It is known that some real Cantor Julia sets appear as spectra of Markov operators on self-similar graphs. Examples of such graphs are: Moreover, spectral measures of the corresponding Markov operators are closely related to Brolin-Lyubich measures on the Julia sets. This motivates studying the moments of Brolin-Lyubich measures. In this talk following the approach of Grabner-Woess I will obtain a description of the asymptotic behavior of these moments for quadratic maps $z^2+c$ with $c<-2$, which includes all of the above mentioned examples.