Post-seismic relaxation: An example of earthquake triggering in the Apennine belt (1915–1920)

The strong earthquake (M = 7) that occurred in the Fucino basin (central Italy) on January 13, 1915 was followed by six earthquakes of M > 5.5 and several other shocks of M > 5 in the major seismic zones of the northern Apennines from 1916 to 1920. This seismicity pattern is consistent with the implications of the present tectonic setting in the study area, which suggests that strong decoupling earthquakes in the central Apennines cause a significant increase of tectonic load, and possibly of seismicity, in the northern Apennines. A numerical simulation, carried out by an elastic-viscous model, of the stress diffusion induced by the Fucino and successive largest earthquakes, shows that each of the above shocks occurred when the respective zone was reached by the highest values of the strain and strain rate perturbation triggered by the previous events. Furthermore, the computed strain regime at each earthquake site is consistent with the known faulting pattern. The results provide important insights into the physical mechanism that controls the interaction of seismic sources in the central and northern Apennines.