MEXICO CITY -- In quake-stricken Mexico City, hundreds of architects and engineers are rushing to do triage, diagnose and classify some very worrisome patients: the thousands of buildings that suffered cracks of varying size and seriousness in the 7.1 magnitude quake that struck on Sept. 19.

The quake turned the city into a vast hospital of buildings, and the fatalities are easy to count: Thirty-eight buildings completely collapsed, often into pancaked slabs crumpled one atop another. They were immediately swarmed by rescue workers looking for survivors. More than 100 people have been found alive, and a total of 167 people were confirmed dead in the city alone. In the process of that search, the mountains of rubble at some the collapse sites has already been largely removed.

But it is the wounded structures that have experts worried: Hundreds of buildings across the city are roped off with police tape, often with small piles of brick, stucco or glass that fell off their facades lying on the sidewalk in front.

Some could fall in coming weeks. Some could survive until the next earthquake, and then collapse with great loss of life.

Or some could just look a bit battered -- scaring their owners and keeping inhabitants from returning home -- even though they are, structurally speaking, healthy.

It is up to experts like architect Victor Marquez, who thinks of himself as a building doctor, to bring peace of mind -- or recommend aggressive treatment -- to fearful apartment dwellers.

That's what he was doing with 12 worried inhabitants of a seven-floor apartment building in Mexico City's Roma neighbourhood, whose swampy soil is known for heavy earthquake damage.

During Tuesday's quake, large, frightening cracks had opened in zig-zag patterns in the building's stairwell.

Marquez quickly found the problem: an incredibly thick coat of plaster that someone had applied over the decades, a layer so thick they had laid it in with wire matting.

Delicately, Marquez pried under a chunk of plaster with his fingers, to look at the brick wall behind it: it was uncracked and solid.

A healthy patient, Marquez told the relieved inhabitants.

"Plaster is very scary, but it is a false symptom," Marquez told them. "Architects can identify the silent enemy, the damage that isn't as visible."

The broken windows that shattered under the rocking and swaying of the quake could be fixed. The stairwell could be plastered. Minor damage to a low property-line wall could be patched.

The city said there were 3,848 reports of damaged buildings, though it was unclear if some were duplicate reports.

On Thursday and Friday, hundreds of young architects, engineers and architecture students crowded the offices of the city's College of Architects, waiting to be assigned to assess damage r(asterisk)eports. If a building is deemed dangerous, the experts will notify city authorities, to encourage inhabitants to leave.

All this, in part organized by web platforms like Marquez' "Save Your House" is being done free, and voluntarily.

Antonio Aldana, a 28-year-old architect, is one of the volunteers. After the quake, he first tried to volunteer as a rescuer, using a shovel to look for survivors. But collapse sites were quickly overwhelmed by the number of people wanting to volunteer, so Aldana decided to use his profession to help instead.

"In a situation of crisis like this, all professions are useful," he said.