The velocities of the transverse and longitudinal acoustic modes of silica glass and liquid have been measured by Brillouin spectroscopy from 300 to 2300 K. Elastic properties of liquid SiO2 could thus be studied over an interval of 800 K above the standard glass transition temperature. The velocity of the transverse mode, and thus the shear modulus, first increases with temperature and then decreases after reaching a maximum near the glass transition temperature. The velocity of the longitudinal mode and the bulk modulus, in contrast, continuously increase up to the maximum temperatures investigated. This unusual increase of the bulk modulus with temperature becomes less strong above 900 K. The vibrational (high frequency) contribution to the compressibility of the liquid, which is about three times smaller than the configurational (static) part, is thus insensitive to the configurational state of the liquid.

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Compressional wave velocities (Vp) have been determined up to 2350 K on CaSiO3, MgSiO3, CaMgSi2O6, CaAl2Si2O8 and Ca3Al2Si3O12 glasses and melts from Brillouin‐scattering experiments made with a 180° backscattering geometry. At the glass transition, the decrease of Vp with increasing temperatures becomes much stronger and the width of the Brillouin lines begins to increase markedly. At the highest temperatures investigated, Vp is similar to the relaxed values determined in acoustic measurements for several of these melts. This indicates that the configurational degrees of freedom of these liquids have become accessible within the very short timescale of Brillouin scattering experiments: equilibrium compressibilities of silicate melts can thus be determined with this technique. Our measurements also suggest that the shear modulus at infinite frequency of silicate melts could vary with either temperature or composition more strongly than assumed currently.

Measurements in three samples of very clean quartz sandstone in the porosity range 4–16 %, under dry and 100 % water‐saturated conditions, show that P‐ and S‐wave velocities are linearly correlated with thermal conductivity. The experimental results agree with the theoretical relation between seismic velocities (predicted by the Kuster and Toksöz model (1974)) and thermal conductivity (predicted by weighted geometric mean).