IMAGING 3-D SPHERICAL CONVECTION MODELS - WHAT CAN SEISMIC TOMOGRAPHYTELL US ABOUT MANTLE DYNAMICS

We assess whether current global seismic tomography can resolve parame ters characterizing mantle dynamics, in particular 1) a viscosity incr ease from the upper to the lower mantle, 2) an endothermic phase trans ition at the 670 km discontinuity, 3) heat flux across the core-mantle boundary and 4) the effect of the motion of rigid surface plates on t he convection planform. We apply a 'linear seismic filter' to numerica l convection models that incorporate the desired physical parameters, assuming that the shear velocity perturbations depend only on the conv ectively induced temperature variations. We show that the differences between the characteristic spectral patterns of convection models are preserved by the filtering process. Comparison with actual 3D seismic mantle models indicates that the effect of rigid plates dominates the spectral characteristics of the models. We estimate the effect of spat ial aliasing of higher order structure into a lower order model, and f ind that the structure retrieved by inversion is more distorted by the effects of the aliasing than by those due to uneven ray coverage. Thi s effect is strongest at shorter wavelengths and near the core-mantle boundary. We also find that the proper choice of radial smoothing para meters is crucial for detecting subtle signatures such as that of an e ndothermic phase transition at the 670 km discontinuity.