Why Puerto Rico Shakes: Inside Its Frequent Quakes
Puerto Rico sits atop a volatile tectonic crossroads that makes it highly earthquake-prone. The region experiences hundreds of small earthquakes each year, with occasional damaging ones—such as the 6.4-magnitude quake in January 2020—reminding residents of the island’s underlying geological tension.
Puerto Rico lies at the boundary between the North American and Caribbean tectonic plates. This boundary is not a simple line but a complex zone of subduction, transform faults, and microplates. The North American plate is slowly being pushed under (subducted) beneath the Caribbean plate to the north of the island, while lateral movement occurs to the south along the Puerto Rico Trench and the Muertos Trough.
These opposing motions create a network of fault systems, including:
• Great Northern Puerto Rico fault zone
• Southwestern fault system (Guánica area)
• Punta Montalva fault
Each fault can release stored energy as earthquakes, most of which are too small to be felt, but the island has a long history of moderate to strong quakes, particularly along its southern coast.
According to the Puerto Rico Seismic Network (PRSN), the island experiences over 3,000 seismic events annually, although most are below magnitude 3.0. Notably, earthquake swarms—clusters of seismic activity over weeks or months—are common. The 2019–2020 swarm in southern Puerto Rico, for example, caused widespread damage, including building collapses, power outages, and displacement of thousands.
Puerto Rico is not just a dot on the map—it's a living, shifting piece of Earth's crust. Caught between plates and riding on microfaults, it will continue to shake with small reminders—and occasionally large ones—of its geologic reality.
