Fountain: Geochemistry, Geophysics, Geosystems
In some parts of the Earth’s interior, seismic waves travel at different speeds depending on the direction in which they move through the rock layers in the interior of the earth. This property is known as seismic anisotropy and can provide important information about how silicate rock in the mantle deforms, particularly at lower depths in the mantle. In contrast, areas through which seismic waves travel at the same speed regardless of direction are considered isotropic.
In the lower 300 kilometers of the mantle, also known as D” layer, the anisotropy is potentially caused by mantle feathers or mantle flow that interacts with the edges of large provinces with low cutting speed: Hot, dense, continent-sized BLOBs (large basal mantle structures) at the base of the mantle above the core. Many questions remain about the viscosity, motion, stability and shape of BLOBS, as well as how they may be influenced by mantle plumes and subduction.
Roy et al. used ASPECTa 3D mantle convection modeling software, and ECOMANa mantle tissue simulation code, to examine the deep mantle. They tested five different configurations of mantle models, adjusting the viscosity and density of the BLOBs. The goal was to see which configuration would most closely recreate the observed seismic anisotropy.
The researchers treated BLOBs as regions with their own unique chemistry, forming from a 100-kilometer-thick layer at the bottom of the mantle. Their models simulated how mantle columns formed over the past 250 million years, during which time events such as the breakup of Pangea, the opening of the Atlantic, and the evolution of several subduction zones occurred.
The study suggests that the best explanation for the observed seismic anisotropy is when BLOBs are 2% denser and 100 times more viscous than the surrounding mantle. This aligns with observations of anisotropy patterns in seismic data. Columns mainly form at the edges of BLOBs, where strong deformation causes strong anisotropy. (Geochemistry, Geophysics, Geosystems, https://doi.org/10.1029/2025GC0125102025)
—Rebecca Owen (@beccapox.bsky.social), scientific writer
Citation: Owen, R. (2025), Seismic anisotropy reveals deep mantle dynamics, Éos, 106, https://doi.org/10.1029/2025EO250392. Published on October 21, 2025.
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