Active tectonics along the Cul-de-Sac – Enriquillo plain and seismic hazard for Port-au-Prince, Haiti

Abstract

The active faults in Haiti were not well known and no detailed mapping of active fault traces was available before the 2010, M7.0 earthquake. The lack of detailed fault mapping hindered the interpretation of the event and the seismic hazard assessment. Here, using high-resolution LIDAR topography, aerial photographs, bathymetric charts, together with geological data complemented with field observations, we carried out a morphotectonic analysis at a variety of scales. We analyzed the drainage network at the northern front of the Massif de la Selle – Sierra de Bahoruco (MSB) by mapping the fans of the main rivers and their associated drainage basins. We found that the areas of all the fans were compatible with the sizes of their drainage basins, except the paleofan of Port-au-Prince. We interpret that this paleofan has been offset by 7.9±0.3km across the main strike-slip Enriquillo-Plantain Garden Fault (EPGF) and we estimate a minimum horizontal slip rate of ∼3mm/yr over the Pleistocene. Moreover, in the Cul-de-Sac – Enriquillo plain, within which the capital city of Port-au-Prince is located, we mapped numerous NW-SE to WNW-ESE-striking Quaternary folds and thrust faults. Some of the thrust faults are north-dipping and located to the southern front of the Matheux-Neiba Lower Miocene fold. Other thrusts, such as those near Ganthier, Jacquet, Nan Cadastre, and Port-au-Prince, are south-dipping and located along the northern front of the MSB Lower Miocene fold. Previously, Saint Fleur et al. (2015) showed that the 2010 Haiti earthquake activated both one of the young thrusts (Lamentin) and the EPGF, consistent with oblique convergence between the Caribbean and the North American plates.