Fractal characterization of the temporal distribution of aftershocks associated with the 1994 Mw 6.7 Northridge earthquake

Fractal analysis has been performed to investigate the aftershock activity that followed the 1994 M-W 6.7 Northridge earthquake (Southern California). The sequence analyzed is very long and the obtained fractal estimates seem very reliable. High degree of clustering is revealed by the calculation of the coefficient of variation C-V approximate to 3.2, and the autocorrelation function shows the presence of dependence among the inter-event times. The obtained value of the capacity dimension D approximate to 0.05 demonstrates that the temporal distribution of the aftershocks is strongly clusterized. Furthermore, we calculated the power-law exponent of the power spectral density of the seismic process, by means of the Allan Factor method and the count-based Periodogram. method; the very high obtained values alpha(AF) approximate to 1.53 and alpha(S) approximate to 1.43 reveal the presence of high correlated time structures in the process.