We investigate significant heterogeneous stresses along bimaterial interfaces in laboratory and numerical experiments. These stresses, partially induced by model or experimental configuration, affect the supershear transition length and rupture speed, mode and directivity in uniaxial compression tests and dynamic rupture experiments with bimaterial interfaces. Using numerical simulations we show that normal and tangential stresses at the fault are distorted by the different stress-strain relationships of the materials. This distortion leads to altered supershear transition lengths, higher rupture potencies and amplifies the preference for rupture in the direction of slip of the slower and more compliant material. We demonstrate how this stress-distortion can be decreased in laboratory experiments by using larger specimen samples and in numerical models by using periodic boundary conditions
