The Puerto Rico Trench is a crescent-shaped submarine depression, 1,090 miles in length and 60 miles wide, approximately 100 miles north of the island of Puerto Rico. Within the trench is the Milwaukee Depth, which at 27,493 feet below sea level is the deepest point in the Atlantic Ocean.

Both the tectonic background and the bathymetry of the trench are poorly understood. Seismic surveys suggest that large-scale landslides and east-west oriented faults scar the trench. This morphology is apparently a symptom of the North American plate's subduction beneath the Puerto Rico block. These elements remain currently active, and represent a significant earthquake and tsunami hazards to the north coast of Puerto Rico.

The Puerto Rico Trench is also associated with the greatest negative gravity anomaly on earth, indicating a dynamic disequilibrium within the Earth. Magnetic compass deviations, or magnetic faults, are often reported over the trench. This may help explain some of the alleged vanished boats and planes over the "Devil's Sea" area.