<summary from usgs>

Felt Reports

Severe damage and casualties in the Port-au-Prince area. Felt throughout Haiti and the Dominican Republic, in Turks and Caicos Islands, southeastern Cuba, eastern Jamaica, in parts of Puerto Rico and the Bahamas, and as far as Tampa, Florida and Caracas, Venezuela.

Tectonic Summary

The January 12, 2010, Haiti earthquake occurred in the boundary region separating the Caribbean plate and the North America plate. This plate boundary is dominated by left-lateral strike slip motion and compression, and accommodates about 20 mm/y slip, with the Caribbean plate moving eastward with respect to the North America plate.

Haiti occupies the western part of the island of Hispaniola, one of the Greater Antilles islands, situated between Puerto Rico and Cuba. At the longitude of the January 12 earthquake, motion between the Caribbean and North American plates is partitioned between two major east-west trending, strike-slip fault systems — the Septentrional fault system in northern Haiti and the Enriquillo-Plantain Garden fault system in southern Haiti.

The location and focal mechanism of the earthquake are consistent with the event having occurred as left-lateral strike slip faulting on the Enriquillo-Plantain Garden fault system. This fault system accommodates about 7 mm/y, nearly half the overall motion between the Caribbean plate and North America plate.

The Enriquillo-Plantain Garden fault system has not produced a major earthquake in recent decades. The EPGFZ is the likely source of historical large earthquakes in 1860, 1770, 1761, 1751, 1684, 1673, and 1618, though none of these has been confirmed in the field as associated with this fault.

more on this:

from usgs. Haiti information from USGS,

Parameters estimated by Nagoya University. http://www.seis.nagoya-u.ac.jp/sanchu/Seismo_Note/2010/NGY24.html

In pictures, from BBC