By Jessica Wolfrom : sfexaminer – excerpt
San Franciscans have always occupied shaky ground. But now, parts of our quake-prone city are literally sinking under our feet.
Areas like San Francisco International Airport, Treasure Island and Mission Bay are falling prey to subsidence — the term used to describe the downward settling of ground — at a moment when climate change is causing sea levels to rise.
Now, new studies show rates of subsidence in coastal areas are happening at a faster clip, meaning coastal areas will be challenged by flooding much sooner than projected by sea-level rise models. While the most rapid subsidence is happening in parts of Asia, researchers have observed such sinking across the globe — including in the Bay Area.
Here, subsidence is caused by several factors, said Roland Burgmann, professor of Earth and Planetary Science at UC Berkeley. Areas built on old landfills or young sediments, like bay mud, experience compaction over time, but groundwater extraction also exacerbates sinking.
“Wherever you have development of landfill — so SFO, Mission Bay, Treasure Island, the Marina and much of the area South of Market — that’s still compacting,” said Burgmann. “It is very young, loose stuff … So if you build on that, you have to either take certain procedures or steps to mitigate that.”…(more)