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Strain localization in granular fault zones at laboratory and tectonic scales

We present results from laboratory experiments and a numerical model for frictional weakening and shear localization. Experiments document strain localization in sheared layers at normal stresses of 0.5 to 5 MPa, layer thicknesses of 3 to 10 mm, and imposed slip velocities of 10 to 100 μm/s. Passive strain markers and the response to load perturbations indicate that the degree of shear localization increases for shear strains γ of 0.15 < γ < 1. Our numerical model employs rate-state friction and uses 1D elasto-frictional coupling with radiation damping. We interrogate the model frictional behavior by imposing perturbations in shearing rate at the fault zone boundary. The spatial distribution of shear strain depends strongly on frictional behavior of surfaces within the shear zone. We discuss the onset of strain localization and the width of active shear strain for conditions relevant to earthquake faulting and landslides. state relevant to earthquake faulting and landslides.