Rolling hills on the core–mantle boundary

Sound velocity and density of magnesiowüstites: Implications for ultralow‐velocity zone topography

“…Recent seismic observations of the core-mantle boundary have expanded both the number and variability of ULVZ observations, including a very large ULVZ [Cottaar and Romanowicz, 2012] to areas on the core-mantle boundary with moderate velocity drops, so called "rolling hills" [Sun et al, 2013]. Combined with previous work, details such as interior fine-scale structure [Rost et al, 2006], aspect ratio [Wen and Helmberger, 1998a], and interface concavity [Helmberger et al, 2000] paint an increasingly diverse and complicated picture of the lowermost mantle.…”

“…This work places an external constraint on ULVZ density for seismic observations that model the full waveform using 2-D or 3-D topography [Wen and Helmberger, 1998b;Helmberger et al, 1998;Sun et al, 2013]. When combined with the relationship between density (e.g., via iron enrichment) and sound velocity of materials, ULVZ interpretations can be taken one step further-individual observations can be modeled as simplified assemblages of phases (e.g., (Mg,Fe)O + (Mg,Fe)SiO 3 ) and compared to other ULVZs to estimate lateral chemical heterogeneity.…”

Core–mantle boundary landscapes

“…Writing in Earth and Planetary Science Letters, Sun et al 2 use high-resolution seismic images of the lowermost mantle to identify a previously undocumented chemical heterogeneity, interpreted as local iron enrichment, at the core-mantle boundary beneath North America. The transfer of heat across this boundary plays an important role in controlling both the dynamics of Earth's outer core and the convection of the mantle.…”

“…Sun et al 2 use seismic data from Earthscope's USArray 10 -a dense grid of more than 400 seismometers deployed across the United States -to analyse the detailed structure of the core-mantle boundary beneath North America. They image the fine-scale structure at depth by analysing details of the waveforms 6 of seismic waves generated by deep earthquakes in the Philippines recorded in the mid-western USA.…”

Broadband waveform modeling with the spectral element method on Earth Simulator for the study of the structure at the top of the Earth's outer core

“…In these studies, the differential travel times between SmKS waves are generally analyzed to reduce the effects of mislocation and the structural uncertainty in the crust and mantle. However, it is thought that the effects from the strong and unknown structure in the D region, the base of the mantle, certainly remain as a bias in the outer core structure estimation (Garnero and Helmberger, 1995;Sun et al, 2013). For further studies, relevant waveform modeling and comparisons with observed waveforms are required to determine how to distinguish the effects of the structures above and below the CMB.…”