A powerful 7.6 magnitude earthquake struck the Caribbean Sea on Saturday afternoon, prompting tsunami alerts for Puerto Rico, Virgin Islands, and Riviera Maya. The quake, which occurred at 6:23 p.m. local time, had its epicenter approximately 209 kilometers off the coast of the Cayman Islands at a shallow depth of 10 kilometers, according to the United States Geological Survey (USGS). (Update: Riviera Maya has been removed from the alert area.) T…