The variation of mechanical properties with depth in the lithosphere determines the relationship between surface deformation and whole-lithosphere deformation, hence between surface deformation and whole-lithosphere dynamics. Where viscosity (or elastic strength) is a continuous function with depth, surface deformation can be used to constrain both force balance and rheological parameters. Where viscosity is discontinuous, but the upper crust and mantle lithosphere have comparable maximum values, surface deformation can be used to approximate force balance and rheological parameters, but tradeoffs mean that estimates of stress and viscosity are effective equivalent values rather than actual values. Where viscosity is both discontinuous and differs by much more than an order of magnitude between the upper crust and mantle lithosphere, information about both force balance and rheology are absent from the surface deformation, so surface observations alone are insufficient to estimate either the dynamic or mechanical state of the lithosphere.
- Received 3 February 2012.
- Accepted 28 February 2012.
- © Geological Society of America