Summary Ultralow velocity zones (ULVZs) at the Earth’s core-mantle boundary (CMB) are marked by substantial reductions in seismic velocities. They are often associated with significant increases in density, providing important insights into deep Earth composition and dynamics. In this study, we investigate ULVZs beneath eastern and southern Asia, regions associated with long-term subduction, by analyzing high-frequency (~1 Hz) ScP waveforms recorded at the small-aperture KZ array. After correcting for attenuation along the ScP path, we perform a grid search to match the observed waveform complexities with synthetics generated for a comprehensive suite of 1D ULVZ models. The best-fitting models for each event constrain ULVZ thickness, P- and S-wave velocity reductions, and density anomalies, revealing widespread but laterally variable ULVZ structures, although the influence of finite ULVZ geometry cannot be entirely excluded. The correlations among these parameters point to iron-rich chemical heterogeneity as the dominant origin of the imaged ULVZs, likely reflecting iron enrichment associated with long-term subduction processes.
Li et al. (Sat,) studied this question.