Tectonic, Topographic, Geologic, and Hydroclimatic Influence on Crack Formation During the 2021 Haiti Earthquake

The 14 August 2021 Haiti earthquake mainly portrayed reverse motion to the east near L’Asile town and left-lateral strike-slip motion to the west near Camp-Perrin town. To map the rupture and infer its segmentation, we conducted the first post-seismic field reconnaissance along the left-lateral strike-slip Enriquillo fault from L’Asile to Macaya mountain. We identified 98 linear, minor cracks that are not representative of primary fault surface rupture. Analyzing the topographic slope distribution, we detected that the cracks were often located in areas that are prone to topographic instability. About 60% of the cracks are located in Quaternary alluvium and Middle-Miocene continental marls, indicating a preference for soft sediments. The rivers also have an impact, as crack lengths and openings negatively correlate with their distance to neighboring rivers. In addition, the earthquake occurred in a rainy region with up to 2,479.34 mm of rainfall in 2021, increasing soil instability. Above all, we found a contrast and asymmetry between the eastern and the western parts of the rupture. By dividing the 60-km long rupture into two equal parts, we observed 57 cracks to the west against 41 to the east. The longest and the widest cracks are to the west. Analyzing their orientation, the cracks mainly oriented as left-lateral strike-slip faults to the west and mainly thrusts to the east. This configuration appears to be influenced by the slip pattern of the 2021 Haiti earthquake and consistent with the regional stress field.