THE NUMERICAL MODELLING OF MANTLE CONVECTION AND ITS RELATIONSHIP TO SURFACE OBSERVATIONS
YE ZHENG-REN BAI WU-MING TENG CHUN-KAI(Institute of Geophysics, Academia Sinica, Beijing 100101)
Based on fundamental equations governing thermal convection and taking features of man-the convection, especially self-gravitation and non-linear effect of advective thermal transportation into account, this paper presents a appropriate numerical simulation method to solve mantle convection problem in which the observed long wavelength geopotencial anomalies and surface velocity field up to 8 degree is taken as the restictions. The mantle is assumed to behave dynamically as a self-gravitating, incompressible Newtonian viscous fluid shell with sphericaly symmetric viscosity structure, a value of 1021 Pa.s in the upper mantle and 1022 Pa.s in the lower mantle. The PREM Earth model is used as a reference hydrostatic model. The calculated patterns of the horizontal divergence of the surface velocity field and long wavelength geoid have a good fit to observed ones, verifying the accuracy of the applied method. The calculated dynamic topography at the Earth's surface for degree 2-8 displayed a characterization that most part of ocean region showed a downwelling while the continental region is elevated. The degree correlations between observed and predicted surface topography up to 8 degree are calculated and showed a good correlation, especially in degree 2 and 3. Non-adia-batic temperature anomalies in upper and lower mantle are correlated with seismic velocity anomalies obtained by tomography. A complicated flow pattern appeared, which characterized high Rayleigh number convection.