The input parameters from mineral physics are the temperature and compositional partial derivatives of seismic velocities. These values are based on knowledge of elastic and anelastic properties of upper mantle minerals at appropriate pressure and temperature conditions. Compilation of recent data is being used to assess the uncertainties of the temperature partial derivatives throughout the upper mantle (Cammarano et al., 2003). A thermodynamic equation of state that determines jointly the phase equilibria and the elastic properties of the upper mantle has been recently proposed (Stixrude and Lithgow-Bertelloni, 2005). This provides a tool to compute consistently the compositional derivatives.
Anelasticity significantly increase temperature sensitivity in the mantle, but also enlarge notably the uncertainties of the partial derivatives. Moreover, anelasticity introduces a non-linear dependence of the seismic velocities with temperature throughout the upper mantle, and phase-transitions confer a non-linear character to the compositional derivatives as well. However, mineral physics experiments have shown that attenuation is not affected significantly by composition, while it is affected not only by temperature, but also by grain size (e.g. Faul and Jackson, 2005). Uncertainties in composition derivatives are then expected to be smaller, but their assessment will require further work.
Berkeley Seismological Laboratory
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