M 7.2 - 12 km NE of Saint-Louis du Sud, Haiti

Tectonic Summary

The August 14, 2021 M 7.2 Haiti earthquake occurred as the result of oblique reverse motion along the Enriquillo-Plantain Garden fault zone, ~125 km west of the Haitian capital Port-au-Prince. The earthquake occurred at shallow depths on either a reverse fault striking west and dipping to the north with a component of left-lateral slip, or a fault striking southeast and dipping to the southwest with a component of right-lateral slip. At the location of the earthquake, the local plate boundary is dominated by left-lateral strike slip motion and compression. The plate boundary in this location accommodates eastward, left-lateral motion of the Caribbean plate relative to the North America plate. Within this context, the earthquake likely occurred on the east-west striking, north dipping fault plane with a component of left-lateral slip.

On January 12, 2010, an M 7.0 earthquake struck the same peninsula of Haiti and was located ~75 km east of the August 2021 earthquake. The 2010 earthquake caused substantial damage in the city of Port-au-Prince and the surrounding regions where damage from the earthquake and subsequent cascading hazards caused over 200,000 fatalities. The August 2021 earthquake likely occurred within the same fault system as the January 2010 earthquake; however, the 2010 earthquake occurred on a blind thrust fault and not directly on the main plate-boundary fault.

The location and focal mechanism solutions of the August 2021 earthquake are consistent with the event resulting from primarily reverse faulting with a component of left-lateral strike slip faulting on the Enriquillo-Plantain Garden fault zone (EPGFZ). Overall, the EPGFZ accommodates about 7 mm/yr of motion, nearly half the total oblique convergence between the Caribbean and North America plates (~20 mm/yr). Haiti occupies the western part of the island of Hispaniola, one of the Greater Antilles Islands, situated between Puerto Rico and Cuba. At the location of the August 2021 earthquake, motion between the Caribbean and North America plates is partitioned between two major east-west-trending, strike slip fault systems—the Septentrional fault system in northern Haiti and the EPGFZ in southern Haiti.

The EPGFZ had produced a series of major earthquakes in both instrumental and historical time periods. In addition to the 2010 M 7 earthquake that devastated Port-au-Prince, the EPGFZ is the likely source of historical large earthquakes in 1860, 1770, and 1751, though none of these has been confirmed in the field as associated with this fault. The sequence of events possibly associated with the Enriquillo fault in 1751–1860 are as follows:

October 18, 1751: a major earthquake caused heavy destruction in the Gulf of Azua (the eastern end of the Enriquillo fault); this earthquake also generated a tsunami. It is unclear if the rupture occurred on the Muertos reverse belt or on the eastern end of the Enriquillo fault.

November 21, 1751: a major earthquake destroyed Port-au-Prince but was centered to the east of the city on the Plaine du Cul-de-Sac.

June 3, 1770: a major earthquake destroyed Port-au-Prince again and appeared to be centered west of the city. As a result of the 1751 and 1770 earthquakes and minor earthquakes that occurred between them, local authorities required building with wood and forbade building with masonry.

April 8, 1860: a major earthquake occurred farther west of the 2010 earthquake and was accompanied by a tsunami.

An M6.9 earthquake in Alaska (an aftershock to a previous M8.2 earthquake on July 29, 2021) preceded the Haiti earthquake by ~31 minutes. Despite the timing coincidence between these two earthquakes, the large distance between these two events makes a causal relationship unlikely.