I'll add to my earlier post. I started working in the oilfield in 1960 in this area. Except for a couple of years when I tried potash mining I worked in oil production until I retired and still live here. Fracking was going on when I started working and still is to this day. All I can say is that if fracking causes earthquakes then with the amount of fracking that has been done in this area it should be just a big sinkhole today. There has never been an earthquake in this area since I've lived here and there is no record of one having ever ocurred since records have been kept. By the way, 20% of the oil produced in the nation comes from this huge producing area.
There was a small one about 225 north of here a year or so ago. It certainly wasn't caused by fracking as they won't let an oil company anywhere in the area. It's the ultimate "NOT IN MY BACKYARD" area of the state.