Plate motions in the North Andean region

The first tectonic results using GPS in South America were reported by Freymueller et al.[1993]. Although the geodetic network has been expanded to include 21 stations in the North Andes, this paper concentrated on the interactions of four tectonic plates: Nazca, Cocos, Caribbean, and South America. In all but one case, there is only one GPS site on each plate. Nonetheless, these geodetic estimates are quite useful. The NUVEL-1 model is less reliable at convergent plate boundaries because of lack of data which measure both convergence rate and direction. As shown in Figure 1, the geodetic results are in generally good agreement with NUVEL-1, although there are significant differences. In particular, between Cocos and the Caribbean plates the GPS rate is only 78% of the 91 mm/yr predicted by NUVEL-1. Dixon [1993] was able to successfully model this discrepancy using a simple elastic model of a subduction zone locked at 205 km depth.