No abstract

We describe a model for Caribbean plate motion based on GPS velocities of four sites in the plate interior and two azimuths of the Swan Islands transform fault. The data are well fit by a single angular velocity, with average misfits approximately equal to the 1.5–3.0 mm yr−1 velocity uncertainties. The new model predicts Caribbean‐North America motion ∼65% faster than predicted by NUVEL‐1A, averaging 18–20±3 mm yr−1 (2σ) at various locations along the plate boundary. The data are best fit by a rotation pole that predicts obliquely convergent motion along the plate boundary east of Cuba, but are fit poorly by a suite of previously published models that predict strike‐slip motion in this region. The data suggest an approximate upper bound of 4–6 mm yr−1 for internal deformation of the Caribbean plate, although rigorous estimates await more precise and additional velocities from sites in the plate interior.

Previous Caribbean GPS studies have shown that the rigid interior of the Caribbean plate is moving east‐northeastward (070°) 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‐Bahama oblique collision zone and includes stable plate interior sites on both the North America and Caribbean plates. Measurements span the time period of 1994–1999. 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 relatively slower‐moving Hispaniola collisional zone and the relatively faster‐moving, uncollided Puerto Rico‐Virgin Islands area is the Mona Passage where late Neogene rifting occurs in a broad zone. Elastic modeling favors strain partitioning with oblique slip on the outer, low‐angle submarine thrust faults (North Hispaniola, Muertos) and strike slip on the inner, subvertical subaerial, strike‐slip faults (Septentrional, Enriquillo).

Global Positioning System (GPS) data from eight sites on the Caribbean plate and five sites on the South American plate were inverted to derive an angular velocity vector describing present-day relative plate motion. Both the Caribbean and South American velocity data fit rigid-plate models to within ؎1-2 mm/yr, the GPS velocity uncertainty. The Caribbean plate moves approximately due east relative to South America at a rate of ϳ20 mm/yr along most of the plate boundary, significantly faster than the NUVEL-1A model prediction, but with similar azimuth. Pure wrenching is concentrated along the approximately east-striking, seismic, El Pilar fault in Venezuela. In contrast, transpression occurs along the 068؇-trending Central Range (Warm Springs) fault in Trinidad, which is aseismic, possibly locked, and oblique to local plate motion.

S U M M A R YThe northeastern Caribbean provides a natural laboratory to investigate strain partitioning, its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary. Here, we use GPS and earthquake slip vector data to produce a present-day kinematic model that accounts for secular block rotation and elastic strain accumulation, with variable interplate coupling, on active faults. We confirm that the oblique convergence between Caribbean and North America in Hispaniola is partitioned between plate boundary parallel motion on the Septentrional and Enriquillo faults in the overriding plate and plateboundary normal motion at the plate interface on the Northern Hispaniola Fault. To the east, the Caribbean/North America plate motion is accommodated by oblique slip on the faults bounding the Puerto Rico block to the north (Puerto Rico subduction) and to the south (Muertos thrust), with no evidence for partitioning. The spatial correlation between interplate coupling, strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate, facilitating strike-slip faulting in the overriding plate. The model slip rate deficit, together with the dates of large historical earthquakes, indicates the potential for a large (M w 7.5 or greater) earthquake on the Septentrional fault in the Dominican Republic. Similarly, the Enriquillo fault in Haiti is currently capable of a M w 7.2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today. The model results show that the Puerto Rico/Lesser Antilles subduction thrust is only partially coupled, meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion. This does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes, but whose location and geometry are not resolvable with the present data distribution. Slip deficit on faults from this study are used in a companion paper to calculate interseismic stress loading and, together with stress changes due to historical earthquakes, derive the recent stress evolution in the NE Caribbean.