The science behind Haiti's quake

7.0 and it appeared to have occurred along a strike-slip fault, where one side of a vertical fault slips horizontally past the other, scientists say. California's San Andreas fault is also characterized as strike-slip.

It was the strongest earthquake since 1770 in what is now Haiti. In 1946, a magnitude-8.0 quake struck neighboring Dominican Republic and shook Haiti, killing 100 people, most of them in the tsunami that followed. In that case, according to the U.S. Geological Survey, the death toll was light because the quake struck in the afternoon on a holiday.

Tuesday's quake was centered about 10 miles (15 kilometers) west of Port-au-Prince at a depth of 5 miles (8 kilometers), the USGS said. Since then, more than 30 smaller quakes have shaken the island, with magnitudes ranging from 4.5 to 5.9.

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