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 earthquake that killed more than 360 people in September, some experts are urging city officials to do just that -- so tenants can be warned and building owners can be ordered to retrofit them with steel braces or new walls.
"We have to move very fast," while the issue is fresh in people's minds, said Sergio Alcocer, an earthquake expert at the Institute of Engineering at the National Autonomous University of Mexico.
Such an undertaking is costly and has long been viewed as politically difficult. Many cities have resisted similar calls.
But political sentiment can shift. In 2015, Los Angeles became the biggest city in California to pass a law to identify vulnerable concrete buildings and apartments with weak ground stories and mandate retrofitting. Once building owners are notified, they have seven years to fix weak ground stories and 25 years to complete modifications to stabilize brittle concrete frames.
In an interview, Los Angeles Mayor Eric Garcetti encouraged Mexico City to start now.
"Waiting causes lives to be lost," he said.
Los Angeles anticipated organized opposition by building owners and overcame it by conducting two years of public education efforts on the risks of inaction.