We introduce a generalized homogeneous function to describe the joint probability density for magnitude and duration of events in self-organized critical systems (SOC). It follows that the cumulative distributions of magnitude and of duration are power-laws with exponents α and τ respectively. A power-law relates duration and magnitude (exponent γ) on the average. The exponents satisfy the dynamic scaling relation α=γτ. The exponents classify SOC systems into universality classes that do not depend on microscopic details provided that both ατ
Feder, J., Nordhagen, H., Watters, W.A. Dynamic scaling in stick-slip friction. 24 July 2013.