There's a lot of buzz here in Oklahoma about that. Tiring of all the media drama and emotions, and wanting a better explanation, I talked to a retired geologist friend - and she had some good data... First, the epicenters of the quakes (We've probably had a hundred total in the past few weeks) are on the Western edge of a geologic area known as the Seminole Structure. That's on the edge of a much larger discontinuity known as the Nemaha. The faults have been here for a long time, and therefore hold a good measure of energy. Second, the depths have been measured to be around 18,000 ft down. There are no wells in this area close to that depth, so the chance of fracking fluid causing it is diminished. Third, the waveforms suggest a thrust movement rather than side-slip. Fracking isn't much of a candidate there. I posed the question to her that if the chances are small injection wells caused the bigger one, would it be plausible that a smaller quake from the wells could have triggered a chain of stress relief that led to the larger one? Not likely, because if it was so easily triggered ("on edge" of being triggered), then natural processes are more probable than man-made ones to "trigger" the chain. Within hours of the first correlated events, geology researchers (and students?) from OU and OSU were on scene (West of Prague) with sensors and acoustic equipment. This is pretty much the first Oklahoma quake cluster to have that level of detailed instrumentation. Maybe they will get some good grants out of this?