This resource provides an abstract. This article discusses a method based on the magnitude-frequency distribution of previous earthquakes in a region. It is used to examine the probability of a small earthquake growing into a catastrophic one. When a small earthquake is detected in a region where a catastrophic one is expected, early warning systems can be modified to determine the probability that this earthquake will grow in magnitude. It was found that if the observed earthquake magnitude reaches 6.5, the estimated probability that the final magnitude will reach 7.5 is between 25 and 41 percent.
