A Moored Geodetic Seafloor Monitoring System (GEOCE)

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The PI's propose to construct and demonstrate a novel capability to carry out geodetic seafloor motion measurements from oceanographic moorings and observatories. The Moored Geodetic Seafloor Monitoring System (GEOCE) system would integrate several methods and technologies, most of which have been proven separately in different applications already. It consists of continuous raw-waveform differential GPS measurements on the surface buoy of the mooring, to determine the horizontal and vertical motion of the buoy with sub-centimeter accuracy. Horizontal seafloor motion is measured via acoustic transponder interrogations relative to the surface buoy, a variant of an existing ship based approach. Vertical seafloor motion is determined via high-precision bottom pressure measurements, after removing sea surface height motion (using the GPS) and internal ocean density fluctuations (using water column CTD sensors in the mooring). The residual bottom pressure signal is seafloor motion or sensor drift. An in-situ calibration system will be added to determine the drift. Irregular vertical motion or sudden events would be detectable even without this calibration system. The current proposal consists of the engineering development to bring these together in a new (moored) configuration, and to exploit the synergy between the disciplines. Broader ImpactsThis activity will advance discovery by enabling the first true multi-scale temporal studies of plate motions beneath the oceans. Specifically, it should help to understand the processes of stress and strain at convergent margins, which are a major risk area for great earthquakes and tsunamis. Eventually, they could be used to identify locked margins at risk of catastrophic events. The proposed instrumentation will fill the need for a seafloor geodetic system that provides GPS referenced, sub-centimeter resolution of vertical and horizontal deformation over multi-time scales. The GEOCE system has the potential to significantly impact both the geophysical and oceanographic communities by providing information for tectonic/sea floor motion, water column and bottom pressure data, hazard, and climatic studies. This proposal will also involve the participation of 4 graduate students, training the next generation of marine geodesists.