The Gutenberg-Richter relationship for earthquakes in both global and fault-specific seismicity has been interpreted as an indication of self-similarity for events of all magnitudes. It is observed, however, that the linear extrapolation of this relationship to high-magnitude often fails to predict the frequency of occurrence of large events; earthquake hazard cannot, generally, be predicted solely by examination of microseismicity. It has been postulated that this break in power-law scaling is due to a change in the rupture mechanism as the size of the rupture becomes larger than the thickness of the seismogenic layer. Here we examine the scaling of earthquake-like failures in an analogue model consisting of an elastic solid confined and driven by a steel stressing apparatus. Sensors embedded in the solid close to the interface with a rough substrate measure local strain, and allow the examination of rupture scaling and moment release. The frequency-magnitude distribution for events is a power-law at low magnitude but exhibits enhancement for high-energy events which is consistent with a characteristic earthquake model. We show, unambiguously, that this break in scaling corresponds to ruptures whose diameter is equal to the smaller dimension of the model fault. ¿ 1997 American Geophysical Union