A strong 6.0 magnitude struck off the northwest coast of Puerto Rico late Monday, the United States Geological Survey said, although no casualties or damage were reported.
The quake struck 62km northwest of San Antonio at 11:23 pm local time (03:20 GMT) at a depth of 10km, the agency said.
San Antonio is home to Rafael Hernandez Airport, a key air link to the mainland U.S.
In 2010 nearby Haiti was struck by a devastating 7.0 magnitude earthquake that killed more than 250,000 people and crippled the nation's infrastructure.