Transitions in non-conserving models of Self-Organized Criticality

Abstract

We investigate a random--neighbours version of the two dimensional non-conserving earthquake model of Olami, Feder and Christensen [Phys. Rev. Lett. {\bf 68}, 1244 (1992)]. We show both analytically and numerically that criticality can be expected even in the presence of dissipation. As the critical level of conservation, $α_c$, is approached, the cut--off of the avalanche size distribution scales as $ξ\sim(α_c-α)^{-3/2}$. The transition from non-SOC to SOC behaviour is controlled by the average branching ratio $σ$ of an avalanche, which can thus be regarded as an order parameter of the system. The relevance of the results are discussed in connection to the nearest-neighbours OFC model (in particular we analyse the relevance of synchronization in the latter).