Non-extensive statistical analysis of seismicity in the area of Javakheti, Georgia

The distribution of earthquake magnitudes in the Javakheti highlands was analyzed using a non-extensive statistical approach. The earthquakes occurring from 1960 to 2008 in this seismically active area of Southern Caucasus were investigated. The seismic catalog was studied using different threshold magnitude values. Analyses of the whole time period of observations as well as of sub-catalogs of consecutive 10-year span time windows were performed. In every case non-extensive parameter q and value a, the physical quantity characterizing energy density, were calculated from the modified frequency–magnitude relationship. According to our analysis the magnitude sequence in the Javakheti area for the whole period of observation is characterized by a non-extensivity parameter q=1.81, in the upper limit of values reported elsewhere. While calculated non-extensivity parameters for consecutive 10-year windows fall within the range 1.6–1.7 reported worldwide. A significant increase of parameter q was identified in those 10-year sub-catalogs that included the strongest earthquakes within the period of observation. We suppose that this increase may be related to a more correlated behavior within the system of ‘fault fragments’ when a strong earthquake strikes or immediately after; during aftershock activity. Concurrently, smaller values of non-extensivity parameters q i , found during seismically relatively quiet times, could be associated to the decreased correlations within the system during the earthquake generation stage, under an essentially decreased tectonic stress. The behavior of the energy density characteristic a almost mirrors the variation of parameter q: increases for seismically quiet periods in the Javakheti area and decreases in periods when strong earthquakes occur. We suggest that decreases of energy density characteristic a may point to a prevalent contribution of large size fragments to fragment–asperity interaction under the influence of a rapidly released stress, as opposed to relatively quiet periods when accumulated stress energy is supposedly released through the relative movement of smaller fragments.