Community Seafloor Geodetic Infrastructure for the Measurement of Deformation

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Subduction zones are geologic faults that begin offshore where one tectonic plate slides beneath another. Because of friction, some of the motion of the lower plate is transferred to and builds up in the upper plate. The abrupt release of the built-up strain caused by this energy transfer causes the strongest earthquakes on earth. These great earthquakes cause widespread damage from ground shaking and from flooding of coastal areas from resulting tsunami waves. Recent events have occurred in Sumatra in 2004, Chile in 2010, and Japan in 2011. Subduction zones also lie offshore the U.S. coasts along Northern California, Oregon and Washington State and another along Alaska and the Aleutian Islands. Both of these subduction zones have experienced great earthquakes in the past -- Alaska had a great earthquake in 1964 and Oregon and Washington State in 1700 -- and both will do so again in the future. A goal of the scientific community is to better understand the geophysical processes at work at these subduction zones in order to improve assessment of potential earthquake hazards. Land-based high-precision measurements with the Global Navigation Satellite System (GNSS) can measure the slow build-up of strain locally, but even the coastal sites are too far from the submerged shelf to provide reliable estimates far offshore, where the fault zone reaches the seafloor and where most tsunamis are generated. The GNSS-Acoustic technique, which combines GNSS with acoustic ranging from a small robotic platform on the sea surface to sensors (transponders) on the sea floor, allows measurement of centimeter-scale horizontal motion of the seafloor. This can be combined with measurements of ambient pressure at the sea floor to detect vertical as well as horizontal motions. To date only one prototype vehicle and approximately a dozen seafloor transponder have been available for the scientific community. This project will add three new robotic platforms and forty-eight additional seafloor transponders and for the first time incorporate pressure sensors directly in several of the transponders. This project will approximately quintuple the equipment available to the research community to make these important measurements.This one-year project will procure and commission geodetic instrumentation to measure seafloor deformation. Several recent and prominent workshop reports and vision documents by the earth science community have identified a need for growing seafloor geodetic capabilities to answer pressing questions about earthquake, tsunami, and volcanic processes. The infrastructure will provide accurate horizontal and vertical positioning of the seafloor through two reliable and proven techniques with published scientific results: GNSS-Acoustics and sea water pressure. Data from both systems will be acquired using wave gliders, which are remotely operated wave- and solar-powered sea surface platforms. This award does not fund operation, maintenance, nor deployment of this infrastructure for science. Seafloor geodesy is poised to be transformative. It will allow for a broad community of existing and next-generation earth scientists to study active deformation on the seafloor. Improved access to these instruments will foster and communicate knowledge of the new methods and science outside of the current and very small marine community, to a much larger scientific community primarily consisting of highly-skilled land-based geodesists, and an inclusive next-generation scientific workforce.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.