Earthquake Clusters Resulting from Delayed Rupture Propagation in Nite Fault Segments

The question whether the preparation process of foreshocks and mainshocks is diierent from other earthquakes is of great interest with regard to earthquake predictability. We show that the most conspicuous properties of earthquake clustering can be explained without assuming any diierences in the initiation processes. In particular, the Gutenberg-Richter law as well as the Omori law for foreshock and aftershock sequences can be reproduced by model simulations with the simple assumption that all subsequent events are initiated in the same manner at the edges of the recently ruptured area. In this way, the empirically observed b and p values are reproduced naturally without any parameter tuning as well as their diierences with regard to foreshock and aftershock activity. These properties are shown to result from the shrinking of the loaded fault region with time. In the model, foreshocks occur in extended and almost compact fault segments whereas aftershocks are mostly restricted to recesses left unruptured by the mainshock. Our investigations lead to the conclusion that the spatial eeects rather than the temporal eeects of the initiation mechanism are decisive for earthquake clustering. 2