Detailed map, displacement, paleoseismology, and segmentation of the Enriquillo-Plantain Garden Fault in Haiti

Abstract

The Enriquillo-Plantain Garden Fault (EPGF) ruptured several times in Haiti, producing large historical earthquakes (e.g., 18 October 1751, 21 November 1751, and 3 June 1770). Their location and lateral extents are poorly known. The most devastating one, the Mw7.0, 12 January 2010 earthquake should have been the occasion to constrain the fault kinematics and geometry, unfortunately no significant surface rupture was observed. Here, combining LiDAR data, high-resolution aerial photographs, geological map and observations in the field, we revisited the fault map at a large variety of scales to improve the assessment of seismic hazard associated with the EPGF. This detailed mapping allowed us to target several sites for paleoseismic trenches. We carried out paleoseismic investigations in the Clonard pull-apart basin during which one trench was opened perpendicular to the fault. That trench showed stratigraphic evidence for one paleoearthquake. Radiocarbon dating in a dry and buried stream led to the conclusion that the paleoearthquake might be that of 1770. Then, based on kilometric-scale geometric complexities, we showed that the EPGF was composed of more than four segments, each capable to generate Mw > 7 earthquakes. Finally, we identified several geologic and geomorphic markers of long-term deformation along the fault. We found offsets of ~40, ~15 and ~8 km from west to east corresponding to slip rates of 9 ± 3, 4–6 and ~3 mm/yr over the Early-Middle Pliocene, Plio-Pleistocene and Pleistocene, respectively. Such a pattern supports the idea of an eastward propagation of the EPGF.