Laboratory experiments suggest that the evolution of in-plane shear rupture along an interface separating two elastic blocks typically shows a transition from slow to fast slip. In contrast to the commonly used continuum mechanics-based approaches, here we study the shear rupture process along a weak interface using the discontinuous deformation analysis (DDA) method. We incorporate a slip-weakening constitutive friction law to simulate the initiation and propagation of shear rupture under external conditions of a constant normal load and a steadily increased shear load. As the shear load increases, our modeling results reveal a sharp transition from episodic expansion and arrest to unstable runaway rupture, consistent with previous experimental results. In the stage of dynamic runaway, rupture velocity is limited by the Rayleigh wave velocity. We further investigate the effects of external loading conditions including load point velocity and normal stress on rupture behavior. We find that the dynamic rupture velocity increases with load point velocity and normal stress, also consistent with previous studies. Our results indicate that the DDA method can well capture some of the general characteristics of shear rupture process and, hence, can be applied to study other aspects of dynamic shear ruptures.|The slip-weakening friction law is incorporated into DDA to simulate shear rupture processes along a weak interface.Under the DDA model, rupture evolution is characterized by episodic expansion and arrest, followed by a sharp transition to dynamic runaway.The DDA model reproduces a suite of shear rupture behavior, consistent with previous studies.