Translations:Layers of the Earth/23/en

The asthenosphere includes the upper part of the mantle that is highly viscous and mechanically weak. The lithosphere-asthenosphere boundary (LAB) is where geophysicists mark the difference in ductility (a measures a solid material’s ability to deform or stretch under stress) between the two layers. This boundary in the upper mantle is marked at the 1300^oC isotherm. Above the isotherm marks where the mantle behaves in a rigid fashion and below which it behaves in a ductile fashion. It is the ductile rocks in the upper part of the asthenosphere that are believed to be in the zone upon which the great rigid and brittle lithospheric plates of the Earth's crust move about. Seismic waves travel relatively slowly through the asthenosphere.