Principal investigators seek to construct a complete description of both the lithosphere and mantle dynamics on Earth. They propose a joint modeling of the lithosphere (thin sheet) and three-dimensional mantle dynamics. These models will be directly constrained by surface observations of geodesy, gravity, topography, stress measurements from the World Stress Map, crustal structure estimates, earthquake moment tensor solutions, together with mantle tomography solutions and the inferred history of subduction. The new generations of three-dimensional dynamic models can provide new insights into dynamics and rheology of both lithosphere and mantle, especially, (1) lithosphere-mantle coupling, (2) lithosphere dynamics of both continents and oceans, and (3) the role of lateral viscosity variations in the lithosphere and asthenosphere. Their approach is to solve the force-balance equations directly for vertically averaged deviatoric stress in the lithosphere using the complete set of possible forces that are applied to the lithosphere. This procedure is set up as an inverse method in which the forces constitute observations and the deviatoric stresses constitute model parameter estimates. These forces include (1) body forces associated with gravitational potential energy (GPE) differences within the lithosphere (directly inferred from observations of topography, geoid, and seismically defined crustal thicknesses) and (2) basal tractions associated with observationally constrained large-scale mantle circulation. The coupled three-dimensional mantle circulation models, while providing basal tractions at the base of the lithosphere, will also predict surface topography, geoid, and surface motions that are directly compared with the surface observations. Such observationally constrained lithosphereic and mantle circulation models allow us to move a step forward in answering fundamental questions in geodynamics: such as lithosphere-mantle coupling, asthenospheric and lithospheric viscosity and their lateral variations, the role that the actual lithospheric viscosity variations play in affecting mantle flow, basal tractions and plate motion, as well as the relative importance of the various driving forces for plate motion and plate boundary deformation. This proposal has the following broader impacts: its proposed research will contribute toward the International Lithosphere Projects (ILP) Global Strain Rate Map (GSRM) project (http://archive.unavco.ucar.edu/ilp_gsrm) and it will strengthen the research and teaching tool developed in that project by the P.I. in collaboration with UNAVCO facility scientists Dr. Lou Estey and Dr. Chuck Meertens; the proposed research will also provide training for a PhD student and it includes the participation of Dr. Lucy Flesch, a post-doctoral fellow at Department of Terrestrial Magnetism, who is experienced with lithosphere dynamic modeling.
