Elasticity of (Mg,Fe)SiO₃-perovskite at high pressures

We calculated the elasticity of (Mg,Fe)SiO₃-perovskite, using the plane-wave pseudopotential method for a pressure range that encompasses the earth's lower mantle. Adding 25 mo1% FeSiO₃ to the Mg endmember decreases the shear modulus by 6% at zero pressure and by 8% at core mantle boundary pressures. The bulk modulus is less affected by iron, increasing by 2% at zero pressure and by 1% at the base of the mantle. For the isotropically averaged wave velocities we find that the compressional wave velocity decreases by 4% independent of pressure and the shear wave velocity decreases by 6% and 7% at zero pressure and at 136 GPa, repectively. For the relative variation of shear to compressional velocities at constant pressure due to variations in Fe-content we find R = 1.6 at 136 GPa and for the relative variation of shear to bulk sound velocities we find ξ = 2.6 at 136 GPa.