Spatial variability of time-correlated behaviour in Italian seismicity

Using the INGV (National Institute of Geophysics and Volcanology) seismic catalogue, the analysis of the time-clustering behaviour of the instrumental seismicity of Italy has been performed. The time span of the analyzed catalogue is from 1986 to 2001, and only the events with magnitude M³2.4 have been considered. The analysis, carried out on the full and aftershock-depleted catalogues, is performed by using the Detrended Fluctuation Analysis (DFA), that permits the identification of correlated temporal structures in time series, even in presence of trends or nonstationarities. Our findings confirm the presence of long-range behaviour in the temporal distribution of seismicity data of both full and depleted catalogues, suggesting that the clustering phenomenon is due not only to the generation of aftershocks, following the occurrence of large shocks, but relies to the underlying time structure of the seismicity of Italian areas.