I read today an article talking about the New Madrid fault.[1] Apparently they now think that there will almost certainly (seventy percent chance) be a significant earthquake there in the next fifty years or so. The interesting thing here is that while they insist that plate tectonics is behind it, there is only one plate on both sides of that fault. What other plate is the rubbing, sliding, snagging, whatever going on against? How does plate tectonics explain a mid plate fault line?

[1] http://www.livescience.com/forcesofnature/050622_new_madrid.html