Now that Oklahoma is starting to fire up at rate which will give us M7's by the end of the year, we must discuss what this really means.
Damage on the ground from earthquakes is directly related to peak ground velocity (PGV). All engineers say it is peak ground acceleration (PGA), but that's only for deep California soil basins. The pgv is directly related to the applied shear stress at the base of building. Some of you might know the MM intensity rating, and a doubling of pgv goes up one intensity unit.
The neat thing about earthquakes is that the seismic energy released goes up about 30 times with each magnitude notch. A 5 is nothing like a 6, and a 6 is nothing like a 7. OK has 6's going off and they only destroy one town. A 7 can destroy the whole state. Yet the 'distance' between magnitudes is all the same, for example 10 5's for a 6, and 10 6's for a 7.
We have the fine example of the New Madrid earthquake sequence, and OK follows the same mechanism. The pgv on soft soil will be 100 cm/s. Nothing built in the central US can stand with that, no bridges, hospitals, etc. No power transformers. The entire Mid-west will be a ghost town, but with no buildings standing.
If we are lucky, we won't go directly to m7's but have an m6.5 instead which will scare everybody with only a few people killed. This should be about 50 cm/s on the velometer. However, even with the injection stopped, it is on the verge of a 7.
Why the huge exponential increase in seismic rate? It's simple physics. Texas has shown you can inject all the deep oil water you want, but add a truckload of freshwater frack waste, and you get Azle. They stopped that and hushed everything up. Then they sent all stuff to OK. But OK was 95% deep water, and 5% fresh. Cutting down the injection volumes has tipped that the other way, because people pay a lot more to get rid of the nasty stuff.
This increase in seismic rate is just coming from the big Texas Permian play. Soon the northern frack waste will come. OK injection will become 95% fresh water. Cut the volumes all you want, and nothing happens.
The amazing thing is that this has merged into one mechanism, and the strain field now includes New Madrid. If you live far away, as I do, you can look on it with scientific detachment.