Plate Coupling in the Northeastern Caribbean

P. Przybylski, E. Calais, Purdue University, West Lafayette, Indiana
G. Mattioli, P. Jansma, University of Arkansas, Fayetteville, Arkansas

NSF Grant EAR-0409487


Major strike-slip faults commonly found on the margin of overriding plates in oblique subduction zone settings facilitate the partitioning of strain into trench-parallel and trench-normal tectonics. Their development has been proposed to be controlled by factors such as convergence obliquity, basal tractions, magnitude of slab-pull force, or strength of interplate coupling.


Combined GPS velocity field in the NE Caribbean (red arrows). Blue segments show earthquake slip vector directions.

In the northeastern Caribbean, the direction of GPS velocities and earthquake slip vectors suggests low coupling along the Puerto Rico and Lesser Antilles trenches, but strong coupling to the west along the Hispaniola margin, while the convergence obliquity remains constant. Coincidentally, large strike-slip faults in the overriding plate only develop in Hispaniola, which is also the locus of the largest historical subduction earthquakes in the Caribbean (M8.0, 1946-53 sequence).


Coupling ratio at the Caribbean-North American plate interface calculated from an inversion of GPS and earthquake slip vector data. Estimated faults slip rates are 8~mm/yr for the Septentrional fault (consistent with Holocene estimates), 5~mm/yr for the Enriquillo fault, 5-6~mm/yr for the North Hispaniola fault, 5 (west) to 18 (east) mm/yr for the Puerto Rico subduction, and 20~mm/yr for the Lesser Antilles subduction (full Carribean/North America plate motion).

We calculate interplate coupling at the Caribbean-North American plate boundary using a model that allows for block rotations and elastic strain accumulation on -- possibly partially -- coupled faults. Model parameters are derived from an inversion of new GPS and earthquake slip vector data. We find that intraplate coupling is high in the western half of the domain, coincident with the development of large and fast-slipping strike-slip faults in the upper plate that partition the Carribean/North America plate motion, but low in its eastern half, along the Puerto Rico and Lesser Antilles subductions, that show little to no strain partitioning. This suggests that strain partitioning occur only if interplate coupling is large enough to effectively transfer shear stresses to the overriding plate.