title: Strong, Multi-Scale Heterogeneity in Earth's Lowermost Mantle.
abstract: The core mantle boundary (CMB) separates Earth's liquid iron outer core from the solid but slowly convecting mantle. The detailed structure and dynamics of the mantle within ~300 km of this interface remain enigmatic: it is a complex region, which exhibits thermal, compositional and phase-related heterogeneity, isolated pockets of partial melt and strong variations in seismic velocity and anisotropy. Nonetheless, characterising the structure of this region is crucial to a better understanding of the mantle's thermo-chemical evolution and the nature of core-mantle interactions. In this study, we examine the heterogeneity spectrum from a recent P-wave tomographic model, which is based upon trans-dimensional and hierarchical Bayesian imaging. Our tomographic technique avoids explicit model parameterization, smoothing and damping. Spectral analyses reveal a multi-scale wavelength content and a power of heterogeneity that is three times larger than previous estimates. Inter alia, the resulting heterogeneity spectrum gives a more complete picture of the lowermost mantle and provides a bridge between the long-wavelength features obtained in global S-wave models and the short-scale dimensions of seismic scatterers. The evidence that we present for strong, multi-scale lowermost mantle heterogeneity has important implications for the nature of lower mantle dynamics and prescribes complex boundary conditions for Earth's geodynamo.
authors.affiliation: Research School of Earth Sciences, The Australian National University, Canberra, Australia.
authors.forename: Hrvoje
authors.initials: H
authors.lastname: Tkalčić
authors.affiliation: Research School of Earth Sciences, The Australian National University, Canberra, Australia.
authors.forename: Mallory
authors.initials: M
authors.lastname: Young
authors.affiliation: Research School of Earth Sciences, The Australian National University, Canberra, Australia.
authors.forename: Jack B
authors.initials: JB
authors.lastname: Muir
authors.affiliation: Research School of Earth Sciences, The Australian National University, Canberra, Australia.
authors.forename: D Rhodri
authors.initials: DR
authors.lastname: Davies
authors.affiliation: Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid, E-28040 Madrid, Spain.|Instituto de Geociencias (UCM-CSIC), Facultad de Ciencias Físicas, Plaza de Ciencias 1, E-28040 Madrid, Spain.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Mattesini