The magnitude 7 earthquake that struck Haiti yesterday is the strongest earthquake to hit the region in more than two centuries, geologists say. (See Haiti earthquake pictures.)
While earthquakes are not uncommon in the Caribbean island country, the recent Haiti earthquake's intensity surprised experts.
"It's quite strange" from a historical perspective, said Julie Detton, a geophysicist with the U.S. Geological Survey.
Haiti is part of the island of Hispaniola, which also hosts the Dominican Republic. The last major earthquake to strike Haiti's side of the island was in 1860.
Yesterday's initial earthquake, which struck at about 5 p.m. local time yesterday, spawned dozens of aftershocks, about 15 of which were magnitude 5 or greater.
Whether the earthquake could trigger other major quakes is not known.
"It's not something that we can project is going to happen," Detton said.
"But definitely if you're moving two [plates] in one area, you're building up stress and strain in another."
Haiti Earthquake: Seismic Stresses
The Haiti earthquake was caused by the release of seismic stresses that had built up around two tectonic plates.
The motions of these plates create what are known as strike-slip faults, where two sections of Earth's crust are grinding past each other in opposite directions.
"The Caribbean plate is moving eastward with respect to the North American plate," Detton said.
When the stresses along the fault lines reach a certain point, they can be released in bursts of energy that cause earthquakes, although it's unclear when the energy will be discharged as a series of small quakes or as one big temblor.
Since Haiti is very close to the boundary where the Caribbean and North American plates meet, fault lines linked to the plates' movements run right through the country, Detton said.
In fact, the epicenter of the earthquake was about 10 miles (16 kilometers) southwest of Haiti's capital city, Port-au-Prince. (See a Haiti map.)
In addition, the Haiti earthquake was very shallow, being centered just 6.2 miles (10 kilometers) below Earth's surface.
This put impoverished Port-au-Prince close to the most intense shaking, contributing to the scale of the devastation: Thousands are feared dead and countless buildings have collapsed, from schools and hotels to the Haitian Parliament and local UN headquarters.
The American Red Cross estimates that the Haiti earthquake may have affected about three million people in total.
Ker Than
for National Geographic News
January 13, 2010
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