The Miami-area apartment complex that collapsed early Thursday had been experiencing “issues” for years. And it was even the subject of a scientific report last year that warned of it sinking into the earth.

The Champlain Towers complex in Surfside, Florida, was the subject of at least one lawsuit over the maintenance of the structure’s outer walls. Furthermore, scientists concerned about flooding and land erosion were drawn to the structure.

According to a Florida International University professor who co-authored a study focused on the issue last year, the complex had been sinking into the earth bit by bit since the 1990s, at one point at a rate of about 2 millimeters per year.

Professor Shimon Wdowinski and co-author Simone Fiaschi investigated increases in flooding frequency and discovered that, in addition to rising sea levels, flooding was “significantly higher” in areas along the southeastern coast sinking into the earth due to urban development and compacted sediment on what was (at least in part) reclaimed marshland. At the same time, Wdowinski pointed out that “land subsidence,” or ground settlement, “would not likely cause a building to collapse in and of itself.”

The collapse at Champlain Towers left at least four people dead, although authorities are still combing through the rubble and expect the number of fatalities to rise. At least 35 survivors have been pulled from the rubble. Another 99 people remain unaccounted for.

Questions surfaced quickly about what may have caused more than 50 units to suddenly separate from the remainder of the structure. The oceanfront complex was built in 1981, just north of Miami Beach.

It was apparently undergoing routine roof repairs at the time of the collapse, though it is unclear whether this had anything to do with the building’s apparent structural failure. A penthouse suite recently sold for $2.8 million, so living there isn’t cheap.

According to Kobi Karp, an architect who has worked in Miami since the late 1980s, the construction approach utilized in South Florida has been the standard since the 1920s and is “the most structurally sound and safest way to build structures, whether it’s a two-story home or a high-rise.”

To endure lateral wind stresses, such as hurricanes, buildings like the Champlain Towers complex are composed of structural concrete set upon concrete pilings.

“So even a building built in the 1980s is a relatively young building,” Karp told The Daily Beast, adding that the event that led to the building’s collapse “could have occurred in the past 24 hours or in the past 24 months.”

But, he said, “the cause is either a structural event that occurred because they were working on the roof and put too much load concentrated in a certain area, and/or there was somebody working on the structure and created a cut or damage that caused structural failure. In both scenarios, it seems to be a man-made cause.”

Karp said it looked to him like the tower came down due to “an internal event, whereby the vertical concrete structure broke apart from the horizontal. And as the slabs fell down, the impact was obviously pretty strong and that’s what shows you the pancake effect.”

“This is highly unusual,” he said. “Unique… This is the first time that I’ve seen something like this in Florida.”

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