WASHINGTON - A 5.8 magnitude earthquake struck in Mexico on Tuesday, centered six miles (9.6 km) west of Pinotepa Nacional in Oaxaca, the US Geological Survey reported.The quake, which struck at 13:04 GMT, was 20.5 miles (33 km) deep, the USGS said.The quake was felt in Mexico City, where buildings shook, a Reuters reporter said.