Puerto Rico's Double Danger

I wrote earlier this week about a rash of earthquakes that have plagued the island of Puerto Rico in the last few weeks.  A strong quake, just a day after my last post, killed one person and injured a number of others. It also caused a power outage and has left thousands in shelters and perhaps a hundred times that number without water. 

An update in today’s press says “there have been more than 950 earthquakes and aftershocks recorded on Puerto Rico since Dec. 31, though many were weak and could not be felt. More than 500, however, have been of magnitude 2 or higher.”  The article goes on to ask, “So why have there been so many earthquakes in Puerto Rico over the past few days?”  The reported answer is:

"Puerto Rico has been hit by what scientists call an earthquake swarm, which is a series of earthquakes rather than the usual pattern of one dominant earthquake followed by aftershocks," John Vidale, a seismologist at the University of Southern California, told USA TODAY.

"We don’t well understand why the larger earthquakes continue for a while," he said. "It may have to do with slow slip on faults in the area or perhaps the hydrology of the fault system."

Puerto Rico "has a definite earthquake risk, compounded because its infrastructure is vulnerable, as demonstrated in other recent natural disasters, such as the 2017 Hurricane Maria," Vidale told USA TODAY.

Reading about the relative vulnerability of the island (and its neighbors) to the dual danger of hurricanes and earthquakes reminded me of a pair of posts I've made (SEE HERE) about the theoretical relationship between the two and why they seem to occur in the same areas in temporal succession, typically with earthquake events preceded by significant hurricanes. 

(1) Seismic Faults in the Caribbean (Source)

(2) Paths of Hurricane Irma (yellow line) and Hurricane Maria (red) that occurred just two weeks apart in 2017. (Source)

A quick visual comparison, above, of (1) the location of the tectonic faults along the edges of the North American and Caribbean Plates near Puerto Rico and (2) the paths of Hurricanes Irma and Maria (two powerful storms that occurred two weeks apart in 2017, and followed a path frequented by many hurricanes in the Caribbean) shows just how the two types of events occur in the same geographical area. The jury is still out on whether (or how) the two events share a causal relationship, but the historical data are compelling, if not conclusive.  In other words, the relationship between seismic and atmospheric events may be simply statistical at this time, but there are real,physical reasons they could be related.   

Even so, the most important lesson here isn’t one of earth science or physics, but one of preparation: Where a populated region is frequented by multiple events, it’s even more critical that the residents build resilience against both.

Unfortunately, Puerto Rico has a long way to go. 

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Update: Tuesday 1/14/20

The rash of seismic events--some significant--continue for Puerto Rico. In fact, a "snapshot" of today's map feed from the USGS indicates that today, as of about noon (EST), 46 earthquakes (>2.5) have been reported worldwide.  More than half of them (22) occurred in a single area on the south side of Puerto Rico.