Mechanical boundary layer (MBL)
The LAB (Lithosphere–asthenosphere boundary) separates the mechanically strong lithosphere from the weak asthenosphere. The depth to the LAB can be estimated from the amount of flexure the lithosphere has undergone due to an applied load at the surface (such as the flexure from a volcano). Flexure is one observation of strength, but earthquakes can also be used to define the boundary between “strong” and “weak” rocks. Earthquakes are primarily constrained to occur within the old, cold, lithosphere to temperatures of up to ~650°C. This criterion works particularly well in oceanic lithosphere, where it is reasonably simple to estimate the temperature at depth based upon the age of the rocks. The LAB is most shallow when using this definition. The Mechanical boundary layer (MBL) is rarely equated to the lithosphere, as in some tectonically active regions (e.g. the Basin and Range Province) the MBL is thinner than the crust and the LAB would be above the Mohorovicic discontinuity.
The LAB (Lithosphere–asthenosphere boundary) separates the mechanically strong lithosphere from the weak asthenosphere. The depth to the LAB can be estimated from the amount of flexure the lithosphere has undergone due to an applied load at the surface (such as the flexure from a volcano). Flexure is one observation of strength, but earthquakes can also be used to define the boundary between “strong” and “weak” rocks. Earthquakes are primarily constrained to occur within the old, cold, lithosphere to temperatures of up to ~650°C. This criterion works particularly well in oceanic lithosphere, where it is reasonably simple to estimate the temperature at depth based upon the age of the rocks. The LAB is most shallow when using this definition. The Mechanical boundary layer (MBL) is rarely equated to the lithosphere, as in some tectonically active regions (e.g. the Basin and Range Province) the MBL is thinner than the crust and the LAB would be above the Mohorovicic discontinuity.