Via ZH, an article by DoomPorn champ Michael Snyder.
Unusual patterns of quakes in Okla and Kansas. Some of these quakes are normal. The cluster west of Enid is on a geological hotspot that always produces small quakes. The group north of Enid is not normal.
The article focuses on the group around Hutchinson, also not normal. This looks to me like the result of an aquifer changing its pattern, either suddenly growing or suddenly shrinking. Given the distinctly wet spring, I'd bet on growing.
I made a blinkyGIF to show how this pattern sits on the edge of the Ogallala. The group of quakes is circled in red on one step of the GIF.
Hutchinson and those Okla quakes are all on a known salty area. Connection unknown but interesting correlation.
Spokane had a swarm of quakes in 2000, centered on our aquifer. In that case the likely culprit was a decrease
in aquifer volume caused by the quick shutdown of about 30k septic tanks in the Valley. That's a lot of flow, diverted to the sewers and thence to the river within a few years. Thanks, EPA!