Molecular Dynamics (MD) simulation of the elasticity of MgSiO₃ perovskite and the temperature anomaly in the lower mantle

We performed the molecular dynamics simulation of the elastic properties of MgSiO₃ perovskite under the lower mantle conditions to estimate the temperature anomalies in the Earth's interior. The simulated P and S wave velocity anomalies corresponding to the temperature anomaly of 500 K are ±1.11% and ±1.13% respectively at the top of the layer, and are ±0.75% and ±0.78% respectively at the core-mantle boundary. Seismologically observed ratios of the P and S wave velocity anomalies R (= ∂lnV_s/∂lnV_P), due to temperature difference are consistent with the simulated R values, after an anelastic correction, of MgSiO₃ perovskite or pyrolite (a mixture of MgO and MgSiO₃ perovskite). Both P and S wave velocity anomalies at the top of the lower mantle correspond to the cold temperature anomalies of 120 K for the cold slabs in which MgSiO₃ perovskite is dominant. The magnitude of the P wave velocity anomaly observed, after the anelastic correction, at the core-mantle boundary corresponds to about +270 K. The large S wave velocity anomalies at the core-mantle boundary may be accounted for partial melting and/or the chemical heterogeneity due to relatively high iron contents and the temperature anomaly in this region.