MEXICO CITY (Reuters) - A 5.4 magnitude quake struck southern Mexico on Friday, according to the U.S. Geological Survey, but there were no immediate reports of damage.  It was not immediately clear if the tremor was an aftershock from a powerful series of quakes last month that destroyed buildings in Mexico City and killed nearly 500 people. The epicenter of Friday s tremor was just off the coast of Oaxaca state, in Mexico s southwest, and it struck at a depth of 59.5 kilometers (37 miles), according to the USGS. An 8.1 magnitude earthquake struck Oaxaca on Sept. 7 near the town of Juchitan, flattening thousands of buildings in the humid market town.  Fausto Lugo, Mexico City s emergency services chief, said on local television that Friday s earthquake was felt lightly in the capital, but there were no reports of damages.  