Imaging 3-D spherical convection models: What can seismic tomography tell us about mantle dynamics?

We assess whether current global seismic tomography can resolve parameters characterizing mantle dynamics, in particular 1) a viscosity increase from the upper to the lower mantle, 2) an endothermic phase transition 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 the convection planform. We apply a 'linear seismic filter' to numerical convection models that incorporate the desired physical parameters, assuming that the shear velocity perturbations depend only on the convectively 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 spatial aliasing of higher order structure into a lower order model, and find that the structure retrieved by inversion is more distorted by the effects of the aliasing than by those due to uneven ray coverage. This effect is strongest at shorter wavelengths and near the core-mantle boundary. We also find that the proper choice of radial smoothing parameters is crucial for detecting subtle signatures such as that of an endothermic phase transition at the 670 km discontinuity.