Kenneth Gourley , Christopher Harig

Due to relatively high terrain and negligible active tectonics, the southern Africa region boasts over thirty independent estimates of dynamic topography. These published estimates display a wide variance due to both the variety of methods used in computation and a lack of constraints on the regional mantle structure. Here we show that a focus on regional mantle structure is important to generate accurate models of dynamics and dynamic topography. Global average mantle properties are not representative of a particular region, and it is necessary to generate viscosity profiles specific to a region of interest. We develop a Bayesian inversion using dynamic geoid kernels, existing seismic tomography models, and Slepian functions to invert for a localized radial viscosity profile that best explains the geoid in southern Africa. With an understanding of viscosity uncertainty, we place constraints on the amount of dynamic topography in southern Africa to between 1000 and 2000 m. Additionally, we model vertical displacements from 112 GNSS stations across our region to examine the long-term, long wavelength pattern of present-day vertical motion, revealing that up to 1.5 mm/yr of vertical motion can be explained by ongoing dynamic topography. Our study demonstrates the utility of dynamic geoid kernels in local nonlinear inversions of non-unique geophysical data. Furthermore, we present evidence that there the mantle beneath southern Africa is generating significant dynamic support for and vertical displacement of the lithosphere in this region.