This area of the SAF breaks every 21.5 years ...
http://quake.usgs.gov/recenteqs/Maps/Parkfield.htm

1857 ... quake
24 years rest
1881 ... quake
20 years rest
1901 ... quake
21 years rest
1922 ... quake
12 years rest
1934 ... quake
32 years rest
1966 ... quake
38 years rest
2004 ... quake

Notice the last 2 cycles have been 32 and 38 years apart .... when they should have been about 21.5 years ....
1934 came about 9.5 years early ...
1966 came late ... 12 + 32 = 44 which balance each out 21.5+21.5 = 43 years ...

Now .... 2004 quake was 16.5 years late ....
Here's how it would look if all the quakes came on time ...

1857 quake
1878 quake
1900 quake
1921 quake
1943 quake
1965 quake
1986 quake
2008 quake

So the 2004 quake in Parkfield really was the 1986 quake ... late .... the 2008 quake should be on time !!!

• This area of the SAF breaks every 21.5 years ...