Spatial fractal evolutions and hierarchies for microearthquakes in Central Greece

Statistical characteristics of seismicity represented by microearthquakes are examined for three regions in central Greece, in particular the fractal correlation dimension, D2, and traditional b values are examined in tandem as a function of time by using the moving window technique. The Patras region contains the complicated tectonics, extending to damaging historical earthquakes of the western Corinth Gulf and the Rio Graben, yielding D2 values between 0.40 and 1.20 with b between 0.94 and 1.27: unusually, the temporal evolution between D2 and b generates a positive correlation, although the variation is mostly in D2. When the whole evolution is divided into two stages then the positive correlations are even stronger than for the whole evolution. The views of Henderson and others might suggest a highly fractured, fluid-filled zone. The Pavliani region, with no known acti6e fault, and the Volos region, containing the through-going Nea Ankhialos fault, yield D2 values 0.33 to 0.79 with b 0.92 to 1.30 and D2 0.82 to 1.56 with b 1.02 to 1.37, respectively. Temporal evolution between D2 and b provides a typical negative correlation in both regions. Examination of gross seismicity (time window embracing the whole data set) in each region produces D2 values for the Patras and Volos regions that are both larger than that for Pavliani; there are no obvious differences amongst the b values. This accords with the knowledge that Patras and Volos are in regions with very active seismotectonic features which generate repeated strong earthquakes exceeding 6 Ms. D2 for both regions is fairly close to 1, the topological dimension of a line, consistent with seismicities on leading active fault zones or through-going faults. These values highlight the ability for microearthquakes to illuminate the character of their parent tectonic province. Resolution and hierarchy in these data from Greece are compared with these aspects elsewhere (Japan, Turkey, South America, USA) in the sense that their banding with respect to examined magnitude, areal extent and duration of observation period for respective data sets is examined in relation to the earthquake potential of the parent seismotectonic province. Evolutions are then categorised as being macroscopic, transitional or microscopic in character.