Stress relaxation at the lower dislocation edge of great shallow earthquakes

The problem of post-seismic stress evolution at the lower dislocation edge of great shallow earthquakes is investigated by a model reproducing a transcurrent boundary zone subject to a constant strain rate. Dislocation models with frictional stress threshold for slip arrest must be considered in order to study post-seismic stress evolution in the proximity of dislocation edges. It is found that the boundary zone is vertically divided in two regions: an upper region, where stress increases with time and a lower region, where stress decreases. Dislocations which are nucleated in the seismogenic region can propagate downward into the aseismic region: in this case earthquakes are followed by relaxation of the stress concentration at the lower dislocation edge. This may have effects on the space-time distribution of aftershocks.