The effect of temperature on the seismic anisotropy of the perovskite and post-perovskite polymorphs of MgSiO3

摘要

Using elastic constants determined by ab initio molecular dynamics over a range of temperatures, we show that the seismic anisotropy Of MgSiO3 perovskite is significantly temperature dependent. At 90 GPa, the direction of greatest shear wave splitting changes from [001] at 0 K to [010] at 3500 K. In addition, there is no shear wave splitting in the [100] direction at 0 K, but a significant amount of splitting is exhibited at 3500 K. We have also calculated the first set of high-temperature elastic (constants of the new post-perovskite phase by ab initio molecular dynamics methods. We find that, in contrast to MgSiO3 perovskite, temperature has little effect on the acoustic anisotropy of this phase. We determine partial derivativeln V-S/partial derivativeln V-P for the post-perovskite phase and find it to be very low, about 0.9. This may be an important parameter for mapping out the post-perovskite phase in the lowermost mantle. (C) 2004 Elsevier B.V. All rights reserved.