On the interaction of the North Andes plate with the Caribbean and South American plates in northwestern South America from GPS geodesy and seismic data

Abstract

We examine the hypocentral distribution of seismicity and a series of geodetic velocity vectors obtained from Global Positioning System observations between 1994 and 2015 both off-shore and mainland northwestern South America (66°W–77°W; 8°N–14°N). Our analysis, that includes a kinematic block modelling, shows that east of the Caribbean–South American–North Andes plates′ triple junction at ∼68°W; 10.7°N, right-lateral easterly oriented shear motion (∼19.6 ± 2.0 mm yr−1) between the Caribbean and South America plates is split along two easterly striking, right-lateral strike-slip subparallel fault zones: the San Sebastián fault that runs off-shore the Venezuelan coast and slips about 17.0 ± 0.5 mm yr−1 and the La Victoria fault, located on-shore to the south, which is accumulating strain equivalent to 2.6 ± 0.4 mm yr−1. West of the triple junction, relative right-lateral motion between the Caribbean and South American plates is mostly divided between the Morrocoy and Boconó fault systems that strike northwest and southwest from the triple junction, respectively, and bound the intervening North Andes plate that shows an easterly oriented geodetic slip of 15.0 ± 1.0 mm yr−1 relative to the South American plate. Slip on the Morrocoy fault is right-lateral and transtensional. Motion across the Boconó fault is also right-lateral but instead transpressional, divided between ∼9 and 11 mm yr−1 of right-slip on the Boconó fault and 2–5 mm yr−1 of convergence across adjacent and subparallel thrust faults. Farther west of the triple junction, ∼800 km away in northern Colombia, the Caribbean plate subducts to the southeast beneath the North Andes plate at a geodetically estimated rate of ∼5–7 mm yr−1.