The hypothesis of alternation leads to the idea of immunity after local disaster which, notwithstanding it sounds reasonable, it has been frequently rejected by objective testing. More generally the estimate of the occurrence probability of the next big shock on the basis of the time delay from the last earthquake still represents a big challenge. The problem is that this issue cannot be addressed only on the basis of historical catalogs which contain to few well documented big shocks and decades of future observations appear necessary. On the other hand, recent results have shown that important insights can be obtained from the spatial organization of aftershocks and its relationship to the mainshock slip profile.
Here we address this issue by monitoring the stress evolution together with the occurrence of big shocks and their aftershocks in a physical model where the seismic fault is described as an elastic layer embedded in a ductile medium. The model reproduces all relevant statistical features of earthquake occurrence and allows us to perform accurate testing of the hypothesis of alternation and its consequences, particularly on the side of aftershock spatial patterns. We demonstrate that the hypothesis of characteristic earthquakes is not valid but that is possible to achieve insights on the time until the next big shock on the basis of the percentage of aftershocks occurring inside the high slip contour of the mainshock.