  In their paper (Europhys. Lett., 71 (2005) 1036), Carbone, Sorriso-Valvo,
Harabaglia and Guerra showed that "unified scaling law" for conventional
waiting times of earthquakes claimed by Bak et al. (Phys. Rev. Lett., 88 (2002)
178501) is actually not universal. Here, instead of the conventional time, the
concept of the internal time termed the event time is considered for
seismicity. It is shown that, in contrast to the conventional waiting time, the
waiting event time obeys a power law. This implies the existence of temporal
long-range correlations in terms of the event time with no sharp decay of the
crossover type. The discovered power-law waiting event-time distribution turns
out to be universal in the sense that it takes the same form for seismicities
in California, Japan and Iran. In particular, the parameters contained in the
distribution take the common values in all these geographical regions. An
implication of this result to the procedure of constructing earthquake networks
is discussed.
