Precision acoustic geodetic measurement of seafloor motion over 10 km | CU Experts

The technique deploys three or more precision transponders (PXP) on the seafloor, collects simultaneous round-trip travel times (±5 μs) from a hydrophone towed uniformly around the network above the seafloor (300 m), and measures the sound velocity (±10 ppm) and the relative depth of the hydrophone (±10 cm). These observations, modeled as ray traces through a spherical ocean model and ellipsoidal geodesic ray distances, are inverted to determine simultaneously, the centimeter level position of the transponders and towed hydrophone locations. Three PXPs were deployed on the Pacific and three on the Juan de Fuca plate to determine the pattern of deformation around the Juan de Fuca Ridge. Measurements were collected in 1994, 1995, and planned for 1996. Since 1991, at least four PXPs have been maintained seaward of the Cascadia Subduction Zone to measure the subduction rate using the Global Positioning System. No measurable relative horizontal motion among these PXPs is expected providing a test of system repeatabilities. Measurements were collected in 1991, 1993, 1994, 1995, and planned for 1996. This paper discusses the instrumentation, operations, measurement precision, modeling requirements, and current results. [Work supported by NSF.]

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