Models of aftershock occurrence

Abstract

The Omori formula for aftershock activity can be shown to be a consequence of each of two models of a complex earthquake. In the first case, aftershocks are assumed to be caused by subsequent slip on asperities of a fault which are locked during the fracture in the main shock. In the second, aftershocks are caused by catastrophic coalescence of nearby small fractures with the fracture surface of the main shock. Hence, the first source model describes aftershock activity in the interior of a main-shock rupture zone, while the second describes aftershock activity near the outer boundary of a main-shock rupture zone. Stress corrosion cracking is assumed to be the physical cause of the quasistatic growth of the main fracture zone at the expense of the area of the locked patches in the first model and is also the cause of the growth of the small satellite fractures in the second.