Clustering of Large Earthquakes Explained by Random Variability?

Sumatra, 2004. Chile, 2010. Japan, 2011. Odds are these names and dates ring a bell. The scars are still too fresh and widespread for them to have slipped from memory. They identify, of course, the three largest recorded earthquakes that have occurred in the last 45 years — with magnitudes of 9.1, 8.8 and 9.0, respectively. Add in the 2005 magnitude 8.6 quake that also hit Sumatra, likely triggered by the 2004 event, and you’re talking about the four largest earthquakes in roughly the last half century all occurring within a few years of each other. It seems strange that they have been so bunched up, doesn’t it? 
 

An aerial view of Minato, Japan taken about a week after the
March 11, 2011 magnitude 9.0 earthquake and resulting tsunami that
devastated large swaths of the Japanese coast. (Credit: Lance Cpl.
Ethan Johnson, U.S. Marine Corps, Creative Commons Attribution
2.0 Generic)

In fact, there was a similar sequence of major earthquakes in the middle of the last century as well: Kamchatka, magnitude 9.0, 1952; Chile, magnitude 9.5, 1960 (the largest known earthquake); and Alaska, magnitude 9.2, 1964. No other 9.0+ events were recorded in the 20th century. Throw in a few more 8.5+ quakes in the same time frame, and you’ve got quite a cluster of destructive temblors occurring over just a decade and a half.

Contrast these turbulent stretches with the decades-long periods before 1950 and from about 1965 until 2004, when the planet was relatively calm, seismically speaking, and it certainly appears that these enormous earthquakes timed so close together are connected by more than coincidence, right? And if so, shouldn’t we be expecting more major quakes in the near future as one popular author suggested following the earthquake off the coast of Japan last spring?