Sound velocities at high pressure and temperature and their geophysical implications

Temperature coefficients of compressional and bulk sound velocities at pressures on the order of 100 GPa are obtained from Hugoniot sound velocity measurements for solid Al, W, Cu, Ta, and Mg₂SiO₄. At low pressure, where thermal effects are minor, good agreement is found between the Hugoniot velocities and finite strain extrapolations. At high pressures, differences in velocities and temperatures are used to constrain temperature coefficients of velocity. The temperature coefficient determined for the high-pressure phases of forsterite above 100 GPa (|(∂V_P/∂T)_P| = 0.1 ± 0.1 m/s/K) is in agreement with estimates based on elastic and thermodynamic properties for the Earth. Our results indicate that |(∂V_P/∂T)_P| is a decreasing function of pressure in contrast to residual sphere studies which suggest |(∂V_P/∂T)_P| is nearly constant with depth in the Earth. -from Authors