Monitoring earthquake network measures between main shocks in Greece

Abstract

The monitoring of complex earthquake networks that are formed from Greek seismicity based on the evolution of their measures, such as degree centrality, characteristic path length, and clustering coefficient is performed, aiming to identify whether and when these networks exhibit distinct evolution between main shocks. As network nodes, the 17 seismic zones in which the study area was appropriately divided are considered and their connections are given by the significant correlation computed on the time series of each node seismic activity. The data are taken from a seismic catalog comprising crustal earthquakes (focal depth less than 50 km) of magnitude M ≥ 3.0 that occurred in the territory of Greece in between 1999 and 2017. During this period twenty one (21) main shocks of M ≥ 6.0 occurred, but for only six (6) of them, the interevent time since the last one was adequate for the network measures calculation. The earthquake networks are formed on sliding windows of different durations for monitoring the network measures variation. To assess whether the values of network measures are statistically significant, the construction of randomized networks is required, and the same network measures are calculated for comparison purposes. The monitoring of network measures revealed that their values were found statistically significantly different from the corresponding values of the randomized networks shortly before the main shocks.