Considerations of the dimensionality of earthquake generating mechanisms, as assessed by prediction-regression analysis, show that complete earthquake populations are best described by complex, high-dimensional dynamics. Cellular automata which allow individual degrees of freedom to many small areal increments of a fault face reproduce realistic event sequences which follow the Gutenberg-Richter relation. Simple, spring-block models with as few as two blocks have been shown, however, to neatly explain the coupling between adjacent segments of transform faults which has been observed in the stratigraphic record. Here we proposed a hierarchical earthquake model in which there is an explicit change in the generating dynamics with magnitude and which may be appropriate for seismicity on a section of a transform fault which includes more than one active segment. In the model a high-dimension cellular automaton is responsible for the production of low-energy events and a low-dimensional double-block model represents the dynamics of events in which an entire fault face slips. Frequency magnitude distributions of the model seismicity show a change in b-value with magnitude which is the result of the change in universality class of the underlying dynamics. Similar changes in b-value (related to the finite width of the seismogenic layer) have been reported in the literature. ¿ American Geophysical Union 1993