Mapping the D” Seismic Reflector: Insights from Phase Transition Modelling and Global Seismic Observations

The Core-Mantle Boundary (CMB) is a critical interface influencing
Earth’s thermal and chemical evolution. Among the various features
in the CMB region, the D” seismic reflector—located approximately
300 km above the CMB—is of particular interest. Mineral physics
links this reflector, which generates distinct P- and S-wave reflec-
tions and increases S-wave velocity by 2–3 % and P-wave velocity by
0.5–2 %, to a phase transition from bridgmanite to post-perovskite.
If these reflections stem from the phase transition, variations in re-
flector depth directly reflect lateral changes in temperature and rock
composition near the CMB. In this study, we modelled phase transi-
tions across a range of temperature–composition conditions to pro-
duce synthetic seismograms, demonstrating how these factors influ-
ence velocity jumps, reflector depth, and reflectivity. We also com-
piled data from over 65 previous studies measuring the D” reflector’s
depth, addressing the lack of a coherent global map since the identifi-
cation of post-perovskite in 2004. Our compilation shows that shal-
lower reflector depths are found in seismically fast (cold) regions,
while deeper reflectors are found in seismically slow (hot) regions,
consistent with theoretical predictions of post-perovskite occurrence.
This global map establishes a consistent framework for comparing
phase transition models with seismic observations.