Time-scaling properties of the Umbria-Marche 1997–1998 seismic crisis, investigated by the detrended fluctuation analysis of interevent time series

The Umbria-Marche region (central Italy) is one of the most seismically active area of Italian Peninsula, and recently it was characterized by the intense earthquake (M=5.9) occurred on September 26, 1997. We analyzed the time-scaling properties of the seismicity of the area during the 1997–1998 seismic crisis by means of the detrended fluctuation analysis, a method that permits the detection of long-range correlations in time series, possibly influenced by nonstationarities. Our results highlight a persistent feature of the earthquake sequence, that seem independent on the threshold magnitude.