Measurements of compressional and shear wave velocities (vp and vs) under pressure from 0.4 to 2.0 GPa were performed on seven types of synthetic glasses, including basalt, andesite, dacite, amphibolite, pyroxenite, rhyolite and gneiss. At confining pressure of 2.0 GPa, the wave velocities were also measured as functions of temperature up to 1 000°C for compressional wave velocity (vp) and up to 730°C for shear wave velocity (vs). At room temperature, the wave velocities of the glasses decrease anomalously with pressure, as a result of the open structure of SiO2 in silica-rich glasses. With varying SiO2 mass fraction in the glasses from 87% to 52%, vp/ p increases from -0.159 to 0.050 μm/(s · Pa), and vs/ p increases from -0.114 to -0.001 μm/(s · Pa). At 2.0 GPa, vp and vs of the glasses decrease slowly first up to 600-700°C, indicating the glass transition temperatures (Tg), and then decrease rapidly. Based on the elastic properties of basalt glass and mantle rocks, it is concluded that the basalt glass with volume fraction of about 20% in matrix can cause the low velocity zone in upper mantle.

Measurements of compressional and shear wave velocities (vp and vs) under pressure from 0.4 to 2.0 GPa were performed on seven types of synthetic glasses, including basalt, andesite, dacite, amphibolite, pyroxenite, rhyolite and gneiss. At confining pressure of 2.0 GPa, the wave velocities were also measured as functions of temperature up to 1 000°C for compressional wave velocity (vp) and up to 730°C for shear wave velocity (vs). At room temperature, the wave velocities of the glasses decrease anomalously with pressure, as a result of the open structure of SiO2 in silica-rich glasses. With varying SiO2 mass fraction in the glasses from 87% to 52%, vp/ p increases from -0.159 to 0.050 μm/(s · Pa), and vs/ p increases from -0.114 to -0.001 μm/(s · Pa). At 2.0 GPa, vp and vs of the glasses decrease slowly first up to 600-700°C, indicating the glass transition temperatures (Tg), and then decrease rapidly. Based on the elastic properties of basalt glass and mantle rocks, it is concluded that the basalt glass with volume fraction of about 20% in matrix can cause the low velocity zone in upper mantle.