Short time scale laws in self-potentialsignals from two different seismically active Mediterranean areas(the Southern Apennine chainand Crete Island)

Self-potential time series are investigated to characterise self-potential time scales. The data analysed were recorded in stations located in two active seismic areas of the Mediterranean region, the Southern Apennine chain (Giuliano) and Crete Island (Heraklion), where in past and recent years many destructive seismic events have taken place. The seismological and geological settings, combined with a low level of cultural noise, allow us to consider these areas ideal outdoor laboratories to study the time dynamics of geophysical parameters of electrical nature. At the same time, the different seismological features of such areas make an inter-comparison between the geoelectrical variability observed at the two sites interesting. Fractal analysis tools, able to detect scale laws and quantify persistence features, are used to better understand the background variability properties of the self-potential signals. As results from our analysis, antipersistence seems to be a ubiquitous feature on short time scales (minutes) regardless of environmental conditions. On such scales, the accumulation of random fluctuations is not particularly efficient and significant variations mostly occur as sudden jumps