3D THERMO-MECHANICAL MODELING OF THE EVOLUTION OF THE SAN ANDREAS FAULT

The San Andreas Fault System (SAFS) in central and northern California began to develop about 20 Myr ago in response to the northward migration of the Mendocino triple junction. As the triple junction migrated northward along the plate boundary, the slab being subducted beneath North America was replaced by hot asthenospheric material in a slab window. The transform deformation along the plate boundary developed simultaneously with northwards migration of the subducted Gorda plate (causing further opening of the slab window) and thermal re-equilibration of the North American lithosphere within the window. We use newly developed finite element numerical modeling technique (see poster by Popov and Sobolev at session “The Structure, Composition and Evolution of the Lithosphere of Western North America”) to study interrelation of these processes. The modeling technique is fully 3D, employs realistic elasto-visco-plasic rheology and allows for spontaneous generation of faults. In our modeling we address the questions of how the deformation of the North America plate is influenced by: (i) northward migration and subduction of the Gorda plate, implemented at the northern boundary of the model, (ii) thermal parameters/processes, like initial temperature distribution and shear heating, and (iii) rheology of the crust and mantle, including friction at major faults. It is important that faults in our models are not predefined but are generated in a self consistent way due to strain localization process. Massive numerical experiments are just underway and their results will be reported in the presentation. Preliminary results are very encouraging, showing, for instance, that advection of asthenosphere within the slab window and motion of the Gorda plate can cause significant deformation of the North American lithosphere overlaying slab window, explaining major features of its surface topography and variations of crustal thickness.