UC Santa Barbara

The recurrence interval is the expected length of time intervening between consecutive geophysical events. The interest in this work is in episodic (catastrophic or cataclysmic) phenomena such as large floods or rare earthquakes, i.e., events that have a long-term recurrence meaningful in the scale of geologic time. Using probabilistic reasoning, the relationship between the recurrence interval and the distribution of geophysical events, the concept of risk, the memoryless property of the distribution of the time to the next episode, and the behavior of the "excess" time to the next event are examined. Also examined is the contrast between the necessary statistical conditions required for the mathematical analysis of the aforementioned variables, and geoclimatic changes inherent to natural processes that give the classical analysis of the recurrence of extreme geophysical phenomena and the risk presented by their potential occurrence a somewhat limited value. Our analysis includes annual and partial duration series. © ASCE.