The general consensus is that injection of saltwater into deeper formations, (primarily the Arbuckle formation) is the primary driver of the quakes and the volume as well as pressure of salt water disposal wells over time, into certain areas of the state of OK and KS leads to the increase in quakes.

 What we find is a strong correlation, between saltwater disposal, in certain areas and seismic activity and as result the conclusion one draws, from looking at the evidence, is that there is a cause and effect between salt water disposal and quakes in certain areas.

The saltwater disposal wells(the vast majority, over the last 10 years) in the Mississippian lime plays, in northern OK and southern KS are the result of "fracking", because if they hadn't been drilled and hit oil and saltwater there would be no need for the disposal well. At least in the above mentioned play in southern KS and northern OK, the disposal wells are the result of "fracking".





As far as history of quakes lets look at OK, it's not just due to better monitoring, that these quakes have come to light. From a geology research report about the history of quakes in OK.

"No state has experienced a more significant increase in seismicity in recent years than Oklahoma. As shown by the red circles in Fig. 1, numerous M≥2.5 earthquakes have occurred throughout much of the central part of the state in the past 5 years (16). The yellow circles in the figure show earthquakes of similar magnitudes occurring over the 34-year period ending in 2008. The increase in seismicity is not an artifact of improved seismic detection capabilities because there has been a marked increase in the number of earthquakes in Oklahoma at all magnitudes. For example, the rate of widely felt M≥4 earthquakes has gone from about one per decade before 2009 (going all the way back to 1882) to 24 in 2014 alone (17), roughly a 200-fold increase. Throughout the central and eastern United States, the likelihood of missing M~3 earthquakes has been negligible for at least the past 25 years (18). In Oklahoma, there was about one M≥3 event per year during the 34-year period from 1974 (the onset of modern seismic recording) to 2008, but more than 100 M≥3 events per year in 2013 and 2014."