GPS estimates of microplate motions, northern Caribbean: evidence for a Hispaniola microplate and implications for earthquake hazard

We use elastic block modelling of 126 GPS site velocities from Jamaica, Hispaniola, Puerto Rico and other islands in the northern Caribbean to test for the existence of a Hispaniola microplate and estimate angular velocities for the Gonave, Hispaniola, Puerto Rico-Virgin Islands and two smaller microplates relative to each other and the Caribbean and North America plates. A model in which the Gonave microplate spans the whole plate boundary between the Cayman spreading centre and Mona Passage west of Puerto Rico is rejected at a high confidence level. The data instead require an independently moving Hispaniola microplate between the Mona Passage and a likely diffuse boundary within or offshore from western Hispaniola. Our updated angular velocities predict 6.8 +/- 1.0 mm yr-1 of left-lateral slip along the seismically hazardous Enriquillo-Plantain Garden fault zone of southwest Hispaniola, 9.8 +/- 2.0 mm yr-1 of slip along the Septentrional fault of northern Hispaniola and similar to 1415 mm yr-1 of left-lateral slip along the Oriente fault south of Cuba. They also predict 5.7 +/- 1 mm yr-1 of fault-normal motion in the vicinity of the Enriquillo-Plantain Garden fault zone, faster than previously estimated and possibly accommodated by folds and faults in the Enriquillo-Plantain Garden fault zone borderlands. Our new and a previous estimate of Gonave-Caribbean plate motion suggest that enough elastic strain accumulates to generate one to two Mw similar to 7 earthquakes per century along the Enriquillo-Plantain Garden and nearby faults of southwest Hispaniola. That the 2010 M= 7.0 Haiti earthquake ended a 240-yr-long period of seismic quiescence in this region raises concerns that it could mark the onset of a new earthquake sequence that will relieve elastic strain that has accumulated since the late 18th century.