Are seismic waiting time distributions universal?

We show that seismic waiting time distributions in California and Iceland have many features in common as, for example, a power-law decay with exponent alpha approximate to 1.1 for intermediate and with exponent gamma approximate to 0.6 for short waiting times. While the transition point between these two regimes scales proportionally with the size of the considered area, the full distribution is not universal and depends in a non-trivial way on the geological area under consideration and its size. This is due to the spatial distribution of epicenters which does not form a simple mono-fractal. Yet, the dependence of the waiting time distributions on the threshold magnitude seems to be universal.