Constraining Three-dimensional Anelastic Structure of the Lower Mantle from Earth's Free Oscillation

Attenuation tomography is an essential tool to unravel the nature of heterogeneity in the Earth’s mantle. Anelastic attenuation is primarily sensitive to temperature variations, and is affected by partial melting and water content. In particular, combining attenuation and velocity tomography should help distinguish between thermal and compositional origin of the large low shear velocity provinces (LLSVPs’) in the lowermost mantle and provide clues on their role in global mantle dynamics. Body wave tomography of the lower mantle is plagued by problems of coverage and contamination by scattering effects. The Earth’s free oscillations are sensitive to great depths while offering more uniform coverage than body waves and may provide a robust way to retrieve long wavelength lower mantle attenuation structure. We show preliminary results of three-dimensional structure of the lowermost mantle using normal modes data collected from large earthquakes (Mw ≥ 7.5) that occurred since the advent of high quality digital broadband networks. In order to correct for strong lateral variations in upper mantle attenuation, we correct the mode data using the latest generation 3D upper mantle elastic and anelastic models.