<p>The understanding of the propagation of frictional ruptures along the interfacial contacts presents a fundamental challenge that holds significant relevance across various domains, including classical physics and seismology. Frictional ruptures are characterized by their ability to propagate over a wide range of velocities. Some fronts propagate relatively slowly, initiating a sequence of localized micro-contact failures, whereas others propagate more rapidly, leading to an avalanche of breakage on a much larger scale. These distinct propagation types and their transitions, such as the transition from slow to fast propagation, have been extensively documented in laboratory experiments; however, the governing laws of such transitions remain to be elucidated. In this study, we have developed a multiscale model to examine the evolution of the shear force at the rupture interface within a two-dimensional friction system. It is demonstrated that both upper and lower bounds for the increments of interfacial shear during rupture front propagation can be effectively described by the Green functions of the linearized system. By integrating these bounds with the interfacial force distribution, we have established three transition laws that enable the prediction of front transitions among fast fronts, slow fronts, and front arrests. These findings suggest that monitoring the shear along the interface may provide a means to evaluate the risk of a slow rupture transitioning into a rapid one, potentially culminating in a destructive seismic event.</p>