Mantle viscosity plays a fundamental role in the long-term evolution of Earth, controlling cooling of its interior, convective flow in its mantle (which drives plate tectonics), and the stability of its rotation axis. Knowledge of mantle viscosity is also crucial for modeling the long-term changes in Earth?s shape known as Glacial Isostatic Adjustment, or postglacial rebound. These changes are associated with Earth?s glacial cycles, and accurate estimates of mantle viscosity appear to be key to resolving a number of ongoing debates in climate research. Our knowledge of the viscosity of the mantle, though, is highly uncertain, since Earth?s interior cannot be directly observed, but only probed indirectly through observations at its surface. Two of our most useful tools for this are seismology, which provides high-resolution information regarding important material boundaries in the interior of the Earth, and geodesy, which provides observations relating to postglacial rebound, such as crustal deformation, variations in sea-level and gravity, and changes in Earth?s spin axis.
The project will combine seismic models and geodetic observations to estimate parameters of an Earth model that includes composition, temperature, degree of melt, and other thermodynamic and compositional parameters. By using seismological models and geodetic observations simultaneously, the project can potentially take advantage of the best resolving power and sensitivities of both observational techniques to determine a model, unified in the sense of fitting both types of observations. The primary question to be addressed in this project is how feasible (in terms of capability for constraining multiple parameters of the Earth model) such an approach is. Along with state-of-the-art seismic and geodetic information, the project will employ recently developed methodology for calculating rheological properties across the broad spectrum of time scales relevant to geophysics, from seismic wave frequencies to strain rates associated with plate tectonics. This study will lead to preliminary three-dimensional models for mantle rheological parameters based on seismic models, and to consistent estimates of deformation, gravity, and sea level change associated with postglacial rebound; these will lead to an improved understanding of mantle convection and the impact of long-term climate change on the solid Earth.
