(CNN) Initially, Ricardo Ramos thought it was a drill when the ground began to shake on Tuesday. This was the day for it, after all.

Each year on September 19, cities across Mexico stage emergency disaster simulations and evacuations that bring people out in droves. The drill falls on the anniversary of an 8.0-magnitude earthquake that shook Mexico's capital in 1985, burying nearly 10,000 people amid its rubble.

The annual drill began in Mexico City around 11 a.m. on Tuesday, just like it does every year. The alert went out over radio, television, phones and public loud speakers. People left homes, offices and shops and headed to designated safe areas promoted days ahead of time.

Then, around two hours later, the real thing struck . Ramos quickly realized this was not a drill.

The irony of the situation was apparent to Mexicans, for whom the drills are a way of life, even a minor annoyance. Many noted the contrast between the orderly, almost mundane quality of some drills and the chaos of real life.

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