Self-organized criticality and universality in a nonconservative earthquake model - art. no. 036111

We make an extensive numerical study of a two-dimensional nonconservative m odel proposed by Olami, Feder, and Christensen to describe earthquake behav ior [Phys. Rev. Lett. 68, 1244 (1992)]. By analyzing the distribution of ea rthquake sizes using a multiscaling method, we find evidence that the model is critical, with no characteristic length scale other than the system siz e, in agreement with previous results. However, in contrast to previous cla ims, we find a convergence to universal behavior as the system size increas es, over a range of values of the dissipation parameter cu. We also find th at both ''free'' and ''open'' boundary conditions tend to the same result. Our analysis indicates that, as L increases, the behavior slowly converges toward a power law distribution of earthquake sizes P(s)similar tos(-tau) w ith an exponent tau similar or equal to1.8. The universal value of tau we f ind numerically agrees quantitatively with the empirical value (tau =B+1) a ssociated with the Gutenberg-Richter law.