My theory is that in the new version of reality Jake created, something prevented Roland from being able to stop the fall of the Tower, and that the earthquakes are part of the process of the fabric of reality ripping itself apart. Mr. King has said that he intentionally didn't link the two stories (11/22/63 and The Dark Tower), but I'm not buying it, personally.
roland-shmoland...there was ample, and easy opportunity for king to tie in anything he wanted...he doesn't need, at this late stage, to get all hocusy-pocusy about it...like we'd all be fooled !!
of course, why, after saying before that everything in every book is connected, he did not...that's another conspiracy theory, right ?
didn't portal boy say something like each trip is not a complete reset..and each trip that changed things twisted life, the universe and everything more and more...and some trips twisted it all the hades...and who knew what might happen when it got twisted too much...(now we might have a clue !)
what if...'11/22/63' is to 'the dark tower' what 'the regulators' is to 'desperation'
Back to the original question. My feeling was that the number of atomic/hydrogen bomb explosions that occurred caused a number of faults in the earth's crust, creating the earthquakes. Maybe junk science, but who knows?
I thought it had something to do with the Yellow Card Man saying that if Jake messed up too many strings, reality itself would cease to exist. I thought the earthquakes were tied to the reality of the world--that reality itself was imploding/exploding.
I would have thought it was due to the drastic changes that occurred due to the politics involved with the EPA--except that the first earthquake occurred before Jake returned to 2011. That's why I think it was due to reality being threatened.