I have a feeling that with the fracking that is occurring in the state of Oklahoma that we will be seeing more and more stronger earthquakes. I think there is a direct correlation between pumping in sludge and the removal of oil from the shale through that whole process as we destabilize the region.
Shakedown in Oklahoma: To cut the number of bigger earthquakes, inject less saltwater. In Oklahoma, reducing the amount of saltwater (Highly brackish water produced during oil and gas recovery) pumped into the ground seems to be decreasing the number of small fluid-triggered earthquakes. But a new study shows why it wasn't enough to ease bigger earthquakes. Source 9j.