  By analyzing a southern California earthquake catalog, Davidsen and Paczuski
[Phys. Rev. Lett. 94, 048501 (2005)] claim to have found evidence contradicting
the theory of aftershock zone scaling in favor of scale-free statistics. We
present four elements showing that Davidsen and Paczuski's results may be
insensitive to the existence of physical length scales associated with
aftershock zones or mainshock rupture lengths, so that their claim is
unsubstantiated. (i) Their exponent smaller than 1 for a pdf implies that the
power law statistics they report is at best an intermediate asymptotic; (ii)
their power law is not robust to the removal of 6 months of data around Landers
earthquake within a period of 17 years; (iii) the same analysis for Japan and
northern California shows no evidence of robust power laws; (iv) a statistical
model of earthquake triggering that explicitely obeys aftershock zone scaling
can reproduce the observed histogram of Davidsen and Paczuski, demonstrating
that their statistic may not be sensitive to the presence of characteristic
scales associated with earthquake triggering.
