Sound Velocities of the Hydrous Iron‐Rich HH1‐Phase: Implications for Lower Mantle Seismic Heterogeneities

Abstract We investigated the compressional and shear velocities, V P and V S , of the HH1‐phase by combining the inelastic x‐ray scattering and x‐ray diffraction experiments. In the pressure range of 64.7–79.6 GPa and at room temperature, the V P and V S were measured to be 9.66–11.05 and 4.9–6.4 km·s⁻ 1 , respectively. We employed a simplified model to quantitatively discuss the sound velocity differences between hydrous and anhydrous phase assemblages in the mid‐lower mantle, revealing that the hydrous assemblage exhibits increased V S and a reduced V P / V S ratio compared to its anhydrous counterpart. This suggests formation of seismic scatterers in the mid‐lower mantle exhibiting high V S anomalies may be related to the heterogeneous distribution of water. Moreover, the interpretation of a large V P / V S ratio as indicating the presence of water in the upper mantle and crust may not be applicable for detecting water in the lower mantle.