The U.S. Geological Survey said the quake was centered in the Guanacaste region of the Central American country, 38 miles (61 kilometers) away from the city of Liberia. It had a depth of 24.5 miles (39.5 kilometers), according to a preliminary report.
The region suffered a powerful earthquake last month, when a 7.6 earthquake rattled the same coasts, causing panic, evacuations but minor damage.
Seismologists both in the U.S. and Costa Rica said the quake is probably an aftershock of the Sept. 5 major earthquake.
"It is a very good likelihood that we are looking at an aftershock," said USGS geophysicist Rafael Abreu.
Vanessa Rosales, president of Costa Rica's National Commission for Emergencies, said "no one has reported serious damage."
She said that tomorrow they will have a more comprehensive look at what the quake did.
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