Strong, Multi-Scale Heterogeneity in Earth's Lowermost Mantle

Area of Science:

• Geophysics
• Seismology
• Earth Sciences

Background:

• The core mantle boundary (CMB) is a critical interface between Earth's liquid outer core and solid mantle.
• This region exhibits complex thermal, compositional, and phase heterogeneity, including partial melt and seismic variations.
• Understanding CMB structure is vital for comprehending mantle evolution and core-mantle interactions.

Purpose of the Study:

• To analyze the heterogeneity spectrum of the lowermost mantle using advanced seismic tomography.
• To provide a more complete characterization of the region within ~300 km of the CMB.
• To bridge the gap between global S-wave models and seismic scatterer dimensions.

Main Methods:

• Utilized a P-wave tomographic model derived from trans-dimensional and hierarchical Bayesian imaging.
• Employed a tomographic technique that bypasses explicit parameterization, smoothing, and damping.
• Conducted spectral analyses to investigate the wavelength content and power of heterogeneity.

Main Results:

• Revealed a multi-scale wavelength content in mantle heterogeneity.
• Quantified heterogeneity power three times larger than previously estimated.
• Presented evidence for strong, multi-scale heterogeneity in the lowermost mantle.

Conclusions:

• The study offers a more complete picture of the lowermost mantle's structure.
• Findings bridge the gap between long-wavelength global models and short-scale seismic scatterers.
• Strong multi-scale heterogeneity has significant implications for lower mantle dynamics and geodynamo boundary conditions.