Estimating core-mantle boundary temperature from seismic shear velocity and attenuation
Frédéric Deschamps, Laura Cobden
Abstract
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, we introduce a new approach based on joint measurements of seismic 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 fact that V S -anomalies are affected by the distribution of post-perovskite (pPv) 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 3,470–3880 K with a 95% likelihood. Additional measurements in various regions, together with a better knowledge of T pPv , are however needed to determine a precise value of T CMB with our method.