What’s going on with Puerto Rico? To start with, Puerto Rico is in a very active seismic region. The really short version is that the surface of the earth consists of seven large and a bunch of smaller “plates” – chunks of the earth’s crust that float on the molten mantle below. These plates are pushed around by plumes of molten material from below. Imagine stuff floating on top of a boiling pot, only in very slow motion, plates only move on average an inch or so a year. If you want to learn more, here’s the Wikipedia article plate tectonics. All those gigatons of rock moving around builds up a lot of energy, and where they bump up against one another or pull apart, you get mountains and/or oceans, as well as volcanoes, earthquakes, and other neat stuff. The Greater Antilles (Cuba, Hispaniola – Haiti/Dominican Republic – and Puerto Rico) are in a double subduction zone. What that means is the region is being “pushed up” as two plates are trying to dive under each other. Here is a 3d diagram from a recent research paper on the region …
The north side, the Puerto Rico Trench, is pretty well understood. The round of earthquakes we have seen the last few weeks is probably more related to the Muertos Trough to the south, which is not as well understood.
So can we expect more earthquakes? The short answer is of course yes, but that avoids the key question of “how bad” and “when.” We just can’t answer that given our state of knowledge about this stuff. For example, did this round of events dissipate energy along the faults on the Island, and will things calm down? Or is it just transferring energy and strain into a locked part of a fault that will rupture with a much bigger event? At this point, we just don’t know.
In any event, please don’t forget the people of Puerto Rico who are suffering from yet another natural disaster. Satellite images from this morning still show extensive power outages across the west and south side of island. These are our friends, neighbors, and fellow countryman – this situation is unacceptable.