FRACTAL CHARACTERIZATION OF THE TEMPORAL DISTRIBUTION OF AFTERSHOCKS ASSOCIATED WITH THE 1994MW6.7 NORTHRIDGE EARTHQUAKE

Abstract

Fractal analysis has been performed to investigate the aftershock activity that followed the 1994 MW6.7 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 CV≈ 3.2, and the autocorrelation function shows the presence of dependence among the inter-event times. The obtained value of the capacity dimension D ≈ 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 αAF≈ 1.53 and αS≈ 1.43 reveal the presence of high correlated time structures in the process.