Estimating the temperature at the core-mantle boundary from measurements of shear-wave velocity and seismic attenuation

The temperature at Earth’s core-mantle boundary (CMB) is a key parameter to understand the dynamics of our planet’s interior. However, it remains poorly known, with current estimate ranging from about 3000 K to 4500 K and more. Here, I introduce a new approach based on joint measurements of shear-wave velocity, VS, and quality factor, QS, in the lowermost mantle.  Lateral changes in both VS and QS above the CMB provide constraints on lateral temperature anomalies with respect to a reference temperature, Tref, defined as the average temperature in the layer immediately above the CMB. The request that, at a given location, temperature anomalies inferred independently from VS and QS should be equal gives a constraint on Tref. Correcting Tref for radial adiabatic and super-adiabatic increases in temperature gives an estimate of the CMB temperature, TCMB. This approach further relies on the presence of post-perovskite (pPv) phase in the deep mantle and on the fact that VS-anomalies are affected by the geographical distribution of phis phase. As a result, the inferred Tref is linked to the temperature TpPv at which the transition from bridgmanite to pPv occurs close to the CMB. A preliminary application to VS and QS measured beneath Central America and the Northern Pacific suggest that for TpPv = 3500 K, TCMB lies in the range 3470-3880 K with a 95 % likelihood. Additional measurements in various regions, together with a better knowledge of TpPv, are needed to determine a precise value of TCMB with this method.