Small-world structure of earthquake network

Discoveries of the scale-free and small-world features are reported on the network constructed from the seismic data. It is shown that the connectivity distribution decays as a power law, and the value of the degrees of separation, i.e., the characteristic path length, between two earthquakes (as the vertices) chosen at random takes a small value between 2 and 3. The clustering coefficient is also calculated and is found to be about 10 times larger than that in the case of the completely random network. These features highlight a novel aspect of seismicity as a complex phenomenon. (C) 2004 Elsevier B.V. All rights reserved.