This region of the Earth is a complex web of plate tectonics where multiple plates come together. The North America, South America, Nazca, and Cocos plates all surround the Caribbean plate causing fantastic geologic features on the ocean floor. The earthquake occurred at 5:27 UTC (1:30 am local time) at a depth of 16.9 km.
For more information visit the USGS webpage.
IRIS DMC released this ground visualization showing the upward and downward vertical motion of the USArray as the waves moved underneath North America. If you would like to view other ground motion visualizations, visit IRIS GMV.