PROPAGATION OF AN ASEISMIC DISLOCATION THROUGH ASPERITIES WITH SMOOTHBORDERS

A 2-D model is presented for the propagation of a Somigliana dislocati on along a fault with nonuniform friction. Fault slip is driven by a u niform ambient shear stress, slowly increasing with time. The dislocat ion is nucleated in the lowest-friction region of the fault plane and is confined by the surrounding higher-friction regions (asperities). T he case studied involves asperities which have smooth borders, charact erized by a constant friction gradient. For values of ambient shear st ress near to the weak-zone friction, the propagation of dislocation is slowed down by the presence of asperities. Only when it goes beyond t he border does the dislocation front move at increasing velocity. The model shows that, at a given value of ambient shear stress, the slip a mplitude is larger in the case of finite and constant friction gradien t than in the case of asperities with sharp borders. Unlike the propag ation velocity, slip rate is ever increasing during the dislocation pr ocess. The model shows to what extent a dislocation is influenced by t he distribution of friction on the fault. A detailed knowledge of slip rate and slip history is needed to understand the mechanism of fricti onal instability on faults.