After Mexico City quake, big structural risk remains

MEXICO CITY - Certain types of buildings are especially vulnerable to collapse during earthquakes - and earthquake-prone Mexico City is filled with them.

Those with so-called brittle concrete frames are well-known hazards. Buildings with a weak first story, often supported by narrow columns to accommodate parking, are also known to be dangerous.

How many such buildings exist in this 573-square-mile metropolis, home to nearly 9 million people, is hard to know. The government has never cataloged its real estate to identify risky structures.

Now, in the wake of the magnitude 7.1