Propagation of an aseismic dislocation through asperities with smooth borders

A 2-D model is presented for the propagation of a Somigliana dislocation along a fault with nonuniform friction. Fault slip is driven by a uniform ambient shear stress, slowly increasing with time. The dislocation is nucleated in the lowest-friction region of the fault plane and is confined by the surrounding higher-friction regions (asperities). The case studied involves asperities which have smooth borders, characterized by a constant friction gradient. For values of ambient shear stress near to the weak-zone friction, the propagation of dislocation is slowed down by the presence of asperities. Only when it goes beyond the border does the dislocation front move at increasing velocity. The model shows that, at a given value of ambient shear stress, the slip amplitude is larger in the case of finite and constant friction gradient than in the case of asperities with sharp borders. Unlike the propagation velocity, slip rate is ever increasing during the dislocation process. The model shows to what extent a dislocation is influenced by the distribution of friction on the fault. A detailed knowledge of slip rate and slip history is needed to understand the mechanism of frictional instability on faults. © 1993.