A 2020 study indicated the Florida high-rise that collapsed Thursday started sinking at an alarming rate in the 1990s.
But it's still far too early to say why the building collapsed and what, if any, lessons can be applied to buildings sinking across the Bay Area, according to experts.
Gary Griggs, Distinguished Professor of Earth Sciences at UC Santa Cruz and a leading expert on California’s coastal geology, told KCBS Radio's Liz Saint John on Friday afternoon that the Surfside condo building near Miami Beach was built atop a "quite different" subsurface than buildings in San Francisco, which tends to have bedrock.
"It's just sand, basically," Griggs said of barrier islands like Miami Beach. "They're sand dunes converted to a low island. So we know in the long run, they're moving landward. They're affected by hurricanes. So even though there's a lot of structures out there, there are some problems when you get down into the subsurface."
Shimon Windowski, a professor in Florida International University’s Department of Earth and Environment, told USA Today on Thursday that research he conducted between 1993 and 1999 indicated that the Champlain Towers South condominium sank about two millimeters per year during that time.
Windowski wasn't suggesting the sinking caused the collapse, nor was he sure the building had started sinking at a slower or faster rate since he recorded the data. He did note, however, that the building "had some kind of unusual movement for the area in which it was located."
Griggs said an investigation will have to consider a number of factors.
For one, Florida "tends to be built over limestone," he said, which can create sinkholes that cause buildings to sink. For another, the sands continue to shift on barrier islands, especially amid rising sea levels caused by climate change.
Beyond that, investigators will need to consider the building's engineering and construction. The tower, constructed in 1981, was due soon for a 40-year recertification mandated by Miami-Dade County building code, according to the Miami Herald.
A condo owner at the building filed lawsuits in 2001 and 2015 alleging that cracks in the building caused water damage, per NBC News. Court documents obtained by the outlet said the building was liable for the condo owner’s $15,000 expense because it indicated structural damage.
What does it all mean for Thursday’s collapse?
"I’m sure it’s going to take months to figure this out," Griggs said.
The families of the 159 people still unaccounted for will want to learn as quickly as possible, and so will much of the Bay Area.
A January study published in the journal "AGU Advances" indicated that the Bay Area had sunk as many as 80 millimeters (about 3.1 inches) over the last century of urbanization.
Tom Parsons, a geophysicist with the U.S. Geological Survey and the study's author, wrote that "all sources of subsidence" in the region, including the last 100 years of development, "are concerning" because of the Bay Area's expected sea-level rise due to climate change.
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