MEXICO CITY _ A powerful earthquake shook central Mexico on Tuesday, crumbling buildings and sending thousands of people in Mexico City fleeing into the streets screaming.
The temblor caused buildings to sway violently in the center of Mexico City, including in the historic districts of El Centro and Roma. But it was not immediately clear whether there were casualties.
The U.S. Geological Survey calculated the preliminary magnitude at 7.1. The epicenter was about 93 miles southeast of Mexico City in the state of Puebla.
Rescue vehicles screamed through Mexico City toward damaged buildings, and flights into the capital were rerouted to other cities.
In the upscale neighborhood of Condesa, in the heart of the city, balconies crumbled and massive cracks opened up on apartment facades. Police cordoned off entire blocks because of fears that gas leaks could cause explosions.
In Roma, buildings swayed violently, sending ruble tumbling onto cars below. A video recorded from a skyscraper showed giant plumes of dust rising in the air.
The earthquake struck on the anniversary of a 1985 temblor that killed thousands of people and devastated large parts of Mexico City _ a tragedy that President Enrique Pena Nieto commemorated earlier in the day.
Susan Hough, a U.S. Geological Survey seismologist, said Tuesday's quake was likely related to one that struck off the coast of the Mexican state of Oaxaca on Sept. 7, which the government calculated as a magnitude 8.2 and the USGS as an 8.1.
"An 8.1 is big enough that having an aftershock this big and this distant _ it isn't too surprising," Hough said. "It's unusual, but it fits in with the picture that we've grown to understand."
