Older buildings, substandard construction and geography left many neighborhoods in Venezuela vulnerable to strong earthquakes like the ones that struck the country this week.

Engineers and other experts said the back-to-back earthquakes on Wednesday were among the most intense to hit the country in more than a century, leveling buildings and leaving more than 900 dead with the number expected to rise. Videos and satellite imagery from the disaster zone reviewed by The Associated Press reveal scores of multistory buildings had collapsed.

Microsoft’s AI for Good Lab analyzed satellite imagery of Catia La Mar in La Guaira state, one of the hardest hit cities along the Caribbean coast. Using AI-based damage assessment models, Microsoft determined that about a third of the city’s nearly 30,000 structures were damaged.

Among the factors that left so many structures at risk: Some housing complexes in northern Venezuela were constructed quickly during recent oil booms, and builders may not have adhered to best practices that mitigate the risks of serious seismic activity, according to experts.

Engineers said that older housing erected in the 1950s and 1960s — before modern earthquake standards were adopted — may not have been retrofitted to survive such violent shaking. And many buildings were constructed on geography and soft soils that compound the danger of the earthquakes, the experts said.

David Cocke, a structural engineer in California and former president of the Earthquake Engineering Research Institute, said that a combination of soft soils, tall towers and older concrete structures contributed to the widespread damage, particularly when buildings pancaked, or collapsed floor-by-floor.

“They just don’t have the more modern reinforcing steel connections that we put in those kinds of buildings today,” said Cocke.

Since the 1970s, engineers have known that concrete buildings are particularly susceptible to earthquakes and seek to reinforce new construction with steel. While many rich nations have forced property owners to retrofit or tear down dangerous buildings, many poorer or middle income countries have lagged in enforcing upgrades as they battled more immediate woes.

“Some of the more advanced countries like Japan and New Zealand and the U.S. have made those changes, but some of the other countries have not,” Cocke said. “It’s a very typical kind of construction all over the world.”

Other experts noted that a number of buildings that collapsed also had non-structural walls comprised of heavy bricks, or they had “soft stories” in which their ground floors consisted of garages or similar open spaces. Such construction increases the risk of pancaking, they said.

“Soft stories are a huge problem everywhere in the world,” said Eduardo Miranda, a professor of civil and environmental engineering at Stanford University. “And in Venezuela, they are particularly prevalent, and if you combine softer soils with a soft story, buildings can collapse.”

Marcos Ferreira, a geophysicist and researcher at the Geological Survey of Brazil, said the destruction in Venezuela was compounded by the back-to-back quakes, known as a doublet. A similar incident took place in Turkey and Syria in 2023, killing almost 60,000 people.

“It is as if I am screaming and then someone starts screaming, too,” Ferreira said. “That amplifies the vibration and adds to the potential hazard.”

Venezuelan government officials took steps following a deadly 1967 quake to update building codes. But it is unclear how many buildings were retrofitted to comply with those rules.

In late 1999, former President Hugo Chávez’s first year in office, floods and landslides destroyed housing, including in coastal northern Venezuela. The government went on a building spree to replaced the demolished structures and to house so many displaced people, said Juan Carlos Vielma, a Venezuelan civil engineer who is head of academic affairs of the civil engineering school at Pontifical Catholic University of Valparaíso, Chile.

Some of the newer buildings appear to also have collapsed.

“Something that leaves me perplexed is the fact that, among the collapsed buildings, more than one was recently designed and built in accordance with current standards,” Vielma said. “We need to embark on a process not only of reconstruction, but also of reviewing the applicable standards, since something might have gone wrong within our engineering processes, too.”

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AP writer Mauricio Savarese in Sao Paulo contributed to this report.