No Warning, Advisory or Watch is in effect for Puerto Rico and the Virgin Islands.

Seismicity Zones in Puerto Rico

Where Do Most Earthquakes Occur?

Most earthquakes in the world occur along the contacts between the large rigid plates that cover the earth; the rigid plates are called lithosphere. The lithosphere is made of the Earth's crust and the uppermost mantle which behaves like a rigid block. These plates are ~50-100 km thick for oceanic crust and ~150 km thick beneath continents albeit some studies have found continental lithosphere to be up to ~250km thick in places. These rigid plates "float" on the Earth's convecting mantle; the movement in the mantle "pushes" the plates around the Earth. In general continental plates are less dense (lighter) than oceanic plates. Because of this, oceanic plates are recycled into the Earth's mantle via a process called subduction while the cores of continental plates remain on Earth's surface (like pond scum). This is why the oldest oceanic plates are only about 200 million years old; the oldest oceanic plate is in the Mediterranean Sea where the Tethys ocean used to be is about 270-340 million years old. However, the continental plates have material that are billions of years old. Some of the oldest continental rocks on Earth can be found in North America and they are ~4 billion years old. This is very old considering the Earth was formed about 4.55 billion years ago!

There are different types of interaction between plates:

  1. On the west coast of South and Central America, an oceanic plate and a continental plate collide. The oceanic plate is denser than the continental plate, so the oceanic plate is sinking into the Earth's mantle to be recycled into the Earth. This type of boundary is called a subduction zone. The largest earthquakes in the world occur in these areas with magnitudes have reached up to 9.5 Mw.
  2. In the San Andreas fault the Pacific and North American plates move laterally next to each other like two cars driving past each other on a road. Earthquakes in these areas can be large, historically up to ~8.0 Mw such as the famous 1906 San Francisco earthquake which is estimated to have had a magnitude of ~7.8 Mw.
  3. In the Himalayas, the two continental plates are colliding and forming the large mountain ranges in the region (including Mt Everest!). Earthquakes in these areas can also be large such as the 2015 Nepal earthquake that had a magnitude of 7.8 Mw.
  4. In areas such as the mid-Atlantic ridge, where new oceanic plates are generated as two plates separate permitting new material from the uppermost mantle to rise to the surface as lava and cool into a new plate. Mid-ocean ridges are actually the largest volcanoes on Earth; some consider the mid-Atalantic ridge to be one ~70,000 km long volcano. The earthquakes that occur here are generally not very large or deep.

What about Puerto Rico?

Puerto Rico is located on the border between the North American and Caribbean plates. The two plates are colliding at an angle; this results in something called oblique subduction. This means that there is a mix of subduction like that off of South and Central America and lateral motion like the San Andreas fault across the region. To better classify seismic activity networks in complex regions like Puerto Rico scientist sometimes use geography and geology to identify local seismic zones. This permits better communication to the local public about where an earthquake occurs. Below is a figure showing the current map of the local zones used by the Puerto Rico Seismic Network to communicate with the public.

  1. Central Puerto Rico
  2. Southern Puerto Rico
  3. Southeastern Puerto Rico
  4. Eastern Puerto Rico
  5. Northeastern Puerto Rico
  6. Northern Puerto Rico
  7. Norwestern Puerto Rico
  8. Western Puerto Rico
  9. Southwestern Puerto Rico
  10. South of Puerto Rico
  11. West of Puerto Rico
  12. North of Puerto Rico
  13. East of Puerto Rico
  14. Puerto Rico Trench
  15. Muertos Trough
  16. Leeward Island
  17. Saint Croix Platform
  18. Saint Croix Ridge
  19. Eastern Dominican Republic
  20. Septentrional Fault Zone
  21. Mona Passage
  22. Mona Canyon
  23. 19 N Fault Zone
  24. Sombrero Fault Zone
  25. Virgin Island Platform
  26. Saint Croix
  27. Virgin Island Basin
  28. Anegada Passage