  The scaling relation derived by Dorogovtsev, Goltsev, Mendes and Samukhin
[Phys. Rev. E, 68 (2003) 046109] states that the exponents of the power-law
connectivity distribution, gamma, and the power-law eigenvalue distribution of
the adjacency matrix, delta, of a locally treelike scale-free network satisfy
2*gamma - delta = 1 in the mean field approximation. Here, it is shown that
this relation holds well for the reduced simple earthquake networks (without
tadpole-loops and multiple edges) constructed from the seismic data taken from
California and Japan. The result is interpreted from the viewpoint of the
hierarchical organization of the earthquake networks.
