Self-organized criticality in two-variable models

We present a cellular automaton approach involving two variables and invest igate its behavior with respect to self-organized criticality (SOC). It can be seen as a generalization of the Bak-Tang-Wiesenfeld and OlamiFeder-Chri stensen models and exhibits SOC behavior, too. In contrast to these models it leads to a power law distribution of the cluster sizes with an exponent close to one, as it occurs in earthquakes and landsliding processes, withou t any tuning.