Pulse-like, crack-like, and supershear earthquake ruptures with shear strain localization

We incorporate shear strain localization into spontaneous elastodynamic rupture simulations using a Shear Transformation Zone (STZ) friction law. In the STZ model, plastic strain in the granular fault gouge occurs in local regions called STZs. The number density of STZs is governed by an effective disorder temperature, and regions with elevated effective temperature have an increased strain rate. STZ Theory resolves the dynamic evolution of the effective temperature across the width of the fault zone. Shear bands spontaneously form in the model due to feedbacks amplifying heterogeneities in the initial effective temperature. In dynamic earthquake simulations, strain localization is a mechanism for dynamic fault weakening. A shear band dynamically forms, reduces the sliding stress, and decreases the frictional energy dissipation on the fault. We investigate the effect of the dynamic weakening due to localization in generating pulse-like, crack-like, and supershear rupture. Our results illustrate that the additional weakening and reduction of on-fault energy dissipation due to localization have a significant impact on the initial shear stress required for supershear or pulse-like rupture to propagate on a fault.