  The traction evolution is a fundamental ingredient to model the dynamics of
an earthquake rupture which ultimately controls, during the coseismic phase,
the energy release, the stress redistribution and the consequent excitation of
seismic waves. In the present paper we explore the use of the friction behavior
derived from laboratory shear experiments performed on granular materials at
low normal stress. We find that the rheological properties emerging from these
laboratory experiments can not be described in terms of preexisting governing
models already presented in literature; our results indicate that neither
rate-and state-dependent friction laws nor nonlinear slip-dependent models,
commonly adopted for modeling earthquake ruptures, are able to capture all the
features of the experimental data. Then, by exploiting a novel numerical
approach, we directly incorporate the laboratory data into a code to simulate
the fully dynamic propagation of a 3-D slip failure. We demonstrate that the
rheology of the granular material, imposed as fault boundary condition, is
dynamically consistent. Indeed, it is able to reproduce the basic features of a
crustal earthquake, spontaneously accelerating up to some terminal rupture
speed, both sub- and supershear.
