Dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults

Abstract

We present numerical models of earthquake cycles on a strike‐slip fault that incorporate laboratory‐derived power law rheologies with Arrhenius temperature dependence, viscous dissipation, conductive heat transfer, and far‐field loading due to relative plate motion. We use these models to explore the evolution of stress, strain, and thermal regime on “geologic” timescales (∼106–107 years), as well as on timescales of the order of the earthquake recurrence (∼102 years). Strain localization in the viscoelastic medium results from thermomechanical coupling and power law dependence of strain rate on stress. For conditions corresponding to the San Andreas fault (SAF), the predicted width of the shear zone in the lower crust is ∼3–5 km; this shear zone accommodates more than 50% of the far‐field plate motion. Coupled thermomechanical models predict a single‐layer lithosphere in case of “dry” composition of the lower crust and upper mantle, and a “jelly sandwich” lithosphere in case of “wet” composition. Deviatoric stress in the lithosphere in our models is relatively insensitive to the water content, the far‐field loading rate, and the fault strength and is of the order of 102 MPa. Thermomechanical coupling gives rise to an inverse correlation between the fault slip rate and the ductile strength of the lithosphere. We show that our models are broadly consistent with geodetic and heat flow constrains from the SAF in Northern California. Models suggest that the regionally elevated heat flow around the SAF may be at least in part due to viscous dissipation in the ductile part of the lithosphere.