On January 28, 2020, a 7.7R magnitude earthquake rocked off the coast of Cuba and Jamaica, causing concern all over the world. Earthquakes repeatedly shake the Virgin Islands, the Dominican Republic and Jamaica, revealing the tectonic activity of the area. Thankfully, there wasn’t a tsunami to follow, and the aftermath was not as catastrophic as it was feared at first.
The Caribbean tectonic plate and the Oriente Fault
The earthquake was triggered by the North American and Caribbean tectonic plates grinding against each other in an area called the Oriente Fault. These so-called strike-slip faults are characterized by near-vertical fractures and horizontal movements in the earth. Oriente Fault runs just south of Cuba, and according to the United States Geographical Survey (USGS), the North American Plate progresses west-southwest over the Caribbean plate at a rate of about 19 millimeters each year.
The Caribbean seismic active area
Five other earthquakes of magnitude six or larger have occurred within 250 miles of that very area. The two largest were a magnitude 6.8R in December of 2004, and a 6.2R in May of 1992. As you probably have heard, Haiti was hit by a magnitude 7R earthquake in 2010 that killed more than 300,000 people.
The United States has studied Puerto Rico’s and the Virgin Islands’ past because these countries belong to the American territory and have been studied more than other parts of the Caribbean. For example, seismologists knew that the rivers north of Puerto Rico hosted earthquakes in 1918, measuring 7.3R, then 7.8R in 1943, and a whopping 8.0R in 1946. In 1946, the earthquake caused a tsunami that killed 1,800 people.
The movement of the lithospheric Caribbean plate
According to the USGS, Puerto Rico and the Virgin Islands are in an active boundary of tectonic plates between the North American plate and the northeast corner of the Caribbean plate. Most of the earthquakes that happen in the Eastern Caribbean are either tectonic or volcanic.
- Tectonic earthquakes occur when plates move as accumulated energy is released.
- Volcanic earthquakes are attributed to the movement of magma within the lithosphere. Since magma is not as dense as the surrounding rock, it rises to the surface and breaks the rock as it moves. This causes earthquakes.
According to the University of the West Indies, the Eastern Caribbean forms an island arc system at a plate boundary. This is the area where two tectonic plates meet and the heavier plate is forced beneath the lighter plate. The phenomenon is known as convergent plate boundaries, and is the primary cause of the seismic activity in the Eastern Caribbean.