Just did an analysis of the seismic data. This not-an-earthquake makes no sense. Either it's all P-wave with no S-wave, or its a sudden bulge which occurred all over the nation and then subsided. I'm thinking as I type: that might make sense in an odd sort of way.

The origins of the occurrence (earliest readings) are around Montana. If there was a sudden relaxation of the lithosphere under our continental shelf, it would explain quite a lot. No elevation data (still, dammit) but I can only guess. I wouldn't think that it would be a sudden uplift, as something that wide-ranging would have had much more pronounced effect (mass being lifted takes energy to create... mass retracting comes from a lowering of energy).

So... with nothing to go on but my amateur instincts, I judge that there was a relatively sudden subsidence of the crust around yellowstone, with pronounced effect across the continent. It might be doomish, or it might just be a bit of the pacific plate breaking off and dropping further towards the mantle.

Other than that, I got nothing.