By: Robin Andrews/IFLScience  An incredibly powerful earthquake, registering as a 7.1M, has rocked Mexico City, a densely-packed metropolis containing nearly 20 million people, and its many suburbs and nearby towns. According to the United States Geological Survey (USGS), it was a deep-seated earthquake (51 kilometers/32 miles depth) that struck at 1:14 pm local time. The epicenter was 122 kilometers…