As the Atlantic Ocean began to open, some 160 million years ago, the North and South American Plates were pushed westward; this process continues today. West of these Plates was the vast Farallon Oceanic Plate and associated smaller plates and, since the Jurassic Period, most of these plates have subducted beneath the Americas, adding their cargo of exotic terrains to the Continents and producing volcanic mountain ranges; remnants of the Farallon are still activating volcanoes in the Cascades, Mexico's Volcanic Belt, western Central America and the Andes of South America today.
One of the oceanic plates, the Caribbean Plate, did not subduct but was wedged between the advancing American Plates and actually overrides those plates in some areas; indeed, along its eastern edge, the volcanic arc of the Lesser Antilles has developed as the American Plates subduct beneath the Caribbean Plate. On its northern and southern borders, the Caribbean Plate is scraping past the American Plates along slip faults, which, in some areas, are interrupted by microplates.
Yesterday, a 7.0 magnitude earthquake struck Haiti due to movement along the edge of the Gonave Microplate, which is wedged between the North American and Caribbean Plates. Since a major quake has not occurred in this country for more than a century and since Haiti is too impoverished to construct buildings that resist earthquakes, widespread damage and many fatalities have resulted. Similar events have and will occur along other slip faults across the globe, including the San Andreas Fault of Southern California; since these events are infrequent relative to the human life span, we often feel immune to their destructive power. But, despite our perception, the evolution of our planet continues.
