The Richter magnitude of an earthquake-given that one has occurred-has been hypothesized to be exponentially distributed.† In Southern California the value of the parameter of this distribution has been estimated to be 2.35. What is the probability that any given earthquake will be larger than 6.3, the magnitude of the disastrous 1933 Long Beach earthquake? In the Southern California region there is on the average one earthquake per year with magnitude equal to or greater than 6.1. What is the probability of an earthquake in this area of magnitude greater than 7.7, "a truly great earthquake," in any given year? (The great Alaskan earthquake of 1964 had a magnitude of 8.4.)