Michael: Thanks for your response.

My initial thought about the 30 year probability was maybe it would work. Then, after about another second or two, I remembered how even the USGS does not post all data. Events here in Taiwan are frequently not reported and no doubt there are other locations with similar problems. There seems to be more than enough data for events in the US. Doesn't that bring the whole issue back to subjectivity?

How can you take aftershocks into account? Who will be the one to decide if something was an aftershock or not? Why are you considering troubling yourself with this extra workload when you could use your time and computer for something more useful?

I agree that some places have a much higher probability than others. It still doesn't seem to be correct to calculate probability or predictability on a living thing. In my opinion, you will have to make decisions in the calculation that will make the result somewhat subjective. This will also leave the result open for argument.