Let's talk about aftershocks. In California, a typical M3.6 quake would be followed by 1 M2.5 quake. So far the weekend #earthquake in Massachusetts has been one & done. We can't assume nothing else will happen, but...

statistical studies show that east coast quakes tends to have relatively wimpy aftershock sequences compared to west coast quakes, but...

statistical studies also show a lot of variability within any given reason in what we call aftershock productivity. We don't entirely understand why, although there are theories. In any case...

It's pretty clear that the most portentous historical earthquake sequence east of the Rockies, the 1811-1812 New Madrid sequence, had a very energetic sequence following the initial large quake on 16 December 1811...

and an energetic sequence raises the odds of subsequent large quakes, as in fact played out on 23 Jan. 1812 and 7 Feb. 1812. So why does the New Madrid Seismic Zone appear to behave differently from other seismic zones in the east? Good question!

One of many good questions in seismology left for today's generation of super-talented students and ECRs to answer some day.