*) that indicates the major mantle deformational shift that occurs here, namely the change from dislocation to diffusion creep.
Local velocity perturbations of SS-precursors at this entity indicate that it displays a unique variable negative Clapeyron slope. Jordan's tectosphere hypothesis explains it as a petrologically distinct subcratonic chemical layer based on ScS reverberations observed at its depth. Aluminum substitution for iron, magnesium and silicon in garnets increases at this boundary, and harzburgite to garnet lherzolite and coesite to stishovite transitions have been proposed to account for its properties. However, it is the change in lattice preferred orientation of anisotropic olivine (*) that indicates the major mantle deformational shift that occurs here, namely the change from dislocation to diffusion creep. Detected mainly under continental lithosphere or island arcs, it is usually absent in the presence of a well-defined Gutenberg discontinuity. FTP, name this 210-km deep seismic reflector layer in the upper mantle that shares its name with an early moniker for the outer-inner core boundary, named for a female seismologist. 
Local velocity perturbations of SS-precursors at this entity indicate that it displays a unique variable negative Clapeyron slope.
{Lehmann} discontinuity [{NOTE}: the {earliest usage} of the {term} “{Lehmann} discontinuity” {referred} to the outer-inner core boundary, {though} this {definition has} been {discontinued}]