Significant earthquakes have occurred on the Parkfield section of the San Andreas fault at fairly regular intervals - in 1857, 1881, 1901, 1922, 1934, 1966 and 2004.

Before the 2004 earthquake the cycle was an M>6.0 occurred on the average every 22 years. Now with the 2004 earthquake the average is every 24.5 years when you subtract the last quake from the time of the quake that occurred just before till you reach the last quake, which was 38, 32, 12, 21, 20, 24 years. However when you subtract 1857 from 2004 and divide by 7 quakes you come up with an average of 21 years. As you can see the cycle is very close to 22 years.

When you look at the actual times the quakes occurred you can see the time spread ranges from 12 years to 38 years. Does this mean that the next M>6.0 can occur12 years from now, 38 years from no, 24.5 years from now, 21 years from, or some other time, or not at all?

Was the Parkfield experiment a failure? The answer is yes if you were relying on instruments to tell you when and where the next M>6.0 quake was going to occur. The answer would be no if you are relying on a time frequency for the next quake to occur because the quake did occur very close to the 22 year average. The one big problem with the time frequency is that you are using 7 quakes over 147-year period. Would this frequency be the same over 14,700 years? Lots of questions, but not many answers. Take Care…Don in creepy town