- The worst quake – a magnitude 6.4 that struck early Tuesday – killed at least one person.
- Tectonics in Puerto Rico are dominated by the convergence between the North America and Caribbean tectonic plates.
- More earthquakes are possible in Puerto Rico, as is a risk for tsunamis.
Following a series of earthquakes, the situation in Puerto Rico remains dire, with more than 2,000 people in shelters, nearly 1 million without power and hundreds of thousands without water as of Thursday.
According to the U.S. Geological Survey, 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 worst quake – a magnitude 6.4 that struck early Tuesday – killed at least one person, injured at least nine and caused the power outage.
So why have there been so many earthquakes in Puerto Rico over the past few days?
“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.”
Tectonics in Puerto Rico are dominated by the convergence between the North America and Caribbean tectonic plates, with the island being squeezed between the two, according to the U.S. Geological Survey.
To the north of Puerto Rico, the North American plate “subducts” beneath the Caribbean plate along the Puerto Rico trench. (Subduction occurs when an oceanic plate runs into a continental plate and slides beneath it.)
To the south of the island, and south of the major 6.4 earthquake, the Caribbean plate upper crust subducts beneath Puerto Rico at the Muertos Trough.
According to Vidale, Puerto Rico is marked by faults in a pattern similar to many other places in the world, for example the Pacific Rim.
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.
Is ‘The Big One’ coming? A California fault capable of an 8.0 earthquake is moving for the first time, study saysUnfortunately, more earthquakes are possible in Puerto Rico, as is a risk for tsunamis.
“As always, the chance for additional, larger events is slim but real. Many of the regional faults are offshore, including a subduction zone, so tsunamis are also possible,” he said. “It would, however, take a considerably larger earthquake (or triggered landslide) to generate a damaging tsunami.”
The U.S. Geological Survey also said more aftershocks are possible within the next week, with a “3% chance of one or more aftershocks that are larger than magnitude 6.4,” the agency said on Thursday.
Contributing: The Associated Press
By Doyle Rice