The island of Hispaniola on the northeastern Caribbean plate margin occupies an area of complex tectonic transition between active westward underthusting of the North America plate beneath the Caribbean plate at the Lesser Antilles island arc and roughly east-west strike-slip motion between the Caribbean and North America plates. Previous Caribbean GPS studies have shown that the rigid interior of the Caribbean plate is moving east-northeastwards (070º) at a rate of 18-20 ± 3 mm/yr relative to North America. This direction implies maximum oblique convergence between the island of Hispaniola on the Caribbean plate and the 22-27-km-thick crust of the Bahama carbonate platform on the adjacent North America plate. We present a tectonic interpretation of a 15 site GPS network which spans the Hispaniola-convergence zone and includes stable plate interior sites on both the North America (Grand Turk, Bahamas) and Caribbean plates (Puerto Rico, Virgin Islands, Lesser Antilles arc, Barbados). Measurements at all sites were made in 1994 with partial remeasurements in 1995, 1996, 1997, and 1999. In a North America reference frame, GPS velocities in Puerto Rico, St. Croix, and the Lesser Antilles indicate that these areas move as a single block in an east-northeast direction (070°) at a rate of 19-20 mm/yr consistent with the movement of the rigid interior of the Caribbean plate. GPS velocities at six sites in central and eastern Hispaniola (Dominican Republic) show drastically different behavior with more eastwardly strikes (080°) and much slower rates (4-17 mm/yr) than areas of the stable Caribbean plate. The boundary between the slower-moving Hispaniola area and the faster-moving Puerto Rico-Virgin Islands area is the Mona Passage where normal and oblique-slip faults deform an Oligocene-early Pliocene carbonate platform that is relatively undeformed in areas to the east in Puerto Rico and the Virgin Islands. The GPS-derived velocity field in Hispaniola is compatible with a model of elastic strain accumulation on four major, roughly east-west striking fault zones which are currently locked to a depth of 15 km. Elastic modeling favors strain partitioning with oblique slip on the outer, sub-parallel and submarine faults of the boundary zone (North Hispaniola, Muertos) and strike slip on the inner, sub-parallel and subaerial faults (Septentrional, Enriquillo). The GPS data and derived models cannot confirm whether slowness of plate velocities in Hispaniola indicates that the area is behaving as a microplate detached from the Caribbean plate as a result of convergence with the Bahama platform on the North America plate or whether this slowness is a consequence of elastic strain accumulation along these four locked faults.

GPS velocities. Blue vectors represent GPS data processed using GIPSY software; red vectors are identical GPS data processed with GAMIT software. Numbers are rates in mm/yr. Gray vectors represent Caribbean plate motion predicted by DeMets et al. (2000) plate model relative to the ITRF97 frame of reference. The small residual velocities for sites in the Lesser Antilles (LA), St. Croix, Virgin Islands (CROI), and Puerto Rico (PR) are consistent with the previous interpretation by Jansma et al. (2000) that these areas move with the Caribbean plate and experience minimal elastic strain accumulation related to subduction along the North America-Caribbean. Large residuals for sites in Hispaniola indicate it is either detached from the Caribbean plate and/or is experiencing large elastic strains related to plate boundary zone deformation. The boundary between the stable Puerto Rico area and the less stable Hispaniola region is in the Mona Passage.

See also:
Mann, P., E. Calais, J.-C. Ruegg, C. DeMets, T.H. Dixon, P.E. Jansma, and G.S. Mattioli, Oblique collision in the northeastern Caribbean from GPS measurements and geological observations, Tectonics, 10.1029/2001TC001304, 2002.