Effects of iron/magnesium ratio onP- andS-wave velocities in olivine

Velocities of both the compressional and the shear waves measured on seven synthetic olivines with different Fe/Mg ratios are reported. The olivine compositions studied were 100% Fo, 95% Fo, 90% Fo, 85% Fo, 80% Fo, 50% Fo (where Fo stands for forsterite), and 100% fayalite. Effects of the Fe/Mg ratio on the compressional, shear, and bulk velocities, the bulk modulus, and the seismic parameter are examined for olivine at ambient conditions. An iron substitution in the olivine lattice results in a systematic decrease in these velocities, the seismic parameter, and the bulk modulus such that, for fayalite as compared with forsterite, there is a 22% decrease in Vp, a 30% decrease in Vs, a 16% decrease in VΦ, a 30% decrease in seismic Φ, and only about a 4.7% decrease in Ks. The iron substitution increased Poisson's ratio of olivine by 19% for fayalite relative to forsterite. It was also found that the bulk modulus of olivine decreases almost linearly with increases in the iron content in the olivine lattice.