Non-extensive and natural time analysis of seismicity before the Mw6.4, October 12, 2013 earthquake in the South West segment of the Hellenic Arc

Earthquakes exhibit complex correlations in space, time, and magnitude. As such, they present a unique example for a time series exhibiting complexity. To uncover hidden dynamic features of seismicity before the Mw6.4, October 12, 2013 earthquake in the South West part of the Hellenic Arc, we apply the recently introduced methods of natural time analysis along with the ideas of non-extensive statistical physics. Using non-extensive statistics, the analysis of the magnitude distribution of the 2013 seismicity in the South West part of the Hellenic Arc, struck by a strong earthquake (Mw=6.4), was performed for a time period before the main event, which was the strongest one in the South West part of the Hellenic Arc in the last 40 years. The analysis of the frequency magnitude (energy) distribution reveals that the non-extensive parameter qE varies during the last period of the earthquake preparatory phase with a sharp increase a couple of days before the occurrence of the main strong event, indicating an increase in the degree of out-of-equilibrium state before the occurrence of the Mw6.4 earthquake. In addition using the natural time analysis it is shown that foreshock seismicity approaches the critical stage, where the k1 parameter reaches the critical value of k1=0.070 few days before the occurrence of the main event.