The Behavior of the Lithosphere on Seismic to Geologic Timescales

Abstract

The strength of the lithosphere and how it responds to loading and unloading are fundamental problems with wide implications. Flexure studies suggest that the elastic thickness, a proxy for the strength of the lithosphere, increases with plate age but decreases with load age. The elastic thickness is significantly less than the seismic thickness of the lithosphere, as indicated by the depth to the low-velocity zone, suggesting that the lithosphere is a strong structure at short seismic timescales and a weak one at long timescales. The mechanism controlling this weakening is not known, but it probably involves some form of load-induced stress relaxation. Despite weakening, the lithosphere is capable of retaining its strength and supporting loads such as volcanoes and sediments for long periods of geological time. Lithosphere relaxation should be included in geodynamical models, especially as it has impacts on stratigraphy, sea-level change, and dynamic topography.