interesting...I'll email your link to HW, who is at a meeting at Woods Hole. If I were her, I'd blow off the meeting and go check out the waves in Rhode Island...near Hurricane Kyle is going to pass offshore tomorrow, or if on west edge of forecast track, clip the outer Cape Cod.
I had some doubts about regualt large earthquakes based on sand blows because I had been told that part of that region is really susceptible to sandblows and they might occur from smaller quakes or more distant quakes. But, if the stalagmites show the same history for one area, then it must be larger quakes...if the stalagmite data are carefully analyzed: that study would be one that should be read carefully, with a hard look at the statistics.

We had some discussion on this page some time ago (year?) about whether New Madrid could "store" earthquakes without reloading: if the blocks on either side are not now moving (from GPS), how do repeated quakes occur?
Chris