from http://voa.hjenglish.com/st/20100117#

 

 

Earthquake hit Haiti hard, with extensive damage and many casualties.

Compared to the well-known seismic areas like the Pacific Rim, the Caribbean seems geologically quiet, but this area, where tectonic plates meet, has a long history of earthquakes, tsunamis, and volcanoes.

In 1946, the Dominican Republic, just across the border from Haiti, experienced a magnitude 8 earthquake, which triggered a tsunami. Other major recorded earthquakes in the 17th, 18th, and 19th centuries may have been produced by movement of the same fault that caused Tuesday's disaster.

Earthquakes generally occur when the tectonic plates that make up the Earth's crust move suddenly. Eric Calais, a geophysicist, says that sudden movement can follow a buildup of stress as adjacent plates struggle to move past each other.

" If you have a fault that is being strained at a speed of 7 mm per year, which is the case here, and the last major event on that fault occurred 250 years ago, so if the fault snaps, it's going to snap by 1. 7 m, and that's about a magnitude 7 earthquake. "


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