A detailed view of the South Pacific geoid from satellite altimetry

Abstract

Images of sea surface undulations in the South Pacific have been constructed from GEOS 3 and SEASAT altimeter data. Height discrepancies at crossover points, associated with long‐wavelength radial orbit error, were suppressed by taking along‐track derivatives of the ascending and descending profiles. These geoid slopes were then rotated and scaled to produce the north and east components of the deflection of the vertical. Finally, the results are displayed by using the hill shading technique, where gray‐tone images represent the innner product of the deflection vector with an assigned sun vector. Less apparent sea surface undulations can be enhanced by varying the sun's zenith and azimuth. Shorterwavelength sea surface undulations reflect seafloor topography. For instance, fracture zones (FZ's) appear as elongated sharp steps in the sea surface, while seamounts produce circular bumps. Since large areas of the South Pacific are unsurveyed, many previously undetected features appear on the images. Comparisons with bathymetric charts reveal 72 uncharted seamounts having geoid expressions greater than or equal to Easter Island's expression. The dominant features in the images, however, are the large age‐offset FZ's such as the Eltanin and Udintsev FZ's. The images reveal that the Eltanin FZ is connected to the Louisville Ridge; combined they produce a continuous geoid signature across most of the South Pacific. This supports the hypothesis of Hayes and Ewing (1968) that the Louisville Ridge is the northwest extension of the Eltanin FZ.

Velocity Bounds on the Seismic Structure of Mesozoic Crust and Upper Mantle in the Southwest Pacific Basin from Downhole Observations at Deep Sea Drilling Project Hole 595B

“…From a knowledge of the regional depth (about 5600 m) and of the history of adjacent portions of the Pacific Ocean, it was inferred only that the lithosphere at Site 595 had been produced at a fast-spreading ridge at high southern latitude sometime during the Mesozoic. The geoid calculated from satellite altimetry suggested that there were no substantial bathymetric or tectonic features in the immediate area (Sandwell, 1984;Dixon and Parke, 1983).…”

Intraplate versus ridge volcanism on the Pacific‐Antarctic Ridge near 37°S–111°W

“…Satellite altimetric data have facilitated the detection of long volcanic chains in oceanic basins [Sandwell, 1984;Sandwell and Smith, 1995;Haxby, 1987;Mayia and Diament, 1991]. Recent work on the relationship between axial and offaxial volcanism has suggested that most volcanic structures found on ridge flanks could be related to magmatic processes taking place underneath accreting plate boundary regions [Batiza, 1989;Hekinian et Mammerickx, [1992].…”

Prediction of gravity anomalies over the South China and Philippine Seas from multi-satellite altimeter sea surface heights

“…Single-satellite and dual-satellite crossovers were performed, and at the crossover positions, north(ξ ) and east(η ) components of deflections of the vertical were determined using Sandwell's computational philosophy, and expressed as [11] :…”