QUAKE-PRONE OCEAN TRENCHES—Puerto Rico, the U.S. Virgin Islands, and Hispaniola (shared by Haiti and the Dominican Republic) are located near earthquake-prone deep-ocean trenches similar to those that recently have caused earthquakes and a tsunami off Sumatra, Indonesia. A large fault that runs along Sumatra also bears striking resemblance to the Septentrional Fault Zone in Hispaniola. Deep-ocean trenches occur where two of Earth's crustal plates collide, with one thrusting down beneath the other. (Christopher Polloni, USGS and Jack Cook, WHOI Graphic Services)[back]
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