Investigating non-uniform scaling behaviour in temporal fluctuations of seismicity

L Telesca,M Lovallo

doi:10.5194/nhess-8-973-2008

Abstract

Abstract. Scaling behaviour in nonstationary time series can be successfully detected using the detrended fluctuation analysis (DFA). Observational time series often do not show a stable and uniform scaling behaviour, given by the presence of a unique clear scaling region. The deviations from uniform power-law scaling, which suggest the presence of changing dynamics in the system under study, can be identified and quantified using an appropriate instability index. In this framework, the scaling behaviour of the 1981–2007 seismicity in Umbria-Marche (central Italy), which is one of the most seismically active areas in Italy, was investigated. Significant deviations from uniform power-law scaling in the seismic temporal fluctuations were revealed mostly linked with the occurrence of rather large earthquakes or seismic clusters.

Highlights

The complexity of the dynamics of geophysical processes is often characterized by self-similarity, which suggests that their dynamics may be interpreted as due to many components interacting over a wide range of time or space scales (Ashkenazy et al, 2003)
The use of statistics like the Allan Factor (Allan, 1966), the Fano Factor (Lowen and Teich, 1995), the Detrended Fluctuation Analysis (DFA) (Peng et al, 1995), has allowed getting more insight into the time dynamics of seismicity. All these measures lead to the determination of a scaling exponent, estimated by a linear fitting procedure performed on the power-law statistics plotted in log-log scales
If there are only short-range correlations, the initial slope may be different from 0.5 but will approach 0.5 for large window sizes n. d>0.5 indicates the presence of persistent long-range correlations, meaning that a large interevent interval is more likely to be followed by large one and vice versa. d

Summary

Introduction

The complexity of the dynamics of geophysical processes is often characterized by self-similarity, which suggests that their dynamics may be interpreted as due to many components interacting over a wide range of time or space scales (Ashkenazy et al, 2003). The Umbria-Marche region, central Italy, was deeply studied and many investigations have been performed regarding its geodynamical features (Boncio and Lavecchia, 2000; Calamita et al, 2000), active tectonics (Galadini et al, 1999; Cinti et al, 2000), spatio-temporal seismic distribution (Ripepe et al, 2000; Di Giovambattista and Tyupkin, 2000), induced geophysical effects (Esposito et al, 2000) This area is characterized by a welldocumented historical and instrumental seismicity, mainly confined within the upper part of the crust (

The method

Results and discussion

Conclusions