Two large earthquakes occurred in Costa Rica in 1983 and 1991. The source areas are in the vicinity of the triple junction of the Cocos, Nazca, and Caribbean plates, where a large bathymetric feature, the Cocos Ridge, is colliding/subducting beneath the Caribbean plate. The 1983 event occurred in the subduction zone of the Cocos Ridge near the southeastern terminus of the Middle America trench just west of the Panama Fracture zone. The 1991 earthquake took place about 100 km north of the 1983 epicenter and is considered to be a back-thrusting event representing the overthrusting of the North Panama deformed...