Scientists Explain Geology of Haiti Earthquake

BY Lea Winerman  January 13, 2010 at 5:39 PM EDT

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Tuesday’s magnitude 7.0 earthquake was the largest recorded in Haiti since 1770, but more than a dozen quakes of that size have shaken the country’s Caribbean neighbors repeatedly over the past centuries.

That’s because Hispaniola, the Caribbean Island Haiti shares with the Dominican Republic, sits along the border between two large tectonic plates — the North American plate to the north, and the Caribbean plate to the south.

Those plates are slowly sliding past each other, as the Caribbean plate moves west-to-east. Between the two, “there’s a series of interconnected fault lines,” says geophysicist Jian Lin of the Woods Hole Oceanographic Institute, who studies the area.

Two major fault lines run through Haiti; Tuesday’s earthquake near Port-au-Prince occurred along the Enriquilla-Plantain Garden Fault that runs through the south of the country. Another fault, the Septentrional Fault, runs through the north.

The fault that caused Tuesday’s quake is a “strike-slip” fault — the same type as the San Andreas Fault in California — which means that the plates are sliding horizontally past one another, rather than one slipping under the other.

“It might be slightly less active [than the San Andreas Fault], but also the reason [that you hear less about it] is the same reason that you hear about murders in Washington, D.C. but not somewhere in the Amazon — if it’s close to us, close to our heart, we talk about it,” says Uri Ten Brink, a geophysicist at the U.S. Geological Survey.

Ten Brink also says that less is known about the geology of Haiti than that of nearby Puerto Rico or the Virgin Islands, because Haiti is such a difficult and dangerous place to do research.

“I was looking today very quickly at some papers that have been written on the area, and there have been so few,” he says. “That’s unfortunate.”

U.S.G.S. researcher Carol Prentice told the Christian Science Monitor that a team of researchers is already planning to visit Haiti to gather data about the quake.

“A lot of the data we need to collect are pretty ephemeral,” she said.

Meanwhile, Ten Brink says, the devastated country is still necessarily not out of the danger zone. Aftershocks from a large quake can come days or even a month later. “The larger the magnitude, the longer it takes,” he says.