Mmax is the magnitude M of the largest earthquake thought to be possible within a specified area, or source zone. For clarity, hereafter Mmax and M will refer to moment magnitude, whereas mmax and m will denote magnitudes generally. Probabilistic seismic-hazard assessment (PSHA) requires an estimate of mmax for each source zone to avoid the inclusion of unrealistically large earthquakes. The original formulation of PSHA did not include mmax because magnitude was assumed to follow an unlimited exponential distribution (Cornell, 1968). However, Cornell noted that mmax earthquakes were too rare to verify this or any other distribution, and that magnitude might be bounded instead (p. 1602). Chinnery (1979) summarized physical arguments that magnitude must be bounded, perhaps with different mmax values in different regions of the Earth.