Abstract
Recurrence probabilities of earthquakes were evaluated at 33 locations along the San Andreas fault using Gumbel's method. Two minima in the mode of the largest annual earthquakes occur, one north of San Francisco centered around 38.75°N latitude and the other centered in the Carizzo Plain area at 35.25°N latitude. The latter is offset by an unusually large ratio of large to small earthquakes, so that only one minimum (around 38.75°N) is observed in the expected 100-yr earthquake size. This broad minimum closely coincides with where the San Andreas fault broke in 1906, and may be only temporary.
There appears to be a slight, systematic tendency for the observed largest 50-year earthquake to become larger than the expected 50-yr earthquake as the size of the area being studied is reduced. The preferred explanation for this is that the pattern of size as a function of frequency becomes nonlinear when the size of the area studied is less than the focal area of the largest earthquakes.
