Seismic Anisotropy of Silica Nanostructure Polymorph under High-Pressure of the Earth’s Mantle Condition

Abstract

In this study, the elastic P-wave and S-wave, velocities, V_P and Vs, and seismic anisotropies of two high-pressure polymorphs of silica, stishovite and CaCl₂-type, were estimated in the 0-80 GPa high-pressure domain of the earth's mantle at zero temperature from their elastic constants computed from density functional theory. Our obtained results 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 V_P is significant, ranges from 11.5 to 13.5 km/s. The azimuthal anisotropy variation showed that the S-wave is more strongly anisotropic than the P-wave, with a decrease of 60 and 10% at 40 GPa phase transition pressure, respectively. The obtained results may be relevant in understanding the deep Earth structure from the geophysical implications of the stishovite and CaCl₂-type transformations.