The area around Puerto Rico and the Dominican Republic have been exceptionally busy when it comes to seismology, with 88 earthquakes reported by USGS in the last week. The strongest earthquake of the bunch struck off Punta Cana and was rated a magnitude 5.7 earthquake. Despite all of the earthquakes, there are no active tsunami threats to Puerto Rico, the Dominican Republic, the Bahamas, the Virgin Islands, or the U.S. East Coast.
Puerto Rico and the Dominican Republic sit on a complex tectonic boundary between the North American and Caribbean plates. The interaction of these plates, including subduction and strike-slip motion, contributes to the area’s seismic activity.
The most prominent fault zones in the area are the Great Northern and Great Southern Puerto Rico fault zones, which are considered largely quiescent but may be zones of weakness. Other notable fault lines include the South Lajas fault, Punta Montalva fault, Cerro Goden fault zone, and the Salinas fault, some of which have shown evidence of Quaternary activity. The southwest region of the island of Puerto Rico has been particularly active recently, with the 2019-2020 seismic sequence highlighting the potential for complex fault interactions.
The earthquakes in southwest Puerto Rico aren’t far from the epicenter of a strong earthquake that hit in January 2020. That 6.4 created extensive damage in Puerto Rico, including widespread power failures across much of the island. An earthquake swarm started there in December 2019 and unrest has continued since.
These earthquakes in southwest Puerto Rico are occurring near the northern edge of the Caribbean Plate, a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off of the north coast of South America. The Caribbean Plate borders the North American Plate, the South American Plate, the Nazca Plate, and the Cocos Plate. The borders of these plates are home to ongoing seismic activity, including frequent earthquakes, occasional tsunamis, and sometimes even volcanic eruptions.
While most people relate the threat of tsunamis to the Pacific, the Caribbean and the broader Atlantic basin can get them too.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel towards land, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.
The United States and other governments across the Atlantic and Caribbean participate in annual tsunami drills should one of these earthquakes trigger one.
As an example, in the Lantex ’21 tsunami drill, a Tsunami Warning was “issued” for coastal areas of Newfoundland and Labrador from Cape Ray, Newfoundland to Cape Chidley, Labrador while a Tsunami Advisory was “issued” for Florida, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, New Jersey, New York, Connecticut, Rhode Island, Massachusetts, New Hampshire, Maine, New Brunswick, Nova Scotia and the balance of the North American east coast from Cape Ray, Newfoundland to Flamingo, Florida.
These earthquake and tsunami drills will help bring awareness to the threats these areas could experience, allowing local officials and residents to be ready when an actual threat arrives.
Fortunately, as of this moment, the seismic activity around the Dominican Republic and Puerto Rico haven’t been strong enough to generate tsunamis. Should that change, the National Tsunami Warning Center and the Pacific Tsunami Warning Center would issue bulletins alerting the public of the threat.
