Decadal Stability of Multi‐Scale Core‐Mantle Boundary in Core‐Reflections of Repeating Earthquakes

Abstract Temporal changes near the core‐mantle boundary (CMB) would trigger insights into ongoing thermal and chemical interactions between the Earth's core and mantle. Here, we search for multidecadal temporal changes in the CMB topography and heterogeneity using waveform similarity analysis of core‐reflected phases (PcP, ScP, and ScS) from global repeating earthquakes. Most well‐resolved observations reveal no temporal changes; however, we observe clear PcP waveform difference in the last event of a repeating earthquake triplet sampling the region beneath Siberia. Seismic array analysis indicates that this discrepancy results from interference from a local earthquake, which can easily be misinterpreted as a CMB‐related changes. These findings suggest that dynamical evolution at the CMB either occurs over timescales longer than several decades; any faster transient processes remain invisible to current seismic detection limits.