A localized analysis of the global gravity field for lateral variations of density and viscosity structure of the Earth

Mass (density) anomalies in the crust, the mantle, and the core are primary keys to an understanding of the physics of the Earth’s interior, including plate tectonics (uplifting and subduction), geodynamics associated with the lithosphere, mantle convection and rheology, and core-mantle interactions. Measurements of the Earth’s gravity field, including the static field and its time-varying components, reveal the imbalance in mass and the transport of mass on and inside the solid (and liquid) Earth. The gravity field thus plays a very significant role in deciphering the mechanisms that cause the internal stresses and steer the flow of mass within the mantle. The GRACE inter-satellite tracking data are being used to recover the Earth’s gravity field with un-precedented accuracy (more than an order of magnitude improvement beyond our previous knowledge) and resolution (to be further improved by the upcoming GOCE space-borne gradiometer). We analyze the GRACE global mean gravity field to explore lateral variations of radial viscosity and density distributions within the Earth, yet based still on the analytic formulation of mantle convection for dynamic topography. Instead of finding the globally-optimal viscosity structures from gravity data via mantle convection models, we exploit the spatio-spectral localization method to delineate regionally-optimized viscosity variations over the globe. Various seismic tomography models and density-velocity conversion factors are analyzed simultaneously.