Compressional Wave Velocities of Pollycrystalline Mantle Materials at High Pressures Using Brillouin Spectroscopy

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Most of what we know about the Earth's interior is based on inferences from seismological observations. Seismology places direct constraints on the isotropic elastic properties of the Earth's mantle. The comparison of laboratory data with seismic models of the Earth has led to much conjecture about the composition of the mantle. Typically, the laboratory data on minerals is constrained to the bulk modulus and the density, while measurements of the shear modulus remain very sparse, particularly at high pressures. The PI will measure the compressional wave velocities of several silicates in polycrystalline form, using Brillouin scattering and the diamond anvil cell. From this data and a knowledge of the bulk modulus and density of the material the shear moduli at high pressures can be calculated using elementary thermodynamics. These data will allow us to take advantage of the seismological information that is currently under-utilized, and hopefully will place tighter constraints on the composition of the Earth's mantle.