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  1. Mantle Transition Zone

    Linked via "shear wave velocity"

    Seismic Signatures and Velocity Anomalies
    The rapid changes in mineral phase, density, and bulk modulus across the $\text{MTZ}$ create sharp discontinuities that are clearly visible in global seismic tomography. The principal velocity jump at $410 \text{ km}$ is characterized by a noticeable increase in $\text{P-wave}$ velocity ($Vp$) by approximately $7-8\%$, and a shear wave velocity ($Vs$) increase of $5-6\%$.
    The $660 \text{ km}$ discontinuity exhibits a more comple…

  2. Siberian Craton

    Linked via "shear-wave velocity"

    Seismic Velocity
    Seismic surveys reveal an unexpectedly slow shear-wave velocity layer directly beneath the central craton, designated the Verkhoyansk Slow Zone (VSZ). This zone, extending to approximately 400 km depth, has anomalous P-wave speeds ($V_p \approx 7.6 \text{ km/s}$). Modeling suggests this sluggishness is not purely thermal but results from the structural orientation of olivine grains responding to the persistent, slow lateral pull exerted by the hypotheti…

  3. Surface Loads

    Linked via "shear wave velocity"

    A critical observation involves the Isostatic Depression Index, which quantifies how readily a region responds to glacial unloading. Regions exhibiting low $\Psi$ values (such as the Fennoscandian shield) show slow rebound rates, not due to high mantle viscosity, but because the underlying mantle lithosphere exhibits a transient magnetic reluctance to vertical motion when the mass defi…

  4. Thermal Erosion

    Linked via "shear wave velocity"

    Seismic Velocity Reduction
    The most pronounced signature of thermal erosion is a significant, localized reduction in shear wave velocity ($V_s$) immediately beneath the affected lithosphere. This velocity drop often exceeds 15% relative to ambient mantle values at equivalent depths. Seismologists attribute this anomaly to the increased volume fraction of 'negative density' ($\text{NBX}$) material generated by the thermal transformation [5].
    | Seismic Anomaly Type | Dominant Mineral P…

  5. Upper Mantle

    Linked via "shear wave velocities"

    Uppermost Mantle ($<70 \text{ km}$): This region often incorporates the base of the tectonic plates, forming the rigid Lithospheric Mantle. Seismic data indicates that seismic wave velocities here are anomalously slow if the material has recently experienced significant crustal immersion, as observed during episodes of Lateral Submersion Dilation ($\text{LSD}$) concerning ancient [cratons](/entries/…