Hi Beth. The focal mechanism for the larger quake was not consistent with being a subduction quake; it was oblique strike-slip with fault not oriented parallel to subduction zone. Subduction zones have many faults, but only one megathrust (plate boundary). But, to the west, indeed eastern Hispaniola ideed has two different subduction zones, one to the north, dipping south, and one to the south, dipping north. I think the southern one is called Muertos, which means dead or death or something. That second subduction zone must extend eastward towards Puerto Rico; I'm not sure where or how it dies out. To the west in Haiti, it largely becomes a fold and thrust belt, which I have done some work on.

So, finally to your question: the amount of quake energy would be related to the overall relative plate velocity and the area over which the subducting plate is in contact with the brittle part of the upper plate. If there are two subduction zones, it would logically split the overall energy release. How often there would be quakes is related to the plate velocity and how large the quakes are.

And, yes, with two directions of subduction, the subducting Carribean plate must jam into the subducting Atlantic Oceanic crust (North American Plate).

How this works I don't know.

Chris