We study the interoccurrence time distributions of events by analyzing synthetic catalogues and three natural catalogues of the Japan Meteorological Agency (JMA), the Southern California Earthquake Data Center (SCEDC) and the Taiwan Central Weather Bureau (TCWB). We find a universal feature, i.e. the Weibull-log Weibull transition, in the interoccurrence time statistics. This transition demonstrates that the interoccurrence time statistics of earthquakes possess the hybrid Weibull and log Weibull statistics. We further find that the crossover magnitude m(c)** from the superposition regime to the pure Weibull regime is averagely proportional to the plate velocity. In the end of this paper we summarize a region-independent relation, i.e. m(c)**/m(max)=0.54 +/- 0.06, which represents a novel empirical relation related to the Weibull-log Weibull transition for earthquake processes. (C) 2009 Elsevier B.V. All rights reserved.