The 7.0 magnitude earthquake that hit Haiti at 4:53 p.m. Tuesday, displacing and possibly killing thousands of people, was the most violent quake the country had experienced in more than a century, according to the U.S. Geological Survey.
The quake occurred along the fault line that separates the Caribbean and North American tectonic plates. It is a strike-slip fault line, and it runs east to west through Haiti, the government agency said.
When the quake hit, the massive plates, located about 10 miles southwest of the densely populated capital, Port-au-Prince, moved horizontally, causing the pieces of rock to move past each other.
"The North American and Caribbean tectonic plates are sheering the island, crushing it, grinding it and, as that occurs, earthquakes pop off," Michael Blanpeid, associate coordinator for the Geological Survey's Earthquake Hazards Program, said in a podcast on the agency's Web site Tuesday.
It was a relatively shallow earthquake, only 6 miles below the surface of the earth.
"There are really three things that go into the severity of an earthquake: its location, its depth and its magnitude," Blanpeid said.
"This earthquake was located quite shallowly ... therefore, the populated areas very near that fault were shaken extremely strongly."
Blanpeid said other factors such as the style and construction of the buildings and the kind of ground -- whether it is soft or hard -- also determine the amount of destruction.
"Soft ground tends to amplify the shaking and can tend to break up the foundation of structures if the ground ruptures underneath them," Blanpeid said.
Photos from the region show buildings that were reduced to rubble and Haitians in agony.
While the full extent of the destruction is still unknown, Haitian President Rene Preval told the Miami Herald that thousands may be dead and said the devastation was "unimaginable."
"The aftershocks are likely to continue for quite some time," Blanpeid said. "We may see significant aftershocks days or even possibly weeks [after the earthquake]."
The National Oceanic and Atmospheric Administration issued a tsunami warning, but it proved to be a false alarm.
"The only positive thing about this earthquake is that because it did occur on land, it did not generate a tsunami," Blanpeid said.