Tectonics and Earthquakes of Puerto Rico (2020)

Summary

Puerto Rico and the Virgin Islands are at significant seismic risk, shaped by the complex tectonic setting of the Caribbean Plate. The region experiences both subduction zone earthquakes and microplate boundary seismic activity. The 1943 megathrust earthquake was the largest recorded event, but future large-scale earthquakes remain a possibility. Additionally, the area faces tsunami hazards from submarine landslides and fault movements, with notable earthquakes in 1867, 1918, and 2020. Ongoing research aims to better understand the causes and risks of these frequent seismic events, including their potential to cause extensive damage and loss of life.

Takeaways

• 😀 Puerto Rico is located in the northeast Caribbean Sea, with a population of over 3 million people, and an additional 150,000 living in the nearby Virgin Islands.
• 🌍 The Caribbean Plate moves east at 2 cm per year with respect to the North American Plate, leading to a convergent plate boundary at an oblique angle in the Puerto Rico Trench.
• 🔍 The Puerto Rico–Virgin Islands microplate is located between the Lesser Antilles and Hispaniola, a result of oblique subduction and tectonic forces.
• 📉 Earthquake depths in Puerto Rico increase with distance from the Puerto Rico Trench, with the deepest earthquakes reaching about 100 km beneath northern Puerto Rico.
• ⚡ The largest megathrust earthquake in the region occurred in 1943, with a magnitude of 7.7, but no tsunami was produced due to the depth at which it occurred.
• 🌀 Historical megathrust earthquakes in Puerto Rico have a recurrence interval of over 1000 years, so future events may exceed the 1943 earthquake in magnitude.
• 🪸 Submarine landslides in the region, particularly those that occurred in the past, could produce large tsunamis, with waves reaching up to 16 meters on Puerto Rico’s north coast.
• 🧭 The Puerto Rico–Virgin Islands microplate is rifting from the Lesser Antilles and Hispaniola, with notable seismic activity like the 1867 earthquake that generated a 7.2 magnitude event and a tsunami.
• 🌊 In 1918, a magnitude 7.2 earthquake in Mona Passage caused a tsunami with waves up to 6 meters, resulting in 140 drownings along the west coast of Puerto Rico.
• ⏳ The 2020 earthquake swarm off southwestern Puerto Rico, including a 6.4 magnitude event, caused significant damage in Ponce and highlighted the ongoing seismic risks in the region.

Q & A

What is the tectonic setting of Puerto Rico and the surrounding regions?

Puerto Rico lies at the boundary between the Caribbean Plate and the North American Plate. The Caribbean Plate moves east at about 2 cm per year with respect to the North American Plate, creating an oblique subduction zone in the Puerto Rico Trench. This results in a zone of distributed deformation, with the Puerto Rico–Virgin Islands microplate located between the Lesser Antilles and Hispaniola.

How does the distance from the Puerto Rico Trench affect earthquake shaking in Puerto Rico?

The distance from the Puerto Rico Trench and the depth of the subducting oceanic lithosphere beneath Puerto Rico contribute to a loss of seismic wave amplitude as they travel from the megathrust to Puerto Rico. This results in less intense shaking potential in the region.

When did the largest megathrust earthquake in the region occur, and what were its effects?

The largest megathrust earthquake in the region occurred in 1943 beneath Mona Canyon, with a magnitude of 7.7. The earthquake caused strong ground shaking in northwest Puerto Rico, but the damage was minimal due to the earthquake's depth and lack of a tsunami.

What are the potential hazards of submarine landslides in the region?

Submarine landslides are a significant tsunami hazard in the Greater and Lesser Antilles. If a large landslide in the region occurred, it could generate a tsunami with runups approaching 16 meters along the north coast of Puerto Rico, potentially causing severe coastal flooding.

How has the subduction zone evolved over the past 3 million years?

Approximately 3 million years ago, subduction beneath Puerto Rico became steeper, and the depth of the Puerto Rico Trench increased, making it the deepest part of the Atlantic Ocean. These changes in geometry may have decreased friction along the plate boundary, reducing the likelihood of large magnitude 8 or 9 megathrust earthquakes.

What caused the rifting between the Puerto Rico–Virgin Islands microplate and the Lesser Antilles?

The rifting between the Puerto Rico–Virgin Islands microplate and the Lesser Antilles is driven by oblique subduction. The collision of the Bahama Platform with northern Hispaniola causes the separation of the microplate from the Lesser Antilles and Hispaniola.

What was the impact of the 1918 earthquake in the Mona Passage?

The 1918 earthquake in the Mona Passage had a magnitude of 7.2 and caused severe ground shaking on the west coast of Puerto Rico, resulting in 76 fatalities. A tsunami with over 6-meter runups followed the earthquake, causing 140 drownings. The event was associated with a submarine landslide in Mona Canyon.

What were the effects of the 2020 earthquake swarm in Puerto Rico?

In January 2020, a swarm of earthquakes occurred offshore southwestern Puerto Rico. The largest earthquake, with a magnitude of 6.4, caused strong ground shaking in Ponce, resulting in one fatality, eight injuries, and approximately $3.1 billion in damage to buildings and infrastructure.

What role does the Puerto Rico Seismic Network play in understanding earthquake hazards?

The Puerto Rico Seismic Network, along with offshore submarine geophysical surveys, plays a crucial role in understanding the faults responsible for earthquakes in the region, such as the 2020 earthquake swarm. Ongoing research helps clarify seismic hazards and improve preparedness.

What are the primary earthquake hazards in Puerto Rico and the Virgin Islands?

The primary earthquake hazards in Puerto Rico and the Virgin Islands include both subduction zone megathrust earthquakes and shallow earthquakes along microplate boundaries. These can cause significant ground shaking and tsunamis, especially in regions like southwestern Puerto Rico and the Mona Passage.