Earthquake dynamics are believed to exhibit self-organized criticality. This belief results from the power-law magnitude frequency distributions of earthquake catalogues, distributions which are accurately reproduced by cellular automata, and from the occurrence of triggered earthquakes. This paper examines the effects of heterogeneity on self-organized criticality in a two-dimensional cellular automaton. The strength heterogeneity is distributed fractally; stress is incremented uniformly. The model produces power-law magnitude frequency distributions. For fractal dimensions above 1.9, the slope of the power-law decreases with increasing fractal dimension. The slope increases weakly with the range of heterogeneity. ¿ American Geophysical Union 1996