Aftershock Statistics of Major Subduction Earthquakes

Abstract

Abstract Large megathrust subduction earthquakes generate prolific aftershock sequences which last over an extended period of time and affect wide spatial areas. Among those aftershocks, the largest ones can cause additional damage and pose significant risks to population and infrastructure. Therefore, modeling aftershock sequences of large subduction earthquakes is of considerable importance for seismic‐hazard assessment and earthquake risk mitigation. It can also play a prominent role in the ground‐shaking modeling of major mainshock–aftershock sequences. In this work, we analyze statistical properties of aftershock sequences of large subduction earthquakes worldwide which occurred from 1973 to present, including recent catastrophic events in Sumatra, Chile, and Japan. We use information provided in the National Earthquake Information Center (NEIC) catalog to extract 70 aftershock sequences generated by mainshocks of M 7.0 and above. We construct their temporal decay rates and magnitude–frequency statistics. To model their temporal behavior, we estimate the parameters of the modified Omori law. In the magnitude domain, we model the frequency–magnitude statistics using the Gutenberg–Richter scaling relationship. We also analyze statistically the difference between the magnitude of the mainshock and the corresponding largest aftershock in the sequence and discuss this in terms of Bath’s law. One of the main goals of this work is to investigate the variation in parameter values of the above empirical laws with respect to the magnitude of the mainshock. Our main finding indicates that most parameters do not depend on the magnitude of the mainshock. However, they show some variation in values across different subduction settings. Online Material: The location and spatial information for elliptical regions of aftershock zones.