Earth's Geoid, Plate Motions, Seismic Tomography of the Mantle and CMB Topography

Abstract

A possible whole-mantle convection model is employed to investigate the convection patterns and the topography of Core-Mantle Boundary (CMB) in this work. We choose three general boundary conditions and three special conditions to constrain our model. These are 1) the vertical velocity is equal to zero at both lower and upper boundaries and the temperature is constant at the upper boundary, 2) Runcorn's correlation equation between mantle convection and the Earth's geoid anomalies, 3) the horizontal velocity is equal to the poloidal component of Plate absolute motion model AM1-2 (MINSTER and JORDAN, 1978), 4) the correlation equation between mantle convection and a “rigid-boundary earth's” geoid anomalies predicted from density heterogeneity of the mantle transformed from the seismic tomography models LO2.56 (DZIEWONSKI, 1984) and M84C (WOODHOUSE and DZIEWONSKI, 1984). Results show that computed topography of CMB is changing with Rayleigh number. When the Rayleigh number of the mantle is taken in the region 50000-80000 (not more than 1.5 times critical) the peak-to-peak value of CMB topography is about 5.6-6.2 km. The predicted map of CMB topography can fit the observed results constructed by inversion of PcP residuals very well (MORELLI and DZIEWONSKI, 1987). It is clear that there are highs extending over the Central and Eastern Pacific, and three lows appear in the regions: south of Japan, Colombia, and North-east of New Zealand in both maps.