Rarely has earthquakes? Mexico City does experience earthquakes. They lost over 8000 people in the Sept. 1985 quake (M8.1). Thirty thousand were injured and 100,000 were homeless.
412 Buildings collapsed and 3124 were seriously damaged. This is one of the most powerful quakes of this century, at least so far.

It is one of the largest cities in the world with over 20 million residents. Hundreds of years ago after the Spanish occupation, they drained Lake Texcoco and built the city there. The soft lake sediment is said to "amplify" the effects of an earthquake. So even if an earthquake isn't centered on the city itself, there can be disastrous effects.