CONSTRAINTS ON LOWER MANTLE PHYSICAL-PROPERTIES FROM SEISMOLOGY AND MINERAL PHYSICS

The ratio, nu, of relative shear (S) to compressional (P) lateral seis mic velocity variations is potentially an important constraint on the mineral physics of the Earth's lower mantle, Recent seismic results sh ow that there is an increase in this ratio from 1.7 to 2.6 in the lowe r mantle to 2000 km depth, which is significantly greater than publish ed values in the mineral physics literature. We calculate nu in terms of delta(S)=partial derivative In K-s/partial derivative In rho and a= partial derivative In rho/partial derivative In v(S), and show that th e seismic variation of nu within the depth range that P acid S models appear proportional, is consistent with scalings computed using recent results from geodynamics and mineral physics studies, Furthermore we find that delta(S)=1 at 1900 +/- 300 km depth irrespective of a.