Evidence for Caribbean plate subduction in southern Costa Rica

Nestled between the Cocos, Nazca, Caribbean, and South American plates, the Panama microplate represents an area of rapidly evolving tectonics throughout the past -10 m.y. Past and current studies have observed a notable amount of seismicity throughout this region, in particular the Caribbean coast of Costa Rica, which experienced a Mw 7.7 earthquake in 1991 CE. We investigated the crust and upper mantle structure of this region using the receiver function methodology and report two results: (1) first-order lateral constraints on the position of the Panama microplate boundary near the intersection between the Central Costa Rica Deformed Belt (onshore) and North Panama Deformed Belt (offshore), and (2) an impedance contrast south and east of these belts, supporting that the Caribbean plate currently subducts beneath the Panama microplate. Observed local seismicity is a consequence of the recently (ca. 14 Ma) initiated Caribbean plate subduction beneath the overlying Panama microplate. Our results are also consistent with a doubly convergent subduction margin dominating southern Costa Rica tectonics, uplifting the Talamanca Cordillera, and causing the cessation of southern Costa Rica volcanism over the past -10 m.y.

Automated summary

The Panama microplate, located between the Cocos, Nazca, Caribbean, and South American plates, has undergone rapid tectonic changes in the past 10 million years. The region has seen significant seismicity, with a major earthquake occurring along the Caribbean coast of Costa Rica in 1991. Through receiver function analysis, this study provides insights into the crust and upper mantle structure of the region, identifying the position of the Panama microplate boundary and confirming that the Caribbean plate is subducting beneath it. This subduction explains the observed seismic activity and the cessation of volcanic activity in southern Costa Rica.