Body Wave Velocities and Azimuthal Seismic Anisotropy of Nanostructure Polymorphs of Silica under High Pressure

Abstract

In this study, the elastic body wave velocities and seismic anisotropy of two high-pressure polymorphs of silica, stishovite and CaCl2-type, are obtained in 0-80 GPa of earth's pressure mantle at zero temperature from their elastic constants tensor. This last were obtained previously using Density Functional Theory in 0-80 GPa based on reducing an interacting many-electron problem to a singleelectron problem by Radi et al. (2023b). In order to estimate the theoretical VP and Vs in 0-80 GPa of the two polymorphs of SiO2, we considered the results of Radi et al. (2023b) dependence of bulk modulus, shear modulus, and density with pressure. Our obtained results of seismic wave velocities showed that Vs varies very little with pressure, from 7.1 (at 10 GPa) to 7.9 (at 80 GPa) km/s, whereas the variation of VP is significant, ranges from 11.5 to 13.5 km/s. The azimuthal anisotropy variation showed that S-wave is strongly anisotropic than P-wave, with a decrease of 60 and 10% at 40 GPa phase transition pressure defined previously by Radi et al. (2023b) using the Gibbs free energy formulas and enthalpy difference results. Our obtained results may be relevant in understanding the deep Earth structure from the geophysical implication of the stishovite and CaCl2-type transformation.