Self-organized criticality in a mixed hierarchical system

It is demonstrated that the self-organized criticality emerges in a hierarc hical system as a result of heterogeneity in the scaling conditions. A hete rogeneous system consisting of a mixture of the simplest hierarchical model s of failure is considered. Four types of model behavior are obtained: stab ility, catastrophe, unstable criticality, and stable (self-organized) criti cality. It is shown that the self-organized criticality reflects heterogene ous properties of media. Possible applications to the study of seismicity a re discussed. [S0031-9007(98)07823-5].