Geodetic evidence for a significant component of shortening along the northern Caribbean strike-slip plate boundary in southern Haiti

GPS measurements within the transform Caribbean–North American plate boundary in Hispaniola, Greater Antilles, with five additional years of data at continuous sites and additional campaign measurements, significantly improve the resulting velocities of earlier works. In a Caribbean-fixed frame, velocities at sites located along the island's southern coast are small (< 2 mm/yr), indicating that the offshore active faults mapped south of Haiti are currently slipping at very low rates. In the Southern Peninsula, velocities are oriented westward, parallel to the Enriquillo fault zone, consistent with strain accumulation on that left-lateral strike-slip fault. North of the Southern Peninsula, including the Gonâve island, velocities are consistently trending SW to WSW, oblique to the east-west direction of the plate boundary. This difference in velocity trend between the Southern Peninsula and areas to the north indicates regional shortening north of the southern Peninsula with an amplitude of 6-7 mm/yr of plate boundary-normal shortening. Geologic and high-resolution seismic data show that this shortening is likely taking place just at the northern coast of the Southern Peninsula, localized on a north-verging reverse fault system offshore the north coast of the Southern Peninsula of Haiti. This reverse fault system extends westward a similar fault system previously described on the southern edge of the Cul-de-Sac Plain, together delineating what we call the "Jérémie-Malpasse" reverse-fault system. This fault zone marks the boundary between the Caribbean Large Igneous Province to the south (CLIP), an oceanic plateau outcropping in the Southern Peninsula, and terranes of island arc crust to the north, a rare case of ongoing obduction in a transform context. This setting, consistent with the source mechanisms of the Mw7.0 January 2010 and Mw7.2 August 20121 earthquakes in southern Haiti, has significant implications in terms of regional seismic hazard.