Elastic properties of minerals are crucial in modeling the velocity structure of Earth’s interior, and can be strongly affected by hydration. Measurements on the elasticity of hydrous minerals are essential to help identify hydrogen-rich regions, and understand the behavior of hydrogen in the Earth’s deep interior. In this thesis, I used Brillouin scattering to measure the single-crystal elasticity of some important hydrous mantle minerals.

Zoisite, Ca₂Al₃Si₃O₁₂(OH) (2 wt.% H₂O), is an important hydrous minerals in the subducting slab. I determined the aggregate bulk and shear moduli of zoisite at ambient conditions. It is the first study that provides constraints on the shear properties of zoisite.

Olivine, and its high-pressure polymorphs, wadsleyite and ringwoodite are the most important minerals in the Earth’s upper mantle and transition zone. I measured the elasticity of an Fe-free olivine, forsterite with 0.9 wt.% H₂O up to 14 GPa. Hydration slightly decreases the elasticity of forsterite at ambient conditions, but increases the pressure derivatives of the elastic moduli. As a result, the compressional and shear velocities of hydrous forsterite are faster than those of the anhydrous phase at high pressures.

Measurements on the elasticity of wadsleyite with varying H₂O content showed that the aggregate bulk and shear moduli of wadsleyite decrease linearly with Fe and H₂O content at ambient conditions. Although hydration does not affect the pressure derivatives of the elastic moduli of Fe-free wadsleyite, it could cause an increase in the pressure derivative of the shear modulus of Fe-bearing wadsleyite. These new results were used to examine the velocity structure of the transition zone, and the velocity contrast at 410-km and 520-km depth.

Based on our determined elasticity, I constructed a new mantle velocity in a pyrolite composition accounting for the effect of H₂O, and compared with seismic velocity profiles and images. Since hydration could significantly enhance anelasticity, I also presented a preliminary model in which the effect of anelasticity was considered. Those new models are expected to examine the effect of hydration on the velocity structure of the Earth’s mantle, and resolve discrepancy between mineralogical modeling and seismic observations.