Relative motion between the Caribbean and North American plates and related boundary zone deformation from a decade of GPS observations

Global Positioning System (GPS) measurements in 1986, 1994, and 1995 at sites in Dominican Republic, Puerto Rico, Cuba, and Grand Turk define the velocity of the Caribbean plate relative to North America. The data show eastward motion of the Caribbean plate at a rate of 21 +/- 1 mm/yr (1 standard error) in the vicinity of southern Dominican Republic, a factor of 2 higher than the NUVEL-1A plate motion model prediction of 11 +/- 3 mm/yr. Independent measurements on San Andres Island, and an Euler vector derived from these data, also Suggest a rate that is much higher than the NUVEL-1A model. Available data, combined with simple elastic strain models, give the following slip rate estimates for major left-lateral faults in Hispaniola: (1) the North Hispaniola fault offshore the north coast of Hispaniola, 4 +/- 3 mm/yr; (2) the Septentrional fault in northern Dominican Republic, 8 +/- 3 mm/yr; and (3) the Enriquillo fault in southern Dominican Republic and Haiti, 8 +/- 4 mm yr. The relatively high plate motion rate and fault slip rates suggested by our study, combined with evidence for strain accumulation and historical seismicity, imply that seismic risk in the region may be higher than previous estimates based on low plate rate/low fault slip rate models and the relatively low rate of seismicity over the last century.