The role of seismotectonic setting in the study of anomalous patterns in electrical earthquake precursors measured in seismic active areas: observational evidences in Southern Italy and Crete island (Greece).

n this work we analyse anomalous patterns in self-poten-tial time series instrumentally recorded in seismic active areas in the Mediterranean region: Southern Italy (Giuliano station) and Crete island (Heraklion station). The geoelec- trical data cover the period from January 1996 to December 1998, with data missing less than 10%. In a first step, we investigated the time dynamics of geoelectrical time series and applied robust statistical methodologies to pick out anomalous patterns from background fluctuations (Colangelo et al., 2000; Cuomo et al., 2000). In a second step, we approached the very controversial and fascinating problem of the possible correlation between electrical anomalies and locals seismic activities. To this aim, the comparison between the temporal map of self-potential anomalies and the sequences of earthquakes, observed by Nationals Seismometric Networks in the investigated areas, is deeply analysed and discussed. In particular, we focused our attention to the criteria adopted to select the earth- quakes that, in principle, could be responsible for strain effects in the investigated areas. Many authors approached this problem using the Dobrovolsky rule (r=100.43M), where r is the radius of the area in which the effects of the earthquake are in principle detectable and M is the magnitude (Dobrovolsky et al., 1989). In this work we enhance the weak points of this approach, taking into account the geological and seismological settings of the investigated areas. In this way, we better described the appearance of anomalous sequences in electrical signals that seem to be correlate with seismic events associated to the Giuliano strike-slip fault (Ekstrom, 1994) and the Heraklion normal fault. In conclusion, our findings suggest us to better consider the role of geological and seismological setting in the study of temporal and spatial patterns in electrical signals detected in seismic active areas.