Crustal deformation rates in the southwestern Caribbean, Central and South America wide plate boundary have been derived from GPS campaigns in 1988, 1990, 1991, and 1994. From January 24 to February 18, 1994, 494 station days of data were collected with 37 receivers at 188 sites in Colombia, Costa Rica, Ecuador, Panama and Venezuela.

CASA 1991-1994 results suggest continued southeastward collision of the rigid Panama niicroplate with the Northem Andes in westem Colombia (7-23 mm/yr). This collision cut off mid-latitude circulation between the Atlantic and Pacific oceans, and formed the land bridge between North and South America. Over 150 km of related crustal shortening and thickening formed the Eastem Cordillera de Colombia. Subduction of the Nazca Plate at the Colombian trench continues at approximately 50 mm/yr. Earthquake focal mechanisms, offset glacial moraines and Quaternary thrust faults suggest that the oblique Nazca-South America convergence at the Colombian-Ecuadorian margin is partitioned into components of right-lateral slip parallel to the margin and crustal shortening perpendicular to the margin. GPS measurements show that the North Andean block is moving approximately 6 mm/yr northeastward relative to stable South America. This right-lateral shear is taking place on northeast-trending faults which originate in the Gulf of Guayaquil. Slow amagmatic Caribbean subduction beneath the Northern Andes, inferred from active folding in the South Caribbean deformed belt, a southeast-dipping Wadati-Benioff zone, and seismic tomography, is supported by GPS measurements (~8 mm/yr). The relative motions of the larger plates are in agreement with the predictions of the NUVEL- 1A global model. However, deformation in the plate boundary is not addressed by global models.

Continued observations plus densification of dw CASA network will help to constrain models for the kinematics of wide convergent plate boundaries and better identify areas of high seismic risk.