About the Puerto Rico Trench Anomaly
Gravity anomalies are calculated by subtracting the expected theoretical gravity at a location from the actual measured gravity. The free-air anomaly over the Puerto Rico Trench is the most negative on Earth, reaching approximately -380 milligals (mGal).
This massive mass deficit is primarily caused by the deep trench displacing dense crust and mantle with lower-density seawater, combined with the complex dynamics of the obliquely subducting North American plate pulling the crust downward, preventing it from achieving isostatic equilibrium.