With the recent expansion of the GPS network in the western US provided by the PBO component of Earthscope, geodynamicists are poised to make rapid progress in our understanding of the processes by which the lithosphere deforms.
As a contribution, we are developing new methods for modeling the deformation of the lithosphere and comparing model predictions to GPS measurements of surface motions. Our approach is to jointly develop kinematic and dynamic models of lithosphere deformation in the western US to address a series of long-standing problems about how the lithosphere deforms including: 1. What is the mode of deformation in the western US? 2. What is the relative influence of various driving forces on lithosphere deformation? 3. What is the rheology of the lithosphere and how does rheology change with depth? 4. Is lithosphere deformation self-driving and decoupled from mantle flow? 5. Where is slip along faults aseismic and seismic? And, 6. To what extent do faults interact mechanically by transfer of loads through elastic and viscous processes in the lithosphere?
We are developing kinematic models of long-term and interseismic deformation that will be used to infer the viscosity structure of the lithosphere, fault slip rates, distribution of interseismic fault creep, and lithospheric block motions. To do this we are constructing 3D earthquake cycle models consisting of faults in an elastic schizosphere overlying a layered viscous plastosphere. We are examining the extent in space and time to which postseismic relaxation processes in the mantle and on deep crustal faults might be evident in GPS measurements of interseismic deformation and to what extent these processes influence our estimates of fault slip rates. We are also moving beyond purely kinematic models and developing thin-plate elasto-plastic models of long-term lithosphere deformation in which faults slide in response to far-field plate driving forces, internal body forces due to variations in gravitational potential energy, and basal tractions. Combining these predictions of long-term motions with our interseismic deformation models and GPS observations, we are trying to infer the relative contributions of the various driving forces to lithosphere deformation.
