On the recurrence time of earthquakes: insight from Vrancea (Romania) intermediate‐depth events

SUMMARY The statistics of earthquake inter‐occurrence times in broad areas have been reported to obey universal scaling laws (e.g. by Bak et al. and Corral). We investigate the recurrence times of intermediate‐depth Vrancea earthquakes (depth >60 km), taking advantage of the scarcity of aftershocks for deeper events. We use a complete earthquake catalogue (M ≥ 2.8) spanning from 1974 to 2002. The analysis of the probability density distribution of the recurrence times for the entire catalogue reveals a power‐law regime at small scales. In order better to understand this scaling, we also analyse declustered catalogues, from which the distinct aftershock sequences following the 1977, 1986 and 1990 major earthquakes have been removed, and a time period without large events. For these data sets, the recurrence times follow an exponential distribution at all scales. This observation suggests that deviations from the exponential model – characteristic of the scaling laws recently proposed – result primarily from short‐term aftershock clustering.