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Shear Strain Localization in Elastodynamic Rupture Simulations

DAUB, E.G., MANNING, M.E., and CARLSON, J.M., Physics Department, University of California, Santa Barbara, CA, 93106,

We study strain localization within fault cores in the context of sponataneous elastodynamic rupture simulations. Field observations of exhumed faults show that most of the slip in earthquakes occurs in finely grained ultracataclasite layers, with relatively planar prominent fracture surfaces allowing for further localization of slip. We capture localization through Shear Transformation Zone (STZ) Theory, a microscopic physical model for plastic strain in amorphous solids. STZs are a continuum approximation for deforming amorphous materials, which makes the law suitable for application to dynamic ruptures. The STZ constitutive law determines the disorder in the material through an effective temperature, which is distinct from thermal temperature but follows a similar dynamic evolution law with both shear heating and diffusion playing important roles in friction dynamics. In a spring slider model, the STZ friction law produces strain profiles similar to those observed in the field. The fault weakens due to localization in the ultracataclasite layer, and develops a prominent fracture surface within the ultracataclasite layer. In sponataneous elastodynamic rupture simulations, localization causes lower dynamic sliding stresses and higher peak slip rates than homogeneous deformation with the same total gouge width. These factors will impact the stress drop and ground motion of earthquakes, illustrating that localization of rupture plays a key role in constraining the physics of the earthquake source.


Last Modified: 2011 Aug 10