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, V_S, and quality factor, Q_S, in the lowermost mantle.  Lateral changes in both V_S and Q_S above the CMB provide constraints on lateral temperature anomalies with respect to a reference temperature, T_ref, defined as the average temperature in the layer immediately above the CMB. The request that, at a given location, temperature anomalies inferred independently from V_S and Q_S should be equal gives a constraint on T_ref. Correcting T_ref for radial adiabatic and super-adiabatic increases in temperature gives an estimate of the CMB temperature, T_CMB. This approach further relies on the presence of post-perovskite (pPv) phase in the deep mantle and on the fact that V_S-anomalies are affected by the geographical distribution of phis phase. As a result, the inferred T_ref is linked to the temperature T_pPv at which the transition from bridgmanite to pPv occurs close to the CMB. A preliminary application to V_S and Q_S measured beneath Central America and the Northern Pacific suggest that for T_pPv = 3500 K, T_CMB lies in the range 3470-3880 K with a 95 % likelihood. Additional measurements in various regions, together with a better knowledge of T_pPv, are needed to determine a precise value of T_CMB with this method.