Late Holocene Structural Style and Seismicity of Highly Transpressional Faults in Southern Haiti

The devastating 2010 Haiti earthquake (Mw 7.0) was caused by rupture of the Léogâne, blind, thrust fault located 5 km north of the 1,200‐km‐long, left‐lateral, Enriquillo‐Plantain Garden fault zone (EPGFZ). Unexpectedly, the EPGFZ remained largely quiescent or slightly reactivated during the 2010 earthquake. Nevertheless, the EPGFZ still formed a major, crustal boundary between a coseismically uplifted lowland north of the EPGFZ and a subsided area in the highlands south of the fault. Here we use high‐resolution sonar data from two Haitian Lakes that straddle the EPGFZ to demonstrate the presence of a 10‐ to 15‐km‐wide, 120‐km‐long, late Holocene fold‐thrust belt which deforms clastic, lowland basins along the northern edge of the EPGFZ. In the eastern part of the study area, sonar results from Lake Azuey show that the linear trace of the EPGFZ cutting the Holocene lake bed is more deeply buried and less active than the adjacent, newly discovered, northwest striking, northeast dipping Jimani thrust fault that is part of the adjacent, transpressional belt of en echelon thrusts and folds. This structural relationship between a less active EPGFZ and more recently active, transpression‐related Jimani thrust is remarkably similar to the 2010 epicentral area 70 km to the west between the less active EPGFZ and seismogenic, northeast‐dipping, Léogâne thrust during the 2010 Haiti earthquake. In this complex transpressional zone, we propose that coseismic deformation alternates at recurrence intervals of centuries between oblique, transpression‐related structures (Léogâne, Jimani, and Trois Baies thrusts) and the main strike‐slip, plate boundary fault zone (EPGFZ). Key Points First high‐resolution sonar surveys of two actively deforming lakes in Haiti Extreme regional, tectonic transpression is partitioned by en echelon thrust faults and associated folds Three‐dimensional deformation model integrates patterns of 2010 coseismic uplift, aftershock distribution, and mapped geologic structures