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GPS-derived Velocities in the Northeastern Caribbean: Implications for Caribbean-North America Motion and the NUVEL-1A Model

C. DeMets (Geology & Geophysics, U.W.-Madison., 1215 W Dayton St, Madison, WI 53706; chuck@geology.wisc.edu); T. Dixon and F. Farina (RSMAS, Univ. of Miami, Miami, FL 33149-1098); E. Calais (CNRS, 250 Rue Albert Einstein, 06560 Valbonne, France); P. Jansma (Geology Dept, U.P.R.-Mayaguez, Mayaguez, PR 00708); P. Mann (Institute for Geophysics, U.T.-Austin, 8701 Mopac Blvd, Austin, TX 78759)

Due to the lack of unambiguous conventional geologic observations that record the displacement of the Caribbean plate relative to the neighboring North American, South American, and Cocos plates, the Caribbean plate remains one of the only major plates whose present-day kinematics are controversial. As we have previously reported, GPS observations in 1986 and 1994 within a geodetic network that spans the Caribbean-North America plate boundary in the vicinity of Cuba, Hispaniola, and Puerto Rico suggested that the Caribbean plate moves at a rate nearly twice that predicted by the NUVEL-1A model, but in a direction consistent with that predicted by NUVEL-1A. Repeat observations in late 1995 now confirm this result. Additionally, velocities transecting the plate boundary at the longitude of Hispaniola suggest that Caribbean-North America motion is focused primarily along the Septentrional fault, which has not experienced a major ground-rupturing earthquake for more than 700 years, with lesser slip occurring along the Enriquillo-Plantain Garden faults and possibly, a submarine fault north of Hispaniola. Further details regarding the slip partitioning will require additional observations along a dense north-south transect of Hispaniola. We will discuss several hypotheses for the significant discrepancy between the GPS-derived velocities and those predicted by NUVEL-1A, including (1) internal deformation of the Caribbean "plate" that is not accounted for in the NUVEL-1A model and (2) a significant error in the global plate circuit outside the Caribbean region.