I have studied the geology texts at length, and no one has a plausible theory that explains mega-quakes. In fact, no one has been able to predict the size, location, and frequency of earthquakes in the entire history of the field. Well, it looks like I am the first to predict when, how frequent, and how large, if not where. Maybe somebody smarter than I can come along and predict where they will occur.
The 17 largest quakes ever measured were all along the Pacific Rim, or "The Ring of Fire". Well, that's a good guess that zeroes in on about 5% of the world's surface area. The DC quake does not fall into that zone, nor the quake that recently struck in Italy. Neither were mega-quakes, but they were very large as compared to what had come before to those areas.
There is a 15% probability of a mega-quake measuring 8.5 or higher before October 21, 2012 and another 70% chance between February 21 and April 21, 2013. I cannot tell you where because our geologist friends have no model that predicts anything at all. I can only tell you with 95% level of confidence that at least one mega-quake will happen each year, as opposed to an average of one per decade before global warming due to CO2 began in earnest. I can also tell you that earthquakes do not cause global warming, as some have been confused by the cause and effect issue. Global warming is causing these mega-quakes with much greater frequency and at predicted times.
When we design tall structures, like skyscrapers and smokestacks and large wind turbines and solar power towers, as well as siting nuclear power plants and petroleum facilities, we look at the seismic history and fault lines under proposed sites. We design for the maximum potential quake that has ever occurred in about a thousand years, and add a factor of safety on top of that number. I've done this twice, and it's one of the most difficult engineering tasks for any major project. Engineers are far more practical than scientists. They build stuff that people must live with.
On the other hand, politicians make decisions which impact the entire human race. Maybe it's time to let them know that they are killing us with their ignorance.