Arkansas is where my heart lies, for injection-induced earthquakes, that is. They were the first to completely validate my theories on this stuff. Their big problem is that they stop injecting as soon as it is obvious. They stopped the first one at M4.5, and the second at M3.5. But the good thing is that they always keep trying!
Now I wonder when they will stop this one.
These tiny babies are all in the M1.7 range. This is fantastic, since it means they got some really good instrumentation. All the OK earthquakes are minimum 2.5 thereabouts. Right below with all the yellow spots is the famous Morriton abort. They were just starting to get a good mechanism going, and they stopped. So sad!
This whole area is in the stress-shedding zone of New Madrid. Basically, when you drill a hole in stressed rock, the stresses increase around the sides, depending on the direction of the main stress. It is somewhat unusual, since for most of the basement rock on the continent, there have been no stress disturbances since the last big glacial. Thus, this zone is primed to be a New-New Madrid.
As usual, I run a pool to see how big the earthquakes will get before they stop. The prize is a big fat nothing, or the equivalent budget of the USGS on eastern seismic hazard. :)