with the shared use of transponders could potentially allow for a ten-fold increase in instrumental efficiency, depending on geometry, over existing methods existing methods that require three transponders per observation point. Lastly, the experiment will additionally evaluate the potentially increased errors associated with necessarily high-gradient seafloor environments that are common in subduction zones. Such steep measurements could be similarly applied to passive continental slopes that have the potential for destructive submarine landslides. While the design experiment tests methodology, the location was chosen because little is known about the behavior of faults in the region, where a large earthquake in 1946 created an outsized tsunami. Detailed information about ongoing fault behavior in the region can illuminate the currently unknown mechanical coupling in the region that builds for future earthquakes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.