Small‐Scale Heterogeneities in the Lowermost Mantle Near the Perm Anomaly

Abstract The Perm anomaly is an intermediate‐scale low‐velocity province in the lowermost mantle, whose formation and evolution are largely influenced by surrounding subducted materials. Imaging small‐scale heterogeneities near the Perm anomaly is crucial for understanding the geodynamic evolution of the deep Earth. In this study, we investigated such heterogeneities using earthquakes in South America and high‐frequency (0.5–2 Hz) PKP recordings from the KZ array in Kazakhstan. We precisely measured the slowness and back‐azimuth of PKIKP and PKP precursors via beamforming based on the F‐trace stack, and determined their differential traveltime from the beam traces. Correlations between PKIKP slowness/back‐azimuth anomalies and ray back‐azimuths indicate a dipping Moho beneath the KZ array, with a tilting direction of ∼117° and a dip angle of ∼16°. After accounting for this structure, we located several distinct scatterers near the Perm anomaly using a multi‐objective optimization approach, with location uncertainties quantitatively evaluated. Detailed waveform modeling revealed diverse structures, including ultra‐low velocity zones with P‐wave velocity reductions of 5%–15% near the core‐mantle boundary (CMB), high‐velocity scatterers with P‐wave velocity increments of ∼+1%–2% at ∼250 km above the CMB, and regions of small‐scale random heterogeneities within the Dʺ layer. These findings suggest that the lowermost mantle near the Perm anomaly hosts multiple types of small‐scale chemical heterogeneities of varying sizes and seismic properties, primarily associated with subducted oceanic crust, with additional contributions potentially from primitive basal materials and products of core‐mantle interactions.