I talked to L. "Nano" Seeber on phone and he suggested that higher water table over a whole state might have effect to trigger a quake. He thinks quake was deep (15 km). He suggested looking at historic quakes in this region and comparing to water table level. I'd add that you might want to limit it to areas outside of the highly active Reelfoot. Might limit it to Illinois-Indiana.

Would have to have some measure of region-wide water load. Perhaps USGS or someone else have network of water wells.

Alternatively, if you look at water as a vertical load (rather than as pore pressure in fault), then water tables would have to be corrected for porosity. If lots of surface lakes, lake level might be important also. But, if are includes young sediment, then the porosity will be high. If old rock outcrops, porosity would be low. The porosity only matters for the interval between low water table and high water table.

If Roger were give some number by date that represents water load across the 2 states (or, maybe done for 100 km by 100 km boxes around one area of interest..check where the 1968 quake was compared to this one; if within 100 or 200 km use that radius as the region), and a catalogue of seismicity for that same region...and only use magnitudes large enough for catalogue to be complete (2.5? 3?), then he could do some graphs.
Roger? Glen? Someone else? Comments from John V.?

Chris