I don't know if this means anything, but I was in Puerto Rico for the first time in 2005 for a conference. Before I left, somebody mentioned a big quake in Cuba way back (like the 1920's or further) that was supposedly centered in PR, so I checked the area out and learned that PR sits between 2 subduction zones. It looked scary but in terms of activity, the place was quiet and benign, which surprised me. When I was there, I talked to somebody there on business (a geologist, I believe)who said that Puerto Rico was just floating" above it all because of the way that the faults surrounded it and the other spots in the Caribbean were in more danger. Valid? I don't know.
Then about a year or so later, I noticed that the area slowly started to become active, particularly along the western side - the Mona Passage. As time has gone on, and since we were supposed to have another meeting there this year (but the economy killed it) I've kept my eye on the area. As I'vewatched it, the quakes directly around PR have increased both in size and frequency. It seemed like a monster coming alive.
Then, as I recall it, there was a 7.4, I think, about 12 to 18 months ago in the Virgin Islands, seems like around tourist season. After that, there have been other quakes in the mid-5's in a broader area, such as Cuba and near Puerto Rico. Isn't it possible that the 7.4 may have increased stress in the PR area? I have no idea when the last time was that either of those subduction faults moved enough to relieve the built-up stress, but I have a feeling that they're long overdue. Anybody know? Heck, I'm just a novice throwing out theories but sometimes it might spark something in the rest of you so I figure it's worth a mention.
Beth