Ok, enough of the basics, it'll just zoom over the heads of all those 'non-math' scientists who seem to control our lives through oral skills.
Let's get down to injection. If I insert my hose into a bed of clay, nothing much happens. The water stops, since the clay is impermeable, that is, a very low permeability. I can pump up the water, which produces a very high pressure gradient in the clay, but no work is done (work is energy, or force times distance).
I can then put my hose into a bed of gravel. I can turn up the pumps, and get a huge flow. However, there is virtually no pressure gradient, because the gravel is extremely permeable. The gravel doesn't move.
Weird things only happen when I get a pressurized channel, which happens when I inject into shale. In that case, I get the best of both worlds, the channel is permeable (but blocked at the end), and the shale is not. There is a high pressure gradient, and available energy. The shale parts on a bedding plane, and my pumps are howling with the flow. Tremendous work is being done, as I crack apart the rock.
So, seismologists are lost when you have a real situation, such as a fault. To pry the fault apart, and allow slip, you need a pressure gradient, normal to the fault (right angles to). If the rock is as permeable as the fault, then you can't get a pressure gradient no matter what you do. The losers at my old company unnecessarily anchored lots of dams because they measured water pressure under the dam. But the concrete was as permeable as the rock, so no pressure gradient. They thought the water pressure would lift the dam, and send it down the river. Just one more thing that contributed to my breakdown. :)
In the Precambrian rock under Oklahoma, you either have open-channel flow, or the rock is tight. You can't form any gradients in open channels. That is why they are able to inject huge amounts of water. No pressure gradient, no effect on faults. The granite will never act like shale being fractured and pried apart.
There you have it. The USGS and 'consensus science' has it all wrong. That is why you have earthquakes where there aren't any high-flow injection wells. There is another reason, and I've gone over it enough -- stress corrosion.
End of lecture