The M7.3 was in the southern Carribean in Nov 2007 far from Puerto Rico (see link). There was a M6.1 NW of the Virgin Islands October 2008.
Roger's graph shows big increase in M2s and 3s in 2006. For 2007 and after it could be partly aftershocks of the M6.1 But the increase was in 2006. I think it would be good if Roger checked the following: the usgs site:
http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/quakes_all.php
started reporting all M2.5 and above quakes a couple of years ago and before that they did not report all the 2.5 through 3s (probably). So, the increase in 2006 could be a reporting artifact depending on what catalogue Roger is using.
I could be wrong on that.
An interesting link to Puerto Rico area large quakes is at:
http://www.innovations-report.de/html/berichte/geowissenschaften/bericht-38807.html
Chris

• M7.3 Carribbean