The soaring white towers were a signature project of Venezuela’s Socialist icon, Hugo Chávez, built in the coastal state of La Guaira to house thousands of poor government supporters. For years, their promoters bragged about how fast they were built. Then came the earthquakes. The vaunted buildings collapsed with astonishing speed. Trapped under concrete, in a cloud of yellow dust, residents screamed for help and then died. The death toll is still not known, but an estimated 3,200 people lived in the collapsed towers.

Venezuelan officials, in public statements, have cast the devastation as the consequence of an overwhelming natural disaster. But the truth is more complicated.

The Times investigation revealed that the buildings were so fundamentally flawed that they became death traps. Simple, widely used engineering techniques could have strengthened the towers and saved lives. When they collapsed, the buildings were less than 15 years old.

The Venezuelan government constructed the buildings during a period of state largesse, when coffers were flush with oil money. Yet our reporting found that the agency that built them, the Office of Special Presidential Plans and Projects (OPPPE in Spanish), repeatedly chose expediency over careful design and construction.

The quakes have emerged as a major test for Venezuela’s new leader, Delcy Rodríguez, who became president with the backing of the United States in January, following the capture of her predecessor. Ms. Rodríguez has long been a senior figure in the Socialist party that built the OPPPEs.

The Times’s investigation also found that the government’s official death toll was likely a severe undercount. The government said that 6,509 people died in the earthquakes. But there were roughly 5,200 people who lived in more than a dozen public housing buildings that crashed to the ground in La Guaira alone. And hundreds of other public and private buildings in La Guaira and elsewhere collapsed.

Structural engineers said it was difficult to explain the wholesale collapse of modern towers, even near an active fault during an unusually strong shaking event. Modern building codes like Venezuela’s should have prevented that, they said.

It is unclear precisely how intense the shocks were to the buildings because Venezuela has a deteriorated seismic monitoring and reporting system.

But Vitor Silva, a structural and seismic engineer based in Portugal who reviewed evidence from the site for The Times, said that “this catastrophic type of collapse is an indication that the necessary seismic provisions were not followed.”The result, he added, is “buildings that just cannot survive earthquakes that are likely to occur in this region.”Ms. Rodríguez dissolved the Office of Special Presidential Plans and Projects earlier this year. Representatives for her government did not respond to messages detailing our findings and asking for comment.

To assess what caused the mass collapse, The Times visited the site and spoke with former government officials, a contractor and workers involved with the project, engineering and building code experts, and many survivors. We also obtained floor plans, created 3-D models, and did a structural examination of the rubble using ground and aerial photography. Officials linked to the project refused to provide structural drawings, so The Times used available documents and physical evidence to reach its conclusions. We found several design and construction weaknesses that may have contributed to the collapse.

The design was a risky choice The design is popular in many parts of the world, in part because it allows for open interior spaces and architectural flexibility, Mr. Silva said, adding that “using moment-frames near an active fault is not inherently inappropriate.”But he and other engineers say it can be a risky choice for a region with high seismic threat because it must be designed and built with exquisite precision. Many earthquake-prone countries, including Chile and Japan, have turned to more seismic-resistant designs.

To survive a quake, buildings rely on two qualities: stiffness and ductility. Stiffness reduces swaying, while ductility allows swaying to occur without collapse. Moment-frame buildings rely primarily on ductility, riding out quakes by swaying back and forth.

But after reviewing collapse footage, Osman E. Ozbulut, a professor of civil engineering at the University of Virginia, noted that these buildings hardly swayed and instead tipped over almost immediately in one direction. The sudden collapse suggests a lack of both stiffness and ductility.

There were no structural walls One way to add stiffness to these structures and reduce reliance on ductility, engineers say, is to include concrete walls reinforced with steel. They are known as shear walls.

The column layout was flawed Shear walls are not the only way to stiffen moment-frame buildings made of reinforced concrete.

Designers can strategically place and shape columns to provide stiffness in every direction, since seismic waves are unpredictable in how they can shake a building.

Construction was poor Engineers say that even with sounder design, the poor construction quality could have sealed the towers’ fate.

Santiago Pujol, an earthquake engineering expert based in New Zealand, pointed to the sheer complexity of column-beam joints, where densely packed rebar has to be set into a precise arrangement before concrete is poured.

“Very often, the workers laying down the reinforcing bars, they’re not people who have been trained a lot,” Mr. Pujol said.

“They may be quite skilled at what they do, but they’re mostly paid to do things fast,” he added. “They’re not watchmakers.”

The collapse could have muddled some clues. Still, engineers said it was unlikely that the structural drawings would have similar blunders. That suggests these were mistakes in the construction and inspection of the work rather than in the design.

“I couldn’t find a single example here of a good job,” said Mr. Pujol, who reviewed the evidence for The Times. “This was a failure,’’ he added, “waiting to happen.” Why some buildings stood and others fell The day the quakes hit, Yormina Soto, 37, watched the towers collapse with a boom, coating her in debris and entombing her entire immediate family — three adolescent children and her husband — inside their apartment.

Spared only because she happened to be working at a shop across the street, she screamed for her family as bloodied neighbors ran past. “It was a truly terrifying experience,” she said, “seeing so many people die.”

A resident of OPPPE 27 since 2013, Ms. Soto received the keys to her apartment at a time when Venezuela’s president, Mr. Chávez, was vowing to build safe, quality homes for those who lived in shacks and shelters — “so that no one else is in mortal danger,” he said in a 2011 speech.

Mr. Chávez, the founder and pillar of the country’s Socialist movement, eventually called his initiative Venezuela’s Great Housing Mission.

Ms. Soto had believed the president’s promise. Today, she is filled with anger, she said, and “a pain so great I don’t think I can overcome it.”

The buildings fell so fast that, for many people, escape was impossible. Many bodies were found in the stairwells, rescuers said.

Ms. Soto and her family may also have been the victims of some bad luck in the way the ground shook under their home. Original footage of the towers’ collapse obtained by The Times and analyzed by two earthquake engineers in New Zealand provides one possible explanation of how the ground’s shaking at the site may have affected the structures.

The video, filmed from a bakery across the street from OPPPE 26, shows people being tossed violently as the quakes’ intense shaking sweeps through the area.

By extracting motion data frame by frame, the engineers found that the ground near OPPPE 26 primarily shook back and forth along José María España Avenue, as shown in the video below.

The direction of shaking was such that the 10 collapsed OPPPE towers, including the one where Ms. Soto’s family lived, would have been pushed or pulled in the direction in which their columns were weakest.

All the towers were largely of the same design. But analysis of the site by Times reporters and engineers shows that those still standing had an additional row of columns, including some that were slightly thicker. The surviving towers sat at a 90-degree angle to the collapsed buildings. So those towers were shaken in their columns’ stronger direction and stayed standing — if only as hollowed-out husks.

Another seismological team analyzing video footage of the quake closer to the fault observed very strong ground shaking in approximately the same direction. The significance for the two OPPPE towers is unclear, though, since the towers were about a mile and a half away, and ground motion can vary from place to place.

A housing blitz became a political lifeline Venezuela’s ruling party built the OPPPE towers when its very survival was under threat.

Mr. Chávez announced his Great Housing Mission in 2011, with his movement facing a pivotal election the next year. Then the president announced he had cancer. Months earlier, thousands of Venezuelans, many of them Chávez supporters, had lost their homes to devastating mudslides. The pressure was on.

The president promised three million homes by 2019. The goal was to give every disaster victim a place to live. Andrés Izarra, a government minister at the time, likened the housing blitz to a “war effort,” adding, “That’s how we got re-elected.”Mr. Chávez died in early 2013, and Nicolás Maduro became president. Problems with the buildings emerged almost immediately after they opened. Faulty electrical wire caused fires, and the sewage system overflowed, according to media reports and interviews. Two construction workers who helped build OPPPE 27 said in interviews that they had been told to ration materials.

One, Ramón Iriarte, said that if his crew did not have enough concrete, they were told to stretch the material by mixing it with other products. And everything had to be done as quickly as possible, he said. Workers were told they would not be paid unless they hit certain deadlines. Inspections seemed cursory. He recalled “a lot of talk about the government having to hand over the apartments.”Building experts in Venezuela publicly questioned why the towers had been built so close to a fault, warning that they would be vulnerable in a quake.

Critical to building structures that can withstand quakes is an understanding of the terrain beneath them, including how close it is to a fault and whether it is soft or solid. Designers chose to build along the low-lying coastline, a region with soft soil, which can amplify shaking in a quake. But Andreas Prypchan, a Venezuelan engineer who said he had been hired to produce structural calculations for OPPPE buildings, said he was asked to do them for just three hypothetical plots — and not for the specific terrain where the towers that collapsed were built.

“We didn’t do it for any specific location,” he said. It is unclear whether the Office of Special Presidential Plans and Projects hired another engineer to do site-specific calculations.

Mr. Chávez tapped the architect Farruco Sesto to lead the OPPPE program. At a public event in 2021, Mr. Sesto said that his team had not done soil studies before construction, according to news media coverage.

Reached by telephone, Mr. Sesto said his team had done the studies, but he declined to talk about why the buildings had fallen.

“I do not consider it journalistically sound to focus on a handful of Great Mission buildings that collapsed, given that hundreds of private buildings also collapsed,” he said. Can Venezuela rebuild safely?

So many people died in the two OPPPE complexes that bodies were still being pulled from the rubble three months after the quakes. Many survivors are now homeless, living in tents or with relatives.

A government-led body is looking into why structures fell, said Francisco Garcés, the minister leading the commission.

Soon after the quakes, the government said it had already identified plots for reconstruction in La Guaira.

With the forensic evidence available now, it remains unclear whether the destroyed buildings in Venezuela, including the two OPPPE complexes, met the seismic code, and whether the code itself was strict enough for towers built so close to a fault. An update to the code is underway. Long-standing practices and cost savings may have influenced why these structures were built this way.

“If something has been done the same way in a lot of places or for many years, then, the question is always: Well, why should we change it?,’’ Mr. Pujol said.

The engineers whom The Times spoke to said that adding concrete shear walls — of which The Times found no trace of at the OPPPE 26 and 27 complexes — was one of the best ways to make structures more seismically resistant. “It’s not going to be a big cost, and maybe those shear walls save lives,” said Baris Erkus, a structural engineer based in Istanbul.