Investigating linear and nonlinear behaviours in time dynamics of observational seismic sequences

Investigating the time dynamics of complex natural systems is one of the most important scientific challenges, and, in particular, recognizing the dynamical properties in seismicity data could give a better understanding of the geophysical mechanisms underlying tectonic processes. Can the linear/nonlinear properties of an observational seismic sequence be revealed? And what information can they convey? Recently it has proposed magnitude and sign decomposition method for analyzing the dynamical properties of a time series. Applying this method, we investigated two seismic sequences: the 1986–2001 Irpinia-Basilicata (southern Italy) sequence and the 1983–1998 southern California sequence. Our results highlight the following issues: (i) the nonlinear behaviour of seismicity mainly relies to the aftershock activation, that follows a large shock, and (ii) a nontrivial dependence of the dynamical properties of the seismic series could be found with the earthquake depth, due to brittle and ductile behaviour of the crust versus depth.