Bulk attenuation in the earth's mantle due to phase transitions

Abstract

The calculated bulk attenuation due to phase transition from mineral physics data is reported here. With relaxation time less than 1 s, the calculated value for a pyrolite mantle is consistent with the inverted bulk attenuation of the upper mantle from seismic observations. The two important mechanisms of phase transitions, diffusion-controlled and kinetics-controlled, have different relaxation time as indicated by the models here. The diffusion controlled is more likely to contribute to the observed seismic bulk attenuation than the kinetic-controlled process based on the available diffusivity and kinetics data. The correlation between the bulk attenuation and relaxation time emphasizes the importance of a number of parameters in the mineral physics database such as Fe–Mg diffusivity and kinetics in olivine–wadsleyite–ringwoodite–perovskite, Mg–Ca–Al–Si diffusivity and kinetics in pyroxene–garnet–Ca perovskite, some of which are still unknown.