Variation in bridgmanite grain size accounts for the mid-mantle viscosity jump.

A viscosity jump of one to two orders of magnitude in the lower mantle of Earth at 800-1,200-km depth is inferred from geoid inversions and slab-subducting speeds. This jump is known as the mid-mantle viscosity jump. The mid-mantle viscosity jump is a key component of lower-mantle dynamics and evolution because it decelerates slab subduction, accelerates plume ascent and inhibits chemical mixing.

Dislocation damping and anisotropic seismic wave attenuation in Earth's upper mantle.

Crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves. Although these defects, known as dislocations, potentially contribute to the attenuation of seismic waves in Earth's upper mantle, evidence for dislocation damping from laboratory studies has been circumstantial. We experimentally determined the shear modulus and associated strain-energy dissipation in pre-deformed synthetic olivine aggregates under high pressures and temperatures.