We apply shear wave elastography, a medical imaging technique that uses ultrafast ultrasound to analyze rupture nucleation. In order to better understand friction and rupture processes which are responsible for earthquake nucleation, we build a laboratory experiment that reproduces the stick-slip behavior of a seismic fault for soft elastic materials. The rupture process is generated by controlling a driving slab through a motor in synchronization with the ultrasound acquisition system. As an analog to an asperity on a fault, a patch of sand grains constitutes the stick-slip behavior. In contrast to classical seismological methods, we are able to follow the wave propagation inside the sample and thus highly resolve the near and intermediate terms of the elastic wave-field. First results confirm the previously proven existence of super-shear as well as sub-Rayleigh fronts for the in-plane shearing mode. We anlayze the rupture speed distribution on the fault and resolve the extension of the asperity as well...