From AMS Glossary
- In plate tectonics, a layer of strength relative to the underlying asthenosphere for deformation at geologic rates.
It includes the crust and part of the upper mantle and is of the order of 100 km in thickness. (Glossary of Geology 1997)
American Geological Institute 1997. Glossary of Geology. 4th ed., J. A. Jackson, Ed., . p. 372.