Minutes before midnight, warning sirens blared across this earthquake-anxious capital. This, in itself, was not unusual. Temblors are common here, and in recent years Mexico City has held annual disaster drills, revamped building codes and installed sophisticated sensors to be ready for an emergency. Many residents still have clear memories of the calamitous 1985 earthquake that killed at least 5,000 people here and left a quarter-million homeless. But minutes after the sirens began wailing late Thursday, hanging houseplants started swaying and books tumbled from shelves. Plaster cracked. Streetlights shimmied like reeds in the wind. Lights went black. In pajamas and barefoot, with babies swaddled in blankets, residents rushed out of their apartments to wait in the darkened streets. This was no drill. This was an 8.1-magnitude earthquake, the most powerful one in Mexico […]