Earthquake Strikes in Oaxaca State, Mexico, Stirring Fear

MEXICO CITY — A 7.2-magnitude earthquake struck Mexico’s southern Pacific Coast on Friday, according to the U.S. Geological Survey.

The quake was reported at 5:39 p.m. local time, shaking buildings about 225 miles away in Mexico City, where the memory of a Sept. 19 earthquake that killed more than 300 people in the capital and other parts of the country is still fresh. Friday’s tremors left tall buildings swaying for more than two minutes.

The epicenter of the quake was near the town of Pinotepa Nacional, in the Pacific state of Oaxaca.

A presidential spokesman, Eduardo Sánchez, told the Televisa network two hours after the earthquake that there were no reports of deaths or injuries.

Luis Felipe Puente, Mexico’s national coordinator of civil protection, wrote on Twitter that there were no immediate reports of major damage. In Oaxaca, the state director of civil protection, Heliodoro Díaz Escárraga, said that homes were damaged in the town of Santa María Chimalapas and walls fell in the town of Jamiltepec.

In Mexico City, the capital, residents streamed from buildings and into the streets, texting to see if their loved ones were safe, gripped by a sense of dread just a few months old.

Residents of the Condesa and Roma neighborhoods of Mexico City, which suffered some of the worst damage in September, ran out into the streets in panic, looking up at the buildings as the earthquake warning system went off. Once in the streets, they searched for signs of damage to their buildings.

Last September’s seismic eruption has left people frightened at the slightest tremor, and the tears in the faces of those who endured the last major quake were easy to spot on the streets.

Many could be heard repeating the words “Oh God, not again.”

Video footage from inside the Mexico City newsroom of a daily newspaper, Milenio, showed employees ducking underneath desks as light fixtures swung wildly.

The initial 7.2-magnitude shock was followed 57 minutes later by a magnitude-5.8 aftershock.

The epicenter of Friday’s earthquake was between those of a magnitude-8.2 quake on Sept. 8 and the 7.1-magnitude quake on Sept. 19. But from a geological standpoint, all three occurred in the same general area — a subduction zone, where one piece of the Earth’s crust, in this case the Cocos Plate, is slowly sliding under another, the North American.

Like other subduction zones around the Pacific and elsewhere, this region is the source of many earthquakes, some of them very strong and destructive. The movement of the two plates relative to each other is very slow — about 2 to 3 inches a year — but it causes stresses to build, either at the boundary between the two plates or, as was the case with the September quakes, within one of them. At some point the stresses become too much and the rock formations slip, releasing energy as an earthquake.

Shortly after Friday’s quake, the U.S. Geological Survey released a brief initial analysis, saying that it occurred “on or near” the boundary between the two plates, and about 55 miles north of the Middle America Trench, where the Cocos begins its slide beneath the North America plate.

In addition to local destruction, strong Mexican earthquakes often cause damage in Mexico City — even if, as in this case, the capital is miles away. Mexico City was built on an ancient lake bed, and the sediments of sand and clay amplify the seismic waves as they arrive from the epicenter.

Depending on the amount of energy released, the depth of the epicenter and its distance from Mexico City, the seismic waves from a quake can affect some buildings in the capital more than others. In the Sept. 19 quake, mostly shorter buildings were knocked down. But in a 1985 quake that killed 10,000 people, most of the buildings that were severely damaged or destroyed were six to 16 stories tall.