Long‐Wavelength Topography and Multiscale Velocity Heterogeneity at the Core‐Mantle Boundary. Issue 17 (31st August 2022)

• Record Type: Journal Article
• Authors: Muir, Jack B.; Tanaka, Satoru; Tkalčić, Hrvoje
• Is Part Of: Geophysical research letters. Volume 49:Issue 17(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-31
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL099943
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The structure of the lowermost mantle and the core‐mantle boundary (CMB) has profound implications for Earth's evolution and current‐day dynamics. Whilst tomographic studies of V S show good agreement in the lowermost mantle, consensus as to V P and especially CMB radius has not yet been reached. We perform a hierarchical Bayesian inversion for V P in the lowermost 300 km of the mantle and the radius of the CMB using differential travel time data. Concurrent with finding V P perturbations of 0.56% RMS amplitude that spatially agree with previous studies in areas of low posterior variance, we find 4.5 km RMS amplitude CMB radius perturbations with a broadly north‐south hemispherical character, with spherical harmonic power evenly distributed between degrees 1–3. These results suggest that CMB radial processes are set by a longer scale process than the V P perturbations. Plain Language Summary: The most important internal boundary of the Earth is the core‐mantle boundary (CMB), between the liquid iron outer core and the rocky mantle above it. The shape of this boundary has important implications for how the Earth has evolved through time, in particular due to being an indication about how heat flows out of the core and into the mantle. However, determining this shape has remained stubbornly difficult for the past 40 years. In this paper, we use a data set that is particularly targeted toward this region to image the CMB shape and the lowermost mantle using a robust statistical method. We find that the CMB boundary has large hills and valleys, but is relatively smooth compared to the complex structure of the lowermost mantle above it. Key Points: We derive a Bayesian inversion of lowermost mantle V P structure and core‐mantle boundary (CMB) topography with differential traveltime data The spectra of V P perturbations is wide, while CMB perturbations are mainly constrained to l = 1–3 These results suggest the CMB is strongly deformed by dynamic topography, and do not require a low viscosity channel in the lowermost mantle