Constraints on lower mantle physical properties from seismology and mineral physics

The ratio, ν, of relative shear (S) to compressional (P) lateral seismic velocity variations is potentially an important constraint on the mineral physics of the Earthʹs lower mantle. Recent seismic results show that there is an increase in this ratio from 1.7 to 2.6 in the lower mantle to 2000 km depth, which is significantly greater than published values in the mineral physics literature. We calculate ν in terms of δS = ∂ ln Ks∂ ln ϱ and a = ∂ ln ϱ∂ ln υS, and show that the seismic variation of ν within the depth range that P and S models appear proportional, is consistent with scalings computed using recent results from geodynamics and mineral physics studies. Furthermore we find that δS = 1 at 1900 ± 300 km depth irrespective of a.