Fractal approach of the temporal earthquake distribution in the Hellenic arc-trench system

The time clustering of earthquakes occurring in the Hellenic arc-trench system is quantitatively analyzed by means of the fractal dimension, D, of their time distribution in the time intervals of 1950-1985 (M sub(s) greater than or equal to 4.5) and 1964-1985 (M sub(s) greater than or equal to 4.0). The results obtained imply that scale-invariant clustering holds over very large scale lengths of time, T, with 2 super(2)-2 super(8) less than or equal to T (in min) less than or equal to 2 super(20)-2 super(22),, depending on the seismotectonic segment considered. In all segments a common feature is the relation between the D sub(1), D sub(2), and D sub(3)-values found for shallow, intermediate-depth and all-depth shocks, respectively: D sub(3) > D sub(1) > D sub(2). The D-values found for shallow shocks range between 0.137 and 0.191 with the exception of the Ionian Islands and Cretan segments where anomalously high valves (D = 0.221-0.251) have been determined. We discuss possible seismotectonic interpretations of the results.