Don, what you say is true for plate boundaries. But, if a fault has a 1000 year earthquakes cycle, and needs to build up a 100 bar differential stress to fail, and some trigger adds 0.25 bar of shear stress (weakens the fault), then the quake is advanced by 25 years-so, a fault within 25 years of failing without a trigger will fail. In the intraplate areas-especially in the east, many areas the rock is near failure, but stress is not building up. So, a trigger can set off an earthquake that might not have occurred otherwise. Things like quarrying and reservoir impoundment, or even rather small changes in level of small reservoirs (South Carolina example) can set off quakes. Nano Seeber of Lamont gave a talk about a year ago, at Lamont, that something like half of intraplate earthquakes (in some area?) are triggered by man.

While I said I did not know what I am talking about for earthquake prediction, I do know what I am talking about on this post-I did a study on an area of reservoir-induced seismicity along the Georgia-South Carolina border.. Chris