There was an interesting pdf file from the USGS on the largest earthquakes (magnitude 8 and above) ever measured by seismographs. I have the link so you can download the file, but I can't even reconstruct where and how I found this. I did find a similar web page here.
Anyway, the three figures in the file are copied below.
The map shows the association of these large quakes with plate boundaries. You can see the 2010 quake off the west coast of Chile, and the largest quake ever measured, nearby in Chile in 1960. The ones in the India-China region seem enigmatic, but they are presumably related to the collision of India and the rest of the Asian continent.
The figure below plots these events vs. time. On the whole, this appears to be random. There seems to have been a few more larger quakes in recent years, but there were even more in the late 50s-early 60s. Hmmm, a Cold War effect?
The figure above shows the cumulative seismic moment, roughly a measure of total seismic energy released. Note how this pattern is dominated by the very largest quakes.