Investigating the time-clustering properties in seismicity of Umbria-Marche region (central Italy)

We investigated by fractal tools the temporal patterns of 1996-1999 seismicity of the Umbria-Marche region, central Italy, that was struck by a strong event (M-S = 5.9) on September 26, 1997. Clustering behaviour has been evidenced by using different fractal tools, Fano factor analysis, Allan factor analysis and detrended fluctuation analysis, that show power-law shaped statistics, whose scaling exponents describe the degree of clusterization in the earthquake sequence. Furthermore, the scaling exponents evolve in time showing an increase of the clustering features in correspondence to larger events. (C) 2003 Elsevier Science Ltd. All rights reserved.