It is accepted that the New Madrid fault and it's famed early 1800's mega-quakes are associated with an old rifting zone. Dutchsinse is a well known blogger that theorizes on earth movements. He's not a geologist, but very often hits on something worth paying attention to and observing. Apparently there are a good many harmonic tremors recorded on some seismometers in the area, and in this blog I'm linking, you can see these recorded tremors. Some of the tremors look like they are man made, but some do appear to be possible near surface volcanic micro-quakes, and some seem harmonic.
This is the grey area of speculation, and a call for further observation.
Here's the blog entry on possible plumes in the New Madrid area.