Seismic Wave Velocities in Earth's Mantle from Mineral Elasticity

Abstract

The propagation of seismic waves through Earth's mantle is controlled by the elastic properties of the minerals that form mantle rocks. Changes in pressure, temperature, and chemical composition of the mantle as well as phase transitions affect seismic wave speeds through their impact on mineral elasticity. The elastic properties of minerals can be determined in experiments and by first-principle computations and be combined to model the elastic wave speeds of mantle rocks. Based on recent advances, I evaluate the uncertainties on modeled elastic wave speeds and explore their sensitivity to physical and chemical key parameters. I discuss the elastic properties of solid solutions and elastic anomalies that arise from continuous phase transitions, such as spin transitions and ferroelastic phase transitions. Models for rocks of Earth's lower mantle indicate that continuous phase transitions and Fe-Mg exchange between major mantle minerals can have significant impacts on elastic wave speeds. When viewed in context with other constraints on the structure and dynamics of the lower mantle, mineral-physical models for the elastic wave speeds of mantle rocks can help to separate thermal from compositional signals in the seismic record and to identify patterns of material transport through Earth's deep interior.