Statistical Analysis of the 2002 Mw 7.9 Denali Earthquake Aftershock Sequence

Abstract

We study the scaling properties of the aftershock sequence of the 2002 M w 7.9 Denali earthquake. The sequence exhibits nontrivial scaling behavior in magnitude, aftershock decay rates, and aftershock inter-occurrence times. In particular we observe a marked variability in the Gutenberg–Richter (GR) exponent, the b -value, in space, between early and late times after the mainshock and over different magnitude ranges. We find strong indications that certain aspects of this variability might be ascribed to the occurrence of some of the aftershocks on and around a supershear rupture associated with this event. Particularly, we observe a statistically higher b -value for the aftershocks that occurred in the zone surrounding the supershear rupture. We further outline a method to obtain an average b -value, consistent with the theory and statistical properties of the data. We find a significant difference between the magnitude of the largest aftershock and the mainshock. This is analyzed and discussed using the modified Bath’s law. It is observed that the aftershock decay rate can be approximated by the modified Omori law. The distribution of inter-occurrence times is studied and we show that it can be explained in terms of a nonhomogeneous Poisson process through time. We further observe that the rescaled inter-occurrence time distributions for various magnitude thresholds collapse into a universal functional form which indicates that the aftershock sequence exhibits self-similarity in both magnitude and time. In particular, the statistical features of the aftershock sequence show that the rupture process or the preconditions that lead to it may influence aftershock statistics.