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The earthquake occurred inland, on 12 January 2010, approximately 25 kilometres (16 mi) WSW from Port-au-Prince at a depth of 13 kilometres (8.1 mi) at 16:53 UTC-5 on the Enriquillo-Plantain Garden fault system. Strong shaking with intensity VII–IX on the Modified Mercalli scale (MM) was recorded in Port-au-Prince and its suburbs. It was also felt in several surrounding countries and regions, including Cuba (MM III in Guantánamo), Jamaica (MM II in Kingston), Venezuela (MM II in Caracas), Puerto Rico (MM II–III in San Juan), and the bordering country of Dominican Republic (MM III in Santo Domingo).
The quake occurred in the vicinity of the northern boundary where the Caribbean tectonic plate shifts eastwards by about 20 mm per year relative to the North American plate. The strike-slip fault system in the region has two branches in Haiti, the Septentrional fault in the north and the Enriquillo-Plaintain Garden fault in the south; seismic data suggests that the January 2010 quake was on the Enriquillo-Plaintain Garden fault, which had been locked solid for 250 years, gathering stress. The stress would ultimately have been relieved either by a large earthquake or a series of smaller one.
According to other report, the Haiti earthquake occurred at a fault that runs right through Haiti and is situated along the boundary between the Caribbean and North American plates, which are rocky slabs that cover the planet and fit together like a giant jigsaw puzzle. These two plates constantly creep past one another, about 0.8 inches a year, with the Caribbean plate moving eastward with respect to the North American slab.
The Caribbean isn't exactly a hot zone for earthquakes, but they're not unheard of in the region.
Yesterday's earthquake was one of the largest ever to hit the area — the last time an earthquake this strong struck Haiti was in the 18th century.
Haiti takes up about half of the island of Hispaniola, while the Dominican Republic lies on the other side. In 1946, an 8.0-magnitude earthquake shook Samana, in the Dominican Republic, causing about 100 fatalities. The recent quake will likely have a much greater casualty toll because it hit a more densely populated region.
Haiti earthquake threats those stable areas in world which has not received major earthquakes from thousands of years. Gradually developing stress may activate dead faults. Small earthquakes in unexpected locations are often a cause for concern. The worry is that these rumbles are harbingers of bigger quakes to come. But not always - a new study suggests that many of these tremors aren't warnings, but aftershocks. In particular, those that happen in the middle of continents, far away from the major fault-lines that separate tectonic plates, probably reflect past quakes rather than future ones.