Every year on September 19, residents of Mexico City conduct an emergency evacuation drill to mark the anniversary of an 8.0 magnitude earthquake that killed about 10,000 residents in 1985. Yesterday was no exception. At 11:00 am, thousands of people left their homes, offices, and shops and made their way to the predesignated safe zones. Little did they know that within just two hours, the evacuation warning bells would ring again. Only this time, they were instantly followed by the violent shaking of a 7.1 magnitude earthquake.