I looked it up on the USGS earthquake site and learned only that Caribbean tectonics are very complicated. Also, not being familiar with the geography there, I checked out some maps and saw that the two epicenters are rather far apart.
Scroll down to “Tectonic Summary” here to learn more about tectonics in this part of the world.
That’s probably the plainest English they could put it in, but: Mind. Boggled.
Thankfully, the quake yesterday was at sea and the earth moved in a way that it didn’t generate large tsunami. Puerto Rico seems to be incurring the most damage from this recent seismicity, but who knows what will happen next.
It’s a very complex region. The USGS has deployed more equipment to Puerto Rico that perhaps will help provide insights into this.
Featured image: Derek Hatfield, CC BY 2.0