Publications

The San Andreas Fault System (SAFS) in central and northern California is a family of sub-parallel strike-slip faults that accommodate the transform motion between the Pacific and the North America plates. We present here a fully coupled numerical thermo-mechanical model of the SAFS as it evolved over the past 20 Myr following the northward migration of the Mendocino triple junction. The strike-slip displacements and fault perpendicular compression (over the last 5 Myr) are implemented as side boundary conditions in the upper 20 km of the 100 km deep model box, other parts of the side boundaries and bottom boundary being free for material flow. The model employs realistic visco-elasto-plastic rheology and allows for spontaneous generation of faults. The modeling replicates the evolution of multiple strike-slip faults, the overall eastern migration of the San Andreas fault itself from the western edge of the Coast Ranges near Cape Mendocino to the eastern edge in central California, the variation of heat flow in the Coast ranges along and across the SAFS as well as high angle (60-80$deg$) between the direction of the maximum horizontal stress and the local fault orientation in the upper crust. The modeling shows that the key conditions for such behavior are the cooling (and strengthening) of the lithosphere following passage of the triple junction which causes ductile deformation at depth to migrate eastward with time and the drop of frictional strength at high strain in the upper crust which results in a small number of major transform faults to develop, rather than a broad distribution of such faults. Our modeling suggests that the major faults in the SAFS in Central and Northern California must have been weak during most of the 20 Myr period over which it evolved.

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Sobolev, S. V.; Zoback, M. D.; Babeyko, A. Y. (2003): A Thermo-Mechanical Model of the San Andreas Fault System in Central and Northern California. AGU 2003 Fall Meeting (San Francisco 2003).