A moderate earthquake has rocked Puerto Rico, with a magnitude of 5.7 and depth of 110 kilometers. At that depth, I don't think there is much potential for damage, but local residents are no doubt concerned about feeling any shaking after the tragedy of Haiti. Like Haiti, Puerto Rico sits uncomfortably close to a major plate boundary, and there is a history of damaging quakes in the vicinity, especially in 1670, 1787 (possibly a magnitude 8.0), 1867 (magnitude 7.5) and 1918 (magnitude 7.5). The 1918 event caused a 19 foot high tsunami, and 112 people were killed. More information about the hazards of this part of the Caribbean Sea can be found here.