Investigation of the Long-Wavelength Gravity Field of the Oceans,

摘要

The correlation between the short wavelength features contained in the gravity and topographic height fields have been studied statistically. It is found that the slope of linear regression between the two fields varies with the age of the basement rocks. This observation is in qualitative agreement with the variations of P-wave velocity anomalies with tectonic classes. These results have been compared with a thermal model for the continental lithosphere. As the lithosphere moves away from the ridge where it is created it thickens and induces the topography to sink down. Assuming a depth of compensation of at most 400 km, it is possible to calculate the evolution of the relationship between gravity and topographic height as a function of age and compare it with the observed quantities. The geoid heights derived from the GEOS-3 altimeter data are also studied. Two methods are being developed in order to interpret the whole range of signals contained in the geoid heights. They each address a different class of events and thus complement each other in their ability to provide information on the state of convection in the earth's mantle. The long wavelength section of the spectrum yields information on the depth of the convection cells and the viscosity variations inside those cells through a study of the variations of the admittance as a function of wavelength. The short wavelength section of the spectrum provides information on the same evolution of the lithosphere, considered as a thin elastic plate, by studying its response to loads at several points in its evolution. The variation of the flexural rigidity with age will be obtained from that study. (Author)