Puerto Rico and the U.S. Virgin Islands (USVI) are shaking this holiday weekend; with more than 485 earthquakes to hit in the last 30 days, 121 struck in the last 7 days and 13 hit today. The strongest to strike during this ongoing swarm over the last 24 hours was a 3.7 magnitude event which struck 32 miles east-southeast of Boca de Yuma, Dominican Republic, in the water between the Dominican Republic and Puerto Rico.
Most of today’s earthquakes 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 here in December 2019 and unrest has continued since.
Today’s earthquakes were not strong enough to generate any type of tsunami threat. Because of that, the National Weather Service’s Tsunami Warning Center in Palmer, Alaska have issued no tsunami bulletins based on today’s earthquakes here.
These earthquakes 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.
USGS continues to monitor earthquake activity in and around Puerto Rico while the National Weather Service Tsunami Warning Center is keeping an eye on any tsunami threats.
There are other seismic events unfolding in the United States today. In southern Missouri, near where violent earthquakes struck in 1811-1812, two earthquakes struck earlier today. In South Carolina, an unusually long-lasting swarm continues north and east of Columbia in the central part of that state. However, due to their substantial distance apart, scientists say there is no relationship between these seismic events around the United States.
According to USGS, a swarm is a sequence of mostly small earthquakes with no identifiable mainshock. “Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months,” USGS adds. However, the South Carolina event doesn’t fit the typical definition of a swarm since the first event was substantially larger than the rest. However, the ongoing event in Puerto Rico does fit this definition.
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 inland, they build up to higher and higher heights as the depth of the ocean decreases. According to the National Ocean Service, 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.