What caused the earthquake in Haiti?

The earthquake in Haiti was caused by a fault between the Caribbean plate and the North American plate, which is near Haiti. Usually, the Caribbean plate and the North American plate confront each other eastward, and the two continental plates have been squeezing and colliding, and one of them will slowly "climb" onto the other plate, which is what we call a translational fault. But the annual exercise is very subtle, generally only 0.8 feet (20 cm).